Help! Drove car to work. Towed back home

[Kenny]

If it's got Rubber in it!

I've replaced customers hoses too for the same reason,Some of them have even replaced Master Cylinder's,Brake Calipers and Rear Wheel Cylinders thinking 1 of these has to be the problem,before bring it to me and have to pay me 40-50 $ an hour!! Buts whats Cheaper,Attacking it with a "Full Assault Wallet"(Thanks "Schrade":L) or have someone that knows what their doing repairing it???

I've been in the auto parts business for 16 yrs. I have lost count of the customers that will throw parts at a problem but not take it to a shop for a repair and would have saved $$$$$$ in the long run.

Also I once bought a used old RV that when I first got it it pulled hard to the right when brakes applied then left when brakes released. The brake hose was BAD replaced both just because

 

[White75]

Thanks. I may have to replace them just for piece of mind.

 

[White75]

Update!!!

Well got her out again today and wouldn't you know. It did the exact same thing, luckily I got her into the neighborhood. It's definitely a brake problem. Both front rotors/pads smoking and very hot. Rears not so bad but definitely show some heat glazing.
Called a buddy who brought a few tools. Popped off the master cylinder cover which was quite hot too (engine heat?) Front reservoir was pretty milky, rubber cover was distorted. Hoped that releasing the pressure would help but did nothing to release the brakes. The pedal had no travel either.
Another neighbor stopped to help (love this neighborhood) and after explaining the predicament, told me to undo the lines from the master cylinder to release the pressure and that would at least get me to the house. I did that and it spewed pretty heavily from the front line and a little from the rear line. Once that was done I was able to drive the vette home and into the garage. Still there is minimal pedal and the brake lights stayed on after she was put away. I ended up disconnecting the battery to get them to turn off. I couldn't pull up the pedal to release the switch.

So after this, it sounds like the master cylinder took a shit. Looks like it could be the original one. I'm hoping that's it. What's your thoughts?

 

[GerryLP]

White,

I presume that your car has brake booster as well? If so, have you looked at the check valve between the booster cylinder and the line that supplies vacuum to the brakes?

The checkvalve prevents bleedback of vacuum from the booster when the vacuum signal changes, but it also opens up when brakes are applied to prevent locking the brakes after the brake pedal has been applied. I wonder if it perhaps failed in the second function I just mentioned?

Your guess is probable as well, but the proportioning valve alocates more pressure to the front brakes. Could it be bad instead? Normally, there is a circuit tied to the proportioning valve to illuminate the brake (problem) light, but if I am not mistaken, it illuminates if the front and rear brakes pressure differential gets closer past a certain value. But if the valve is directing most of the pressure to the front brakes, it would probably not illuminate the brake system light, que no?

I mean, that is what a line lock essentially is, hydraulic pressure held against the front brakes by a solenoid AND bypassing the proportional valve.

GerryLP :cool

 

[White75]

I got power brakes. Is that check valve the cylinder in the line between the booster and the intake manifold? what can be done to test it?

White,

I presume that your car has brake booster as well? If so, have you looked at the check valve between the booster cylinder and the line that supplies vacuum to the brakes?

The checkvalve prevents bleedback of vacuum from the booster when the vacuum signal changes, but it also opens up when brakes are applied to prevent locking the brakes after the brake pedal has been applied. I wonder if it perhaps failed in the second function I just mentioned?

Your guess is probable as well, but the proportioning valve alocates more pressure to the front brakes. Could it be bad instead? Normally, there is a circuit tied to the proportioning valve to illuminate the brake (problem) light, but if I am not mistaken, it illuminates if the front and rear brakes pressure differential gets closer past a certain value. But if the valve is directing most of the pressure to the front brakes, it would probably not illuminate the brake system light, que no?

I mean, that is what a line lock essentially is, hydraulic pressure held against the front brakes by a solenoid AND bypassing the proportional valve.

GerryLP :cool

 

[Hib Halverson]

That the brakes are obviously dragging and the brake lights are stuck on such that even pulling up on the brake pedal won't turn them off has me wondering if you don't have some mechanical problem with the brake pedal assembly that's limited its travel such that the brakes are partially applied and the brake lights are stuck on.

Also, a couple of observations:

1) C3 stop light switches are on the brake pedal not in the proportioning valve.

2) Braided brake hoses have a teflon not a rubber core. In fact they are correctly known as braided-stainless-steel covered teflon brake hoses.

3) A proportioning valve does not "allocate" more pressure to the front brakes. In fact, that would be impossible because the proportioning valve could not increase brake pressure above what's generated by the master cylinder. What proportioning valve does is limit pressure to the rear brakes.

4) The explanation of the "check valve" above is not correct. The check valve does only one thing...it prevents atmospheric pressure from entering the booster when the engine is turned off. That is a safety feature to give the driver a couple of power assisted brake applications after the engine stalls. The check valve has no role in "preventing" brake lock up.

I'll be interested to hear the final diagnosis of this car's problem.

