help with brake problem

[John C.]

Re: help with brake problem

John -

Can you post a photo of the master cylinder and booster so we know what you're dealing with? All Corvettes with power brakes use a vacuum booster; none ever used a hydraulic booster, although some have been converted to an aftermarket "Hydroboost" system that gets its power from the power steering pump.

4-wheel disc brake Corvettes prior to 1977 or so don't use a proportioning valve - proportioning is designed into the system via different bore diameters for the front and rear caliper pistons.

If your master cylinder and booster are factory, they'll look like the photo below.

Yes sir, that is exactly what mine looks like. Thanks a million for posting the pic!
I called Eklers earlier today (before I read your post) to buy a rebuild kit and was told by them, quote; "65's weren't available with vacuum assist power brakes, that option wasn't available until 67". "The brakes were either manual or hydroassist". They didn't have (according to the guy I spoke with) a rebuild kit or even an entire twin chamber master cylinder for a 65. They said someone must have put a system off a 67 on my car.
I'm so glad I joined the NCRS. You guys are a wonderful source of information. Can you tell me where to go to get a rebuild kit for my master cylinder? It says it's a 1" bore on the side of the housing.
I want to be able to learn more about the car and all the date codes, vin number decoding, etc. Can you reccomend a book that will explain all this including what was factory installed and optional from GM.
Thank you, JC

[Dick W.]

Re: help with brake problem

John, Corvette Stainless Steel Brakes has the master cylinder and booster for your car

[John C.]

Re: help with brake problem

John, Corvette Stainless Steel Brakes has the master cylinder and booster for your car

Superb! Thanks Dick
JC

[Michael W.]

Re: help with brake problem

I called Eklers earlier today (before I read your post) to buy a rebuild kit and was told by them, quote; "65's weren't available with vacuum assist power brakes, that option wasn't available until 67". "The brakes were either manual or hydroassist". They didn't have (according to the guy I spoke with) a rebuild kit or even an entire twin chamber master cylinder for a 65. They said someone must have put a system off a 67 on my car.

That's frightening.

In doing some additional research, I understand that there are two versions of a '65 PB master cylinder that differ primarily in the size of the outlet lines ie 3/16" vs. 1/4". Might want to check if replacing rather rebuilding. If your M/C is the original, hold onto it anyway.

[Rob M.]

Re: help with brake problem

I'd also suggest that you choose one of your two threads on this subject

https://www.forums.ncrs.org/showthre...83342&uid=6540

and have the moderators close or merge the other.

Two thread merged...

[John H.]

Re: help with brake problem

Can you tell me where to go to get a rebuild kit for my master cylinder? It says it's a 1" bore on the side of the housing.
I want to be able to learn more about the car and all the date codes, vin number decoding, etc. Can you reccomend a book that will explain all this including what was factory installed and optional from GM.
Thank you, JC

John -

Long Island Corvette Supply (www.licorvette.com) has your master cylinder rebuild kit, which includes both pistons - their #52-19C2. Get their catalog too.

Suggest you order the following books to start your technical library - all are available from the NCRS on-line store ("NCRS Store" at the top of the page):

NCRS 1965 Corvette Technical Information Manual & Judging Guide

1965 Corvette Assembly Manual

Noland Adams' Complete Restoration & Technical Guide, Vol. 2, 1963-1967.

1963 Corvette Shop Manual, and the 1965 Supplement.

1965 Corvette Owner's Manual

You'll find many others as the disease takes hold, but these are the essential foundation for your library.

[John C.]

Re: help with brake problem

John -

Long Island Corvette Supply (www.licorvette.com) has your master cylinder rebuild kit, which includes both pistons - their #52-19C2. Get their catalog too.

Suggest you order the following books to start your technical library - all are available from the NCRS on-line store ("NCRS Store" at the top of the page):

NCRS 1965 Corvette Technical Information Manual & Judging Guide

1965 Corvette Assembly Manual

Noland Adams' Complete Restoration & Technical Guide, Vol. 2, 1963-1967.

1963 Corvette Shop Manual, and the 1965 Supplement.

1965 Corvette Owner's Manual

You'll find many others as the disease takes hold, but these are the essential foundation for your library.

Thank you ! I'll get to ordering. it's nice to know where to go to get "accurate " information.

