Frustratingly braked out!

[Subzilla]

Subjuect vehicle: '83 K2500 Sub with 13" drum brakes

Symptom: Low speed (parking deck speed), rear brakes are locking up and will drag. It is very random but always seems to be at low speeds and it is worse when turning. It doesn't seem to do it at higher speeds and the wheel/lugnuts are not hot to touch after a trip.

R&Red: Replaced master cylinder twice, replaced leaky proportioning valve, replaced rubber brake line down to the axle, replaced all rear brake hardware (springs, adjusters, etc.), new shoes, turned drums, replaced wheel cylinders, loosened parking brake cable, adjusted shoes in and out multiple times, bleed the system multiple times, even ground down the small wear ridges on the backing plate where the shoes ride.

I really have no idea what to do next. After I work on it, it seems to not do it for a few days, then it starts showing up again. I haven't checked any steel lines yet. Could there be a blockage? If so, it would seem to be more consistent and not so random. One more note, it seems to be both sides that are randomly locking up but more so on the right - enough to make it pull to the right. I keep thinking it's the front but after it happens, I look at the back tires and see "skid" marks on them.

[Robyn]

Is there any chance that the long shoes are in the forward position.

Usually this is the culprit when having locking issues at low speed.

Possibly the brake shoes are not properly "Arced" a set of shoes that are arced wrong will grab the drum and "wrap" in really harsh.

Ya might try a different set of shoes.

Years ago, we always put the shoes on the arcing machine and cut them so the "Toe" of the front shoe did not contact the drum, but instead the contact point was closer to the middle of the shoe.

If the toe hits first, then this causes the shoe to Grab and then it in turn forces the rear shoe to engage at the bottom and "wrap in"

Out of the box shoes are supposed to be arced but, if the drums have been worn some and then turned, the as sold configuration may be off some.

Out on the road with the vehicle at speed, the "Momentum" of the rig will usually stop this issue from happening.


Yank the drum/drums off and then remove at least one front shoe. Lay the shoe into the drum and press it up to the braking surface. Now look and see how the face of the shoe contacts the drum.

If the shoe lays in perfect contact with the radius of the drum, there is the issue most likely.

The shoe should actually touch in the middle and be slightly away from the drum at the ends. (sort of rock back and forth)

Under actual operation the shoes will flex a little at higher braking pressures and then the entire braking surface comes into contact.


Give this a look see.

Missy

[Subzilla]

I did check to make sure the long shoes in the back. And I just put on brand-spanking new shoes 3 days ago. The old shoes did this, the new ones are doing it. This is the first time I have turned these drums and I don't remember how old they are. I know I've replaced them since I've had the vehicle.

The funny thing is after the vehicle sits here at work the whole day, it will sometimes still be up when I begin making the urban parking deck turns (I hate working in the city but I love living out in the country). And I will get the tire chirping at every turn.

You realize you're asking me to remove the back tires and brakes for the 20th time in the last 6 months!! I've about worn out the lugnuts! Guess I need to do it and check the arcness. I still have the old shoes so I can easily remove the drum and use the old shoe to check.

Thanks for the advice! As always!

[Robyn]

That's about the only thing I can think of.

keep us posted

Missy

[DmaxMaverick]

Proportioning/Isolator valve.

[JohnC]

Are you getting the chirping in conjunction with brake application or not?

What kind of differential (locking?) do you have?

[Subzilla]

Dmax, I don't recall have a separate valve on the rear like I've heard others talk about.

John, the chirping/brake drag occurs after the brake application, randomly occurs usually when making a turn AND flexing the vehicle as in a steep driveway or the speed humps in my workplace parking deck, it will continue dragging after I let up on the brakes and will stop again at random. Reapplying the brakes does not seem to take it away or make it worse. What are you thoughts?

I'm wondering if my ebrake cable might be bouncing around and binding up the brakes?? Just got home tonight (9:30) and it's in the 20's. Didn't have the urge to mess with it.

[JohnC]

I was thinking if it is not directly coupled with brake application but always coupled with turning it could be a locking differential not allowing the two rear wheels to turn at different speeds.

You're not stuck in 4wd are you?

[Subzilla]

I've got an open diff - nothing fancy here. I asked the same question to others locally and they seemed to dismiss the possibility. Could an open diff randomly lock up both wheels?

I thought about the 4WD thing but IF the transfer case were stuck in 4WD, the front manual locking hubs would also have to be locked up to create this situation. But it does have very similar characteristics - 4WD on dry pavement.

