Brake lock up

[Jim Nolan]

If the check valve on the power booster sticks and doesn't release pressure will the brakes lock up. The Z was sitting for about 2 months and I took it out for a ride and one of the brakings the brakes stayed applied, the brake pedal was full up, hard as a rock, with no give to it. After the car was shut off for about 10 minutes then started back up all was normal. This happened about 5 years ago once and never again until yesterday.

The service manual does not give instructions for replacing. Is it just prying the old one out and lube and install the new.

Also no MPH reading and FX3 codes 23

Jim

[mike100]

The only thing vaguely similar to this that i have ever experienced was swollen rubber brake lines that acted like a one way check valve of sorts. Delayed braking response and a delayed release- although not anything like you describe. in my example, the car pulls to one side.

I guess it is possible the rod is getting hung up in the master cylinder. I would brake flush the car thoroughly.

[mike100]

you should not have run out of vacuum- the booster check valve is available anywhere and looks to be the same on many GM cars- i would grab one from Napa or even the junkyard to give it a shot. even removing yours and trying to blow air thru it to see if it works every time or not.

[Jim Nolan]

The first time it happened, to be safe, I replaced all the brake hoses and flushed the system. I went to the local parts store and the check valve is not available only the entire power booster.:cry:

Jim

[mike100]

The first time it happened, to be safe, I replaced all the brake hoses and flushed the system. I went to the local parts store and the check valve is not available only the entire power booster.:cry:

Jim

I think any 90's small block car or truck would possibly have the same part that you could get from a wrecking yard for a couple of dollars. It is probably a PBR aussie part, but still...

[mike100]

http://www.summitracing.com/search/part-type/brake-booster-check-valves?sortby=Default&sortorder=Ascending

[WVZR-1]

If the check valve on the power booster sticks and doesn't release pressure will the brakes lock up. The Z was sitting for about 2 months and I took it out for a ride and one of the brakings the brakes stayed applied, the brake pedal was full up, hard as a rock, with no give to it. After the car was shut off for about 10 minutes then started back up all was normal. This happened about 5 years ago once and never again until yesterday.

The service manual does not give instructions for replacing. Is it just prying the old one out and lube and install the new.

Also no MPH reading and FX3 codes 23

Jim

Do the VSS check for the Code 23 and no MPH display first I believe. Clean the under-car connection at the VSS first, it wouldn't be unusual to have a situation there. That would have this issue out of the way. You don't mention the year and the VSS is of different construction '90 MY and then the later '91+ years. Which is yours?

THE BRAKES?

The OE/GM check valve is still available from GM but the price will take your breath away. The OE/GM # 12521454 did NOT fit anything other than the C4 Corvette. The grommet was also a C4 only application and that is NLA. Will the other $4 choices do for the valve?

I believe I'd do a salvage part and get the grommet with it if I wanted to try the check valve.

even removing yours and trying to blow air thru it to see if it works every time or not.

This I don't believe would be very wise. I might try a very LOW controlled vacuum suction on it and see if it maintained but a blow through I believe could just as easily ruin maybe a good one. Just my thought! Check the price of the OE first. That could be a game plan changer!

Which brake locked? There are two hydraulic lines from the master to the ABS module on the LT5 that of course seldom fail but you did mention lock up so maybe that would be a good place to start.

[Jim Nolan]

Went to the local NAPA and ordered the check valve, none located in the local area. It'll be a few days. It didn't cross check to be compatable with other vehicles. When I pulled the check valve out it had a vacuum on the backside (front side of the power booster). Is this right? If I understand this right when the brake is released the pressure should dump to release the boost, yes.

On the no MPH and FX3 code 23, manual says rt. front sensor. I have too many things on my plate now. That will have to wait until later in the week.

[WVZR-1]

Went to the local NAPA and ordered the check valve, none located in the local area. It'll be a few days. It didn't cross check to be compatable with other vehicles. When I pulled the check valve out it had a vacuum on the backside (front side of the power booster). Is this right? If I understand this right when the brake is released the pressure should dump to release the boost, yes.

On the no MPH and FX3 code 23, manual says rt. front sensor. I have too many things on my plate now. That will have to wait until later in the week.

Code 23 for the FX3 I thought was generally set when the key had been cycled 3 times and the car hasn't been moved. I think it also stays as a H code so it's suggested to clear it. You mentioned NO MPH also though and that I believe would hint that there's a VSS issue and that also would set the 23. I'm pretty sure. Your car is a '92 maybe? If you don't have a speedo issue the 23 SRC code should go away by just driving it.

[Jim Nolan]

Yes a '92. I ruled out the key 3 times and not moved because it should reset after shutting it off driving and shut off and restart. Time permitting I'll jack it up and check wiring at VSS first. I don't know what the sensor costs but I guess it isn't cheap. I can't believe no one has ever heard of this problem and cause?

