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Front Calipers not releasing


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clatonious
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Apr 7, 2013, 11:34 AM

Post #1 of 19 (881 views)
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Front Calipers not releasing Sign In

1995 buick roadmaster

Front calipers are not releasing 100%. I discovered this issue while replacing the brakes, went ahead and did calipers, rotors, and wheel bearings while in there so I'm all new on both sides (so rule out the obvious like calipers need lube). Both sides will not spin freely and are heating up when driven. If I open either bleeder then they BOTH release...demonstrating it is not a faulty flex hose. Therefore it can only be: A) bad master cylinder, B) push rod out of adjustment (I did buy it used and have no idea what's been done), or C) a bad combo/proportioning valve.

I don't think it's an ABS issue, nothing indicates there's any failure there. I'm trying to avoid just throwing parts at it and would rather diagnose my way through the issue so I'm looking for a way to test each component listed above to see where that last few pounds of pressure is not being released.

I know for starters the push rod adjustment can be tested by breaking the master cylinder free from the booster thus creating slack. So that solves B.

Any suggestions on isolating that unrelieved pressure?

OR, am I missing something else?

PS: I can't see it being an issue of wrong parts, it all fit together precisely as it should have. The only deviance from OEM I've made is the car is lowered on drop spindles and I put ceramic pads on the front. I can't see how either would have any bearing on this issue.


(This post was edited by clatonious on Apr 20, 2013, 7:57 PM)


Hammer Time
Ultimate Carjunky / Moderator


Apr 7, 2013, 11:46 AM

Post #2 of 19 (875 views)
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Quote
Therefore it can only be: A) bad master cylinder, B) push rod out of adjustment


I think you hit the nail on the head there.

The next time the brakes are locked up, get the front wheels off the ground and then loosen the hold down bolts to the master and slide it away from the boost by a quarter inch and see if the brakes free up. That will tell you if it's a rod adjustment problem. If that doesn't release them, crack the line loose at the master and see if that does to indicate a bad master.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
Veteran / Moderator


Apr 7, 2013, 12:16 PM

Post #3 of 19 (848 views)
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Also before you unbolt the master from the brake booster to see if the brakes release, pull the booster check valve out of the booster to relieve the vacuum in the booster to see if the booster is the culprit. Seen that happen on a few cars.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 7, 2013, 12:25 PM

Post #4 of 19 (846 views)
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Hammer's suggestion is right on target. I can't imagine both flex hoses at once doing this. You may notice unusually little freeplay at top of brake pedal now.

This happened to me just once with a new master cyl that was in fact defective - whole batch was. I can't think of the pushrod being too different after doing brakes unless it was messed with or replaced. Master must let fluid back in of course so is highly likely to have a problem doing that. This is unusual to me for just doing routine brake job but that would explain it,

T


clatonious
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Apr 7, 2013, 2:18 PM

Post #5 of 19 (827 views)
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**UPDATE**
Jacked up the car this morning and both wheels were fairly free spinning. Started it up and pumped the pedal several times, holding it and such, and eventually they got pretty tight. Cracking it at the master cylinder did free them up.

One more odd thing...since I've gotten the car I've always felt a slight click in the steering wheel whenever I first tap the brakes. My neighbor was helping me today and pointed out that while I was pumping the brakes to get them to lock up the whole booster was flexing (which explains the tapping sensation). As the pedal goes nears the floor (and the piston in the mc nears its end) you can see the flex occur...which would lead one to thing the rod is too long or the pedal out of adjustment.

So I consulted my buick service bulletin on this which tells me NOTHING is adjustable, if rod is too long replace entire booster!


First off the booster is operating just fine.

Secondly, the resistance is right at the end of the pedal run, meaning the piston in the mc is just about fully engaged when the resistance hits, causing the booster to physically flex.

Is it possible that the mc is indeed toast due to A) it releasing pressure by cracking the line and B) having something in it that doesn't allow the piston to fully compress, thus causing resistance to the pedal/rod to the extreme that it actually makes the booster flex against the firewall?

I REALLY don't want to replace the booster, looks to be a super hassle.


Hammer Time
Ultimate Carjunky / Moderator


Apr 7, 2013, 3:26 PM

Post #6 of 19 (815 views)
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I advised you to loosen the mounting bolts on the master before cracking the line open. Did you ignore that step?




