Power brake booster and M/C

James Stern · #1 (**permalink**) 03-08-2016, 12:25 PM

I really need some help on my CRII. I am looking to replace both the power brake booster and the master cylinder. The booster currently on the car is 7 1/4" in diameter.
The master cylinder has the brake lines running to the driver side. The brakes are disc front and drums rear.

Does anyone know what make/model booster and master cylinder used by Classic Roadster (around 1998)

Thank you for your help.

Double Venom · #2 (**permalink**) 03-09-2016, 04:02 AM

The M/C is a 1987 Corvette with 4 way discs. The booster was changed to a 7" Booster. These can be found in almost all parts Catalogs, Speedway, Yogi's, etc..

James Stern · #3 (**permalink**) 03-09-2016, 07:16 AM

Ed (DV),

Thanks for your response. You say the master cylinder for a CRII with rear drums is a Corvette with 4 way discs? I know the booster is 7" but I am looking for a current part number for the correct bolt pattern.

Jim

Wisconsin_Snake · #4 (**permalink**) 03-09-2016, 09:00 AM

I have seen only 2 bolt patterns, the Ford (which is the ~9 inch dual diaphragm unit) where the bolt do not make a square as on is off set by like half an inch.
The others all have the setup where the bolts make a square (or are 90 degrees of each other.) Very universal.

Too bad I did not have this info and I get the Ford ~9 inch dual diaphragm unit which will make things tight. Oh well, I have come to learn that is my luck.

Double Venom · #5 (**permalink**) 03-09-2016, 09:05 AM

Jim it will work, BUT will be better to switch to 4 way discs!

Wisconsin_Snake · #6 (**permalink**) 03-09-2016, 09:40 AM

Perhaps the question should be asked, do you have disk brakes in the rear?

I would think that the M/C should be matched to if the car has disk/drum brakes or 4 wheel disk brakes.

bjretired · #7 (**permalink**) 03-09-2016, 09:49 AM

Check your Vac. pressure. You will need 16lbs if not you will need a boost pump.

MaSnaka · #8 (**permalink**) 03-09-2016, 04:40 PM

James I just had to replace my master cylinder. I used one made by CPP (Classic Performance Products) 4 disc Corvette style cast listed at $59.00, p/n M-C1516-L. They carry boosters as well as lots of brake components. Check them out at Disc Brake, Steering and Suspension Products for classic Chevy and Ford cars and trucks 800-522-5004. Getting parts is the easy part...changing them out is the pita. I pulled out the side vent which made access to the brake lines much easier and also pulled the steering wheel to get into the pedal box area. Good luck!!

John

Double Venom · #9 (**permalink**) 03-10-2016, 02:32 AM

W. SNAKE, Normally correct, but with the MII FRONT DISCS AND THE STOCK drums on the rear, the ratio of the two front bore sizes allow them to work. I"m just saying 4wheel disc would/will be a great upgrade and with the Corvette Master you won't need to change down the road.
DV

C5GTO · #10 (**permalink**) 03-10-2016, 02:43 PM

I recently had the plastic fitting where the vacuum hose attaches to the power booster break off on mine. It's not fun when you have power brakes one minute and don't the next, but that's another story.

I had the 7" booster, single diaphragm before. I replaced it with a Summit brand dual diaphragm also in 7" (or maybe 7 1/4" or so). The dual diaphragm is an inch or so thicker but the brake lines had enough slack that it still worked. It basically bolted right in with the master cylinder now spaced further out.

The braking is now better and I can bring the car to a quick stop now without over straining my leg muscle. I'm a big guy with strong legs and I needed them with the prior power booster. I'd recommend the dual diaphragm if you can.

MaSnaka · #11 (**permalink**) 03-10-2016, 02:46 PM

James,
I had front disc brakes from either a Mustang II or a Pinto, maybe one in the same and drums in the rear with no booster when I first bought my car. I upgraded the fronts to Wilwood 11" (which were about 20lbs lighter per wheel) and kept the rear drums in place for a future project as funds would allow. My breaking ability improved greatly with the upgrade to the front brakes alone. Eventually I did replace the drums with Wilwood 11" discs, a new MC , an adjustable proportioning valve and still no booster. I cant say there was a big difference in stopping ability switching from rear drums to rear discs but they sure look better. I'm sure if I ever got my car onto a track and really put the brakes to task there would be a noticeable improvement but so far just a street cruiser. No booster but I did find there are two different pivot points for the pedal ratio power vs. manual in the pedal box. Of course mine was wrong and I had to change it which made a huge difference in the pedal pressure required to stop hard.

John

James Stern · #12 (**permalink**) 03-11-2016, 07:13 AM

Thank you for your input. I settled on the AutoZone brake booster with disc/drum master cylnder. The car goes to the car clinic on the 21st for the install. The bolt pattern looked like the correct one for my car.

Wisconsin_Snake · #13 (**permalink**) 03-11-2016, 08:57 AM

Quote:

Originally Posted by MaSnaka

James,
I had front disc brakes from either a Mustang II or a Pinto, maybe one in the same and drums in the rear with no booster when I first bought my car. I upgraded the fronts to Wilwood 11"...
My breaking ability improved greatly with the upgrade to the front brakes alone. John

I plan to upgrade the front at some point but decided it is more important to get my car running, painted and registered otherwise upgrading things would add more years on to the already painfully slow build.

Double Venom · #14 (**permalink**) 03-12-2016, 02:56 AM

John,
Don showed the better bolt pattern at one time. Actually made it the 6:1 proper ratio. Braking was tremendously improved. It's in the archives somewhere?
DV

MaSnaka · #15 (**permalink**) 03-12-2016, 01:58 PM

DV,
6:1 or 7:1 would be correct for the manual brakes. I had to make a slight mod to my brake pedal arm to accommodate the higher ratio. Pictures are in my gallery. I forget what the other ratio was but it was closer to 4 or 5:1. If anybody need clarification on what a pedal ratio is there is a nice graphic at the Wilwood web page.

John