Move Pinion forward and back per Les Andrews

[Al 29Tudor]

Hi Gents,
We are in the middle of dis-assembling a 1928 differential.
In Les Andrews red book, page 1-95 picture in lower right hand corner he shows two gear teeth with wear patterns and text says, "move pinion forward" and "move pinion back"
I don't think there is any adjustment for pinion other than Preload.
Am I missing something.
Thanks for your help.
Al Leach, Venice, FL

[Tom Endy]

The only way you can move the pinion forward or back is to either take a cut on the bearing stop on the pinion or add shims. I don't believe any of this is necessary. I have never found shims on a pinion and I have had a great many apart.

Once the pre-load is set on the carrier and pinion bearings a backlash adjustment is made by shifting the banjo gasket Left\right. This moves the ring gear either closer or farther away from the pinion. The pinion is straight down the center line of the car and you cannot shift it left\right.

Suggestion:

Got to the web site of the Santa Anita A's of Arcadia, California at www.santaanitaas.org . Put your cursor on "Technical Reference" , my name will drop down below. Click on it and it will bring up a menu of technical articles. Scroll to the three on differentials. You can download them. This may be of help.

Tom Endy

[Al 29Tudor]

Thank you Tom.
Sent you a PM earlier.
Yes, I didn't see any provision for adjustment of the pinion other than pre-load.
Your tutorial from earlier this year on the 1928 differential has been really an excellent guide for our project.
I'm setting up a step by step list of everything to do with a check box so we don't miss anything.
Thank you again.
Al Leach

[Tom Endy]

Originally Posted by Al 29Tudor

Thank you Tom.
Sent you a PM earlier.
Yes, I didn't see any provision for adjustment of the pinion other than pre-load.
Your tutorial from earlier this year on the 1928 differential has been really an excellent guide for our project.
I'm setting up a step by step list of everything to do with a check box so we don't miss anything.
Thank you again.
Al Leach

You need the 2014 tutorial, it is pretty much a check list.

Tom Endy

[Al 29Tudor]

OK Tom, I'll get it
Thanks again.
Al

[BILL WILLIAMSON]

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Remember, as to the ring gear tooth contact area, you try to get a PEANUT shaped area, CENTERED on the ring gear TOOTH!
Bill W.

[Al 29Tudor]

Thank you Bill.
We will try to get that pattern.
Tomorrow we will install another members engine and then get back to the rear-end project full time. (well full time ???)
Al

[Jim Brierley]

Both articles by Tom and Les are very good. I do have a disagreement with Les when his book says to bolt both axle housing halves together to get a preliminary pre-load check. (or words to that effect). Bolting the halves together without shims (gaskets) can bend the housings and result in leaks. I recommend bolting the left housing on,(I use only 4 bolts at this ( time) place the assembly on end and slip the right side on. Now measure the gap between the housing and the center section. This will tell you how many gaskets to use. Now install half that thickness on both sides and check backlash. This is time consuming but worth the effort. Just my opinion!

[Jim Mason]

Seems to me the depth of the pocket for the pinion double cup was changed at the same time the gusset was added. either on vince's or marco's site for the drawing...

[Al 29Tudor]

Jim,
I think Les starts with an equal number of shims on each side and reduces from there.
Your comment explains why - so the housings are not distorted.
Thanks.
Al

[Tom Endy]

Originally Posted by Jim Brierley

Both articles by Tom and Les are very good. I do have a disagreement with Les when his book says to bolt both axle housing halves together to get a preliminary pre-load check. (or words to that effect). Bolting the halves together without shims (gaskets) can bend the housings and result in leaks. I recommend bolting the left housing on,(I use only 4 bolts at this ( time) place the assembly on end and slip the right side on. Now measure the gap between the housing and the center section. This will tell you how many gaskets to use. Now install half that thickness on both sides and check backlash. This is time consuming but worth the effort. Just my opinion!

