Drum brakes over-adjusting

[Cruisertrash]

The drums get hot with fully loaded travel or unloaded street driving. I daily the 60 so I've been checking every time when I get out of the truck. When they're hot I've jacked them up and it's difficult to rotate the tire - it definitely doesn't spin freely. The pedal feel also gets more stiff when the brakes are hot. Feels like I could stop on a dime haha! Both of those two scenarios - tire free spin and pedal feel - happen after the brakes cool down, too. I'm using "hot" as a way of knowing the brakes have over-adjusted.

Early 60s like my 1982 have a very basic PV attached to the brake booster that cannot be independently bled. It is not load-sensing and it's not on the rear axle. The axle-mounted, load-sensing PV was at least on 62s and possible post-1985 60s. The false check valve theory is interesting though. I'm going to back off the adjusters and then not use the hand brake at all for several days or even a week. If they're still getting hot I'll know the issue is pneumatic and not mechanical. If they remain cool, I'll be looking back at the parking brake/adjuster wheel setup. I've already been pretty sparing in how often I use the hand brake and how far I pull it up since this started happening, but having driven only manual transmission vehicles since 2001, I'm very much in the habit of using the hand brake every time I get out of the truck.

Other brake work done in the past year:
New 60 Series Aisin MC (4/2023)
Tested and verified original brake booster (4/2023)
Verified booster pushrod adjustment (4/2023)
All new brake soft lines (7/2022)
New/reman calipers (7/2022)
New Advics pads (7/2022)
New Toyota rotors (5/2023)
Pedal adjustment per FSM (7/2022)
Flush & fill with DOT4 fluid about 3 times in the past year

The only things I haven't changed are the proportioning valve, the booster (which was verified good), and the hard lines. I could throw a Wilwood manually adjustable PV at the situation, but I want to figure out exactly where the problem lies before throwing more parts and money at solutions that may not work. Or at least get closer to having a suspicion about the root cause of the problem.

 

[DaveInDenver]

Speaking of hard lines, have you run over them looking for excessive bends or kinks? One I've seen a couple of times is where the hard line following the axle leaves the tube and goes to the backing plate. When trying to work leaf packs in it can get snagged. One time *someone* (author clears throat) did this and caused the line to bend too sharp at the flare nut, this pinched it and made a surprisingly effective shut off valve to the wheel cylinder. But that's the sort of thing a PO could do, pull it back and never think it was a problem but a restriction may remain.

 

[Cruisertrash]

I don't think I bent any hardlines but I'll check. That would be an easy error to overlook. I did replace the hardlines at the front knuckle last year with brand new OEM ones. Amazing what's still available for these old trucks.

You're thinking a pinched hardline could act as a one-way valve? Easier for the fluid to flow outward with pressure than backwards when you let off the brake?

 

[Crash]

Checked with BVB band his ‘87 60 doesn’t have an lspv. His brake system is stock.

 

[60wag]

I'd try adjusting the belcrank levers on the parking brake to have less travel. Too much travel might be what is allowing the star wheel to continue to be turned too much.

 

[Cruisertrash]

I'd try adjusting the belcrank levers on the parking brake to have less travel. Too much travel might be what is allowing the star wheel to continue to be turned too much.

The pivot pins can’t really be moved and the bell cranks are 3/16” steel. Not sure where I would be able to adjust them. There is an adjustment for the stop screw and I did that per the FSM. There’s actually a little gap that gets left there, 0.8mm.

 

[Cruisertrash]

I’ve got this cross posted on Mud, and there’s an interesting theory emerging over there. The adjustment lever sits on and pivots from a post. A c-clip keeps it held down but the end of the post is tapered allowing for axial play in the lever. This lets the lever move outward over the pawls of the adjustment wheel. Apparently there may or may not have been a washer on the post underneath the lever. I don’t see it on the parts diagram and it wasn’t present when I opened my drums up, but…

This washer would still allow for some axial play so the lever could move outward as each adjustment wheel pawl passes underneath it, but it would limit the play. Maybe when the adjustment process is dialed in this washer would ensure that the lever doesn’t grab yet another pawl beyond the limit of good adjustment.

Photos from Mud:

 

[Cruisertrash]

Additionally there is some talk about “c-clip” versus “e-clip”. What I’ve always called a “c-clip” (also heard it called a circlip) is properly referred to as an “e-clip”. A c-clip is the kind you have to mash down with a pair of pliers - flexible steel in the shape of a U that you install and bend to tighten into more of a C. Some folks are saying a c-clip should be used to hold the adjustment lever down rather than the e-clip (pictured above) that come with the brake hardware kit. I think the c-clip is thicker and serves the same function as the washer: take up space to tighten up the axial play in the lever.

Supposedly proper c-clip in place:

E-clip:

 

[Crash]

I think I have some spare C-clips if you want them.

 

[DaveInDenver]

I don't think I bent any hardlines but I'll check. That would be an easy error to overlook. I did replace the hardlines at the front knuckle last year with brand new OEM ones. Amazing what's still available for these old trucks.

You're thinking a pinched hardline could act as a one-way valve? Easier for the fluid to flow outward with pressure than backwards when you let off the brake?

Not necessarily one-way but more like an orifice that acts like the shim stack in a damper, so the actuation is slowed. When you let off the brake the cylinders retract slowly and the extra dwell time drags the shoes for few seconds extra each time.

It might not be as obvious when you push the brake pedal because the force is much greater in one direction. Retracting the pads and shoes is relatively weak just being the return springs verses engaging the brakes has a lot of advantage from your foot plus booster and so on.

This theory would require that you engage the brakes often enough and the few joules generated is not offset by the cooling such that the thermal mass heat soaks enough.

 

[Cruisertrash]

Ok, so I finally got time to dig into the rear brakes today. I’ve just been backing them off through the window on the backing plate every couple days and that’s getting old. Everything inside on both sides looked good. It was quick work to pop the washer behind the adjusting lever.

So far so good. I’ve used the parking brake half a dozen times today and drove up to Louisville and back to run an errand. Everything stayed cool all day. I’m hoping this is the ticket. If not I will get the proper c-clips and try those too.

Note the washer on the post behind the adjusting lever:

Also, I bought this thing called a “drum brake resetting tool” for $40 and it’s worth every penny. It adjusts to the inner diameter of the drum and has a second set of arms with the same measurement that you can hold up to the shoes to check clearance. My drums measured 295.5mm. New drums are 295mm and maximum allowable wear is 297mm, so I have plenty of life. I also rotated it inside the drums as an inexact way to measure the roundness of the braking surface and both drums felt pretty darn round. Then I used to the tool to dial the shoes back 0.8mm from the 295.5mm number - the factory spec clearance for drum installation. Despite being from Amazon and being analog (not digital) it’s a nice well made tool for the money.