Brake petal goes low intermittently

[jrd1990zr1]

Took my 1990 out today, was running great. After about a half hour of driving when coming to a light to stop, petal went way down before the brakes engaged. Brake light on for a short time. Petal felt strange. Brakes seemed to work after that but then it happened again after about 6 or so more stops. Fluid in the two reservoirs are where they should be.

Any thoughts on what may be causing this?

Thanks in advance.

[GOLDCYLON]

Took my 1990 out today, was running great. After about a half hour of driving when coming to a light to stop, petal went way down before the brakes engaged. Brake light on for a short time. Petal felt strange. Brakes seemed to work after that but then it happened again after about 6 or so more stops. Fluid in the two reservoirs are where they should be.

Any thoughts on what may be causing this?

Thanks in advance.

Maybe a Compromised brake booster? Open the hood. With the car running have somebody push the brake a couple of times and hear if you have any vacuum noise Coming from the booster area

[Young1]

Install a new master cylinder immediately. Do not drive it anymore.

[jrd1990zr1]

Install a new master cylinder immediately. Do not drive it anymore.

Two questions. Why do you think it is the MC rather than the booster? Any idea where you can find a new MC or have this one rebuilt? Rockauto are mostly out of stock.

[jrd1990zr1]

Maybe a Compromised brake booster? Open the hood. With the car running have somebody push the brake a couple of times and hear if you have any vacuum noise Coming from the booster area

GC, So if I hear a vacuum noise does that mean the diaphragm is shot in the brake booster? If I don't hear a vacuum noise is it possible it is a bad MC? Do you know of anyone who can rebuild a C4 MC or booster, or a place to buy one?

Thanks.

[GOLDCYLON]

GC, So if I hear a vacuum noise does that mean the diaphragm is shot in the brake booster? If I don't hear a vacuum noise is it possible it is a bad MC? Do you know of anyone who can rebuild a C4 MC or booster, or a place to buy one?

Thanks.

Normally yes and yes

I hope it's the master cylinder as those are easier to find and the 4 bolt vacuum boosters are a bear to find.

[Young1]

Booster is an assist and has nothing to do with the height of the pedal. The pedal went down because fluid escaped past the pistons in the master cylinder. That causes the light to come on. It happened to me once, right before my favorite twisties. O Reillys has a master cylinder for you for under $150.00. Brakes are life and death and thus my abruptness brother.

[jrd1990zr1]

Booster is an assist and has nothing to do with the height of the pedal. The pedal went down because fluid escaped past the pistons in the master cylinder. That causes the light to come on. It happened to me once, right before my favorite twisties. O Reillys has a master cylinder for you for under $150.00. Brakes are life and death and thus my abruptness brother.

Steve, I was able to confirm the booster is functioning. Are you aware of a way to 100% verify that it is the MC. I am not questioning your expertise, I don't want to pull it off and have to rebleed the entire system if there is any possibility it could be something else. Looks like the replacement shouldn't be too difficult, 1 electrical connection, two hydraulic lines and a couple bolts. Any other advice would be appreciated. BTW O'Reillys in upstate NY wants $170.00 for the MC. Thanks, John

[conesare2seconds]

Tricky part of the MC replacement is the C-clip from the pedal to the rod. You?re upside down with your head in the footwell and it?s dark even with a good light. Be patient, it will work.

[GOLDCYLON]

If the booster is good to go then the master cylinder is the culprit. Looks like you are in good hands advise wise. GC

[jrd1990zr1]

Tricky part of the MC replacement is the C-clip from the pedal to the rod. You?re upside down with your head in the footwell and it?s dark even with a good light. Be patient, it will work.

If the booster is good, do I have to remove it and disconnect from the pedal? I thought the MC is bolted to the booster and you separate it there? Am I mistaken? Thanks.

[secondchance]

If the booster is good, do I have to remove it and disconnect from the pedal? I thought the MC is bolted to the booster and you separate it there? Am I mistaken? Thanks.

You can remove the MC without removing the booster. Pretty simple.

[jrd1990zr1]

You can remove the MC without removing the booster. Pretty simple.

Thanks, I thought so. Not sure what the other guy was saying about removing it from the brake petal.

[Stingray1967]

Is the ZR-1 master cylinder any different than the base engine master cylinder?

[secondchance]

Is the ZR-1 master cylinder any different than the base engine master cylinder?

There are variations depending on years. Whether interchangeable between standard C4 vs. ZR1s, I don?t know.

[secondchance]

https://corvetteparts.com/catalog/Davies-Corvette/2?yr=C4&q=Brake+master+cylinder

According to above, perhaps 92 to 95 had minor difference (fluid reservoir?) specific to ZR1s.

[jrd1990zr1]

https://corvetteparts.com/catalog/Davies-Corvette/2?yr=C4&q=Brake+master+cylinder

According to above, perhaps 92 to 95 had minor difference (fluid reservoir?) specific to ZR1s.

Mine is a 1990. Shows up on page 1 of that link.

[conesare2seconds]

Thanks, I thought so. Not sure what the other guy was saying about removing it from the brake petal.

Sorry, I was thinking of the clutch master. My bad.
Tom