Sticky brakes?

[78 GMC Jimmy]

So on a 78 K5 with a new brake booster and new master cylinder, the brakes seem to be "sticky". What I mean is that when you have the truck on level ground, it will roll easily. If you press the brakes and then let up, the truck will not roll easily until it sits for maybe 5- 10 seconds. Same for on a mild incline. Coast to a stop and then it will roll backwards. Push the brakes, and the vehicle comes to a stop, and then you let up on the brakes and it doesn't start rolling for about 5 - 10 seconds, when the brakes "release". It increases clutch wear / more prone to stalling if I come to a stop and then immediately start moving again, such as at a stop sigh. Its not super noticeable, but its definitely something i would like to fix. I checked all 4 brakes after driving a while, and they are not hot. The brakes are not dragging, they just release slowly. Thoughts?

 

[rampage]

How old are the rubber hoses - the two in front and the rear one at the T? The rubber can break loose inside the line and create a piece the flaps, kinda like a check valve. Does it pull to one side when you apply the brakes?

 

[78 GMC Jimmy]

How old are the rubber hoses - the two in front and the rear one at the T? The rubber can break loose inside the line and create a piece the flaps, kinda like a check valve. Does it pull to one side when you apply the brakes?

Hi.

I should have thought about them. Your probably right. I just need to get all 4 wheels off the ground and have someone press the brakes and spin a tire by hand to see which one doesn't free up tight away, and then replace that rubber hose. Good call.

Not sure on the age of the hoses, but I will see if any are cracked on the outside.

It does pull, but I also have rear brake shoes soaked in diff oil, since I need to replace seal on one side. So I assume that's the cause of the pull.

 

[Bent77]

I would start with the oil soaked one, then revert to jack stand tests if needed

 

[78 GMC Jimmy]

I would start with the oil soaked one, then revert to jack stand tests if needed

The sticky brakes thing is a new symptom. The leaking oil on the brakes has been there for ever. I agree that does need to be resolved though, sooner or later. At first i though I had a problem with the booster or master cylinder, but I bet its a hose like he said.

 

[max 02]

A 78 … oil soaked drum for sure. Soggy brake lines yes, and sticky front callipers. Basically all of the above.

 

[BoondocK5]

Yep, several issues all causing same problem.

 

[Wes Harden]

grooved backing plate broken return spring/s. This is may be just me, but I could never run more then to the next weekend with oil fouling my drum brakes. Braking effectiveness, and the ability to stop straight are compromised. We all know these old heavy trucks don't stop as well as newer stuff on the road with us.

 

[78 GMC Jimmy]

So I did the test. The rear tires are slow to release after brakes applied. Its just the 1 foot rubber hose above the diff? Also the front left spins free, front right had a little drag that does not dissipate with time. Both front brake hoses seems to have some outer coating that is loose. Inner part of the hose seems solid. So replace replace all 3 hoses I guess?

 

[rampage]

Yes, just the one rubber line above the rear diff.
I’d replace all three lines. Maybe support a vendor on here like ORD.

 

[78 GMC Jimmy]

So I replaced the rubber hose at the rear axle. I could not get the bleeder open on one side, even with a special bleeder wrench, or a socket. Forcing it any more will certainly round it off, or break it off - so I just bled the system through the other side. After bleeding, I pumped it a bunch to work any air bubbles out of the other line and bled again.

Result:

Brakes seem to grab about 30% better, are more responsive, and release properly now.

The hose must have been restricted in both directions, making it hard to apply the brakes - as well as not letting them release as quickly as they should.

I love the way the brakes work now. Its funny - when we are kids we don't care about brakes, we just want more HP. Once ya grow up a little, good brakes become a much higher priority.


Thanks for the info guys.

 

[78 GMC Jimmy]

So for the one front wheel that doesn't spin 100% freely, I don't think its a check valve'd brake hose issue. Might be a funky manual hub that's not unlocking. The hubs feel differently when I turn the nobs to unlock them. One nob spins VERY easily, the other has some resistance when going from locked to unlock. How do I confirm that the manual locking hubs are actually unlocking?

 

[rampage]

Can you stick something through the axle shaft where the u-joint is? Then try spinning the wheel.

 

[78 GMC Jimmy]

Can you stick something through the axle shaft where the u-joint is? Then try spinning the wheel.

That is a fantastic idea. I will try that for sure.