Thanks!

Jim

[WVZR-1]

Yes a '92. I ruled out the key 3 times and not moved because it should reset after shutting it off driving and shut off and restart. Time permitting I'll jack it up and check wiring at VSS first. I don't know what the sensor costs but I guess it isn't cheap. I can't believe no one has ever heard of this problem and cause?

Thanks!

Jim

The '92 VSS is very "inexpensive" if it comes down to the purchase of one. Very "inexpensive".

The brake issue - you had it once before you mentioned also and it just went away for 5 years. I can't imagine the booster check doing the fix but I hope so for you. What is the ID of the grommet since you have the check-valve out. It might be interesting to measure the diameter of the bore in the booster also. Those dimensions could be very useful.

I would think the only way to deal with it would be that when it happens you actually take the time to see which wheel (s) are locked. I realize that's a damn nuisance because you would likely need to do the jacking on the road side!

Were it me I'd buy an IR gun and carry it. You'll find many other uses for it also and it's just a real nice device to have around. You could snap the temps from the rotors in maybe less than a minute for the whole car when it does happen.

There are less expensive available but a friend has had a Raytek for years that he uses to check the cure of his fiberglass/SMC repairs. I use it for temps on cars, trucks, electronics, the plasma display. It's a very useful tool! You would never regret the purchase. Here's a link to a Raytek automotive IR:

http://support.fluke.com/raytek-sales/download/asset/9250070_eng_b_w.pdf

There are less expensive models and brands for the "hobbyist" but the $80+ ones seem to do real well.

[mike100]

This I don't believe would be very wise. I might try a very LOW controlled vacuum suction on it and see if it maintained but a blow through I believe could just as easily ruin maybe a good one. Just my thought! Check the price of the OE first. That could be a game plan changer!

...

I never even considered that my post would be interpreted as using compressed air. I meant to test using your mouth. I guess I have been a mechanic too long. Eating lunch with greasy half washed hands just doesn't bother me nor does the taste of hydrocarbons in the name of scientific method.
:p

[WVZR-1]

I never even considered that my post would be interpreted as using compressed air. I meant to test using your mouth. I guess I have been a mechanic too long. Eating lunch with greasy half washed hands just doesn't bother me nor does the taste of hydrocarbons in the name of scientific method.
:p

That thought crossed my "feeble mind" just as I was adding the final punctuation BUT I thought OH WELL!

OP and all:

I believe if I had a '92 car with ABS/ASR and a similar situation I'd first check for codes in the ABS/ASR. 5E-11 covers it well, the codes can't be cleared easily by error such as battery disconnect. Tech 1, CCM procedure or 50 key cycles is the only way. So if there were an error it should still be there.

Rather than link to the Corvette Central procedures I think the OP needs to check the diagnostics from the CCM in 8D of the FSM. Ironically the OP mentions code 23 for the FX3 which is a VSS fault (and mentions no MPH) but there's a 23 code for the ABS/ASR also which is the RF sensor which he also mentioned. It's difficult to determine just where he was doing the diagnostics from. The ABS/ASR would be my first thought to check because the OP mentioned "LOCK UP". That in my "feeble mind" hints hydraulic. The OP also had this failure he mentioned 5 years ago. An EBCM "hiccup"?

[mike100]

Do you think it is possible for the ABS assembly to trap pressure down stream? I thought it was only capable of bypassing pressure on a circuit.

[WVZR-1]

Do you think it is possible for the ABS assembly to trap pressure down stream? I thought it was only capable of bypassing pressure on a circuit.

I don't really know - I haven't read that much but the '92 would also have ASR and this problem the OP mentioned was there once 5 years ago, went away and returned just recently. I can't think of anywhere else to start. It's only a matter of checking codes and doing some serious reading. I think if I had the situation I'd do the IR gun I mentioned and when it surfaces again I'd know which or how many wheels were involved. Five years ago he did what we all might have done "replace the wheel brake hoses" and it went away!

I sold the two braided hoses from the master to the EBCM "NEW" to someone several years ago but I don't recall what the reason was. At that time I would have generally ordered the same parts for myself but I certainly don't recall doing that with those lines.

[Jim Nolan]

I'm at a standstill here. I did an ohm check on the sensor and wiring and all checked good the FSM states that you have a code 23 on the FX3, which it does, and no code 24 in the ecm with no MPH then change the Selective ride control module. No parts dealer heard of one and the 3 sets of part #'s I pulled off the module come up blank. I'm at a loss now. The only thing left to try is to change the ride control when I take it out tomorrow and see if it acts differently..

[Schrade]

Maybe we can rule out some stuff here, with respect to a locked up brake [s]...

