I don't know why they call them a gasket. It really doesn't contain fluid or anything. I refer them as a dust seal. That's all it is. Foam dust seal.
If you don't install them, I suppose that missing thickness would be missing in the important gap between MC & booster.

I recall my new master came with one seal. You should try to buy them if you can.

 

I forgot to mention, I have no power going to the top of the combination valve that illuminates the brake light. All other inst. panel lights are ok.

 

I only bring this old post of mind to give some background of the issues I have had with the brakes. To continue, I had the 5th mechanic install the combo valve hoping that was the issue. IT WAS NOT. I disassembled one of the new M/C's and all was good. took off front left (car pulled right when brakes applied) and no restrictions. The 5th mechanic does not want to trouble shoot any further.
My question to this knowledgeable group is what would you guys suggest I do next? Everything new except rotors. Mechanic #3 checked run out and reported no issues. The rotors have less than 1200 miles.
I would burn it to the ground but i'd get caught with matches.

 

Back to post # 22. The brake warning light can only activate if the IGN key is on. You tested the dash lights, likely w/o a key. Maybe just a bulb issue.

Was a original Delco type Proportioning Valve installed, or a aftermarket? Was the Prop Valve the correct year or just a general fits all?

You disassembled the MC, all was good. How did you come to that conclusion? Even if you properly bench bled, the MC may not build pressure. The MC needs to be tested on the car w/o brake lines attached. That will once & for all, make or break questioning the MC. If you want info on how to go about testing, let me know.
Otherwise, I have no input to add.

 

Thank you Mr. Heads U.P. appreciate your patience. All the components were in good order within the M/C. Springs, rubber as new.
Please tell me how to test the M/C on car. I bled with the rear of car up and bubble in level towards rear of car and pushed pedal. No bubbles.
I will not ever bring up this issue again.
Thank You

 

First off, there are people in mental institutions walking the hallways with a bottle of DOT3 in their hand. It will drive you nuts.

You need to purchase two prefabbed brakelines. Prefabbed means a brass fitting is on one end. The other end can be open or have fittings. I found some at NAPA and are one foot long.
Keep in mind the two line ports on the MC are not only different diameters but different thread pitch too. I do not know those sizes off the top of my head. But you will need a one foot long brakeline for each port, correct size fittings. Then see if you can get the parts counter guy to bend those to a 90* angle, so as the line comes out of the MC, it will clear the fender.
On the other end of the prefab line, your choice, you can just bend, smash, squeeze, pinch them off. Or find a brass cap to seal the end fitting. ( I use them as bench bleed return lines also)
So, for about $20 you have MC test lines you can use over & over.
Attach the "test lines" to the bench bled MC. Open the drivers door and stand on the brake pedal. It should not budge. And it should hold all day long. Then you know the MC has tested ok and your issues are elsewhere. If the pedal sinks, look no farther.

Do not use a bolt to plug the brakeline ports. Inside that port is a flare that is part of the casting. A bolt will damage the flair rendering the MC as unusable.

 

I just read through this entire thread, and your being given some really good guidance. The trouble is your not coming up with answers to the guidance given.
For instance, in post #4 and 5 7T1 and HeadsUP suggested a procedure to confirm you have the correct rod length, but you haven't let us know if you've measured it, and in post # 7 you dismiss that because "you don't think it's the cause". But what if it is!

In post #9 Interpon poked you about pushing on the pedal with engine running vs engine off.....no response

In post 17 & 19 you were told how to reset combo valve and to watch dash light with key on, you said you'd report back.....no response

Do you see a trend here? It's hard for the members to help you, because of your refusal to follow the help.

You've been fighting this issue for quite a while, and I'd sure like to see you get it fixed, but you need to help us help you.

 

Michaelroy, you said the brake pedal was hard when the you stood on it with the engine off, is this still the case? If yes what happens if you take the car to a deserted road and stand on the brakes from 30 mph do the wheels lock up?