My technique is to bolt the right axle housing to the right side of the banjo with no gaskets and torque the bolts down to 35 ft. lbs. With the carrier assembly installed I add two .010 gaskets to the left side of the banjo and attached the left axle housing and begin pulling all the bolts down toward 35 ft. lbs. stopping periodically to check that I can turn the ring gear with my finger by reaching in through the torque tube flange on the banjo. If I feel it getting too tight I stop and add one or more gaskets. In this manner no strain is put on any of the hardware.

Two .010 gaskets is the least amount of gaskets I want to end up with. Anything less and there is liable to be an oil leak.

Tom Endy

[Al 29Tudor]

I'm putting this out there to see if I understand the procedures.

1. Carrier pre-load. Assemble and install carrier, no spider or axles, bolt up both axle housings. Add spacers under carrier bearing races in axle housings until carrier won't turn. (Is it ever necessary to shim the races?)

2. Bolt up banjo and right axle housing and set in carrier. Add minimum of two .010 gaskets, then bolt up left axle housing, maybe more gaskets, until carrier turns snugly, making sure I never bind up or distort the axle housings.

3. Now divide the gaskets 1/2 on each side and proceed to pinion and ring gear pattern and backlash. Always keeping the same gasket stack and locating the gaskets to either side as required to achieve proper wear pattern and backlash.

Please correct me or confirm I got it right.
Thank you Tom and Jim for your time and patience.
Al

[Al 29Tudor]

Tom,
[1. Carrier pre-load. Assemble and install carrier, no spider or axles, bolt up both axle housings. Add spacers under carrier bearing races in axle housings until carrier won't turn. (Is it ever necessary to shim the races?)]
Page 34 of your 2014 dissertation answers this question and states any shims required can go under the bearing - easier than the race in the axle housing.
Next get a handle on the yoke.
Wow!
Al Leach

[Dave in MN]

Sorry, I have not read Les Andrews section in his book about shimming the pinion. I am offering the following from a recent experience regarding the ill fit of a new 4:11 gearset.

Last year, early in the driving season, I lost a tooth on my 4:11 gearset when the double nuts on the pinion gear loosened. I ordered a replacement 4:11 set and installed it using Tom Endy's very detailed write-up. Upon completion and with the maximum number of gaskets shifted to lessen the backlash between the pinion gear and the ring gear, I still had an excessive amount of backlash in the neighborhood of .070".

Not being satisfied with this amount, I contacted Steve Becker at Bert's who gave me the name and contact info of the manufacturer of the gearset. The manufacturer coached me on the procedure of centering the pinion gear to the ring gear prior to starting the assembly procedure. I determined I needed and then machined a shim that was .067" to place between the pinion gear and the first tapered bearing. With this shim in place and again using Tom Endy's procedure, I was able to obtain about .005" backlash with adequate but not excessive gaskets to provide a good seal to the components. The assembled rear end is very quiet and took us to Loveland and back this summer.

Because of the difficulty I had with acheiving proper backlash in my own rearend assembly, I decided to put on a differential rebuilding clinic at my workshop. There were about 20 local club members in attendance for each session. I held one session where we took two assemblies apart and evaluated their condition and developed a list of repairs to complete and components to purchase for restoration. After the components were repaired and new parts purchased, I hosted two additional Saturday sessions where we assembled the differentials. One assembly needed shims at the pinion gear to get the backlash exactly where we wanted it. The other assembly did not require any shims.

It is often said or assumed you can only get the backlash as good as the shifting of gaskets will allow. This statement is true if you don't try adding shims between the pinion gear and the first or rear tapered bearing you press on to the pinion. The bearing shims sold in .005" thickness for shimming the carrier races can be used between the pinion gear and the rear bearing that is pressed on to the pinion. They fit the components perfectly. During the clinic I hosted, we did use 7 of these shims to obtain the proper pinion gear centering on one differential.

