Pinion backlash

[Floats]

Hi Gents,
I am having difficulty in understanding how to measure the rear end backlash. The 'book' says it should be set by gear patterns and then checked to be .008" to .010"
How is this checked?

[tbirdtbird]

http://www.santaanitaas.org/wp-conte...vised-2014.pdf

http://www.santaanitaas.org/wp-conte...orial-2015.pdf

[BILL WILLIAMSON]

Generally speaking, when checking contact pattern with dye, grease, etc, strive for a "peanut" shaped contact, centered mid-way on a ring gear tooth. With that, the backlash "should" be OK.
If not centered, look for info on which way to move what, to correct it.
I HATE TO DO DIFF OVERHAULS! I like "FUN STUFF", like, flirting & drinkin' exotic COFFEES.
Bill W.
Bill W.

[Tom Endy]

Backlash between the ring and the pinion is established by moving banjo gaskets left and right. This should only be done with the quantity of gaskets that were selected during the carrier pre-load process.

By grasping the drive shaft and rotating it back and forth gently before the axles and spider gears have been installed it is easy to feel the teeth of the pinion gear coming in contact with the ring gear. You should be able to determine the distance by feel, or measure how much the drive shaft rotates between contacts.

What is critical about backlash is to have some, otherwise the gears will be binding. I have heard of a number of specifications quoted. What I try to do is minimize it best I can with the given amount of gaskets I am working with. Excessive wear on the ring & pinion gears will also increase the backlash.

I have rebuilt many differentials in Model A's that were running and driving just fine and had 1/4" of backlash (which is certainly excessive) when I checked it before I took it apart.

Often you hear people talk about bluing. I don't see where it is necessary on a Model A. You set the backlash depth with the banjo gaskets, which moves the ring gear either closer or further away from the pinion gear, which is fixed down the center of the car. The only other option is to move the bluing pattern fore or aft so the pattern is more centered to your liking on the ring gear. To do this you would either have to place a shim under the rear bearing on the pinion gear or take a cut on the bearing stop on the pinion gear. I have never found this to be the case on any Model A differential I ever worked on.

Tom Endy

[Mitch//pa]

you can also feel the back lash through the drain or fill holes and hold the pinion tight...

[BILL WILLIAMSON]

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Also, moving the pinion depth in or out, affects the pattern location. I forget which way?? does what???
Bill W.

[Floats]

Hi Guys,
I have moved all the carrier shims to the left as well as the pinion as deep into the banjo as it can go before touching the carrier.
There is no significant improvement in the backlash. Should I take a cut in the mating surface of the ring or carrier in order to move the ring closer to the pinion.

[Floats]

Any advice will be much appreciated

[Kurt in NJ]

Can you post pictures of the gear teeth, from you description of all that you have moved the gear and still have excessive backlash it would seem that the gears are quite worn ---it could be the only proper fix is new gears

[Floats]

Hi Kurt,
Thanks, they seem to be fine without any wear. But this is not a factory matched pair.
I am busy changing my RPU 4.11 diff ratio to a 3.57 by swapping the ring with a standard sedan one.
Have a look at the pictures,

[Floats]

Here is a photo of the ring.
I think my photos are to big, I can only load one at a time.

[Big hammer]

IMO I would not cut metal from your housings. With your mix match gears what happens if you have to go back the way it was? Others will chime in!

[Kurt in NJ]

So you are trying to use a 4:11 ratio pinion gear with a 3:78 ring gear?? --a mismatch like that won't have good results, the teeth are cut different

[Fullraceflathead]

The pinion and rings gears are a matched set. Sometimes you can use a different gear as long as they are from the Same gear ratio. Just because the tooth count is the same on the pinion but from a different gear ratio doesn't mean it will interchange. The ring gear thickness and pinion gear diameter is different with respect to each gear ratio set.
The only way to simply be able to just drop in a set of gears to change gear ratios is to have a Quick Change center section. The Old Hot Rodders Set up.
Sorry this is not the News you want to hear.

[Tom Endy]

There has been a lot of discussion over the years about the ring & pinion coming from Ford as a matched set. To match them they would have to have been run somehow in lapping compound. I don't believe Ford did that. After about 500 miles of service they are a matched set.

What I have noticed after rebuilding about 500 rear axle assemblies in the last 25 years is that an original R&P set has matching numbers on it. A number is machine stamped on the end of the pinion gear. If you clean the crud off the flat side of the ring gear and hold it at an angle to the light you will see where someone (presumably a factory worker at Ford) took an etching tool and in free-hand inscribed the matching number. I think they did this so that if it was ever disassembled the R&P could be kept together as a matched set.

I suspect when a rear axle assembly was being put together at Ford the workers were instructed to pull a pinion gear from one stock shelf and a ring gear from another and write the corresponding pinion number on the flat side of the ring gear.

I have talked to several old fellows who told me they had successfully matched up a non-mated R&P and that it quieted down after a number of miles, and I suspect that is true. I personal would not attempt it. I always check for matching numbers.

Trying to match up a 411 pinion with a 378 ring gear I think is out of the question.

Tom Endy

[Bob C]

Don't know about the cars but the AA ring (AA-4207-B) and pinion (AA-4609-B) were
sold separate unless it was for passenger service then they were a matched set
AA-4203-B.

Bob

[Floats]

Thanks Gents,
I did not realise that the cut was different but it does make sence.
Thanks for your advice, much appreciated.