Brake pedal sticking/brakes staying on

[krustyballer16]

So my brake pedal keeps sticking down a little bit, engaging the brakes.

Not locking them up, just dragging.

And my brake lift stays on too since the pedal doesn't come back up all the way.

 

Got a new booster, 2nd new one actually because on the first one, the rod was too long and the brakes kept locking up and staying on and wouldn't release.

So got a 2nd booster...

It had a junk yard Grand Cherokee master cylinder on it. We replaced it before changed the booster.

So it's got a 2nd, brand new MC on it...

 

Is there a maximum amount of vacuum to be run to these boosters?

 

My alternator creates vacuum for brakes and we're not sure of maybe it's killing all the boosters we put on.

These two problems (locking up 1st time and sticking a bit now) didn't happen as soon as new parts were installed. It's taken a couple months for the problems to start back up again...

 

Any ideas?

[cruiser54]

Ever seen this?

 

[ParadiseMJ]

My alternator creates vacuum for brakes and we're not sure of maybe it's killing all the boosters we put on.

 

 

How does that work?  All my vehicles get their vacuum from the intake manifold.  I've never seen a system where the alternator supplies the vacuum.

[krustyballer16]

Well I swapped in a 3.3 Cummins...so needed a vacuum pump to make vacuum

It's an alternator/pump off an Isuzu diesel.

[HOrnbrod]

Stick a vacuum gauge on it and see how much it's pulling and if vacuum is steady at the booster. Check for leaking / collapsing booster vacuum hose, and if the check valve is working.

[krustyballer16]

Ever seen this?

 

Ours is non adjustable, of that is what you're pointing at.

On the first booster we had, the rod was too long and wouldn't release.

[krustyballer16]

Stick a vacuum gauge on it and see how much it's pulling and if vacuum is steady at the booster. Check for leaking / collapsing booster vacuum hose, and if the check valve is working.

New check valve, all lines are good.

We took everything apart and put it back together, the same, nothing caught our eye as wrong or malfunctioning, and now it seems to work fine. Well for 1 day so far.

[A-man930]

Intrigued 

[krustyballer16]

Update: it seems that after just taking everything apart and putting it back together fixed he problem.

 

Not a clue what was wrong...

[cruiser54]

Update: it seems that after just taking everything apart and putting it back together fixed he problem.

 

Not a clue what was wrong...

Needed to be taken apart and put back together...LOL. 

[krustyballer16]

I guess sometimes that's all it takes...

[krustyballer16]

Didn't fix it....

Brake light stays on again...

I'm frustrated with it!

Brakes stay on just enough that I can't roll the truck by hand. And with a trailer it's multiplied...

[HOrnbrod]

Try these brake booster checks:

 

Test Power Brake Booster

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.

[A-man930]

What kind of free play is there in the pedal linkage?

[krustyballer16]

Everything checks out how its supposed to. Feels the same as my dads mj. We'll take the MC off this weekend and warranty it out and try another new one.

Wish there was a spring on the pedal...

[cruiser54]

This might help.

 

[HOrnbrod]

Krusty, I have this brake pedal return spring kit if you want to try it. I'll never use it. 

 

http://comancheclub.com/topic/46872-brake-pedal-return-spring/?hl=tsb

 

Image Not Found

[krustyballer16]

Bolt is in right.

[A-man930]

I'll bet there's an issue with the "return" spring in the booster just not having enough umph.  hornbrod, did you ever locate that TSB?

[HOrnbrod]

I found this: Jeep TSB 05-51-92, Brake Lamps Stuck On/Speed Control Inop - Spring Kit, 4720825.

 

It says 91, but it should work on any MJ brake pedal and shaft.

[krustyballer16]

Mine is a 91!

But I think first step, we're gonna warranty out everything again and start over

[HOrnbrod]

If you want to try the pedal return spring later, shoot me a PM.

[krustyballer16]

I guess mine being a 91 doesnt matter... it was an automatic and we took the pedals out of an 88...

[krustyballer16]

New master cylinder Saturday... haven't had any issues yet. We'll see.

[krustyballer16]

Well, made it two weeks and now the pedal is back to sticking on... hmm......