An interesting side to all of this was that when the pinion was properly centered and the backlash was correct, we had a good contact pattern when checking the assembled components with yellow bearing grease laced with yellow pigment.

The first photo (white lithium grease) shows the contact pattern before shimming the pinion gear. It has a bad pattern with the pinion gear teeth riding over the edge or crest of the ring gear teeth. This state would not last long. This contact pattern was the best I could achieve by just shifting gaskets at the pumpkin. Excessive backlash was very evident in this case. This was a new 4:11 gearset.

The next two photos show a more centered engagement on both the thrust and coast side of the 4:11 ring gear. This pattern was achieved with shims (.067") at the pinion as described above. The backlash was about .005".

Good Day!

[Jim Mason]

Bad memory it was the axel housing that was changed

http://www.abarnyard.com/workshop/rearend.htm

[Al 29Tudor]

Thank you Dave,
That's great information and I have filed it for our project.
Our banjo is cracked at four tube mounting holes/bosses so a new banjo may require shimming.
Thank you again,
Al Leach

[Ed Saniewski]

Dave, any chance someone recorded the work session and could post it on youtube? A class like that would be wonderful to share with us. Thanks, Ed Saniewski

[Jim Brierley]

I find it very rare to need shims under the bearings when using all factory parts. The only time I've had to shim was when setting up an early Halibrand quick-change diff.

[larrys40]

Originally Posted by Tom Endy

My technique is to bolt the right axle housing to the right side of the banjo with no gaskets and torque the bolts down to 35 ft. lbs. With the carrier assembly installed I add two .010 gaskets to the left side of the banjo and attached the left axle housing and begin pulling all the bolts down toward 35 ft. lbs. stopping periodically to check that I can turn the ring gear with my finger by reaching in through the torque tube flange on the banjo. If I feel it getting too tight I stop and add one or more gaskets. In this manner no strain is put on any of the hardware.

Two .010 gaskets is the least amount of gaskets I want to end up with. Anything less and there is liable to be an oil leak.

Tom Endy

Al,
Like Tom I have done many rear axles... our only difference is I go ahead and split the .020 thickness and mount a .010 gasket on each side as a starting point.And adjust add subtract, change left to right as needed for proper gear contact and preload. dab 4 small points of rtv at equal places to hold the gaskets and then see where things fall. A agree with Tom that I have never had to shim or adjust the Pinion bearing/race by shimming it. Your tooth contact is dictated fine by the preload and shim of the carrier bearings by the various gasket thicknesses.

Once correct gasket thickness is determined seal well with a skim of rtv including a little on the threads ( especially lower half) of carrier bolts to ensure that there is no leakage there.

Good luck!
Larry Shepard

[Dave in MN]

Originally Posted by Jim Brierley

I find it very rare to need shims under the bearings when using all factory parts. The only time I've had to shim was when setting up an early Halibrand quick-change diff.

The two differentials where we shimmed the pinion were assembled with after-market gear sets. My new 4:11 set was of great concern to me as I knew it would not hold up with the excessive backlash and a contact pattern terminating at the crest of the pinion teeth. The differential assembled at the clinic would have worked without shimming the pinion but it was far from ideal with as many gaskets moved as possible.

The reason for my post and hosting an in-shop clinic was to get the info out there that an almost perfect fit can be obtained by shimming the pinion gear.

Good Day!

[Dave in MN]

Originally Posted by Ed Saniewski

Dave, any chance someone recorded the work session and could post it on youtube? A class like that would be wonderful to share with us. Thanks, Ed Saniewski

The clinic was filmed by one of the attendees but the editing is not yet completed. He recorded it for our Club library. If it is good enough to put out there...we would.
Good Day!

[Dave in MN]

[QUOTE=Tom Endy;1348631]The only way you can move the pinion forward or back is to either take a cut on the bearing stop on the pinion or add shims. I don't believe any of this is necessary. I have never found shims on a pinion and I have had a great many apart.