[John C.]

Re: help with brake problem

Two thread merged...

Thanks Rob !

[John C.]

Re: help with brake problem

That's frightening.

In doing some additional research, I understand that there are two versions of a '65 PB master cylinder that differ primarily in the size of the outlet lines ie 3/16" vs. 1/4". Might want to check if replacing rather rebuilding. If your M/C is the original, hold onto it anyway.

In my search last pm to try and discypher (did I spell that right), I did notice that there were two different line sizes put out that year. I've ordered the black book and will soon have access to date codes so as to determine if my master cylinder is the one that came on the car. There is a company that is reproducing "new" master cylinders with the correct date codes stamped on them, with permission from GM. Supposedly, exactly like the original.
JC

[John C.]

Re: help with brake problem

John:
Obviously the MC is not fully releasing (to uncover one of the orifices to the reservoir) once the vehicle/system is at operating temp. The items to check are, 1 the interface between the MC and Power brake booster for a mismatch of parts; or 2 the most likely cause, an incorrectly adjusted pushrod or incorrect part. page 5-11 in your service manual, or 3 missing springs or stuck pistons in the MC itself.

Ok. I spoke with the guy that did the brake work on the car. He said he replaced all the brake components except the M/C (including the booster). So, I guess it's possible there could be a mismatch of parts between the M/C and the booster.
Also, the M/C is 45 yrs old, good possibility it's bad.
If the pushrod is adjusted wrong, wouldn't it act up all the time, not just after 20 min. of driving??? The pedal gets tight after driving for a while. Then releases after sitting, indicating that your thoughts about the fluid being trapped and not being able to return to the M/C could be happening.
The M/C hasn't been apart, so everything inside it is as it came, inc. the springs.
My guess, after hearing your thoughts as to what might be happening, is the piston is trying to stick, not allowing the fluid to return properly??????
JC

[Dick W.]

Re: help with brake problem

. There is a company that is reproducing "new" master cylinders with the correct date codes stamped on them, with permission from GM. Supposedly, exactly like the original.
JC

That would be Corvette Stainless Steel Brakes

[John C.]

Re: help with brake problem

John,

I had exactly the same problem on my PB '65. In my case, the rear compensating port in the master cylinder was plugged.

If you look into the fluid reservoir, the compensating port is the small hole to the front in each reservoir. If all 4 are locking up, the compensating port in your rear reservoir may be plugged.

The compensating port allows expanding (due to heat) brake fluid to flow back into the reservoir. If it can't expand back into the reservoir, it applies the brakes, which generates more heat, which expands the fluid more, which applies the brakes more.

I wound up at full throttle in 1st gear and the car just ground to a halt.

I would get it to lock up again and pull the master cylinder loose from the booster to see if that fixes it. It is possible that your master is not fully retracting and the piston seal is covering the comp. port. If that doesn't fix it, try running a paper clip into the port to clear a clog. That fixed it for me.

Bill

I think you are exactly right. That is precisely what it's doing. After it sits for a while , it cools and the brakes release. Another gentelman said the same thing (kinda). He said if the fluid couldn't return due to a sticky piston or a clogged port inside the M/C, it would do the same thing.
So, apparently, it's one of the two. I think I'll go ahead and rebuild it since it's 45 years old and not that big a deal. It's amazing how much you can learn from a forum filled with guys like yourself that have been there, done that.
I really appreciate all the responses I've gotten from all you guys.
Thanks a million!!!!!
JC

[Domenic T.]

Re: help with brake problem

Agree with the compensater valve not releasing preasure. You can see it work on some master cylinders if you remove the cap and have someone push the brake and release. You will see a ripple come out of the tiny hole (if visible) releasing the fluid back to the cylinder.

DOM

[John C.]

Re: help with brake problem

Agree with the compensater valve not releasing preasure. You can see it work on some master cylinders if you remove the cap and have someone push the brake and release. You will see a ripple come out of the tiny hole (if visible) releasing the fluid back to the cylinder.

DOM

Funny you should mention that. I checked that the other day and it appeared the rear return port was clogged. I have since pulled it off and apart, cleaned it and it now apprears to be free of any debris. Rebuild parts should be here thur. I'll keep you posted.
Thx guys, JC