Drum Brake Auto-adjusting Too Tight

[JohnBravo]

2000 K2500 Crew Cab 5.7l 4l80e 3.73 14bolt SF w/13" drums in rear 244k mi original engine/transmission

I have been struggling to figure out why this is happening; my left rear brake repeatedly self-adjusts to drag heavily (left rear wheel is consistently hot to touch). I've pulled the drum and backed-1off the brake a few times, but after a couple hundred miles unloaded it starts dragging again. I've modified my driving style trying to avoid heavy pedal pressure, but the problem persists.

I guess it started after a local shop replaced drums/shoes for me 2yrs ago before helping my father-in-law pick up a new tractor for their farm (he guessed trailer and all it was pushing 10k lbs)...seemed to go well, but when my wife and I moved into a new house the problem worsened. I was pulling a trailer with our stuff (maybe 5-6k lbs at most, nothing crazy) and when I parked on an incline pushed the parking brake maybe a little too hard. My uncle helped me back off the brake 2mo ago...e-brake was not stuck as I had figured, instead backing off the adjuster brought it back enough to rotate freely and all was good until a month ago...

Wife and I bought a Honda Pioneer to do some trail riding, and I find myself pulling that around quite a bit. Coming down a steep hill one day while pulling it (guessing 4k lbs trailer and all, no trailer brakes) a light turns so I had to apply heavy pedal pressure. Within a couple miles I notice the brake dragging again. I find some time after work one day to pull the drum to back off the adjuster, and all is good.

We celebrated our anniversary last weekend by taking the truck and buggy up into Wisconsin to ride some trails and see the leaves changing...trip started fine, but as the terrain got more hilly (up and down) I noticed the truck lugging a little more, struggling up hills and shaking heavily going down with light pedal pressure (worsens as brakes heat up). I get out and wouldn't you know it the left rear wheel is hot to touch compared to the other three.

I'm at a loss. Truck runs great otherwise. Brakes don't start shaking until they heat up (and I suspect it's just that left rear causing the shake)...I'll gladly entertain any suggestions or ideas, much appreciated!

Jordan

P.S. - if this needs to be moved to one of the "stupid questions" threads, I'll allow it haha I don't know much about drum brakes so it could be something simple I'm missing.

 

[DerekTheGreat]

You sure the wheel cylinder isn't hanging up? Backing off the self adjuster would mask that. Hitting the brakes harder and noticing sticky brakes seems to suggest that's a possible problem- The wee little pistons in there don't move much under normal use, but when loaded or under a panic stop they go into an area within the bore that has schmutz or something on it and hang up.

I'd compare the problem side to the good side to verify the brakes were put back together right and then I'd take notice of the self adjuster on the problem side and compare to good side. If it looks hyper extended compared to the good side, then maybe the wrong star wheel was put on. If it looks fine, I'd suspect a sticky wheel cylinder. On one of our half tons, a sticky wheel cylinder took out the backing plate as only one side stuck.

 

[JohnBravo]

Thank you so much for your suggestion! Sounds like a real possibility (I recall asking the shop to replace both wheel cylinders and associated hardware while doing the job and I was told 'everything looked fine so we just did the drums and shoes'). I'll take it apart as soon as I have time, perhaps I should just plan to replace both wheel cylinders.
Regards,
Jordan

 

[GoToGuy]

It's not a complex or difficult. On the my K2500 i noticed some fluid on the bottom of backing plate. Uh oh. You know the drill. Ok turn drums, new raybestos shoes, clean everything, hardware good. One leaky cylinder. Replaced BOTH. I look at them operating as a team. Reassemble bleed. Don't be afraid to bleed fliud. Brake is hydroscopic(?) It attracts moisture. And water has higher specific gravity so it finds the lowest point. One reason corrosion is found in calipers and brake wheel cylinders. So pushing a little extra fluid out is a benefit as you add new fluid. ( out with the old in with the new). Thats my technique for family and equipment service. Good luck. There is also a residual pressure check valve, but that would probably affect both rear wheels, not one side only.

 

[Schurkey]

As said, verify that the brakes are assembled properly.

Some folks tighten the park brake cable to reduce the travel of the park brake pedal, when they should adjust the service brakes which would reduce pedal travel of the park brake AND the regular brake pedal.

The shoes MUST touch the anchor pin at the top of the backing plate when there's no pedal pressure on either the main brake pedal or the park brake pedal. If one or both shoes aren't touching...the first suspect is over-tightened park brake cable.

Verify no brake fluid or grease-seal leaks. Either fluid inside the drum makes the shoes grabby.

Are the return springs worn-out? Common to have to replace the return springs, the hold-down springs, and whatever other springs are behind the drum.

The shoes touch the backing plate in three places for each shoe. Top, middle, bottom contact pads. The backing plates get grooved from shoe movement. Then the shoes hang-up in the grooves. Some guys MIG-weld the grooves, then use an angle-grinder to get the weld bead flattened-down to the height of the rest of the contact pad.

 

[sewlow]

I don't think that the backing plate is the prob.
If the new drums rub & the old ones didn't using the same backing plates, then I can't see the backing plate being the problem.
Is there any casting flash around those edges of the drum hiding under that nice new black paint?
Because, y'know...Chinesium off-shore.
Warped drums (& rotors) right outa the box is not an uncommon occurrence. More than a few members can attest to that.
If they're warped, they'll rub.
I always get new drums turned. From the box to the lathe. If the drums are not so outa whack that they can be internally machined back to being true round, that leading edge will still be slightly out. Throw in some lazy casting clean-up & clearances start to get tight.
If the guy on the smart end of the lathe knows what he's doing, that edge can checked & cut down at the same time, if it's not quite right.

 

[Frank Enstein]

Check to make sure the backing plates do not have a groove worn in where the shoe touches.

Smooth out as needed and put a light smear of brake lube where the shoes touch being careful not to get any on the friction surface.

Make sure the front calipers slide on the pins freely. A one finger push should slide them when the pads are removed.

Sticking parts will upset the balance of the brake system.

Set the parking brake often to keep it free. Some drum designs adjust by setting the parking brake.

Please keep us posted so we can help and learn.

 

[Pinger]

I'd suggest checking the left rear flexible hose hasn't collapsed internally and is trapping the brake on - were this not a 10 month old thread....

 

[Dariusz Salomon]

I'd suggest checking the left rear flexible hose hasn't collapsed internally and is trapping the brake on - were this not a 10 month old thread....

Glad you added to it,as otherwise I wouldn't have come accross it. I seem to have similar problem-my mechanic friend suggested to replace handbrake cables, as he can't see anything else happening there(it happened during MOT you see-couldn't adjust it,adjusted it just about,and as I was coming home the right rear seized and I had to loosen it completly).

 

[evilunclegrimace]

I know that this is an old thread but I would like to point out that brake fluid is HYGROscopic not HYDROscopic.

Hygroscopic vs Hydroscopic: 7 Important Comparison -

The terms hygroscopic and hydroscopic may sound similar but their meanings completely differ from one another.

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