Once the pre-load is set on the carrier and pinion bearings a backlash adjustment is made by shifting the banjo gasket left\right. This moves the ring gear either closer or farther away from the pinion. The pinion is straight down the center line of the car and you cannot shift it left\right.


Tom,
Please consider the following:

I agree with you in that I also see no need to ever make a cut on the bearing stop of the pinion gear. I, like you, have never seen one too tight or with too little backlash.

I disagree with you that it is never necessary to shim the pinion. As you can see from the photo in my original post (#14), when studying the contact pattern with white lithium grease, the contact pattern was not even close to satisfactory. This condition was caused by excessive clearance between the pinion gear and the ring gear and that equates to excessive backlash. This photo was taken with all but one gasket moved to the other side in an effort to lessen the backlash.
I agree that it is obvious that the centerline of the pinion gear can not be changed from left to right by adding shims to the pinion but since the pinion gear has a basic cone shape, moving it towards the rear, with a shim, will decrease the clearance between the pinion and the ring gear. Just as important, moving the pinion back may better center the contact pattern of the gears.

When I was rebuilding the rear end assembly for my touring car, I contacted the manufacturer of the gearset because just shifting gaskets was far from what was needed to obtain a good contact pattern and backlash. The first thing he asked me was, "Did you visually center the pinion gear on the ring gear?" He also said: "The only way to obtain proper meshing is to complete this step and that will require shimming the pinion gear." Now remember, he was specifically talking about the gearset he manufactured. After installing and adjusting the thickness of the shim at the pinion, everything came together almost perfectly. Now remember, this gearset is a 4:11 and is likely a ratio not many people purchase new and install. The other ratio gearsets may be manufactured differently and may not require shimming to obtain an acceptable backlash.

I know you consider the backlash adjustment "the least critical of all the adjustments" and in your restoration guidelines state that: "Generally you may end up with more backlash than you want. This is usually due to the wear in a used ring & pinion gearset, and it cannot be avoided." I'm just proposing that it is possible to obtain a very good tooth contact pattern with no excessive backlash if the extra step is taken to shim the pinion when warranted. IMO: A worn/used gearset may warrant shimming the pinion.

Installing and adjusting the thickness of the shims between the pinion gear bearing stop and the pressed on taper bearing takes extra assembly time. I pressed the rear bearing on and off several times, each time adjusting the thickness of the shim, to obtain the proper mesh and backlash. It is not hard and like the rest of the rebuilding process just tedious.

By the way Tom, Thank you for your very detailed and well written Model A Ford Rear Axle Assembly Restoration (2014 Revision) Technical guideline. I used it as a manual for the differential clinics I hosted this past winter. I printed it in whole for each attendee to refer to during the clinic and to take with them.
Good Day!

[Al 29Tudor]

Thank you all very much.
I hope to get into the carrier this week to evaluate things inside. The outside of the carrier looks like something came loose in the banjo in the past because it is very banged up. This car was never driven by the present owner but came to him from his grand father. There are no chips or debris so it is a running unit.
I'll try to get some pictures to keep you posted.
Thanks again,
Al Leach

[PalAl]

Originally Posted by Dave in MN

The clinic was filmed by one of the attendees but the editing is not yet completed. He recorded it for our Club library. If it is good enough to put out there...we would.
Good Day!

Dave, I know our Club (Rock-Ford-A's IL) would be interested in your recording, seeing the process of a rebuild and adjustment helps take the guess out of the work. No matter what the quality is it would be better then no video! We have had two members within a year that have had to do this repair. We always have lots of helping hands ideas/opinions, a video would be a huge help. This is a tough repair that most of us would have a hard time handling, seeing the tools, and the process of the adjustments would be a great help. Hope your Club will consider making the video available.

