PLEASE: need help with brake problem!

[SD_rdcruzer]

Just re-installed the prop valve and even with it fully cranked out (maximum rear line reduction) the right rear still locks up.

He has a prop. valve.

You said earlier that you changed out the MC because the rear line had a leak in it.

Have you put the old MC back in to see if that works?

 

[Magnum44]

This may not even be close but does your rear calipers have an adjustable e-brake in them or shoes in the rotor or nothing at all? Just curious. If they are adjustable is one side adjusted up more than the other?

 

[4x4Poet]

I'll throw another one out there.

...Did you bench bleed the master?

I re-read all your posts and noticed you posted that you bled the thing "to death", but you never said that you bled the master. Air in the master could affect only the front brakes.

Any pedal symtoms?

 

[johmbie]

SD: I've been thinking of reinstalling the first, or even second master, but of the three this one seems to get the best pedal. I had the same symptoms with all three.

I didn't actually replace the master because of the leak on the rear line: I replaced it because a week or so after I fixed the leak, my pedal got mushy and the right rear started locking up. that said, if I don't get it figured out pretty soon, I'm going to switch back to the first, just to ease my mind about that...

Poet: yes, I bled the master; bench bled it, installed, re-bled, attached lines and power bled the whole system including pumping the pedal under vacume, which sort of re-bleeds the master.

Shawn: prop valve aside, that's sort of where I'm stuck. is the rear locking too soon, or is the front not locking soon enough? hopefully will figure it out this morning. ideally I'd have a set of pressure gauges to see exactly what I'm getting to the front and what I'm getting at the rear. unfortunately a set of gauges is proving difficult to find.

Magnum: these are the front monte carlo calipers with no parking brake. there's no adjustment on them. I sort of wish there was: it would make diagnosing this thing a little easier!

OK: after all that, I'm left wondering if I've gotten bad information regarding residual valves. each time I've asked and everything I've read about the residual valves in regard to this 80 series master says that I shouldn't need proportioning valves or residual valves. information regarding if there are actually residual valves built in to the master itself or if they're externally mounted in the 80 itself is lacking.

hmmm... think I'm going residual valve shopping.

thanks for the help guys!

 

[e rock]

A residual valve will not address the problem of one rear tire consistently locking up before the other one. And until you know that you are getting equal pressure to both rear calipers, you cannot adequately balance the pressure bias to the front.

 

[johmbie]

might be overkill, but it should answer a few questions about this problem and let me know for sure where the problem lies...


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Item Id: WEBEQ0397

Simplify brake and ABS diagnostics and eliminate costly misdiagnoses!

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[Tankota]

Was there anything in the rear "T"? you can blow out the rear brake line all the way to both rear calipers (each side at a time then together) with compressed air to make sure there isn't something in there.

Since its only one side locking up and you swapped calipers side to side and it didn't make a difference I'd concentrate on the line going to the side that DOESN'T lock up. Crimped line, internal collapse under pressure, blockage or?

One other thing...are your caliper brackets perfectly lined up? (Both of them).


PS What kind of shape are your front brakes in? I've had the caliper piston boots allow water in and slowly start to seize up the caliper pistons resulting in reduced braking power...very slow change which was almost unnoticeable for quite a long time.

 

[johmbie]

the fronts seem to be fine, from what I can tell. that's part of the reason for the gauges: I want to be able to tell for sure. I replaced the pads, calipers, and rotors about 14 years ago, which is a lot, but actualy only about 12k miles. the pads are still probably 2/3 of new.

when you had the problem with your front calipers seizing did both sides do it at once?

I'm going to recheck the rear line and blow it out like you mentioned. even though the line is new there must be some sort of restriction there.

thanks for the help!

 

[Tankota]

the fronts seem to be fine, from what I can tell. that's part of the reason for the gauges: I want to be able to tell for sure. I replaced the pads, calipers, and rotors about 14 years ago, which is a lot, but actualy only about 12k miles. the pads are still probably 2/3 of new.

when you had the problem with your front calipers seizing did both sides do it at once?

