The Stovebolt Site Forums The Shop Area The HiPo Shop The brakes again.

I have decided to have the system flushed and see what happens on a short test drive. If it is still the same issue I will have it towed home. I went to Napa and they ascertained it probably was a 68-69 Corvette MC. Then I called the place I got the kit from and they could not tell me exactly what it came from but he said their stock master cylinder would work and it was not too overpriced. But they have changed their stock numbers because Bare bought them and moved to Tennessee. But the big glaring question is, other than it needs to be dual and power will most any MC work?

We need a bit more context for what is going on in your head.

Based on your earlier post, I assume the problem you are trying to solve is what sounds like a leak.

Did your mechanic find a leak in the master cylinder?

If you are looking at replacement MCs, it needs to have the right physical connections (mounting flange, hose connections, etc). You can change the bore size, but doing that will affect both the travel and feel of the brakes.

If what you have is a C3 Corvette one (which is extremely common in conversions) and you were happy with it until this new problem developed, I would stick with that.

If you know the sizes of your slaves (if drums) or pistons (if disks) then you can calculate the effect of changing the master cylinder bore.

The truck has disks on the front and drums on the rear. Napa says it is a 68-69 Corvette but Amazon says it is not compatible with a 1969 Corvette. At this point, I just want to get it home. I want to have it ready for the Sept. gathering At Mongos. Tomorrow he is to have it back together and I am going to take it on a short drive to see if I have breaks. If not he has a trailer or I get can get a local towing service. It is less than 5 miles from home. I am just thankful that there have not been more issues in the 40,000 miles that I have driven it.

You were talking about replacing the MC before anyone had even looked at it. Did your mechanic actually inspect the system for leaks and determine that the MC is bad?

Amazon's compatibility charts are sketch at best. Where did you get the part number you are looking at there?

A 68-76 Corvette should have the same master cylinder if it had power brakes.

He had it off and thought Maybe it needed a new seal but a seal only comes in a kit at $40.00 plus installation. A new MC from the brake kit co. Brothers Trucks. company is $74.97. I have the receipt and until I looked at I did not realize that I bought the kit in 2004 not 2012 as I thought. It is coming home for now.

I'm confused. Did the problem turn out to be a leaking master cylinder? Was it fixed?

Well, we will never know for sure. I just got it home after I took it for the first test drive and it drove fine. Mostly what he did was flush the brake system twice and it had some trash in it. It looks like it had some moisture in it. I drove it in town then then paid him and took it home. A country highway with little traffic so I did some panic stops with no problem and a good brake feel. Hoping that took care of it.

Ron, I posted similar in the Spoon a moment ago, but it would be advisable to closely monitor the brake fluid level.

RonR

100% Taco on this one. Its not clear what diagnosis was done, but it sure sounds like the mechanic took it apart, said it was fine, and put it back together.

Brake problems don't just hallucinate themselves into and out of existence. Be real careful Ron!

. I will keep it under a hundred.

Just for conversations sake, conversions using the 68 and up camaro, and 68 amd up vette are really common and the guys with the passenger cars have been using those masters for years now. All drum conversion, you want a 1 inch bore master. For disc drum you want a master with a 1 1/8 bore.

Now, one small rub. The original single pot master had a pressure residual valve built in. One thing to keep in mind, new masters no longer come with pressure residual valves. Original gm dual masters had them and real professionally rebuilt masters had them but no more. The residual valve kept a little pressure on the back of the cups of the wheel cylinders and helped keep the shoes from completely completely retracting. You really should have them on an all drum system, and at least one for the rear brakes on a disc drum system. Wilwood sells their 10 pound valves that get plumbed in line, preferably close to the master.

https://www.moserengineering.com/260-1876-Wilwood-10lb-Residual-Pressure-Valve.item

If you are having a real gm master rebuilt, have the rebuilder install the stock type duck billed residual valves.

let’s talk brake shoes. When these cars were new, brake shoes were made out of asbestos. Worked great as a friction material and the cars and trucks stopped just fine. good for braking, not so good for our health or the environment.

todays over the counter brake shoes use an organic material. What is in it, no one really knows.

in 2015 I redid a drum brake system on a 57 car I own. I installed new everything, including brand name shoes. Car would just not stop. Terrible really. I have owned and driven that very car for 47 years so I know exactly how the car should stop on drum brakes and those shoes were not doing the job.

A friend turned me on to Muscle Car Brakes and their ceramic matrix brake shoes. They are not inexpensive, about 120-130 for each of the front and back.

I bit the bullet and installed them and what a big difference. Stops just like it should. So in my mind, those are the only shoes you would want to use on all all drum system if you really want to do everything possible to improve the braking, and if MCB offers shoes. Call them if they don’t, they may be able to do a custom job, you never know.

http://www.musclecarbrakes.com/bib5170chevy.html

If your disc set up uses the chevelle D52 caliper, a common caliper to use, or some other type of common caliper, you might use some Hawk Street 5.0 pads. The more aggressive friction will also help get the truck stopped in better order then over the counter organic pads.

The master on the left is a camaro/GTO manual drum brake master. Next photo is the 68 vette style disc drum master. Hawk pads for chevelle caliper. And on the right, see the duck bill looking things with the springs, those are the pressure residual valves. Those come in a Raybestos rebuild kit. Original masters can be rebuilt with these valves installed. New masters do not have removable seats so no way to install them so you use the Wilwood inline versions.

One last thing, if using a gm style proportioning valve, remember to buy the little tool to lock the shuttlecock in the valve in place while you are bleeding the brakes. Otherwise it will trip and only half of your system will work. And they are a bit of a pain to reset.

https://techtalk.mpbrakes.com/proportioning-valve-bleeding-tool