The Stovebolt Site Forums The Shop Area Driveline These 52 new drums and shoes are HOT!

Finally have the 52 GMC driving around the neighborhood and trying to work out some bugs. Five-mile cruise on mountain roads, 35 mph max, probably hit the brakes 25 times for stops, steep hills, testing, etc. Truck stops well without pulling.

LF, RF, and LR drums are HOT to the touch upon return. New NAPA drums, shoes and wheel cylinders on all four wheels. Drums have been turned lightly to true them up. Dual master cylinder conversion, new brake lines and hoses. No pre-load on master cylinder and I don't think it's hanging up.

I spent quite a while with the wheels jacked up tinkering with the anchor point and tapping the backing plates to center the shoes and backing all four shoes off to the point where I don't hear any drum-to-shoe contact when spinning the wheels. I don't have all the adjusting screws identical- each is backed off to the point where the rubbing stops.

So, friends, is some heat to be expected during break-in of new shoes and drums? Will it quit in a hundred miles? Should I continue to tinker with shoe-to-drum adjustment? I'm reluctant to get on the highway at higher speeds until I figure this out. Thanks! Dave

Sounds pretty normal to me Dave, and I've been doing brake
work for most all of my adult life, and it's been a long one.

You're dealing with a friction device that has to absorb a lot
of kinetic energy especially as you've mentioned, on mountain
roads. Those drums will get quite hot to the touch. Remember
when they're hot they're expanded so as long as they're not
hanging up on the shoes, not to worry.

There is a break in period where the shoes will not be making
full contact but once the shoes have lapped into the drum you
will need to re-adjust them. Bringing them up tight and
backing them off just till you hear them clear the drum is
good procedure. You may here the drum ever so slightly touch
a shoe but that's fine, no drum or hub or bearing adjustment
is absolutely perfect and a couple thousands run out is to
be expected.

This is the kind of situation where if I weren't being paranoid and feeling the drums, I'd never know the difference. There's no outward sign of a problem except for the heat. What about the RR brake drum being the only one that isn't hot? Should I tighten that one up a little bit or am I overthinking this? How many miles until readjustment?

1952 brake adjustment might be similar to 1951 (back off 14 notches). (seems like a lot of back off)
1954 brake adjustment - back off 7 notches.

Brake drums will get hot if not adjusted with enough "back off".

I could try backing off the 3 hot drums some more. There's little to no contact now though when manually spinning the jacked-up wheels.

You might want to back off at least 7 clicks/notches and then take it for a ride.

You may want to jack up that wheel, and have someone spin it, and step on the brakes to see if that one is even working.

Agree with Dave, in a hydraulic system all the space has to be
taken up before pressure will build. You may have something
hanging up back there.

If you back the shoes of to much you're going to have a low
pedal. As I mentioned earlier, the shoes just need to clear
the drum. And that is a better judge of the clearance than
trying to judge a click on the adjuster. I often find with
Huck brakes that once the shoes are lapped in and making full
contact, that backing off only three notches per shoe is
enough. They are not going to get any tighter, the shoes
won't expand, the drums will, just common sense.

dg

1951 1/2 ton Chevrolet truck changed to Bendix brakes in 1951.

Are 1952 GMC 1/2 ton brakes Huck-style brakes?
By 1952, were 3/4 ton brakes still Huck style?

I agree with Denny regarding Huck brakes.

I agree with the Shop Manuals for 1951 and later Bendix brakes (introduced in 3100 in 1951).

I mistakenly assumed this post was about a 1952 GMC 1/2 ton. Sorry.

I have backed-off-from-rubbing (not the 7 clicks) on my 1954 1/2 ton brakes and they heated-up and rubbed after a short trip. I do not back off 14 clicks/notches - 7 clicks/notches seem to be sufficient.

Huck brakes till '54 in the 3600 Tim and '51 up for the 3100 was Bendix.

dg

I've been away from the computer for a couple days- utility company lost power to our area for over a day. These are Bendix brakes. I'll have someone help me with checking the RR brake for operation. I'll also re-tighten and re-loosen each wheel to get an accurate count on the number of clicks per wheel. It seems like such a luxury to have brand new pads and drums versus the old, used Huck components on my other trucks. That enables me to back off the shoes and still have adequate brake pedal instead of having the wheel cylinder adjusters maxed out (or nearly so) in order to have brakes. I usually am much closer on the shoe-to-drum clearance on the Huck brakes. I'm trying to get a feel for how the Bendix vs. Huck upgrade applies to performance and adjustment tolerances.

