Hydroboost and right rear dragging

[Warkmeister]

Hey guys my 81 k30 CCLB SRW is giving me fits. I got it with a partially completed rear disc conversion and finished that up with the appropriate parts. After a few miles/minutes of driving and fluid heats up, I notice that the right rear brakes starts to drag and eventually almost locks up. I’ve only pushed it once and had to get home, and the brakes started smoking it got so hot.

This last time that it happened I tried separating the master cylinder from the boost unit thinking I might have the wrong master cylinder or too much input pressure from a long rod, but the pressure didn’t change. They were apart about 3/8”. In order to get home, I had to open the bleeder at the caliper just to be able to drive. My question now is do I simply have air in that line and need to perform a full system flush and bleed, do the pad guides just need to be lubed, or do I need to potentially get a new master cylinder as this one doesn’t seem to be relieving pressure when you let off the brakes? I ordered a hydroboost seal kit because I know it weeps a little from the top port just above the mc mounting side.

What area of system failure only affects one wheel? Other brakes may be dragging, but it’s imperceptible due to the severity of the right rear. All rear brake components are new, as is MC, and stainless rear lines from the Tee to calipers.

 

[78C10BigTen]

I dont have hydro boost and i still have drum brakes in the back of my 78 but i have issues pretty much the same as yours. Randomly if i touch the brakes, even a gentle press the right rear locks completely and squeals the tire. It seems to be completely random too. Im confused. But i had an 87 celebrity that used to do the same thing only after a rain. Someone said its due to the shoes sucking up moisture and swelling but my 78 will do it on a hot summer day...

 

[Blue Ox]

I dont have hydro boost and i still have drum brakes in the back of my 78 but i have issues pretty much the same as yours. Randomly if i touch the brakes, even a gentle press the right rear locks completely and squeals the tire. It seems to be completely random too. Im confused. But i had an 87 celebrity that used to do the same thing only after a rain. Someone said its due to the shoes sucking up moisture and swelling but my 78 will do it on a hot summer day...

Are they adjusted correctly? Sometimes if they're too sloppy that "self energizing" thing makes them grabby.

To the OP, are you sure the caliper is moving freely in the slides? Otherwise the only thing I can think of that would only affect one side is the piston isn't retracting.

Wait, I can think of another thing. If you have calipers you'll have hoses. A faulty hose can do exactly that.

 

[Snoots]

X2 for above and, did you do a COMPLETE flush of brake fluid?

 

[78C10BigTen]

Are they adjusted correctly? Sometimes if they're too sloppy that "self energizing" thing makes them grabby.

Ive driven it for almost 2 years with no issue then all of a sudden one day...

 

[highdesertrange]

x3 caliper is hanging up. highdesertranger

 

[highdesertrange]

if a drum brake is doing it. either the shoes are not installed properly or the drum is out of round. highdesertranger

 

[Blue Ox]

Ive driven it for almost 2 years with no issue then all of a sudden one day...

Okay, what's your point?

Not trying to sound like a douche, but something happened. You need to give it a looksy. Maybe it's out of adjustment, maybe the shoes are worn out, maybe the drum warped. Before I did the JB7 brake upgrade, my Suburban went through a complete set of brakes every 12K mi.

 

[Warkmeister]

Thanks for the ideas guys. It has discs in the rear, and the rear lines are brand new as well. I did NOT do a system flush and I know that’s an easy first step. I also did not double check to see if the pads are hanging up on the slides. I need to do these basic first steps, so I’ll report back to see what comes of them.

How critical are the pad clips that wedge inside the piston? They seemed like they wouldn’t be of much use in anything, but they are in there. Do I need to bend them to make them tighter?

 

[1987 GMC Jimmy]

I’ve found that those clips don’t like being removed and reinstalled a bunch of times, and I had to bend them to make them do what they’re supposed to. The pads should go “click” when that’s doing what it’s supposed to. I don’t think that’ll be a make or break for the issue you’re having. Like it was mentioned above, I think something’s funky with the caliper or the hose. How old’s this caliper?

@78c10bigten, how was the Celebrity? When I tell people of the attributes you want in a good first car, I use the Celebrity as an example because of good visibility, the easy to work on Iron Duke, and it’s relatively compact size. I’ve never had one, though, so I might be mistaken there.

 

[Warkmeister]

Calipers are both napa remans, less than a month old

 

[1987 GMC Jimmy]

That’s strange. It sounds like, aside from the flush, everything was done by the book.

 

[Snoots]

Could be a bad spring on the brake assembly?
Bad bump could've messed with the adjuster?

You're gonna have to pull the drum and check.

And Blue Ox, what's this 'JB7 Upgrade'? I couldn't find diddly when doing a search.

 

[Blue Ox]

JB-7 is the brake package on a C6P 8600 GVW chassis.

It's kind of a halfway between a 20 and a 30. So it uses larger calipers and pads on the front, but the same rotors as a regular 20, and 13" drums on the rear as opposed to the 11" on a regular 20, but with a narrower shoe than a 30. I believe they also all use Hydroboost like a 30 would.

The 'burb was a K1500 with a JB-5 brake package which I considered about equal to the brakes on a full size Cadillac. That was probably okay for a car, but on a 6000 lb truck they left a lot to be desired on stopping power and they didn't last for spit. So at some point I acquired a 14 bolt FF and converted all the brake gear to match my pickup which was a JB-7. After that the stopping power was much improved and I wasn't doing brakes in less than a year.

 

[78C10BigTen]

I’ve found that those clips don’t like being removed and reinstalled a bunch of times, and I had to bend them to make them do what they’re supposed to. The pads should go “click” when that’s doing what it’s supposed to. I don’t think that’ll be a make or break for the issue you’re having. Like it was mentioned above, I think something’s funky with the caliper or the hose. How old’s this caliper?

@78c10bigten, how was the Celebrity? When I tell people of the attributes you want in a good first car, I use the Celebrity as an example because of good visibility, the easy to work on Iron Duke, and it’s relatively compact size. I’ve never had one, though, so I might be mistaken there.

I bought mine right outta high school with my graduation money $400. I loved the hell outta that car. Mine was a 2.8L v6 station wagon. Id recommend them as a first car. Theyre cheap, take a beatin and last forever. I had mine for a few years then gave it to my dad and bought a truck. He ran it daily for years also till one day it just wouldnt start and we never figured out why. Worst part about that car was being it was an 87 the body was rotting quick.