Mechanical Brake Tracks & Rolling Pins
 

Mechanical Brake Tracks & Rolling Pins: (Posted on other Forum also)

1. During Model A Mechanical Brake restoration, many have experienced a mechanical moving parts area within the brake drum area that wears quite a bit, (metal to metal) caused by the movement of the mechanical brake rolling pins,(A2045) on the tracks. These front & rear roller track part numbers are: Front A2011C, & Rear A2011D, more expensive with accompanying bushings & housing.

2. Depending on the amount of wear, & degree of restoration desired, these tracks are often built up with weld & re-surfaced; or, removed & replaced with new tracks riveted in place. As these brake tracks wear, they affect the top & bottom centering of the brake shoes in the drums.

3. In the recent past, some have totally replaced original mechanical brake parts within the brake drums with the more modern Flathead Ted's Front & Rear Brake Kits, by Mr. Ted Spain in New Zealand. Many, even salesmen at Model A parts vendor companies, who own Model A's, report that Mr. Spain's altered mechanical brake system is excellent.

4. Other Model A owners prefer to stay more original & replace worn parts with standard replacement parts offered by Model A parts vendors.

5. After re-building my entire mechanical brake system some time ago, using "standard" replacement parts, (except for installing the more modern front brake floater/equalizer, (A2051F) ), I saw Mr. Ted Spain's square headed brake pins in a parts catalog. They were advertised to be used only on the rear brakes.

6. I then inquired firstly, if these square headed pins could be used in conjunction with "standard" replacement parts, as opposed to only being provided the entire modern kit; & secondly, could these pins be used also for the "front" brakes.

7. The vendors reply to both questions was: "I am not sure."

8. Thinking that these square pins would greatly improve the wearability of the Model A brake tracks & rolling pins, by e-mail inquiry I asked Mr. Ted Spain the same aforementioned two (2) questions.

9. Mr. Spain said these square pins would work with "standard" mechanical brake replacement parts, would also work with a floater/equalizer on the front brakes; & that furthermore, would greatly reduce the wear of all eight (8) mechanical brake tracks. (He also did mention that his total replacement kits, front & rear, would work better).

10. Also, "if" tracks are worn enough to be rebuilt or replaced, one does not have to remove the old worn tracks. One can grind these worn tracks down flat & level, & provide these new square headed pins which can adjust the centering of the brake shoes by turning these pins 90 degrees for each different setting until shoes are centered.

11. These square headed brake track pins contact the tracks with a much larger contact sliding area, (less pounds per square inch), than the much smaller tangential area of the brake rolling pins,(A2045). Then after a little "standard" rolling pin wear and/or track wear, these "standard" rolling pins cease to roll & begin to slide with more pounds per square inch at their smaller contact points on the tracks.

12. Just trying to pass on this bit of trivial information in case some may be interested.

Re: Mechanical Brake Tracks & Rolling Pins
 

I do not know much about the multi-dimension square headed pins. These parts need to have a certain hardness and I do not know if they are hardened.

I do know that it is a mis-conception that the pins roll. Originally the pins were a tight fit in the shoe and were not supposed to roll. The only things that roll are the two large rolling washers. If the shoes are loose on the pins then they must be made tight. People have bushed the holes and resized them to get a snug fit.

Regardless, the over riding consideration is doing the brakes properly. This does take some special tooling and careful thought. Lots of new or NOS parts, shoes arched to the drums and properly centered. A Barrett Brake Doktor is a wonderful tool to own, but that is a tough expensive tool to find.
Done right, 100% original brakes are a wonderful thing.

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Kevin,


I was thinking that it appears that the main difference between well fitted round brake pins & well fitted square headed brake pins on similar tracks & mechanical brake systems on any vehicle is that:


a) If any metal, mechanical brake track is for example approximately 1/8" thick; &,

b) If any mechanical brake springs are compressing brake pins on a track for example at a rate of approximately 15 pounds;

c) therefore, a 1/2" wide square pin can exert approximately 240 pounds per square inch on this particular 1/8" width of track; however,

d) a round pin contacting a track on its circumference could apply approximately 8,000 pounds of pressure on this same track; hence,

e) the round pins exert approximately 33 times more pressure in pounds per square inch, (psi) than that of the square pins.

f) If both brake pins remain clean, adjusted, & lubricated, my thoughts were, which track under which of these two (2) pins will wear first?

g) Having never tried this, time will tell -- nothing like a risk!

Re: Mechanical Brake Tracks & Rolling Pins
 

A friend bought a set of the incremental square pins a couple months back and I was surprised when I saw them. I heard of them but never looked at any. The increments are so large I consider them useless unless you get lucky. I'd be surprised if one in ten people got their shoes close enough to center to wear-in under 5k miles. The concept is relatively good but the approach needs to be a bit different.