[Growley bear]

Originally Posted by Jim Brierley

Both articles by Tom and Les are very good. I do have a disagreement with Les when his book says to bolt both axle housing halves together to get a preliminary pre-load check. (or words to that effect). Bolting the halves together without shims (gaskets) can bend the housings and result in leaks. I recommend bolting the left housing on,(I use only 4 bolts at this ( time) place the assembly on end and slip the right side on. Now measure the gap between the housing and the center section. This will tell you how many gaskets to use. Now install half that thickness on both sides and check backlash. This is time consuming but worth the effort. Just my opinion!

Yes, and that process can ruin cups and cones if squeezed too hard. They end up looking like a pinion bearing that had the preload set with a rattle wrench.

[redmodelt]

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I put the shim under the cup in the housing because we have the tool to remove it and because so many carriers are marginal re fit of bearing in the first place. I have found that we having more carriers with spun or close to spun bearings so do not want to be pulling the tapered bearing on and off any more then necessary. While there are maybe a lot of carriers out there, does not mean that they are usable. If the spider gear wear area is bad or the bearing just drops on they are toast. Sometimes they can be saved, but not all the time.

[Mike Peters]

Dave in MN: We are rebuilding a rear end right now and have established a nice carrier bearing preload with a .010" gasket on each side of the banjo. But....there is a lot of pinion to ring gear back lash, maybe .070" or so, and no where to go on banjo gaskets. So tomorrow we are going to experiment with shimming the pinion and see what happens.
Thanks for the tip!!

[redmodelt]

Shiming the pinion will move it out and away from the teeth not closer. Try thinner gaskets. You can get thinner ones in the set. You would have to reset the preload. You might even have to use shim under the cup or bearing on the carrier. If you shim the carrier bearing/cup you can move it over. How are you checking you clearance? The way I check is with a dial micrometer, everything assembled except the T tube and take a reading off the pinion nut.
YOU DO NOT HAVE TO STICK WITH .010 ON EACH SIDE.

[denniskliesen]

Starting with Timken bearings can give better results. I found that out from the last rear axle and differential I rebuilt.

[Tom Endy]

Originally Posted by Mike Peters

Dave in MN: We are rebuilding a rear end right now and have established a nice carrier bearing preload with a .010" gasket on each side of the banjo. But....there is a lot of pinion to ring gear back lash, maybe .070" or so, and no where to go on banjo gaskets. So tomorrow we are going to experiment with shimming the pinion and see what happens.
Thanks for the tip!!

In order to reduce the backlash you need to move the pinion gear closer to the ring gear. The pinion gear is attached to the drive shaft and is located dead center of the car. You cannot move it, but you can move the ring gear. To do this you need to remove the carrier bearings and put a shim under each. This will require the addition of more banjo gaskets in order to re-establish the carrier pre-load. The additional gaskets will give you a latitude to shift the ring gear closer to the pinion gear.


Tom Endy

[Dave in MN]

Originally Posted by Tom Endy

In order to reduce the backlash you need to move the pinion gear closer to the ring gear. The pinion gear is attached to the drive shaft and is located dead center of the car. You cannot move it, but you can move the ring gear. To do this you need to remove the carrier bearings and put a shim under each. This will require the addition of more banjo gaskets in order to re-establish the carrier pre-load. The additional gaskets will give you a latitude to shift the ring gear closer to the pinion gear.


Tom Endy

Tom,
Moving the pinion gear back also decreases the space between the meshing gears thus reduces backlash. The always dead center pinion gear is cone shaped, smaller at the rear...larger at the front, moving it rearward causes an area of the gear that has a larger circumference to mesh with the ring gear thus reducing clearance between the two rotating parts.

My previously described process of shimming the pinion gear to reduce the backlash is derived directly from information provided by the manufacturer of the gearset. The manufacturer of the gearset stated it was necessary to shim the pinion to get it centered with the ring gear. (See the description below that explains what "centering the pinion" means.) I followed his instructions and ended up with proper backlash, proper contact pattern and a rear end assembly that dosen't leak, whine or clunk when shifted. Following his instructions worked for me.


