Brake Lock-Up

[Joe L.]

Yesterday I took the '92 out for a drive as I have not driven it for several months. Well, within less than a mile of the house it felt like the there was very little pedal travel upon depressing the brakes. Next thing, the brakes seemed to lock up. I turned back to home immediately but it was a difficult drive even though it was just a mile, or so. The front brakes got very hot and were both smoking. When I got back home I measured the front wheel hub temperature close to 300 degrees. The rears were a little hot, too, but not smoking. I had serviced both the front and rear brakes not too long ago after a similar, but less "dramatic"" incident. I found no problem with the brakes but I replaced the pads with NOS.

I'm thinking I have either a master cylinder or brake booster problem, most likely the latter. Anyone have any other experience with C4 brake lock-up or ideas on the root of my problem?

[Rich G.]

Re: Brake Lock-Up

Brake hose collapsed?

[Stephen L.]

Re: Brake Lock-Up

I had a similiar problem with my 67 years ago. I had replaced the M/C. I could drive a few miles and then it would lock the brakes. Let things cool down for awhile and I could then drive for a short distance. The problem turned out to be "check valves" in the M/C. Turns out a drum brake car uses check valves but disc brakes do not. The other possibility is there is too much brake fluid in the M/C and the space for fluid expansion isn't enough. Another possibility would be the holes in the M/C are "covered" so that the fluid cannot return to the M/C after release of the brakes, which acts like you are driving with the brakes applied..........

[Dave P.]

Re: Brake Lock-Up

... within less than a mile of the house it felt like the there was very little pedal travel....the brakes seemed to lock up....The front brakes got very hot and were both smoking.

I'm thinking I have either a master cylinder or brake booster problem... Anyone have any other experience with C4 brake lock-up or ideas on the root of my problem?

Joe and I have our differences so we avoid interaction on here, but I offer this: -

I had this exact same scenario with my current 1992 when I worked on it for the PO 10 years ago, again on the drive home when I purchased it in 2022, and the few times I drove it after purchase every time out until I figured out what it was and fixed it. Because the ABS could have been the 'problem', and for 1992 the ABS is also part of the TCS system, I spent a lot of time learning about, then proving, the ABS/TCS system functionality and that it was not the cause of the lock-up. The consensus on CF was "brake hoses". The OEM hoses are still on the car today; not the hoses.

It was the Master Cylinder.

I purchased a Chinee Centric from RockAuto and put it on. (It's all I found without searching.) The 92 reservoir has a "prime pipe" nipple that was not on the replacement. I was gentle and careful, and had no difficulty transferring the original reservoir to the Centric. I use a Motive pressure bleeder on all my cars. On the 92, the Motive at 15psi was unable to expel fluid at the rear calipers. I had to 'assist' the Motive by applying foot pressure to the pedal; 3-count to down, 3-count to release, wait 10 seconds and repeat.

I have substantial things-automotive experience. The brake system on the 92 had me scratching my head for a couple of weeks. Perhaps these hints will help.

Cheers

[Joe L.]

Re: Brake Lock-Up

Brake hose collapsed?

Rich------

Thanks, Rich. There's no apparent problem with the hoses. Plus, it would require both to be collapsed since the problem affects both front brakes (and, maybe, the rear brakes, too).

I may have a cure for the hoses, though. When I ordered the car new I wanted the J-55 brakes but the only way to get them was to order the Z07 suspension package. I did not want that so I asked if I could get them to factory install the J-55 brakes on a "special order". The dealer checked but they could not.

So, right after I bought the car, I ordered all the parts I needed to convert the car to J-55. I thoroughly researched it and all that was required was the front rotors, front calipers, caliper brackets, pad pins, and brake hoses. I still have them all in the GM boxes. So, maybe now is the time to install them and eliminate the possibility of a brake hose problem.

[Joe L.]

Re: Brake Lock-Up

Joe and I have our differences so we avoid interaction on here, but I offer this: -

I had this exact same scenario with my current 1992 when I worked on it for the PO 10 years ago, again on the drive home when I purchased it in 2022, and the few times I drove it after purchase every time out until I figured out what it was and fixed it. Because the ABS could have been the 'problem', and for 1992 the ABS is also part of the TCS system, I spent a lot of time learning about, then proving, the ABS/TCS system functionality and that it was not the cause of the lock-up. The consensus on CF was "brake hoses". The OEM hoses are still on the car today; not the hoses.

It was the Master Cylinder.

I purchased a Chinee Centric from RockAuto and put it on. (It's all I found without searching.) The 92 reservoir has a "prime pipe" nipple that was not on the replacement. I was gentle and careful, and had no difficulty transferring the original reservoir to the Centric. I use a Motive pressure bleeder on all my cars. On the 92, the Motive at 15psi was unable to expel fluid at the rear calipers. I had to 'assist' the Motive by applying foot pressure to the pedal; 3-count to down, 3-count to release, wait 10 seconds and repeat.