I'm going to recheck the rear line and blow it out like you mentioned. even though the line is new there must be some sort of restriction there.

thanks for the help!

Both fronts did the "slow seize" evenly. You can check it by pulling them off and seeing how the piston retracts with pressure on it from a prybar or by hand or the like (can't feel it with a c-clamp though). Mine were very difficult to move with a prybar and if you pulled up on the boot slightly you could see the rust permeating the area badly.

btw, friend of mine a few years ago swapped on discs and did a bunch of other things. He could not get one rear side to bleed. Drove him nuts. Finally gave up and took it to a brake shop. They pointed out his u-bolt was clamped on top of his brake line on one side Good story and a laugh but when you are staring too close at something it may be hiding something in plain sight.

btw, if one of the caliper brackets is bent or slightly off it could significantly reduce the contact surface of the pads. Swapping calipers won't show this prob.

 

[johmbie]

that's really good to know about the slow-seize bit, thanks a lot! I'll be looking at that shortly.

meanwhile, my gauges got here yesterday while I was at work, so I have NEW TOYS! I'm on my way out to play now, but I'll be checking those pistons while I'm at it. Thanks again!

 

[Tankota]

Well I'm looking forward to hearing what the problem was. I always find it interesting as to what the solution to a problem was. Good luck and keep us informed.

 

[johmbie]

Survey says: faulty proportioning valve I got from downey when I did the disc swap.

installed gauges on the fronts first since I already had the wheels off. did about 8 tests, resetting the gauges each time and came up with an average of 700 lbs (engine not running).

then moved the gauges to the rears and repeated the process... 700 lbs average. hmm, maybe I have this prop valve turned the wrong way, but I thought it was all the way out for the maximum pressure reduction.

so, repeat the process with the prop valve turned all the way in and got.... 700 lbs. I'm kinda dumb, but I'm thinking that means that that prop valve isn't doing a thing other than costing me money!

I must say, though, Downey going under is a bummer. my guess is Jim would have made this right, no questions asked. I spoke to him on the phone and he was one of the best informed people I'd ever spoken too about cruisers, and very eager to help and give advice. this is just one of those parts that doesn't work; it happens.

that said, I suppose it's time to go prop valve shopping!

 

[TRoss]

A residual valve will not address the problem of one rear tire consistently locking up before the other one. And until you know that you are getting equal pressure to both rear calipers, you cannot adequately balance the pressure bias to the front.

x2

Was there anything in the rear "T"? you can blow out the rear brake line all the way to both rear calipers (each side at a time then together) with compressed air to make sure there isn't something in there.

Since its only one side locking up and you swapped calipers side to side and it didn't make a difference I'd concentrate on the line going to the side that DOESN'T lock up. Crimped line, internal collapse under pressure, blockage or?

One other thing...are your caliper brackets perfectly lined up? (Both of them).


PS What kind of shape are your front brakes in? I've had the caliper piston boots allow water in and slowly start to seize up the caliper pistons resulting in reduced braking power...very slow change which was almost unnoticeable for quite a long time.

x2

You've got something going on with the left rear circuit/caliper/bracket. You didn't need fancy gauges to figure that out.

How long have the Monte calipers been on there? When have you serviced them last? They float, unlike Toy calipers. One could be seizing up and not reacting like the other... ????

I used 2# residual, Summit prop all on an 80 series master with Cheby rear disks on my '85 mini FWIW.... works great and yes, the prop is all the way out to get proper bias.

Good luck with it!!

 

[johmbie]

the 'fancy gauges' tell me I get the same amount of pressure left and right. it seems that the right rear was locking up first because that side had less weight on it: my fat butt was on the left

the monte's have been on there about 3 months. now that I have the problem localized I can get down to tuning.

thanks for all the help everyone!