Back story: After following your (Tom Endy's) Rear End Assembly Tech Article to the letter, I found I had an unacceptable amount of backlash. I called Steve Becker at Bert's who sold me the 4:11 gear set. He politely offered to replace it with a set of NOS gears. I declined and asked him to provide me the name of the manufacturer. I knew that if I was having a problem, others using this same gear set would too...I wanted to make the manufacturer aware there was a problem with their gear set.

When I called the manufacturer and explained I had set up the assembly with the proper pre-loads and had adjusted the ring gear as close to the pinion as possible and had excessive backlash, the first question he asked me was: "Did you center the pinion gear on the ring gear?" I said: What?
He then said: "The pinion gear should have an equal margin of tooth protruding beyond the front and rear of the ring gear when it is properly centered. (He described a centered pinion as the condition where the pinion gear is properly aligned forward to rear (centered) with the ring gear.)
The production manager then politely explained to me the process of centering the pinion to the ring gear (moving it back) by placing shims between the pinion and the tapered bearing closest to the pinion gear.

When I took the assembly apart to inspect the centering, I could see that the pinion gear was too far forward to call it centered. I machined a shim to a thickness that was more than I needed and test fit it. Too tight...Now I had no backlash...I took it apart and machined the shim thinner. I over shot with my machining but corrected my error by adding a .005" Differential Gear Case to Bearing Shim to my machined shim to provide for proper centering and the proper backlash.

Since building up the above described assembly for my touring car, I have built 11 rear end assemblies for customers cars. I have found it beneficial to shim the pinion bearing on only two 2 of the assemblies. It appears it is not all that common a need to shim the pinion but when it is necessary, because of too much backlash, it is the solution if you cannot shift any more housing gaskets. I no longer machine shims...it is much easier to stack the number of .005" Differential Gear Case to Bearing Shims necessary to achieve proper clearances.

"And now you know the rest of the story... Good Day"

[Mike Peters]

Update: I ground the inside tab off a pinion thrust washer and shimmed the rear pinion bearing with it. It's pretty thick. Reassembled the axle housing. Backlash disappeared, but it binds a little bit in one spot when I rotate the driveshaft around the entire ring gear. So now hunting for a thinner shim. Dave is correct in saying that the pinion gear is cone shaped, so shimming the pinion to the rear DOES reduce back lash between the ring and pinion. A larger question is: Is this the best way to adjust backlash? Tom Endy may still be correct in adjusting backlash strictly with banjo gaskets and carrier shims. It can be done either way, but Tom's method keeps the pinion centered on the ring gear. I will defer to the experts on this question.

[Dave in MN]

Originally Posted by Mike Peters

Update: I ground the inside tab off a pinion thrust washer and shimmed the rear pinion bearing with it. It's pretty thick. Reassembled the axle housing. Backlash disappeared, but it binds a little bit in one spot when I rotate the driveshaft around the entire ring gear. So now hunting for a thinner shim. Dave is correct in saying that the pinion gear is cone shaped, so shimming the pinion to the rear DOES reduce back lash between the ring and pinion. A larger question is: Is this the best way to adjust backlash? Tom Endy may still be correct in adjusting backlash strictly with banjo gaskets and carrier shims. It can be done either way, but Tom's method keeps the pinion centered on the ring gear. I will defer to the experts on this question.

I also used a thrust washer to start with as a test. I also found it too thick.
Snyder's sells shims that will stack to your needed dimension. Order part A-4221-SH. Each shim is .005". Measure the thickness of your fabricated washer (it should measure between .060" and .067") and order shims to result in about .01" less. You will likely need 10 shims. You will find it works well. As you have verified, the designed and machined shape of the pinion gear allows it to be moved forward or back as necessary to "fine" tune the fit. BTW: I do not suggest shimming the pinion if the proper lash can be achieved by shifting the housing gaskets.
Thanks for reporting back.
Good Day!

