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#46 olcowhand ONLINE  

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Posted July 15, 2014 - 09:17 PM

My son's Chevy S10's ABS did the opposite....no brakes at all at least 2 times.  He pulled the fuse & brakes were perfect from then on.  


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#47 trowel OFFLINE  

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Posted July 16, 2014 - 04:26 AM

We have always coined ABS as American Bull Sh*t, nothing but trouble, for a machine that lives outside for the rest of it's life it should never see a computer, nothing but expensive problems.


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#48 Alc ONLINE  

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Posted July 16, 2014 - 05:33 AM

If it's the ABS keeping the brakes applied it would be the first time I heard of , not even sure how it could . But not knowing how the valving is inside one maybe . I know first hand with my old car the ABS came on while braking with snow on the ground  , the next brake application the brakes felt spongy , so I went into a empty parking lot and kept locking the brake up and it freed up a solenoid for one of the front wheels , got lucky I guess . Other vehicles weren't so lucky , replacement parts were needed . Wheel speed sensors , whole ABS units . All those were spongy or ABS was coming on without wheel lock-up ( bad sensors , broken pick-up on a halfshaft ) 


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#49 johndeereelfman OFFLINE  

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Posted July 16, 2014 - 09:01 PM

As stated, I pulled the ABS fuse last night, and I drove the truck to work this morning, roughly 21 miles, without any troubles at all. Later in the morning, about 9:30, I had to drive to a job site to meet a couple of installers that we hired out, and put another 78 miles on the truck, most of which were highway miles. About halfway into the trip, I noticed a little brake grabbing, but nothing like I had before. As I was getting off at my exit, I went for the brakes, and the pedal almost went completely to the floor. The brakes were working but barely. I went roughly a half mile, and my brake pedal seemed normal again each time I used the brakes after that. I stayed at the job site for about three hours, so if the brakes were hot, they had plenty of time to cool. Anyway, on the return to the office just after noon, I noticed the brakes again starting to stick a little roughly about 3/4 of the way back, but again, nothing like before. I got back to the office, and the truck sat in the parking lot for about 3 1/2 hours before I started home. The whole way home, again roughly 21 miles, I didn't have any trouble. Since there is still some sticking every now and then without the ABS, this would tell me the ABS is good and don't need to be replaced, correct?

 

Things are better without the ABS fuse in, but the brakes still want to stick just a little when the truck seems to be hot from running. I think tomorrow night I'm going to try draining all of the brake fluid and bleeding all of the brake lines, and fill everything with new fluid, just to see if that makes any difference. I starting to think too now, that the fluid is contaminated and isn't flowing like it's supposed. If I drain the fluids and find that the brakes still want to stick, then I think I'll bite the bullet an take it to a mechanic and see about checking the brake module and master cylinder. I was hoping to save some money and things myself, but if I have to spend the money to get it done right and keeping everybody safe, then I guess that's what I have to do.

 

How hard is it to replace a master cylinder myself? Do you recommend I can do it, or does it have to be done by a mechanic? Does anybody know where the brake module is located on these GMC trucks? How hard are they to replace? Something I can do, or needed done by a professional?



#50 trowel OFFLINE  

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Posted July 17, 2014 - 04:54 AM

I have done it before on the old trucks from the 80's, master cylinder, diaphragm and booster with the primitive ABS but these new ones are a new ball game i don't fully know. As far as changing parts it's rather straight forwards, easy, not really, not much room to work with, after the change then the computer likely will spit codes and have fits requiring a computer to ''reprogram''.

 

Hopefully someone who has more knowledge then me could help, at least you was able to drive the truck without it locking up instantly which states the brakes are working without the ABS ramming it closed but i am questioning the ''want'' to stick, it seems there is a underlining problem.

 

Here is something to try, when in question disconnect and blow out each line individually with a strong air compressor, the lines can take a lot of PSI so no worries there, pore in more fluid and blow it out again, that should remove any contamination without wasting lots of fluids.


