Brake Problem Diagnosis

[MaineShark]

So, I get in my Shark after it sits a few days, and the "brake" light on the dash is on. The pedal is soft, and goes almost all the way to the floor before it has any effect on the car.

I recently had a new wheel bearing put in, so my first thought was that the shop damaged the caliper hose and the fluid from the rear circuit leaked out (would have been nice - quick fix, and give me a chance to put in braided hoses). Unfortunately, the resevoir is full, and stays that way.

So, bad master cylider, right?

If so, has anyone here bought one of the replacements from Ecklers? Anything to watch for when swapping them out? Any special procedures (other than the obvious, like bleeding the air - I've always wanted an excuse to buy a bleeding kit).

Joe

 

[BlackNBlue95]

So, I get in my Shark after it sits a few days, and the "brake" light on the dash is on. The pedal is soft, and goes almost all the way to the floor before it has any effect on the car.

I recently had a new wheel bearing put in, so my first thought was that the shop damaged the caliper hose and the fluid from the rear circuit leaked out (would have been nice - quick fix, and give me a chance to put in braided hoses). Unfortunately, the resevoir is full, and stays that way.

So, bad master cylider, right?

If so, has anyone here bought one of the replacements from Ecklers? Anything to watch for when swapping them out? Any special procedures (other than the obvious, like bleeding the air - I've always wanted an excuse to buy a bleeding kit).

Joe

Could be a master... but here is what makes that light come on 3 things can possibly do it.. 1 the resivoir being low (if it have a float in the resivior), a hydralic leak, or the parking brake not being fully released.. I would check it over make shure there are no leaks evident even if the fluid level appears find.. before condeming the master cycelnder.. btw almost every master I have bought has come with a bleeder kit.. I would goto a local parts store.. try to get one through a brand name such as wagner.. I can't vouch for ecklers master cyclendersI never orederd one from them.. I've always bought them throughmy shops distributors and local parts stores..
-Rick

 

[MaineShark]

Thanks for the insights. I was curious exactly which conditions can turn the light on, since tha manual only says to see the dealer.

I guess I can rule out low fluid (even if the float were stuck low, that wouldn't explain the very real differences in the brake system).

A leak sounds possible. I will carefully measure the fluid level, then pump the brakes a while and see if the level changes. I'll also put some paper on the floor at the same time, and see if I get any fluid on it.

Is there any way which the parking brake being stuck could cause the differences I noticed in the way the brakes operated?

Joe

 

[ChuckG]

There's a fourth reason why the light will come on, and that is to show a "differential" in pressure between the two halves of the brake system. That function is controlled by the so called proportioning valve.

One of the most common Corvette brake problems is air pumping back into the calipers caused by rotor runout. Air pumps back into the caliper, causing loss of pedal, and air in the system without any fluid leak. If the differential pressure between the two systems is not equal, THAT will turn the light on too.

SO....sounds like the MC, but could be rotor runout. If you bleed the system, and find air in the calipers, I would check the runout. Hope this helps. Chuck

 

[MaineShark]

One of the most common Corvette brake problems is air pumping back into the calipers caused by rotor runout.

Or maybe a mechanic who wasn't careful with the caliper when he removed it, and allowed the piston to extend a bit too far? I hope that's all it is; would be nice to have an inexpensive fix, like just buying a bleeder and some fluid...

Joe

 

[lrh]

Mine has started doing the same thing only with a slight click in the pedal just before the break light comes on. Does yours do that? MC is full but I have not tried bleeding yet.

 

[cdhorn]

Hi:

I just replaced the master cylinder this summer on my 81. I procrastinated two seasons because of the job it was changing it on my 77. The 81 is a piece of cake and only cost about $20.00 from my local auto supply store. You now only need to replace the cylinder itself. All the linkage etc. stays in place. This was a major improvement on GM's part. Bleeding instructions and tubes were included in the kit.

I too had a loss of pressure after applying the brake with a small jerk in the pedal pressure and then the light would come on. After repeated pumpings, the light would go off, but the pedal would periodically lose firmness on application. (Not a safe way to drive). Bleeding did not improve the performance.

I had the air problem from rotors in my 77, but only after replacing with SS calipers and going to DOT 5 Silicon brake fluid.

I'm going to stick with Dot 3 in the 81, but I'll be bleeding through new fluid every few years to prevent moisture and crud buildup.

Now if I could only get my clutch linkage problem fixed as easily. It's disconnected at the pedal arm, and I can't even see up there to see how it's attached.

Clark

 

[BlackNBlue95]

Hi:

Now if I could only get my clutch linkage problem fixed as easily. It's disconnected at the pedal arm, and I can't even see up there to see how it's attached.

Clark

GOOD LUCK! LoL they don't make it easy.. Like my boss always says if it was easy you wouldn't be doing it.. cuz I'm good like that.. LoL
-Rick

 

[MaineShark]

Bled the system, brakes work fine.