I have substantial things-automotive experience. The brake system on the 92 had me scratching my head for a couple of weeks. Perhaps these hints will help.

Cheers

Dave-------

Thanks very much. I think your information is exactly what I need to address this problem. I was very worried, too, that the problem might be connected to the ABS even though no ABS trouble indicator was illuminated. So you have saved me the effort to research that further and I greatly appreciate that. I think if it had been an ABS problem I'd sell the car.

Believe it, or not, I do not have an NOS master cylinder in my stock. So, I'll either have to rebuild mine or obtain an aftermarket replacement as you did. I might even send mine off to Cardone and have them custom-rebuild it. The GM master cylinder for 1992-94 is long since GM discontinued and was replaced by the 1995-96 master cylinder. The latter does not have the "prime pipe" on the reservoir and GM instructed that for 1992-94 SERVICE the reservoir needed to be transferred from the replaced master cylinder. The latter master cylinder was also discontinued quite some time ago so there is now no GM sourced replacement available. There is an AC-Delco replacement but I'm virtually certain it's the same part sold under all of the other brands.

I think that all of the aftermarket master cylinders available regardless of brand have the same manufacturing source. However, I note that there are differences with respect to the brake warning switch tapping. Some are, apparently, 3/8" and some 12 mm. I think the 1992 used the 3/8". Can you confirm which?

[Dave P.]

Re: Brake Lock-Up

So, I'll either have to rebuild mine or obtain an aftermarket replacement as you did. I might even send mine off to Cardone and have them custom-rebuild it.

Some are, apparently, 3/8" and some 12 mm. I think the 1992 used the 3/8". Can you confirm which?

I just took my OEM 92 take-off cyl to the bench. The switch bore is definitely NOT 3/8 (it's bigger), 7/16 is close, but doesn't fit 'right', and 1/2" is too big. The 12-1.5 is closest, but only threads in about 1 turn, then binds, suggesting it is not 1.5 pitch. I had no trouble transferring the switch to the Centric replacement.

One other thing, although I don't believe you have your 92 judged. The date code on the end of the hex plug is well-known to the C4 team chassis judges. They look for it. It is probably very common to transfer the plug to the replacement cyl. I did this on my 85 and 90. I did not attempt the transfer on the 92 because I didn't trust the Chinee part to be the same thread, and didn't want to ruin a $175 part, and have to buy another one. It's Chinee, but it isn't inexpensive.

Cheers.

[Joe L.]

Re: Brake Lock-Up

There are two retaining pins inserted from the exterior, then "plugged" to seal them. One in the proportioning valve section, and one between the front and rear sections. For rebuilding, the FSM says "remove retaining pin". It does not suggest HOW to remove or reinstall these pins. I see no way to do it, but that doesn't mean it can't be done. I'd just find a replacement.

I just took my OEM 92 take-off cyl to the bench. The switch bore is definitely NOT 3/8 (it's bigger), 7/16 is close, but doesn't fit 'right', and 1/2" is too big. The 12-1.5 is closest, but only threads in about 1 turn, then binds, suggesting it is not 1.5 pitch. I had no trouble transferring the switch to the Centric replacement.

One other thing, although I don't believe you have your 92 judged. The date code on the end of the hex plug is well-known to the C4 team chassis judges. They look for it. It is probably very common to transfer the plug to the replacement cyl. I did this on my 85 and 90. I did not attempt the transfer on the 92 because I didn't trust the Chinee part to be the same thread, and didn't want to ruin a $175 part, and have to buy another one. It's Chinee, but it isn't inexpensive.

Cheers.

Dave-----

Thanks again. Very useful information. I greatly appreciate it.

The Centric master cylinder as well as most of the others have a "12 X 1 mm" switch port. So, if your switch installed properly I expect it's the "12mm" variety and that's the one I'll need if I go with a new master cylinder.

You were indeed, wise, to not attempt to remove the plug. I also have found in the past that some aftermarket parts, while functional as a unit, are not made to original specs in just the way you anticipated. I try to keep my car as original as possible but I do not have it judged. Still, this might bode for me to have Cardone rebuild my master cylinder. I'd do it myself but I don't know where to obtain the necessary parts. Somehow, big commercial rebuilders are able to obtain such parts.

[Patrick H.]

Re: Brake Lock-Up

Dave-----

Thanks again. Very useful information. I greatly appreciate it.

The Centric master cylinder as well as most of the others have a "12 X 1 mm" switch port. So, if your switch installed properly I expect it's the "12mm" variety and that's the one I'll need if I go with a new master cylinder.

You were indeed, wise, to not attempt to remove the plug. I also have found in the past that some aftermarket parts, while functional as a unit, are not made to original specs in just the way you anticipated. I try to keep my car as original as possible but I do not have it judged. Still, this might bode for me to have Cardone rebuild my master cylinder. I'd do it myself but I don't know where to obtain the necessary parts. Somehow, big commercial rebuilders are able to obtain such parts.

