'85 4x4 frustrating brake problem

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Apr 22, 2011 | 01:20 PM

Steaksauce

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From: Hawaii/Palmyra Atoll

'85 4x4 frustrating brake problem

Here's my problem, I hope someone can help me figure this out: My brakes are not releasing pressure. After using the brakes four or five times I have to pull over and crack the bleeder on one of the callipers to release some pressure or they just keep getting tighter.

I have replaced both callipers (with new pads too) and replaced the master cylinder. rotors are good. I have bled the bejesus out of the system--bench bled the master and bled each wheel going furthest to closest to the cylinder.

I replaced the booster a year ago. The back shoes may be getting worn but at first attempt I couldn't get the drums off (the threads stripped) and haven't had another go at it yet.

If it was a flexible hose it seems like it would be one wheel or another not consistent throughout the system?? and they both feel hard/not collapsed. If it was air in the system it should be spongy but it is firm. I tried adjusting the pedal to make sure the master was able to retract fully to uncover the return port.

could the back pistons be affecting the fronts? or could a weird napa booster be stopping the master from releasing? I saw one post that mentioned the proportioning valve but it doesn't make sense to me that it would stop the master from letting pressure go.

any ideas would be appreciated a LOT. This is getting kind of old. Thanks

Apr 22, 2011 | 01:30 PM

Broknbonz

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From: Unionville, Tn

if the calipers are releasing when you crack the bleeder screws then it sounds like your flex lines are collapsed or swollen internally. if they are original they are due replacement either way

Apr 22, 2011 | 01:34 PM

Steaksauce

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From: Hawaii/Palmyra Atoll

Good point. If that's it it'll make my day and if it isn't I should replace them anyway. logical next step. It still seems a little weird to me that the tension is perfectly even side to side if it's hoses. I'll try it. Thanks.

Apr 22, 2011 | 02:09 PM

corax

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From: PDX

Quote:

Originally Posted by corax

before you replace the master cylinder, adjust the pushrod - if the master cylinder pistons aren't coming back all the way it will hold residual pressure in the system. Brake pedal should have a slight amount of play (not related to the MC push rod), but also make sure you're brake light switch isn't holding the pedal down.

The pushrod adjustment trick I learned was to put a dab of grease on the end of the shaft and then put the master cylinder in place. Remove the master cyl and look at how much grease is left on the end of the shaft. If there is zero clearance when assembled, the grease gets completely squeezed off the end of the shaft.

https://www.yotatech.com/forums/f116.../#post51680199

There are 2 adjustments - one for the pedal->booster and one for the booter-> master cylinder. My money would be that the booster->MC pushrod is too tight

here's another one:
https://www.yotatech.com/forums/f116.../#post51200704

Last edited by corax; Apr 22, 2011 at 02:11 PM.

Apr 22, 2011 | 05:55 PM

Steaksauce

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From: Hawaii/Palmyra Atoll

It looks like that was it. I didn't know about the MC>booster adjustment. It's obvious when you look at it but I'd have never known it was there. Thanks for re-posting that. Even though It seemed like it was fixed a couple times before, I can tell by the way it feels now that was the issue the whole time. . .makes perfect sense. Glad to have the new hoses on there too. Thanks you guys.