Ideally you want to get everyone to a specific starting point as to the dimension of the track. This could be accomplished by providing a simple, cheap template to use as a guide for grinding down the worn tracks. That would get everyone close to the same starting point so you aren't attempting to crudely compensate for variations that could well exceed 1/8" (.125"). Then you could size the pins based on that starting point and dramatically reduce the increments to something like .015". With that type of arrangement folks have a chance of getting close enough that the brakes can actually have decent shoe contact.

I told my friend to toss the pins and we'll just do his brakes properly to begin with. I'm not concerned about the wear factor with the original design.


http://www.snydersantiqueauto.com/up...HT-7515-xl.jpg

So how does it work
 

I have been trying to figure out how the original setup works. I have even tried to make an animation of the shoes moving out towards the drums. Looking at the front brakes the concept as I see it is that you adjust the shoes so the ends of the linings on the shoes are equal distance from the center of the axle (centering the shoes). This is done by modifying the height, relative to the axle, of the roller tracks. Then you have to adjust the positioning of the shoes with the brake rods and with the square headed adjuster at the top of the backing plate. In the following I am assuming that the parts are in excellent contrition and that the arc of the shoes matches the drums. By adjusting the brake rods you will be moving the bottoms of the shoes out towards the drums. At some point the bottom of the shoes will contact the drums and the drum will lock up. When this point is reached you back off the rods so there is just a little contact and the drums can be easily turned by hand. Then you adjust the square headed adjuster at the top of the backing plate. Again you turn it until the drums lock up. The back it off until there is just a little more drag than there was after the rods were adjusted. At this point you should get good contact across most of the shoe to the drum when the brakes are applied. To adjust the front brakes so they apply a little after the rear brakes the square adjuster is backed off for both front brakes. Here is where I have a problem. The animation I did showed less than full contact when the top of the shoe was backed off. When the brakes are applied the bottom of the shoe moves out towards the drum. The top of the shoe is fixed, i.e. the distance the lining is from the drum does not change. Thus the bottom of the shoe is applying more pressure to the drum than the top of the shoe. The more the top of the shoe is backed off the greater the loss of pressure at the top of the shoe. However if the front brake rods were backed off to change the front to back braking (instead of the square adjuster). You would get a more even pressure across the length of the front shoes.

Does any of this make sense? What Have I missed?

Bob

Re: Mechanical Brake Tracks & Rolling Pins
 

Bob,

Makes lots of sense to me, & think you missed nothing.

Admire you car in the upper left doing a "wheelie" on take off.

Sincere thanks for taking lots of your valuable time to write same & sharing your observations & your thoughts -- very much appreciated.

Re: Mechanical Brake Tracks & Rolling Pins
 

As a followup to what I noted on the problems with the new eccentric pins above, below is a page I ran across that Craig Likon posted about three weeks ago. It's a bit small to read but possible (too lazy to scan my book). The optional square pin (section F, #2) is done in .005" increments so it's actually possible to center the shoes with some accuracy. I actually forgot I had this as it isn't applicable for me.

https://www.fordbarn.com/forum/attach...1&d=1353447575

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Marco,

As Bob Johnson indicated above what some may think a mystery, front & rear mechanical brakes can be explained as:

1. The front & rear drums can be turned to be fairly accurately concentric with the axle.

2. If the shoes were not re-arched, all of the brake bands can be ground to be fairly accurately concentric with the axle. (Remember that the short distance from the outer surface of the brake bands to the tops of the rivets is critical "when", not "if" the brake bands wear).

3. The front & rear brake adjustment wedges (A2041) were & most likely are still are accurately positioned in a fixed position in the front & rear backing plates & cannot move.

4. The front brake adjustment shafts (A2042), & the rear brake cams, (A2230) can be fairly guaranteed to be of equal lengths if provided new; hence, maintaining a fairly accurate concentric position of the ends of the adjacent brake bands correctly positioned in the concentric drums.

5. The front brake operating wedges, if new, can guarantee that adjacent ends of the shoes remain fairly accurately concentric to the drum.

6. The front brake front to back positioning of the brake shoes can be equalized if one uses front brake floater (A2051F), which allows the brake shoes to be equalize as that of the rear shoes with the sliding cam.

7. Next, providing new roller pins, (A2045) & new adjusting shaft pins (A2740) in serviceable brake shoes can help achieve brake bands that are again fairly accurately concentric with concentric drums;

8. After achieving items 1. through 7. above, & possibly other tweeks, one can achieve very close to concentric brake bands that are fairly accurately concentric with concentric brake drums.