 

[GerryLP]

Hib,

On your first point, I meant the indicator brake light that comes on when there is something wrong with the brake system.

On your third point, you say tomatoe, I say tomato...:L...If something is limiting a pressure level, and in turn a tied system ends up with a higher pressure isn't that the same as saying that more pressure goes (or is allocated) to the tied system than to the limited system? ...shish, Hib... take it easy with my brain limitations. You are an expert with the written word, and obviously I am not.

on the fourth point, I honestly went and grabbed my book to make sure I was not confusing something. The check valve is attached to the booster housing. If it failed, it would mean a booster change, and I don't think that is the problem. But I recall sometime ago reading about one of the valves inside the booster (control valve or reaction valve), and I understood that if one of them failed, it would keep pressure on the booster piston and basically the brakes would remain applied. I'll try to find it.

As reference, I can say that in my L81 book, page 5-6, the cause table seems to suggest the following causes for ,"brakes slow to release":
Contaminated Brake fluid
Restricted air passage in power head
damaged power head
Improperly assembled power head valving
Restricted brake fluid passage or sticky caliper piston
faulty metering valve
Brake pedal linkage interference or binding (this one is identified as more probable)
Improperly adjusted master cylinder push rod
sticking caliper piston
proportional valve

White, in either case, keep searching and report back your findings, man. Sorry for confusing my words...

GerryLP:cool

 

[White75]

After letting everything cool down overnight, the pedal has returned to full travel. I haven't gotten to play with it much but looking underneath the dash, I don't see anything that looks like it would cause any binding.

 

[Hib Halverson]

Ok , I checked it out, point taken. So are all braided lines constructed this way ? Is it possible that the OP may just have some crap brand replacement lines?

I won't say that ALL are constructed this way but the ones I've worked with--name brands such as Aeroquip, Stoptech, Earls and XRP are made that way.

It is possible that in ancient times, they were braided stainless over rubber, but my experience with hoses like that only goes back about 20 years and in that time, the products I've used have been Teflon hoses.

 

[Hib Halverson]

Hib,
(snip
On your third point, you say tomatoe, I say tomato...:L...If something is limiting a pressure level, and in turn a tied system ends up with a higher pressure isn't that the same as saying that more pressure goes (or is allocated) to the tied system than to the limited system?
(snip)

Again, a "brake proportioning valve" does not "allocate" pressure nor does it increase pressure to the front brakes. It only affects the rear brakes and it decreases pressure.

Originally, I wasn't going to elaborate much more than that because I didn't want to make it seem like like I'm picking on you, but, since the debate continues, I'll tell you that you are incorrectly identifying the valve in question as a "proportioning valve" which it is not. Thus, the whole discussion about a brake proportioning valve possibly being faulty and causing "White75's" problem is irrelevant . Brake proportioning on for all 65-82 Corvette disc-brake systems, with exception of 65-68s with J56, was accomplished by the differences in brake piston diameters front-to-rear, ie: there is no proportioning valve on those cars.

Have you ever wondered why the front pistons are so big and the rear pistons are so small?

Well..."proportioning" is your answer.

Some C3s w. J-56 used brake proportioning valves and it was an adjustable unit. It was in the line to the rear brakes downstream of the other valve discussed next. It's function was to decrease rear brake pressure and made the car's brake balance adjustable beyond what was available through the difference in piston diameters, alone.

The other valve in the system, the one into which the brake warning switch is installed and...the one you think is a proportioning valve, is actually a combination of a distribution block and a differential pressure switch. It distributes brake fluid flow from the master cylinder to the two pipes feeding the front and rear brakes and to the single pipe feeding the rear brakes. It, also, senses a front-to-rear brake pressure differential and, if such a difference occurs, turns on the brake warning light.

If your book ID's that valve as a proportioning valve, perhaps you should correct that in its next printing.

on the fourth point, I honestly went and grabbed my book to make sure I was not confusing something. The check valve is attached to the booster housing. If it failed, it would mean a booster change, and I don't think that is the problem. But I recall sometime ago reading about one of the valves inside the booster (control valve or reaction valve), and I understood that if one of them failed, it would keep pressure on the booster piston and basically the brakes would remain applied. I'll try to find it.

I was only talking about the check valve, as discussed above--the one on the outside of the booster, mounted in a rubber grommet.

 

[Rex S]

Ok , I checked it out, point taken. So are all braided lines constructed this way ? Is it possible that the OP may just have some crap brand replacement lines?

I can't answer what other companies use but in years past (befor we became a dealer) the hoses we bought & used looked just like BQ's. The inner lining has been around for quite a while on bikes but with a plastic cover rather than SS.

 

[GerryLP]

Again, a "brake proportioning valve" does not "allocate" pressure nor does it increase pressure to the front brakes. It only affects the rear brakes and it decreases pressure.

..., I'll tell you that you are incorrectly identifying the valve in question as a "proportioning valve" which it is not. Thus, the whole discussion about a brake proportioning valve possibly being faulty and causing "White75's" problem is irrelevant . Brake proportioning on for all 65-82 Corvette disc-brake systems, with exception of 65-68s with J56, was accomplished by the differences in brake piston diameters front-to-rear, ie: there is no proportioning valve on those cars....