A "floating" brake assembly like the Bendix with no bottom anchor CANNOT be adjusted by listening or feeling for drag as the adjuster is backed off. One brake shoe can, and often does stay close enough to the drum to hear a scuff until the brakes are applied and the brake self-centers. Too much release during adjustment causes a low pedal. Tighten each wheel until there is a firm drag (not a locked wheel) and then back off a set number of clicks. For manual-adjust brakes I've used 10 notches for the past 50 years with no problems. Self-adjusting brakes with the fine tooth adjusters get backed off 20 clicks after the drag is felt.
Jerry

I had the same issue with my truck (front disk, rear drum). My research showed that this is not uncommon in installations where a new master cylinder is installed (generally dual replacing the stock single). Typically it was the front brakes not releasing fully. My problem was the dual master cylinder also. It took a while to find the right adjustment of the push rod, where I had good brake and the brakes would fully release after letting off the pedal. If your truck doesn't "roll" easily after using the brakes for a while, it could mean the wheel brake cylinders have not fully released. Possibly the the travel on the master cylinder push rod needs adjustment. In any case, my research showed that to be a common cause, and that solved my problem as well. Maybe something to look at if all else fails.
don

I found a couple of things out of whack. My RR wheel wasn't engaging because I had failed to properly install the wheel cylinder-to-brakeshoe rod on one side. Only one shoe was trying to expand against the drum. Not very effective. Also, all four sets of shoes were backed way too far away from the drums due to me being too worried about eliminating every vestige of rubbing brakeshoe noise. I tightened and backed-off 10 clicks per Jerry's suggestion. Way more brake pedal now. I test drove the vehicle and it stops well with all 4 drums equally hot. The dual master cylinder is releasing OK. I have also had the issue that Don mentioned happen before so I am on guard about that. So, it paid off to be paranoid and feel the brake drums after test driving because I did indeed make some mistakes with my installation. I've also found some additional bugs to work out but I can't use brakes as an excuse to not get out on the highway. Thanks everybody! Dave

Sounds like you nailed it! Good show! As long as the drums dissipate the heat as fast as it's generated by the shoes, no problem if they get too hot to touch. When the heat goes into the drum faster than the air passing over it can blow it away, you get "fade"- - - -lots of pedal pressure, but no stop. That's one of those "OH S--T!" moments, especially if there's cross traffic!

Jerry

Congratulations, Dave

It is good that you found the misaligned rod/shoe, and good that you have sufficiently backed-off the brake shoe adjustments.

You can save your brakes by down shifting in the hills to slow down.

Good advice, Carl

I have always used engine-braking with my trucks (and did not know for many years that is what it was called). It was needed in the mountain and piedmont roads in VA (or, your brakes would fade-away).

I use engine braking quite a bit, even exiting my own driveway. It also serves as an indication whether my engine has decent compression or not.

Its a personal thing with me guys, and I've driven a lot of different vehicles in my life, but to down shift without a GOOD valid reason goes against my logic. Back in high school I had a couple buddies who would always cram the tranny into a lower gear when slowing down an stopping. To hear the engine scream and rev up was,to me, un-called for......but I will admit, there are times it may be called for but to do it as a habit is hard for me to understand.

I don't do it as a substitute for using the brakes approaching a traffic light on level ground. I don't do it to slow down from a higher speed to a lower speed. I generally do it on a steep grade to keep from increasing my speed to the point that I'd otherwise be riding the brakes.

Downshifting to brake is not engine breaking.

"Engine braking is what occurs when a driver removes their foot from the accelerator to allow the vehicle to slow down due to the compression and friction from moving parts of the engine slowing the vehicle."

https://en.wikipedia.org/wiki/Engine_braking#Petrol_.28gasoline.29_engines

You simply take you foot off the brake and let the engine slow down the vehicle.

Some people downshift to engine brake (shift down and let off the gas and release/engage the clutch). I did this once in a VW on snow - the Squareback did three pirouettes (and checked to see if I wet my pants).

I've always downshifted a vehicle when slowing down. Have always
done it with my bikes and I even downshift with an automatic
trans when I have one that will allow me to.
We're not talking about running 65 and shifting into first gear.

Engine brake in third, then second and finally first.

Denny Graham
Sandwich, IL

One thing I'll add...today's brake shoes are different (no asbestos in them). If you're used to the old style shoes, they didn't seem to make the drums run as hot as the new types do.

How are your return springs doing? Old? New?

They are used return springs but seem strong. I've run another 50 miles on these brakes and they haven't given me any more trouble. Thanks!

Very glad things are working out for you Pinetree!
Good work Buddy.