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



clatonious
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Apr 7, 2013, 3:40 PM

Post #7 of 19 (811 views)
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ignored is not really the right word but yes I did start with the lines on the mc first because the car is out there and the computer is in here and I didn't remember the order. It's really not a big deal to go through it again because more than anything I want to understand what's going on here...leave it to me to have the flexing firewall.

Just bear in mind there was too much rod (or not enough room left in mc) to begin with otherwise I'd have never felt that sensation in the steering wheel from day one. Also, none of this was a result of the new calipers/brakes/rotors/bearings...I'd noticed the heat before but figured bad caliper.

I'll retest because I see now that cracking the lines would've relieved pressure from the lines OR from the rod...I get it.

BUT the fact remains I am flexing the booster due to too much rod or not enough mc and that's got to tell us something. I cannot believe GM is saying there's no adjustment, and I cannot understand how a rod would grow??? It would make more sense that there's gunk or something in the end of the mc and that's not allowing the piston to get full run.


(This post was edited by clatonious on Apr 7, 2013, 3:44 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 7, 2013, 3:57 PM

Post #8 of 19 (801 views)
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Just my two cents for now but I'm not too thrilled with the booster flexing as said? No - never noticed that myself but I also don't ride under a hood when someone slams on the brakes either. Also didn't think pushrod was adjustable on much of anything like this car. For the moment and waiting I think the booster has some strange problem either itself or plain not mounted right??

T
_________________________________________
Long retired now


clatonious
Novice

Apr 7, 2013, 4:26 PM

Post #9 of 19 (792 views)
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I can't find anything to suggest the booster is mounted improperly. Think of it this way...I was splitting wood not too long ago and was into a big old gnarly stump. The wedge buried into it and the pump kept pushing the cylinder out but it had nowhere to go because the wood simply wasn't giving anymore. There was actually enough force to make the heavy channel iron frame start to flex - same thing here.

So I either have a rod that's somehow too long OR an mc piston that cannot travel its full run. I just am trying to figure out which hole to start throwing money at. AND let's not forget this may be totally unrelated to calipers not freeing completely!

I'm hoping there's a collapsed spring in the mc or a bunch of gunk or a bad grommet. New mc and wham bam pressure is relieved and booster rod is allowed to travel its full run unhindered.

Flip side of that coin is that somehow booster rod is too long and 14 hours later whole booster is replaced. Boosters and mc's cost about the same.


Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 7, 2013, 4:52 PM

Post #10 of 19 (784 views)
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What would be the difference if master was pinned to the bottom vs just the massive force of braking? Nothing. If I read this correctly this problem was there before your brake work - right? Still does it now so being BOTH wheels suggests a problem with either master or booster OR could as DS said the booster just keeps working a bit after you let go?

You have to test the suggestions out already mentioned, we can't. I still don't like it that booster can visually move like that. There's a clue of where the problem is,

T
_________________________________________
Long retired now


clatonious
Novice

Apr 7, 2013, 6:07 PM

Post #11 of 19 (772 views)
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**Update**

Bled the car out totally.
Pumped it up while on blocks, couldn't build much resistance in calipers.
Drove it around a couple miles without brakes being touched, no heat.
Did a couple quick stops, virtually no heat.
Drove it around with light stops, medium heat (could barely touch finger to rotor).
Drove it around as if in city conditions, stopping often, heavy heat (rotors hot enough to fry skin and I could feel heat on my face coming through wheel).
Jacked it back up.
Wheels at this point almost frozen but still turnable.
Pulled booster vacuum line where check valve goes into booster. Pretty significant whoosh sound and wheels suddenly nice and free.
Started it up while still in the air, pumped it a few times till I felt some slight resistance building again, killed it, pulled line and again, smaller whoosh but wheels freed right up.
Blew/sucked into check valve, working properly.

So bad booster?


Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 7, 2013, 6:36 PM

Post #12 of 19 (759 views)
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None of us are there with your techniques. Of course brakes get hot but how much is near impossible to say on circumstances they were under. You have new brakes so they aren't quite done a full break in yet I think. Right out of the gate with new parts they can take some stops to be at their best - how many depends on the parts and situation too. Brand new they might even give an odor for a few stops.

I never did a brake job without driving a car a couple miles before handing it over to a customer. Not everyone can do that where they work.

