I am continuing to sort my new 66 project. She has what appears to be a very clean single chamber master, no boost. Just got her on the road this weekend and the brakes just do not stop well at all. She will stop but with great pedal effort, no pulling right or left. Could not come close to locking her up. I did get as far as jacking her up and getting her on stands. All wheels spin free enough. Wife hits the brake pedal and all four corners and locked. I am guessing that tomorrow I need to pull the tires and look at calipers but I wanted to reach out and see what you all think. Did not see anything about this in the FAQ section.

 

start with the soft rubber hoses that go to each caliper. then bleed the brakes again

 

Could have "performance" pads. I'd replace with known items.

 

How clean does the MC look? Does it look brand new with no signs of brake fluid spills anywhere? I ask because the proper way of bench bleeding a new MC can get messy. So if its new and very clean its possible someone installed a new MC without bench bleeding so the engine compartment would look nice. Problem is that can leave air that is hard to purge.

 

Yeh there is no way it's an original MC, real pretty inside and out. I'll pull the wheels tomorrow, inspect the hoses, order up some pads, bleed and see. If no joy I can pull the master and look up the bench bleed process.
A follow up, would not air in the system give me a soft or spongy pedal? The amount of pedal travel feels normal. It moves about what you would expect, firm with increased resistance until your straining your muscles. Car comes to a stop in about three times the distance you want. I never had race pads before but have read about how they don't work well until their hot. The ones on her may even be contaminated from a sloppy installation.
I'll get on it and report back. Thanks all.

 

R66 had the original master cylinder (or at least the numbers matched) and it is bright and shiny in the bore with no pits. The bore miked out, but it was leaking past the rear cup into the floor boards.
After bleeding, we had good brakes for a while but then it sucked air and the pedal started to sink a little. Could get good brakes for a while longer by pumping them. The cups were hard and not sealing. I just changed to a dual master cylinder rather than rebuild the single, not that it is really any better for stopping power.

 

C2Dude,
I too like the safety of the dual brake system. If you get to the point of removing the MC you have, you might consider making that change. It may not be original, but it is safer.

 

Or they may be functioning properly and you have higher expectations.
I have the same system on my 66 and best describe them as go-kart brakes.
I can lockem up but it isnt easy.

 

This is a clue.

If it's not original, then it's possible the bore size is incorrect for the application. In particular if the bore is larger than it should be, you will have to push the pedal with more force to get the car to stop.

If someone installed brake pads with low friction coefficient, pedal effort will be greater. I think this is unlikely since even the cheapest brake pads have reasonable friction coefficients.

Some racing brake pads, as you've heard, have to get really, really hot to work well. When cold, they don't inspire confidence. What do you really know about the pads on the car?

If there is a firm pedal, bleeding the brakes won't help.

Bottom line, I'd look first at the master cylinder and figure out if its bore size is proper.

 

When you are at the wheels checking the calipers, check to see if the pads and or rotors are glazed. If everything is functioning as it should, and you have glazed components, your car will exhibit the problems you are having. Jerry

 

That is sounding more reasonable to me. I am new to "turning wrenches" as a hobby but I like to read and learn. Air or soft brake hoses, as I mentioned, should generate a spongy pedal which I do not have. The glazing suggestion is not something I thought of but now mentioned reminds me of several uncomfortable instances in my youth attempting stop drum brake cars. That sensation of pushing against a hard pedal with unacceptable results probably best describes what I am currently experiencing. The mention of bore size makes sense as well. My last/first project was re- engineering a Austin Healey replica. At one point the master rear seal failed after a bleeding session. I swapped it out with a unit with a smaller bore and the results were hypersensitive brakes. That said the master in the Vette looks like the OEM unit. If the actual OEM unit failed and the last guy bought a aftermarket unit, I would think the bore would have been the same, unless this style of MC was used on many different cars with different requirements/bores.
If the master turns out to be the culprit, a duel chamber unit would be the way to go, just some re-plumbing issues to deal with. As far as high expectations, there is probably some of that involved but it is hard to imagine this could be normal. If I were traveling at any rate of speed and had to stop rapidly due to a car in front of me, I do not see how I could avoid an accident. I did once own a 66 about 10 years ago (really should have held on to that, cost me considerably more the second time around), with the same set up and never noticed this (going from rack and pinion to recirculating ball....I noticed!). Regardless and just so I have something to chew on, if I replace the MC with a duel unit, ought I not add a booster and really improve the system?