 

OK here goes: Thanks Heads UP I will definitely do that. I am going away for a few weeks but will be back to the Vette as soon as I return.
To sstocker31: In my post of 12/05 I sent a picture with the length of the rod 2 7/16". That is the same length if the original booster rod and of the other 2 boosters i purchased. In that same post you will notice the orange color on the rod. That color transfered to the M/C end. All 3 I assume were not the wrong size.
I have said from the beginning that I have somewhat of a pedal after bleeding(about 20 times) maybe just off the floor but when I start the engine, the pedal goes to the floor.
I can't tell while I type this which post 17 and 19 are, however I did stomp on the pedal. I posted that I have no power going to the valve. I assume the e brake switch may be bad. I haVE one on order which should have already arrived. I put new bulbs in my dash a while back but I couldn't sware that there is a bulb in the socket. I don't really recall ever seeing a brake light sense I've owned the car. I never use the e brake.

Trust me Mr.sstocker I have followed all suggestions that have been given to me by all of you guys. I apologize if It appears that I don't. I've had a 1965 GTO for 10 or 12 years now that I have wrenched on forever and I have always figured out ( a lot of times with the help of the Pontiac forum) how to fix the problems that i have had, but this issue is beyond my abilities and 5 real mechanics who, by the way refuse to do any more to the car.
What I really can't understand is what the engine has to do with the brakes? Sorry to go on and on!

 

It's not the front/rear brass warning switch below the master. That wouldn't have a thing to do with the engine running or not. It seems to me that it's all connected to the booster since nothing appears out of the ordinary until the booster is activated. I'm only vaguely familiar with how the booster works but found this:
brake booster check valve

The check valve is the vacuum connection elbow on the booster and worth a shot to check out and maybe replace it and the grommett. Do a google on it as there appears to be some validity to the failure of the check valve to soft brakes.

 

Well, like they say, only believe about one third of what you read on the internet. I don't know who the author is with the highlighted box above but only one of the statements is verified.

Feels spongy. Air in system
Pedal hard to press. Yes, could be booster / check valve.
Pedal goes to floor: Leaks somewhere, calipers, MC, fittings, hoses & steel lines, etc Not the check valve.

The booster is strictly an assist with tenderfoot drivers. The check valve holds vacuum briefly in the booster in the event the engine stalls.

 

Bad boosters will let the pedal move towards the floor then stop. I had one that went bad and with the engine off I had a hard pedal. With the engine on it would press hard then with pressure on it it would slowly go to the floor. I got fed up with all the different after market designs so I bought a matched set from Tuff Stuff. That way of there was an issue it was on them and I could get a warranty on either end.

I would take it somewhere with no traffic and see if yo ucan get any brakes to lock up. If just the rear or front do, then you can eliminate the working system. If its all soft its in the master or booster.

 

Going back to the original thread I would send back the 2 master and booster and get a matched set and start there. And make sure you get a set that is for disc/ disc fron to rear some still say disc drum although those c3's dont exist. Even a distributor can screw you and you wouldnt know it. They obviously dont or there software designer doesnt
https://www.tuffstuffperformance.com...8-5-7-350.html

good
https://www.tuffstuffperformance.com...nc-2129nb.html

incorrect even though the search engine was used
https://www.tuffstuffperformance.com...-2129nb-2.html

 

The quote was from the article I linked. A similar thread appears on the HAMB/ Jalopy Garage forum.
How about the return spring on the valve side that pushes the diaphragm back toward the driver? If that is weak or broken then I'd think the engine vacuum would pull the diaphragm too easily... ?

 

I had a similar problem with my car after changing out the MC from NAPA. Tried everything but the pedal would go to the floor as yours upon engine start and depressing the pedal. Tried bleeding the master again, all 4 wheels to no avail. Took the MC back to NAPA got another and installed. That was the fix. Just because it is new doesn't mean it will work.

 

Ok, so you say the car will stop? So if you perform an emergency stop from 30 MPH will the wheels lock up? If it won't, will it do so if you pump the pedal a couple of times and then slam the brakes on?
You say you can't understand what the engine has to do with the brakes? Well the engine supplies the vacuum that provides the power assistance to your braking effort.
My C3 with the brakes in good condition has more pedal travel when the engine is running than my C4 for comparison but they are about the same when the engine is off.

 

Well lets hope it's a faulty master cylinder, and changing it out fixes your problems.
It wasn't really discussed within this thread, and I'm assuming the 5 guys that looked at it before know about this and did it properly. When bleeding the rear calipers there is a procedure to follow to do it properly....... RR inner, RR outer, LR inner, LR outer. If you don't bleed the inners first, your doomed to have a soft pedal.