If releasing vacuum from the booster frees up the wheels that is interesting. I don't think that should matter as essentially it's just to magnify the force you give it as in "power assisted" brakes which about everything is out there.

Long retired but this isn't all rocket science in a Roadmaster or shouldn't be.

You see the booster move oddly or that's how I understand it without seeing it myself so that's a judgment call. I can't know how hard you pushed and it would show some reaction but nothing to catch attention IMO.

A situation like this to me points towards a bad booster. Can't be sure of anything - this is a website not an actual repair shop being right there with on sight inspection.

For now I think you should consider the booster as the problem but it's still your call,

T
_________________________________________
Long retired now


clatonious
Novice

Apr 7, 2013, 6:54 PM

Post #13 of 19 (755 views)
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Just as an FYI I've put well over 150 miles on the car since the brakes/rotors/bearings/calipers. Like I said, it was sticking before but I assumed bad caliper and thus did the whole 9 yards and just drove normally and softly but it kept eating at me and I started digging.

So anyway I am thinking things are broke in.

I'll give this a couple of days and see if anyone else says much about it and then probably move forward with a booster.


Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 7, 2013, 8:55 PM

Post #14 of 19 (745 views)
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As said, long retired but still do my own stuff. This is BRAKES and all regulars here don't like tossing parts as a fix but I would call this an exception by what I understand so far. If it was my own I would NOT tolerate a brake problem like that at all. If somehow brakes got way too hot and you didn't notice then call it "fade" and they may not work well or worse terrible and an accident that could be avoided over chasing this down even if it takes a few bucks is cheap.

Quick look showed them as "remans" for under $100 (exchange for yours) or a deposit lost. I doubt this one is that difficult and haven't had the fun of doing one on any of these cars but probably takes some tools to get at the thru bolts, unhook the rod to get out starting from underdash. Just nuts on studs that go thru firewall. If enough flex in master cyl to move it still intact shouldn't be that hard but could be wrong.

It seems to be the common denominator of the problem. If it makes you feel better let a tech look at the problem and you can decide on DIY or what. Now you could look to see the 3-4 nuts the hold it and the rod and know if you can get at them with the tools available to you.

It's your responsibility to make this car stop properly if not for yourself for innocent other(s.) If you can't or don't want to finish out a perfect diagnosis let a shop take care of it. The car must stop. Going is not my concern with this.

Do the right thing,

T
_________________________________________
Long retired now


clatonious
Novice

Apr 20, 2013, 7:54 PM

Post #15 of 19 (666 views)
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UPDATE

New MC, new booster, new back brakes (needed done anyways), new fluid of course and survey says.................same problem still.

Only 2 things haven't been replaced new front to back now - combo valve and front hoses (of which no test really pointed that way).

So, I'll replace the both of them....which leaves the final option - the ABS junction/system.

I understand how the combo or hoses would still be the issue but can someone explain how the ABS box or system would be behind this?


Hammer Time
Ultimate Carjunky / Moderator


Apr 20, 2013, 8:00 PM

Post #16 of 19 (662 views)
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Or you could just perform the test that you were asked to in the beginning and loosen the master cylinder mounting bolts to find out once and for all if the pressure is originating at the master.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



clatonious
Novice

Apr 20, 2013, 8:05 PM

Post #17 of 19 (658 views)
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OR you could realize that MC means master cylinder and A) that test was done and B) I put a new one on read above

Hey thanks for the help genius...great board you're running here


Hammer Time
Ultimate Carjunky / Moderator


Apr 20, 2013, 8:09 PM

Post #18 of 19 (655 views)
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You're getting one warning and one warning only. Don't run your mouth around here or you will be gone in a heartbeat.

You may think you know it all but you really don't. A new master cylinder does not eliminate an incorrect push rod adjustment. There are ways to test for all these issues instead of your method of simply throwing parts at it.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator


Apr 21, 2013, 11:11 AM

Post #19 of 19 (646 views)
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This is too important to wait. Fix it now. This is only web site not there in person or some things might be obvious.

Do the right things to fix this. No head games with Hammer Time or any body. Here for free to help so you get your money back in full - ZERO.

Nice round #. No problems folks, if you don't like this place just go away - easy! Many of us can do that for you!

Tom
_________________________________________
Long retired now




Front Calipers not releasing


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