[Growley bear]

Originally Posted by Mike Peters

Update: I ground the inside tab off a pinion thrust washer and shimmed the rear pinion bearing with it. It's pretty thick. Reassembled the axle housing. Backlash disappeared, but it binds a little bit in one spot when I rotate the driveshaft around the entire ring gear. So now hunting for a thinner shim. Dave is correct in saying that the pinion gear is cone shaped, so shimming the pinion to the rear DOES reduce back lash between the ring and pinion. A larger question is: Is this the best way to adjust backlash? Tom Endy may still be correct in adjusting backlash strictly with banjo gaskets and carrier shims. It can be done either way, but Tom's method keeps the pinion centered on the ring gear. I will defer to the experts on this question.

Tom Endy is an expert.

[Growley bear]

I disassembled a differential a couple years ago and the pinion bearing was a combination of two carrier/pinion cones, two carrier cups with a stack of two rear axel bearing retainer rings between the two cups. The pattern was great, I don't know who or when but it is still going strong.
If it ain't broke_____________---.

[redmodelt]

The shims sold by Snyders are for under the bearing on the carrier, at least the ones I have seen in the catalog. The outside diameter would be too small. I have resorted to making my own when shimming the carrier race in the axle housing. You would need to make your own to shim the double race in the housing, it has the same outer diameter as the races in the axle housing.

[Tom Endy]

I have disassembled literally hundreds of Model A rear axle assemblies in the last 30 years and I have never found a shim under the rear bearing on the pinion gear.


If it is necessary to move the pinion gear in one direction it would seem that sometimes it would be necessary to move it in the opposite direction. In that case you would have to take a cut on the bearing stop on the pinion gear to achieve that.


To the best of my knowledge I have never encountered that either.


A number of years ago an article appeared in the Restorer where the author rebuilt "one" rear axle assembly and was convinced by another Model A enthusiast who lived in another state that it was necessary to "blue" the ring & pinion and center it. They shipped the pinion gear back and forth several times where the guy in the other state took a number of cuts on the pinion gear before they were satisfied it was centered. I don't believe any of this is necessary. All the article did was confuse a lot of people.


I can rebuild a Model A rear end and achieve proper carrier pre-load, pinion pre-load, and Ring & Pinion backlash with banjo-gaskets and if necessary shims under the carrier bearings. I have never had to resort to moving the pinion gear in a fore or aft direction using pinion gear bearing shims or taking a cut on the pinion gear bearing stop.


I don't think it is that critical that the pinion gear be perfectly centered on the ring gear. There is plenty of latitude in the design.


The only machining I have had to do on a reproduction pinion gear is machine the surface where the forward bearing resides. The originals have two dimensions The rear bearing should press on with an interference fit. The front bearing should be able to be moved to set pre-load. If it goes on tight you will have a devil of a time setting the pre-load. The difference in the two surfaces should be about .0015".


Tom Endy

[Paul Bjarnason]

I cannot figure out how to accurately measure backlash. Before, I was using the driveshaft movement compared to axle movement, but there's looseness due to the spider gears that makes it appear there's more backlash than there actually is. I've read in Tom Endy's publications that you're supposed to measure backlash with the axles out of the housing, which makes sense, but if the axle tubes and pinion are mounted on the banjo, since everything is closed up, you can't see in there -- so, how is it possible to see movement between the ring and the pinion gears? Thanks.

[Dave in MN]

If you have the required preload on the carrier, any backlash between the pinion and the ring gear can be felt when turning the pinion assembly clockwise and counterclockwise.
If you are not feeling it, you may not have any backlash.
Good Day!
Dave in MN

[redmodelt]

I bolt a dial gauge to the housing with the driveshaft tube off and take a reading off one of the corners of the pinion nut. Get you real close.