Hib, I know that the correct name for the valve, in the L81 Vette, is,"combination valve". Quoting from the shop manual, "The proportioning section of the combination valve proportions outlet pressure to the rear brakes after a pre-determined rear input pressure has been reached. This is done to prevent rear wheel lock-up on cars with light rear wheel loads."

When I used the word,"allocate", I did not mean it to imply that somehow the valve multiplies the pressure value going through it. If my words gave you that impression, I apologize. What I meant by the use of the word, is that the valve, whether by limiting the rear brake system pressure or by ensuring that the front brake system pressure is higher, or however does it, the valve monitors a pressure differential. I suspect that if the valve was not needed, GM would not have added one. Which makes me think that even though the brake caliper piston sizes may be larger in the front by 1/2", that there can still be a situation in which the conditions would require a proportioning valve.

....If your book ID's that valve as a proportioning valve, perhaps you should correct that in its next printing...

Cute! :L When I say ,"my" book, I don't mean a book that I wrote, but rather a book that I own.

But let me apologize to White75, for allowing my own stubbornness hijack this thread. Something is causing the front brakes in his Vette from releasing. White, look in your car's shop manual, and there should be a procedure for testing whatever valve is in your brake system that helps it either by-pass when either, the front or rear brake system, fails, or perhaps a way to test a brake pressure differential switch, if so equipped.

GerryLP:cool

 

[Vettehead Mikey]

Brake proportioning on for all 65-82 Corvette disc-brake systems, with exception of 65-68s with J56, was accomplished by the differences in brake piston diameters front-to-rear, ie: there is no proportioning valve on those cars.

Hib, I know that the correct name for the valve, in the L81 Vette, is,"combination valve". Quoting from the shop manual, "The proportioning section of the combination valve proportions outlet pressure to the rear brakes after a pre-determined rear input pressure has been reached. This is done to prevent rear wheel lock-up on cars with light rear wheel loads."

1978-82 Corvettes indeed have a proportioning function incorporated into the combination valve. Gerry is correct on this point.

 

[rbryce]

Let me ask this question. It seems like the discussion is either hoses (not likely to me that since each caliper has it's own hose, more than one hose would be failing at the exact time to cause the locking of both front brakes), the proportioning valve, the master cylinder or the booster. Since it was also brought up that this year corvette does not have a seperate proportioning valve, that sort of eliminates that! One comment was that the brakes were both locked up and the brake pedal could not be released. What is the one thing that will cause BOTH to occur? Since the master cylinder and the booster are two seperate parts, will a failure of the master cause a lockup in the booster to prevent the pedal from returning? I'm not an expert on all of these, but it seems to me that if the master has locked up, the booster, not being internally physically connected to the master cylinder, would return to it's previous state and release the pedal. Since the pedal was reported to have been locked up as well, would that point to the booster more than the master cylinder? :confused

 

[Vettehead Mikey]

An easy troubleshooting step would be to loosen the two nuts that hold the M/C to the booster. If the brakes release, this eliminates the flex lines.

 

[JohnZ]

An easy troubleshooting step would be to loosen the two nuts that hold the M/C to the booster. If the brakes release, this eliminates the flex lines.

Correcto. Something in the master cylinder, booster, or pedal pushrod is preventing the master cylinder pistons from returning to their normal position, so the (normally-open) compensating ports are blocked; that's why the brakes are dragging.

 

[GerryLP]

That's clever Mikey.

So if indeed this test does work, then I guess White75's Vette could be having a bad spring in the master cylinder or a bad power booster, right?

I have changed the power booster in my Vette twice, and it is not a task I look forward to...hnoes:ugh;squint:

GerryLP:cool

 

[petes74ttop]

As reference, I can say that in my L81 book, page 5-6, the cause table seems to suggest the following causes for ,"brakes slow to release":

Improperly adjusted master cylinder push rod

When you separate the M/C from the Booster see if the rod has an adjustment, if it does make it a half a turn shorter.
Regards, Pete.

 

[Vettehead Mikey]

That's clever Mikey.

So if indeed this test does work, then I guess White75's Vette could be having a bad spring in the master cylinder or a bad power booster, right?

I wouldn't come to either of those conclusions just yet. Possibly just some crud in the M/C.

 

[Hib Halverson]

1978-82 Corvettes indeed have a proportioning function incorporated into the combination valve. Gerry is correct on this point.

"Vettehead Mikey", "GerryLP", you're right.

Early this morning, I went up in to my storage and retrieved my 71, 76 and 83 editions of the Corvette Parts Manual and the 83 book shows that in 78, that pressure differential valve became a "combination" valve.

So, I'm going to go through a little crow on the barbie.

65-77 w/o J-56 no prop. valve
65-68 w. J-56 adj. prop. valve
78-82 fixed prop. valve inside the "combination" valve.

As for "White75's" brake problem...the world awaits the diagnosis.