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#51 toppop52 ONLINE  

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Posted July 17, 2014 - 06:33 AM

A power bleeder would be best if you can borrow one. If the fluid is contaminated, the master cylinder may well be bad, as the contaminated fluid will ruin the internal seals and such often times.


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#52 MH81 OFFLINE  

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Posted July 17, 2014 - 06:42 AM

Just out of curiosity, what kind of contamination is everyone suspecting? Water, particulates, ?
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#53 Alc ONLINE  

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Posted July 17, 2014 - 06:58 AM

Troy did you figure out what wheels the brakes are sticking ?  Does this truck have discs or drum rear brakes ? 


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#54 DougT ONLINE  

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Posted July 17, 2014 - 07:06 AM

Just out of curiosity, what kind of contamination is everyone suspecting? Water, particulates, ?

Throw petroleum products in the mix too. I would suspect that or particulates for this problem. The master cylindrer has built in check valves that hold a small residual pressure in the lines. If the check holds too much pressure the brakes lock up. If you have the brakes locked up you could loosen the line nut at the master cylinder and see if they release.

 

Another thing I ran into once was an overfull master cylinder and that didn't have enough room for the fluid to expand when hot and would apply the brakes. I've seen boosters apply the brakes themselves but the pedal height was always affected.


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#55 TAHOE OFFLINE  

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Posted July 17, 2014 - 07:41 AM

Now that you say it went to the floor the one time, that leads me to believe the master cyl is the culprit as others also mentioned. 


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#56 Alc ONLINE  

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Posted July 17, 2014 - 08:41 AM

 

If you have the brakes locked up you could loosen the line nut at the master cylinder and see if they release.

Doug  that's a great idea when troubleshooting a problem like this  :thumbs:


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#57 Bmerf OFFLINE  

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Posted July 17, 2014 - 08:09 PM

I've been :watch_over_fence: Most of the stuff I have worked on is older, but time for my $.02,

... As I was getting off at my exit, I went for the brakes, and the pedal almost went completely to the floor. The brakes were working but barely. I went roughly a half mile, and my brake pedal seemed normal again each time I used the brakes after that....

 

This was probably caused by the warped rotors.

Let me try to explain;

On any properly working brake system; The front gives ~70% of the stopping power. The rear is what gives you a high pedal or pedal "feel". Rear drum brakes worn or out of adjustment? Low brake pedal. Air in line? Soft or spongy feeling brakes.

On a disc brake system there is no check valve in the disc brake line, as in a drum brake system. The check valve in the drum system keeps a little (less than 2 psi) pressure on the drum brake shoes to keep the pedal from being moved excessively before brake application, otherwise the drum springs would retract the shoes, creating excessive "space" before brake application.

On the front disc system, no springs to overcome or pull pads away from rotor. The "wobble" of the rotor (even perfectly round/square rotors) pushes the pads back for clearance. On warped rotors, the pads are pushed farther away. After a long drive without applying the brakes, the first time the pedal will move excessively toward the floor because it needs to move the pads back into contact with the rotors. It will feel as if you need to "pump them up" to work.

Now if a caliper is "sticking," Vehicle will usually pull to that side when the brakes are not applied. That side will get hot and cause the fluid to "boil."  This will usually cause the vehicle to pull in the opposite direction upon the application of the brakes.  As the fluid "boils," it looses it ablity to remain solid and forms an "air" bubble. This causes brake fade. "Air" in the the system will compress without pushing on the pads, the opposite side will still be fine and grab the rotor, pulling the vehicle to that side upon brake application. When the fluid cools, the "air" which is actually gases, will be reabsorbed into the fluid. The caliper however, will remain stuck, and the process will repeat. The rotor will be very hot and may even glow red after a drive.

As for the master cylinder, my experience is either they work or don't. Never had one that applied the brakes by themselves, they usually will fade to the floor, interal by-pass. But I suppose a piece of the rubber seals could be blocking the line port and causing a "check valve" effect. Fairly easy to replace. Make sure to bench bleed and follow all the included instructions.