9. Then, here comes the Devil: (well noted in your reply no, 4 above): The new or "used" metal tracks, possibly not accurately positioned & riveted in "used" backing plates. (Mr. Les Andrews & others mention tweeking same up or down with a wrench)

10. Many tracks have been re-worked in every manner imagineable whereby the flat surfaces of the tracks are perhaps misaligned at an angle, or are installed while not having the proper dimension from the axle to provide concentric positioning of the brake bands in the concentric brake drums.

11. "If" the tracks were at any time improperly installed with re-worked rivet holes etc., the above flat surfaced pins accompanied with possible re-working of tracks could possible help to properly position the brake bands in a more concentric position.

12. These flat surfaces of the flat headrd pins, if lubricated, could extend the life of the track wear. As the tracks wear, as many do with round pins, the concentric bands begin to move slightly towards the tracks.

13. Realizing that flat headed pins may not be for everyone, & also that flat headed pins can be home made, do you know of someone who sells flat headed pins with incremental dimensions similar to those indicated in your reply no. 4.

And again, most sincere thanks for all that you do.

Re: Mechanical Brake Tracks & Rolling Pins
 

True.

As with all riveted linings.


True, but must be free of gouges that distort the positioning of the shafts.

Not exactly. The shafts have a needed taper as the angle changes as they are adjusted outward. That same taper allows the heel of the shoe to shift including up/down on the fronts and fore/aft on the rears.

This is true but not many shoes remain true enough today.

True.

Not true, see #4 above in this message.

The up/down positioning of the front shoes and fore/aft positioning of the rears is ENTIRELY dependent on the roller pin tracks and roller pins due to #4 above.

To make it worse, I see many folks reference the original position of the track surfaces from the rivets which ads another variable albeit small if those numbers are close. Originally the track surfaces were dimensioned (in thousandths) from the centerline of the brake housing. They were machined after assembly to guaranty accuracy until very late 1931 when the process was changed for the use of hardened tracks. I've posted those specs over the years but they were lost on both Ahooga and the old Fordbarn. I can't locate the Ford drawing at present.

This is true.

Most of the ones I've worked on had an unworn point of reference near the center of each track allowing for quite an accurate repair without the use of a milling machine. Unfortunately with modern restoration efforts being more prevalent this is becoming less common.

The currently available square pins are of no help here as noted previously. They will more likely encourage haphazard hacking away at the tracks without any good point of reference.

That's true but I don't know many folks that put 100k miles or more on their cars.

It would be interesting to know who produced them back in the forties and fifties but nobody has been smart enough to do so in current times. Now with that said, what some of us do today we would need a variety of sizes or must custom make them as we've done. Once you go with an oversize drum you need undersized pin to compensate. If you install an original drum that cleaned up at .044" over you want a pin with a head diameter of .044" UNDERSIZE to keep the shoes centered. Personally I will NOT alter a track from it's factory configuration.

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Marco,

No doubt mechanical brakes can function "if" accurately installed.

Thanks again.

Re: Mechanical Brake Tracks & Rolling Pins
 

Good stuff Marco, I didn't realize some of that, but I understand more now. Thanks guy's.

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Marco,

"Originally the track surfaces were dimensioned (in thousandths) from the centerline of the brake housing."

This track surface to center critical dimension in thousanths of an inch in paragraph no. 9 above would no doubt be very helpful rather than trying to tweekthe ends of tracks up & down with a wrench.

I always doubted the rivet to track dimension also because of the rivet holes getting enlarged and maybe re-positioned with each track installation.

It would also be interesting to find out how many sets of tracks the many parts vendors have sold in the past 12 years or so, then someone just getting into this Model A hobby could imagine the probability of obtaining original tracks when buying backing plates on e-bay.

Thanks.

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Marco,

This may be it:

Distance centerline of housing to track surface:

Listed on the other Forum under: "A Little Trivia:, dated August 20, 1998, 14 years ago.

"Originally the track assembly was installed (riveted) to the backing plate and then the tracks were machined for accuracy.This provided a track surface that was perpendicular to the centerline of housing plate and 4.625" (if I remember correctly) from the center of the plate.

In late 1931 the procedure was reversed to allow for the roller track to be hardened prior to riveting.The hardened track assembly was then made available to the dealers to service housing plates with worn tracks."

Re: Mechanical Brake Tracks & Rolling Pins
 

Hi Marco,

Just checked a dimension on a front backing plate I refurbished 19 years ago -- it is 4-5/8" = 4.625 -- right on.

Hope this helps someone.