Rear Brake Drum gets hot

[packmaster2r]

Actually I should say that it gets hotter...hotter than its companion on the opposite side after any given amount of use. I recently did the rear brakes and noticed this when I was adjusting them. ( I adjusted the brakes by seating the shoes wile spinning the wheel, then backing off a few clicks).

I can't perceive any drag by (1) spinning the wheels, (2) driving and braking or (3) driving and coasting. I raised both wheels up and supported the vehicle and verified that the rear brakes seem to grab and realease normally, at least under a no-load condition. The brakes "feel" and perform fine, yet the one drum is noticeably hotter after even a short drive. The wheel is not hot, neither is the hub or axle tube-just the finned area on the perimeter of the drum.

I removed the drum in question for a second look at my work, but can't find anything out of order. I had done a pretty thorough job anyway, making sure to clean everything and lube what needed lubing. I did not however, replace any hardware.

A failed hub seal had leaked, which caused this whole mess to begin with. The drum in question was thoroughly de-greased during the brake job, though the porous outside of the casting is still "impregnated" with oil. Could the oil prevent the drum from dissipating heat at the same rate as the other "dry" drum ?

Also, I had recently replaced the frame rail brake line and bled the brakes. If I left any air in the (opposite side) hydraulic line, could that cause the side in question to be "overworked" ?

Thanks for looking !

Eric/packmaster2r

[NH2112]

Which model truck is it? 1-tons and HD 3/4 tons have full-floating rear axles and if you have the wheel bearings adjusted too tight they'll heat up. Holding your hand near the hub will tell one way or another. If it's a light-duty 3/4 ton or 1/2 ton, the problem is likely a seized bearing or a lack of oil. Did you jack up each side to let gear oil flow to the other bearing, then check the oil level again?

[packmaster2r]

Phil,

Thanks for your reply,

My truck is a 3/4 ton with a GM full floating axle. I did pre-soak the bearings in 90W, and did tilt the axle, and did check/add fluid, and adjusted roller bearings per service manual. I rechecked the bearing adjustment when I had the drum off the second time.

The first thing I thought of was the wheel bearings, but the hub and axle tube don't heat up, just the perimeter of the brake drum. Though I wonder, could a bad bearing(s) transfer its heat to the brake drum without also heating up the hub ?

Eric

[twaddle]

How hot is hot, Is it HOT or just warm compared to the other?

If the bearings are causing the heat they will heat the hub first. How hot is the hub? If it is not hot then the fault is with the brake.

Was there any springs or retainers that may have jumped or broken?
Is there any noise when the brake is applied?

Regards

Jim Twaddle
Biggar, Scotland

[packmaster2r]

The best way to describe the difference in the heat between the drums: after a short trip of about 1-5 miles, you touch the left drum and it feels warm, maybe a little uncomfortable after five seconds. Then touch the right drum, and you can't stand to keep your hand there at all. The hubs do not even feel warm, neither do the axle tubes in the area near the hub.

I did not notice any visible flaws with the springs, though I suppose they could be stretched. They they do seem to retract inasmuch as there is no noticeable drag on the wheel after the brake is released

I'm starting to think maybe the wheel cylinder on that side ids hanging up intermittently

Eric

[twaddle]

Hi there,
Jack up the "warm side" and turn the wheel. It will probably be dragging a bit compared to the other side.
If you can back off the adjuster which is not easy as you have to hold the spring off the notched wheel and turn back the adjuster, not easy at all.
Now drive the truck to test the brakes, stop and jack up the hot side and turn the wheel, if it still easy to turn the fault was over adjustment, if it is now tight there is a fault and the brake is sticking on.
You need to strip it down again and find the fault.

Good luck

Jim Twaddle
Biggar, Scotland

[packmaster2r]

Good advice Jim, but I've tried that. I've even tried generously increasing the shoe clearance on the offending side. It does not make any difference.

I'm going to bleed the lines next. I had to replace the rear line (frame rail) a while back, and perhaps I left some air in the left side circuit causing the right side to do most of the work (?) It's a pain to bleed since the valve buts up against the leaf springs, but it won't hurt to try.

Thanks for your help- if and when I resolve this I'll post what I find.

Eric

[twaddle]

Hi Eric,
Just thought of something else to try, you may have tried this.
Jack up the offending wheel, while turning it give the parking brake cable a good shake, if the wheel loosens it's a sticking brake cable if it doesn't loosen it's the cylinder.

Regards

Jim

[HowieE]

Who adjusted the brakes and what standard did the use whan adjusting them.
Noone beleave this but the rear brakes on a 2500 full floating rear have to be set with a backoff of 33 clicks. This is a direct quote from the GM shop manual and I will e mail anyone who wants a copy.
Ever time I have let a so called "mechanic", GM or local shop, adjust my rear bakes I get between 10 and 50 miles before the rear heats up to the point you can smell them. It took 3 times for me to give up on "mechanics" adjusting my rear brakes.

[RT]

This is EXACTLY the problem I was having after I just completed the same work. I tired adjusting the 33 clicks, I tried just backing off a little, etc. a GM Tech who is a buddy of mine said that the brakes self adjust every time you use the parking brake. I have tested this and he is in fact correct! If I back off the adjusters the 33 clicks the brake pedal is soft. When I then hold the parking brake release and pump the parking brake pedal(repeatedly) the brake pedal softness then goes away and starts to feel normal. The drivers side drum heated up way more than the passenger side on my truck. My theory is the newly assembled and lubricated adjuster is doing its job too well on that side as I found that the "hot" side would drag more than the other after the brakes self adjusted correctly. My solution was to allow the brakes to self adjust and then NOT use the parking brake! The hot drum issue has gone away and the brakes work fine. I figure that when the brake pedal starts feeling soft I will use the parking brake again and let it all self adjust. At some point the lube on the adjuster will harden a bit, crap will get on it and it will go back to normal. For now when I park on a hill I use a wheel chock instead of the parking brake. This is not the optimum solution however I cannot see any other way to correct it. Try it, it may work for you. RT