You know, the more I think about this, the more annoyed I get. I mean, they damage my car, refuse to take responsibility, and want to charge me muchos dinero to fix their mistake (they wanted $250 for the master cylinder - I didn't even wait around to see how many hours they would have wanted to charge me for replacing it). And the worst thing is, they would have gotten away with it, if I didn't smell a rat. After all, they would have bled the brakes during the installation of the master, so the problem would have been fixed.

Anyone know the address of GM's service office?

Joe

 

[Stallion]

So it was a problem with the brake fluid? What exactly?

Thanks!

 

[WhalePirot]

Do you have a conumer protection section in the state's DA office that deals with auto repair shops? In CA, the best shops are AAA certified and are BAR (Bureau of Auto. Repair) compliant.

Next time, get a strong referral to an honest mechanic!

 

[BlackNBlue95]

Bled the system, brakes work fine.

You know, the more I think about this, the more annoyed I get. I mean, they damage my car, refuse to take responsibility, and want to charge me muchos dinero to fix their mistake (they wanted $250 for the master cylinder - I didn't even wait around to see how many hours they would have wanted to charge me for replacing it). And the worst thing is, they would have gotten away with it, if I didn't smell a rat. After all, they would have bled the brakes during the installation of the master, so the problem would have been fixed.

Anyone know the address of GM's service office?

Joe

Did the shop open the system to air? did they have to open a bleeder or did they open one up rather because I could do a wheel bearing and not do that you can just push the caliper pistons back in the bore and not open it to air.. could also have this condition if the wheel bearing is not properly adjusted the condtion of pedal going the floor because the rotor surface may not be in contact with the the pad ect.. well if your convinced after bleeding and road testing it that the problem is gone.. then I would be happy I saved 250$ plus labor.. but brakes are not something to mess around with... so just be safe and road test it after checking the system out and making sure you have a good pedal feel..
-Rick

 

[MaineShark]

So it was a problem with the brake fluid? What exactly?

There were air bubbles in the brake lines. Brake fluid is incompressible. Essentially, you have a solid rod that can bend around corners. Air is compressible. It's like adding springs in that rod - it takes more force and motion to have the same effect at the other end. Now, you could operate your brakes with air in the system, if the master cylinder was designed for it (not that you would want to, but it would be possible). However, your brake system is designed for no air, so even a little bit of air can have very bad effects on your braking.

Did the shop open the system to air? did they have to open a bleeder or did they open one up rather because I could do a wheel bearing and not do that you can just push the caliper pistons back in the bore and not open it to air..could also have this condition if the wheel bearing is not properly adjusted the condtion of pedal going the floor because the rotor surface may not be in contact with the the pad ect..

Well, from the comment by a previous poster about the result of not being careful to retain the pistons allowing air in, and since bleeding the system solved the problem, I think it's likely that they did allow air in.

well if your convinced after bleeding and road testing it that the problem is gone.. then I would be happy I saved 250$ plus labor.. but brakes are not something to mess around with... so just be safe and road test it after checking the system out and making sure you have a good pedal feel..
-Rick

I started with a bit of testing on some isolated roads (including a couple "panic stops"), before I ever drove on a populated road. Since then, I've put 65 miles on it with no reduction in braking, so I think it's working properly again.

WhalePirot: Yeah, I'll contact the Better Business Bureau, but I figure that GM can probably put some pressure on them to shape up their act. I never would have even went there instead of my regular mechanic, except he didn't have the tools to do the bearing. Of course, with what they ended up charging me, I could have bought the tools, had my mechanic do the bearing, and come out even money (but I'd also have the tools to keep). Ah, well.

Joe

 

[vettte_wings]

Brake system contamination

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.



http://www.xs11.com/tips/maintenance/maint1.shtml

 

[Bob Chadwick]

I recently had a new wheel bearing put in

Joe,

If this comes back I would suspect that the bearings have not been adjusted properly causing pulsation on the pistons, which will then suck air.

Bob

 

[vettte_wings]

Combination Valve…

The combination valve, found on 1978-82 vehicles, is mounted on the frame and is connected to the hydraulic lines from the master cylinder. The proportioning section of the combination valve proportions outlet pressure to the rear brakes after a predetermined rear input pressure has been reached. This is done to prevent rear wheel lock up.



The valve is designed to have a bypass feature which insures full system pressure to the rear brakes if the front brakes system fails and full system pressure to the front brakes if the rear brake system fails.



The warning switch is designed to constantly compare front and rear brake pressure from the master cylinder and turn on the light on the dash in case of front or rear system failure. The warning light switch portion of the combination valve is not serviceable. If the switch is found defective the combination valve must be replaced.



Testing…



With the vehicle raised and the master cylinder full attach a bleeder hose to a rear brake screw immerse the other end in a jar of clean brake fluid.



1) Turn the ignition switch to ON and open the bleeder screw while a helper applies moderate pressure to the brake pedal. The warning lamp should light. Before the helper releases the brake pedal, close the bleeder screw. Press on the brake pedal and the light should go out.



2) Then attach the bleeder hose to the front brake bleeder and repeat. Then turn the ignition switch OFF.



If the warning lamp does not light during 1 &2 but does light when a jumper is connected to ground, the warning light switch portion of the combination valve is defective and the combination valve must be replaced.