[DmaxMaverick]

If front and rear are both not releasing, that only leaves the hydroboost unit or mechanical linkage hardware (between the pedal and HB). Sounds like the only relevant parts you haven't replaced. If it happens mostly during turns, it could be a hydraulic issue, as the brake boost pressure can/does drop with more power steering demand. A worn out pump will cause low brake boost performance, but won't cause brakes to not release. A bad pump can dump enough crap into the HB unit, causing it to fail, though.

The rear/center hose has a milled junction block (which you should have replaced, according to your list of new parts). Not certain, but always believed it was an isolator. I can't imagine it not having one on the rear.

If you are unsure if it is staying in 2wd, jack one front wheel and spin it. If it doesn't spin, it's locked in 4wd (or the brakes aren't released....loosen the bleeder to check/release pressure). This shouldn't be an issue, unless BOTH hub lockers, AND the transfer case have failed, locked in, at the same time. Not likely, but worth a check. The auto locking hubs can cause issues if the transfer case isn't staying disengaged.

[crashz]

I was thinking like John when I first started reading this. Maybe you have already done this, but try spinning the wheels with the rear axle jacked up ( on stands of course). It is always possible that a spider gear may have failed. I had axle failure on both of my 1983 K2500's with the semi floating 14 bolt rear axle. But they both started as pinion bearing failure and were noticably load when coasting.

[Subzilla]

Dmax, I do have a splitter block that sits right on top of the diff. I always thought it was just a splitter. And you're right, I didn't replace it. Tried to find one on line but they must not be too popular. Couldn't find a single listing.

crashz, I did wonder about the spider gear but would this failure act like brakes grabbing and pulling to one side? If I spin the tires, what am I looking/listening for? When I threw on the new shoes this past Monday, I got the usual opposing spinning of the opposite wheel with the open diff.

[DmaxMaverick]

Dmax, I do have a splitter block that sits right on top of the diff. I always thought it was just a splitter. And you're right, I didn't replace it. Tried to find one on line but they must not be too popular. Couldn't find a single listing.

Rockauto has the center/rear hose assy, and it appears the "block" is part of the hose. The pictures are small, hard to tell. The "Isolator" on early models is a simple valve, which only "shuttles" when there is a significant pressure differential between the sides, such as a broken line or blown slave. It prevents excessive fluid loss, air introduction, and loss of brakes on the good side.

crashz, I did wonder about the spider gear but would this failure act like brakes grabbing and pulling to one side? If I spin the tires, what am I looking/listening for? When I threw on the new shoes this past Monday, I got the usual opposing spinning of the opposite wheel with the open diff.

If the side gears, R/P or bearings fail, you'll hear and feel it easily while spinning it by hand. If the axle turned easily and quiet, with the opposing wheel doing what it should (opposite direction with open, same direction with L/S), that isn't likely the problem. You'd have other indicators as well, it wouldn't be limited to braking, and it won't last long before puking parts through the rear cover (been there, done that, too many times).

[87max]

Any luck with this? How about Bearings?

[Subzilla]

Well, sorta but not really. I replaced the shoes with midgrade stuff and had the drums turned. That seemed to resolve the touchy brakes I've had for the last year or 2 but not the real grabby/locking issue I was trying to fix. It's locked a couple of times since I replaced the shoes (one being this cold vacation morning in TN). Just grabbed very first thing in the parking lot as I was rounding the corners. Then didn't do it again.

I haven't messed with the ebrake cable or checked the arc of the drums per Robyn. Weather has been nasty for the last month and times have been busy. I do have the splitter block and it is part of the rear brake hose which I replaced. I don't remember the axle bearings having any major resistance when I replaced the brakes. I'm still leaning toward the ebrake cable. I'll update the thread when I get a moment to experiment with it.

[vault]

I have a very similar issue except it doesn't really happen when I apply the brakes. more often randomly or when I hit a bump or turn. will release just as randomly but will for sure release if the truck rolls backwards a little when I'm at a stop light. It is worse (more frequent) AFTER towing.

[Subzilla]

I think I fixed it by replacing the front brake rubber lines. I really had thought it was the back brakes locking but the more I diagnosed it and watched it, the more I realized it was the front brakes. It was so random and I couldn't really get out to see what was going on.

I've had the Sub for the last 15 years and not touched the lines so I'm guessing they might be the originals from '83! Replaced them 4 months ago and have not had them lock up at all. Must have been collapsing internally and causing some major blocking of fluid but only when I was turning and flexing the front suspension. Guessing the lines were twisting.

[HH]

That's a tough one to diagnose! I had a similar problem, but it was the parking brake cable sticking on one side, yet the pedal would come back up.

[87max]

Pop always said it's the last place you look & theres the problem! Thanks for the follow up.