 

Since you stated you are new to turning wrenches, replacing the single MC with a dual reservoir MC isn't just a matter of removing one and bolting in the new one. Not overly difficult, but not just a bolt-on solution. Read thru this thread to see what's involved. https://www.corvetteforum.com/forums...onversion.html

 

I assumed the two rear discs would be fed by the existing single line that splits out back. The article you gave indicates that both rear brakes are fed by dedicated lines? Booster may need shimming to clear the hood. Brake switch may need some re-working to function once system converted to boost. Am I correct that boosting is a worthwhile modification?

 

I'll assume your 66 manual brakes are the same as my 65 manual brakes, big jar style master. Using DOT 5 my car stops on a dime with pedal pressure slightly above that of a vacuum boosted master. So you are right, something is wrong. Assuming your rubber lines are good, your steel lines are not crushed anywhere from a tow chain, I predict the master is the culprit. I would bench bleed a replacement & put it on. My bet is that will fix it.


It is inarguable that a dual circuit system far safer, but I wouldn't do it. A hobby car that is highly maintained and inspected by its **** owners is just fine with its stock brakes.


As for boosted brakes on a C2, these are not for me. I enjoy the slightly elevated apply pressure and feel of manual brakes on these cars, power brakes dull the feel and that big cadmium plated can on the firewall is unpleasant to look at.


Dan

 

Well fair enough. I'll concentrate on the master and attempt to restore the original set up where it works as it should. Then I can judge it they are acceptable to me or if further modification is warranted.

 

Front Caliper
Front Pads

This is what I know. Pulled all wheels. All brake steel lines and hoses are new. Both rear calipers are new with numbers Drivers Side: 5473807 (a screw head pointing to 9:00 followed by 1227, followed by screw head pointing to10:00), Delco Moraine R6. Passengers Side: 5465905, 3 207 Delco Morane Pads: 5032 BXHQFF 7028A, all new Rotors look new.

Up front the passengers side caliper looks old, the drivers side newer but not as shiny new as the rears. Drivers side: 5465952, (11:00-152-2:00), Morane 2 Passengers side: 5473796 Delco Morane 2 Pads look new: 5032 BXHQFF 7028A

Not having any luck decoding any of that and may not be important. The casting number on the master is R 2225032. This matches the Corvette Central GM licensed MC casting number. The Corvette Central unit specs a 1" bore so I assume that is what I have although I would need to pull it and measure it for sure. So no smoking gun yet. Would an improperly bench bleed MC still have a firm pedal? I could go ahead and bench bleed her in situation by leveling her up and installing a clear tube between the fluid port back into the chamber. Have the wife gently pump until any bubbles disappear. What say you all?

REAR CALIPER:

Rear Pads

 

If you have a firm pedal, you don't need to bleed the brakes. And it won't help.

 

There is another test you could try before pulling the MC, but it may not be a better choice. If you can round up a pressure gauge you could test the line pressure when the brake pedal is depressed. I don't know the target PSI, but I'm sure someone here does.

 

Master cylinder. All the squeeze comes from there. They are cheap and easy enough to change out and I would start there given what you have already done. Bench bleed it and put it on. I bet it will clear up.

I have a 60 Electra that behaved this way with a newly rebuilt cylinder I had sent out to an expert. Took it off, put one on from a parts house and wah lah, it worked. Never could 'splain it.

Dan

 

Driving a 4-wheel, manual disc brake car takes some getting used to. I picked up a '73 Corvette with manual brakes in the late 80's and remember well having to remind myself each time I drove it that it required greater than normal pedal pressure to stop. It requires a different driving style, particularly today where cars require less reaction time than they did before power brakes became almost standard. The first time someone jams their brakes on in traffic with little warning and you find yourself diving for the shoulder, you'll understand.

Back in the 60's when Shelby added manual front disc brakes to the GT-350's he found it necessary to add this dash placard to the cars...



Good luck... GUSTO