Now you said the calipers have been replaced? I would say this should eliminate them as being bad. (they still could be though) Next thing to look at would be old rubber lines, deterioration could cause a "check valve" effect, holding pressure in the system. I like the idea of loosening a line to see if there is alot of pressure in the system. (there should be none to very little) New lines you say? Look at the fluid, bleed brakes with new. As you are currently are contemplating.

Only other thing to suggest would be to look at the steel hard lines, maybe one is kinked/smashed? Is there a braided line from the master cylinder to the proportioning valve/ABS thingy? It could have internal deterioration.

And one other thing: I know this is far fetched and highly unlikely, but I have personally seen it happen, are the lines connected backwards at the master cylinder? Drum check valve holding pressure on the calipers? Brakes will stay applied and drag!

 

I know this was long and of little help, but as one of my old instructers used to say thirty+ years ago, "brakes are easy, wait until they figure out how to install a computer to make them hard." Good luck and keep us informed


Edited by Bmerf, July 17, 2014 - 08:25 PM.

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#58 toomanytoys84 ONLINE  

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Posted July 18, 2014 - 07:15 PM

I ca understand your theory of warped rotors causing the problem. But I have been horrible about replacing brakes in my younger days when I was poor. I've had rotors warped so bad that when you press on the pedal the vehicle felt like you were going to shake apart but never had the pedal go to the floor. I've had pads with not brake material left just metal on rotor and still felt horrible but stopped with a roaring screech.

I don't see water causing this either unless it's rusted stuff up. Water won't compress. I have been underground in the coal mine and blew a brake hose on a rail bus. I had a hose but no fluid so rather than walk 14 miles to the elevator I filled the master cylinder with water and bled the brakes. Worked perfect. Long term it will ruin calipers.

He had had 2 sets of rotors put on this truck. I don't see rotors as the problem.

Edited by toomanytoys84, July 18, 2014 - 07:16 PM.

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#59 Reverend Blair OFFLINE  

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Posted July 18, 2014 - 08:08 PM

A little out of left field, but I had a similar problem on a 1976 van.  Turned out to be the proportioning valve.  Not sure if they have such a thing on these new trucks, but they must have something that does the same job.

 

Nobody back then had ever heard of such a problem, so I must be special. Perhaps you're special too?



#60 Jack OFFLINE  

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Posted July 18, 2014 - 08:33 PM

Troy I have fought this same problem a few times before. Having replaced all the parts you have been
through on several occasions.. The problem showed up once just from a long extended idle and the brakes would apply themselves with out the truck even being driven. It was always worse on a very hot day.
This is what I found. With the truck sitting on a very slight incline it would not roll on its own. I found that if I put my foot under the brake pedal and pulled up on the pedal the brakes would free up and the truck would roll. After looking at TSB's and talking to several GM service techs we found a
"service bulletin" that listed a shim for the brake booster. This was not something GM made available to the public as they do not want to say there is a problem that could lead to a recall etc. Anyway on to the fix...As we did not have that shim we improvised and spaced the booster out from the firewall with a couple flat washers slipped on to each of the four booster mounting studs. It worked much better for a while however the
problem did slightly return. The final fix was two dealer boosters and then a third one that was aftermarket reman before the problem was finally resolved. The key to figuring this out was the loss of any free play in the brake pedals travel when the problem was occurring. The pedal would apply right at
the top with no real travel before they started to apply. I think your problem is going to take a
booster to finally repair the problem. In our case it took three. Plus a lot of unneeded burnt up
brake parts getting there. If you can get the brakes to drag again try the pulling up on the pedal and see if they free up. If they do the booster IS the problem. I hope this helps you out. Jack... PS- I think it is related to high underhood temps causing the booster to apply by its self but I can not explain why this happens but it does..

Edited by Jack, July 18, 2014 - 08:46 PM.

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