[larrys40]

I agree with tom on his assessment. I have also torn down and rebuilt more than a couple hundred myself, i have two to do this week ... and have also never seen nor have ever had the call to use pinion shims. I agree that a carrier shim to move the ring gear closer is the solution. I’ve also never removed any original ones of those either. Are there anomolies,sure. But my bet is that the normal process will correct it with proper installed and parts to spec.

I do start with a.010 gasket on each side and find that’s generally close to the norm.
I do think it’s important to use Timken bearings and races as they are of a know quality and dimension.

Good luck
Larry shepard

[steve hackel]

Hello to all; "please" excuse the origin of my question, but with 41 posts and so many different opinions on the subject of shimming the pinion - can one of you post a picture or at least a sketch of how and where you are installing the shims to move the pinion into or away from contact with the ring gear teeth? I am "SO" confused...… Steve

[redmodelt]

You pull off the bearing on the carrier and add a shim behind it, or as I do behind the cup in the axle tube.

[Tom Endy]

Steve Hackel:


Photo shows a pinion gear: To the left is a shim that slides over the pinion sleeve to up against the stop right before the gear. The bearing goes on next to right up against the shim. This will push the gear toward the rear and away from the ring gear.


If you want to move the pinion gear forward instead of a shim you would have to chuck the pinion in a lathe and take some metal off the stop.


The same shim will fit over the hubs on the carrier assembly. The four bearings used in the differential are all the same part number.


Bratton's sell the shims. They are all .005 thick. If you need more shimming you can stack the shims.


Tom Endy

[Dave in MN]

Steve Hackel & Tom Endy:

The photo I have included shows where the shims are added to the assembly to move the pinion gear back. Placing the 5 (.005") shims in the location shown will move the pinion back .025" and decrease the backlash. Because the pinion gear is basically cone shaped, moving it back will cause a larger circumference area of the pinion gear to engage with the ring gear thus decreasing clearance between the gears and decrease the backlash. Left click on the photo and the increased photo size will show where the shims are placed in the assembly.

As Tom Endy states: "If you want to move the pinion gear forward instead of a shim you would have to chuck the pinion (gear) in a lathe and take some metal off the stop."
Taking a cut from the bearing stop on the pinion gear will move it forward in the assembly and increase the clearance and backlash between the ring gear and the pinion gear. FWIW: I have never seen it necessary to take a cut on the pinion gear stop on the rear ends I have worked on.
Good Day!

[redmodelt]

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Thank you Tom and Dave. I get it and understand.

[steve hackel]

Thanks for all the help and pictures : its just another weapon in the arsonal of tools and techniques needed to do the job the right way the first time!

[denniskliesen]

Model A differentials aren't as critical as far as gear mesh, compared to modern and high pressure use. My past experience with differentials has been Construction Equipment. You better make sure if working on one know what you are doing and do it properly, no guess work. Generally the depth of the pinion gear in relation to the ring gear is referred to as cone center. Dave in MN touches on this in his post #45 as saying the pinion is basically cone shaped. To get an accurate cone center means if you knew where the point of the cone is, then that point would be in relation to the center of the ring gear. That is where the pinion depth would need to be. Aftermarket gears and industrial applications have these numbers scribed on the gear set. They usually sell the tools to set and or measure the pinion depth for their gear sets if they are marked.
Otherwise you need to be able to check tooth contact pattern. You don't mismatch those gear sets. Most people will say it's not that critical to know what the backlash is precisely. I have never read or been told who does or has the tool to precisely measure backlash between ring and pinion. Finger feel is not good enough for me. Therefore I made tools to take the guess work or finger feel out of the equation. Granted I have not done hundreds of Model A differentials I have never had a Model A differential fail that I worked on. And I have the tools to accurately measure backlash. But seldom does a Model A ring and pinion that I have been told or read about fail, unless the backlash is set too close or no backlash at all.