1) Doesn't ABS function by 'letting go' of brake line pressure, AFTER IT'S APPLIED?

And if ABS is not working, then isn't it the case, that it doesn't let pressure off, AFTER IT'S ALREADY APPLIED???

2) Does ASR function by APPLYING BRAKES (to the slipping wheel)? Or does it function by REDUCING THROTTLE?

The former seems like a dangerous liability, with an ASR malfunction applying brakes to one wheel unexpectedly.

I cannot imagine what malfunction could APPLY brakes.

I HAVE, on the other hand, seen GM brakes RETAIN APPLIED PRESSURE in a malfunction condition - and a common one at that. My '98 GMC, ONLY WITH the engine running, and AFTER applying brakes, would somehow allow vacuum pressure to be transmitted to the brake lines, and collapse the rubber liners in the line, thereby retaining APPLIED pressure.

I DO suppose that if the MC piston was stuck forward in the MC cylinder, that could RETAIN pressure. Never seen that tho'...

But once vacuum abated, after engine shutdown, the line pressure released.

The only thing otherwise, that I've seen retain brake pressure, HAVING NOTHING TO DO WITH FLUID PRESSURE, is a stuck caliper...

[WVZR-1]

I'm at a standstill here. I did an ohm check on the sensor and wiring and all checked good the FSM states that you have a code 23 on the FX3, which it does, and no code 24 in the ecm with no MPH then change the Selective ride control module. No parts dealer heard of one and the 3 sets of part #'s I pulled off the module come up blank. I'm at a loss now. The only thing left to try is to change the ride control when I take it out tomorrow and see if it acts differently..

You don't Ohm check a VSS - a VSS is an AC generator. You mentioned you lost MPH and also have the code 23 SO just remove the VSS and spin it with a rotary tool and see if you then get MPH on the cluster. If you do then the VSS is fine. If you don't get MPH you need likely a VSS. If you want the VSS for the '91+ is rather inexpensive so you could buy a new one and use it to spin and check the cluster etc. I would think you can buy a '91+ VSS for less than $35. I don't have the later VSS or I'd just send you one to check it.

Have any parts store change any of these #'s for you, 10456089 GM (original part), VSS46, 5S4637, SC13 or SU1005.

SRC module I'd think very unlikely! If you mentioned you had MPH and still the SRC code then maybe but you originally mentioned no MPH either. Has that changed?

[Jim Nolan]

I hadn't thought about removing the VSS and spinning it. I'll give it a shot tomorrow. I'm sure it's its key on and engine off , right.
I hope it's the problem because I just off the phone with the local dealer and he said GM no longer stocks the module.

Just to be clear it did not pull and all wheels seemed to lock with the brake pedal full up and hard as a rock. I think I'll wind with 2 problems.

Thanks Jim

[WVZR-1]

I hadn't thought about removing the VSS and spinning it. I'll give it a shot tomorrow. I'm sure it's its key on and engine off , right.
I hope it's the problem because I just off the phone with the local dealer and he said GM no longer stocks the module.

Just to be clear it did not pull and all wheels seemed to lock with the brake pedal full up and hard as a rock. I think I'll wind with 2 problems.

Thanks Jim

I don't see where you mentioned trying the after-market vacuum check valve for the booster. Have you? It did or didn't fit? I mentioned maybe measuring he diameters while you had it apart. Did you?

[mike100]

2) Does ASR function by APPLYING BRAKES (to the slipping wheel)? Or does it function by REDUCING THROTTLE?



Yes to both conditions if I recall well. Not on ZR-1's, but the regular coupe even got a big upgrade in 95,96 to a faster acting system with updated control. The C4's ASR was capapble of applying a rear brake along with throttle reduction to stop spinning tires and to induce a yaw correction in a sliding condition. The inputs should be individual wheel sensors, the yaw sensor in the depths of the console or ABS well (don't recall). The lack of a speedo signal may very well be part of this mystery- i would try to fix that regardless.

The year of the car was never mentioned so it would have to be a 92-95 model to have ASR. if it is a 90 or 91, all this is moot- ABS only and shouldn't be able to lock up a wheel...but who knows for sure.

[Jim Nolan]

I changed the check valve and used the old gasket. The valves are exactly the same the replacement gasket did not impres me that much, not enough overlap on the booster unit. One thing I did notice the new NAPA valve had less resistance then the factory doing the Mike check.

As for the MPH problem; I forgot that when the gearing was changed to a 3:91 for speed correction an electronic correction was used for the correct MPH. I checked all the connections, ohmed the wiring put it all together and took it out for a test run. One other thing I did and I'm sure it did not factor into it. I put the dyno tuned e-prom back in. Ran like a champ. About $100 worth of rubber on Hwy. 98