Front axle brake shoes wear out faster than rear axle brake shoes?

[Wildchild467]

I checked the front axle brake shoes and they are worn down more than the rear axle brake shoes. I would say there is only about .010 inch left before it hits rivets. When I checked the brake shoes on the rear axle they still look great. Its hard for me to estimate how many miles are on the brake shoes, but I put 25,000 miles on it since I got it and the truck was in great shape. You wheel cylinders looked to be replaced before I got the truck (uncle sam changed them last). The truck now has about 50,000 miles on it. I just wanted to give some of those specs so you know what situation I am in. So who knows exactly how many miles are on the shoes.

Now, I am fairly sure the truck has the same wheel cylinders all the way around. If all the wheels turn the exact same speed and all the brake pressure is the exact same all the way around, why would the front shoes wear out faster than the rears? I really do not think I have any stuck wheel cylinders because they looked to be new when I got the truck and it has good brakes for a deuce. I also had similar brake drum temps when I checked them with an IR heat gun. I heard the M35A3 has bigger diameter wheel cylinders, is this true? I did a search and did not find an answer.

Long story short, I am going to replace the front shoes. I just want to understand why the fronts would wear out faster… ASSUMING Uncle Sam put all new brake shoes on the truck when they did the wheel cylinders.

 

[steelandcanvas]

The braking system is designed to give the front brakes more authority than the rear. The increased pressure and heat causes them to wear out faster. Google "proportioning valve".

 

[Wildchild467]

But the M35A2 Deuce does not have a proportioning valve. If I blow one line, I lose everything. It has the single circuit brakes, not the split brake system like the M35A3. Even with the M35A3, I don’t know what that brake system is like other than two air packs. I should try to find a brake line diagram… there has to be one out there.

 

[gringeltaube]

........ I heard the M35A3 has bigger diameter wheel cylinders, is this true? I did a search and did not find an answer.......

See this thread... and measure the diameter on your front WC's.


G.

 

[clinto]

The braking system is designed to give the front brakes more authority than the rear. The increased pressure and heat causes them to wear out faster. Google "proportioning valve".

Proportioning valves are typically found on vehicles with front or all-disc brake systems. I have never encountered a vehicle with 4-wheel (or 6-wheel) drums that had a proportioning valve.

I've owned all sorts of 1950's, 1960's and 1970's Mopar and Chevy vehicles and I've wrenched on hundred of others, everything from Pre-A 356 Porches to Fords from the Seventies and if they had 4-wheel drums, they had a distribution block, which simply..................... distributes brake fluid to the opposite ends of the vehicle.

 

[Wildchild467]

Thanks G! I’ll have to check them out when I change the brake shoes.

So these bigger wheel cylinders are usually only found on the front of A3 deuces? They never put the 1.5" bore wheel cylinders on a rear axle?

Original early A2 deuces just had the same size wheel cylinders all the way around, right?

 

[steelandcanvas]

Proportioning valves are typically found on vehicles with front or all-disc brake systems. I have never encountered a vehicle with 4-wheel (or 6-wheel) drums that had a proportioning valve.

I've owned all sorts of 1950's, 1960's and 1970's Mopar and Chevy vehicles and I've wrenched on hundred of others, everything from Pre-A 356 Porches to Fords from the Seventies and if they had 4-wheel drums, they had a distribution block, which simply..................... distributes brake fluid to the opposite ends of the vehicle.

True, I think my reply was a generality, and not specific to military vehicles...my bad.

 

[Recovry4x4]

Front brakes do a greater portion of the braking on all vehicles. Much of this is attributed to weight transfer.

 

[emmado22]

Don't assume Uncle Sam does a "complete axle brake job" when something goes wrong.

 

[clinto]

Front brakes do a greater portion of the braking on all vehicles. Much of this is attributed to weight transfer.

This is why when you stand up on the brake pedal in an all drum brake equipped 383 Road Runner or 396 Chevelle, the front rolls and the rear smokes!

 

[gringeltaube]

..... So these bigger wheel cylinders are usually only found on the front of A3 deuces? They never put the 1.5" bore wheel cylinders on a rear axle?

Correct. According to the books, at least...

Original early A2 deuces just had the same size wheel cylinders all the way around, right?

Yes, M35, M35A1 and M35A2 came with Ø 1-3/8" WC's, all around.


G.

 

[SP5]

Energy goes up as the square of the velocity. If those trucks were/are driven at the slow speeds the military envisioned, with a few tons of weight in the back, the brake wear becomes much more even front to back.

 

[gringeltaube]

I still don't believe that the reason for that much faster wear would be (abnormal)weight distribution- or weight transfer.
In this case, who knows if all three axles- or just the rear axle brakes were serviced at that time?

Differences in brake lining material- and hardness play a big role, as well as (eventually)having larger wheel cylinders, of course.


G.

 

[SP5]

Sure, looking at the weight data plate, you see that standing still, and unloaded, the front axle is carrying almost as much weight as both of the rear axles combined.
Under hard braking, without any load in the back, the two front brakes are doing at least ~60% of the total effort, with only half the number of shoes. One might expect that the front shoes would wear 2>3 times as fast.

 

[gringeltaube]

Assuming the rear wheels don't lock every time you step on the brakes... then all wheels will do (almost) identical number of revolutions during a deceleration from speed X down to speed Y. That, while the pressure applied to every single of all 12 brake shoes is exactly the same. Why should they wear differently?


G.

 

[TMNT]

Do you know if all of the brakes were adjusted properly/the same? Maybe the rear brakes aren't adjusted up as tight as the front?

 

[SP5]

It comes down to the weight transfer loading, normal front/rear bias is ~60/40, and in a deuce, without a proportioning valve, and a single curcuit, the two unloaded rear axles, do not contribute nearly as much braking effort as the fronts.

 

[doghead]

Consider a modern vehicle will usually need front brakes starting at around 50-60K miles and the rears closer to 100-140K miles.

You got 25K miles out of unknown(if they were new when you started) brakes.

Replace them and have a nice day.

 

[SP5]

We have to realize that one brake assembly, (two shoes, one drum), in a duece, has ~12kw of energy dissipation. That equals about 15 HP. That 15 HP. times six, = about 75 total HP.
So, a deuce has about twice as much "go" power than it has "slow" power,,take it easy, it's a 65 year old design.

 

[Squirt-Truck]

?????????????????
Check your numbers, I believe that you will find that the brakes on a 2-1/2 are capable of developing well over 500Hp. Tire limited. (Ever calculate how long it takes to stop 13,000# from 50MPH to 0 vs. starting at 0 and getting to 50MPH??)

I go with the fronts were an adjustment or total time in service issue. Replace after 25k , smile and have fun.