While not a cheap experiment, you would wonder if the internals used in the current ACDelco/Raybestos product could be removed from a new master cylinder and used in yours. It might still be less money than having yours rebuilt.

[Owen L.]

Re: Brake Lock-Up

I had a similiar problem with my 67 years ago. I had replaced the M/C. I could drive a few miles and then it would lock the brakes. Let things cool down for awhile and I could then drive for a short distance. The problem turned out to be "check valves" in the M/C. Turns out a drum brake car uses check valves but disc brakes do not. The other possibility is there is too much brake fluid in the M/C and the space for fluid expansion isn't enough. Another possibility would be the holes in the M/C are "covered" so that the fluid cannot return to the M/C after release of the brakes, which acts like you are driving with the brakes applied..........

This is a thing? I've not heard of it before, but it does seem to fit a problem a guy had on the CF a year or two ago. He was convinced it was heat related but that seemed unlikely to me. I don't recall anyone else offering this suggestion but it seems plausible.

[Dave P.]

Re: Brake Lock-Up

416+O9ctvuL._SX300_SY300_.jpg

I found this image of a Delco 175-260 repair kit on amazon. The part is "not available".

My parts fiche shows an MSRP of $188 for this kit in 2001. 20 years later the complete Delco replacement cyl is $194.79 on rockauto. The complete replacement is going to be cheaper, quicker, and best chance of a successful repair over a "kit" or rebuild, if you can find one.

While researching this post, I found that I actually used an AC Delco 18M391429. I ordered a clutch master at the same time, same order. The clutch master was a Centric. Not the brake master.

[Joe L.]

Re: Brake Lock-Up

While not a cheap experiment, you would wonder if the internals used in the current ACDelco/Raybestos product could be removed from a new master cylinder and used in yours. It might still be less money than having yours rebuilt.

Patrick------


I think that would depend on just how the currently available master cylinders (and, as I mentioned before, I think that all on the market, regardless of brand, originate from the same manufacturing source) were created. If they were created from the same tooling used by PBR but transferred to another manufacturer, then I think the current master cylinders would likely be identical to the originals. However, if they were created by some sort of "rough reverse engineering", then it would be a crap-shoot as far as interchangeability of components goes.

[Joe L.]

Re: Brake Lock-Up

This is a thing? I've not heard of it before, but it does seem to fit a problem a guy had on the CF a year or two ago. He was convinced it was heat related but that seemed unlikely to me. I don't recall anyone else offering this suggestion but it seems plausible.

Owen----


Heat could not have been the source of the problem in my case. Both times it occurred I had just taken the car out of the garage and traveled a short distance when the problem occurred.

[Joe L.]

Re: Brake Lock-Up

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I found this image of a Delco 175-260 repair kit on amazon. The part is "not available".

My parts fiche shows an MSRP of $188 for this kit in 2001. 20 years later the complete Delco replacement cyl is $194.79 on rockauto. The complete replacement is going to be cheaper, quicker, and best chance of a successful repair over a "kit" or rebuild, if you can find one.

While researching this post, I found that I actually used an AC Delco 18M391429. I ordered a clutch master at the same time, same order. The clutch master was a Centric. Not the brake master.

Dave------

Yes, it's quite a complete rebuild kit and at a premium price. It was also known as GM #12509987. However, at that time the complete GM master cylinder carried a GM list price of $513.00. Both were discontinued not too long after 2001.

Using the kit to rebuild a master cylinder might have seemed like a good way to go at that time considering the price of a new GM master cylinder. However, your advice to use a new master cylinder now is definitely good advice. The kit, even if I could obtain one, would only be useful, now or ever, if the master cylinder bore were, as you know, perfect. What are the chances of that----slim to none.

If a rebuilder like Cardone has the ability to stainless steel sleeve these master cylinders, then having mine rebuilt might be feasible. I'll contact them to find out but I highly suspect the most they'd do is to hone the bore. I don't want a master cylinder with a honed bore.

The Delco 18M391429 remains available so I think I'll follow your lead and go that route.

[Rod K.]

Re: Brake Lock-Up

Gentlemen: While I am not necessarily familiar with this or other later Corvette generations, I can relate a potential cause for this problem which I experienced with a foreign model car some years ago. I don't see that Joe mentions having removed or otherwise adjusted the MC prior to this problem occurring, but in my case I had either rebuilt or replaced the MC (don't recall which) and the very condition described started occurring almost immediately, (short drive, 5-8 miles and the brakes (front disc, rear drum) would lock up). Cool down for half an hour and all is fine until driven again. The problem? The MC push rod from pedal to piston was mis-adjusted too long semi-applying the brakes, and when they had dragged for a while, fluid was heated up and expanded and forced the brakes to apply. Readjust the rod to provide "lash" and all is well. As I said, it occurred when my MC was rebuilt or replaced but it would be worth checking to see if this one has sufficient free play in the push rod.