Manual brake conversion


Buckeye Bullet
May 26, 2002
I am getting ready to convert to manual brakes. I have searched and came up with some good info. I am going to be running Wilwood 12" dynalite big brake kit in the front, and stock drums with S10 cylinders in the rear (might switch to 11" drums, but will still be drums because I have c clip eliminators).
I read some are using a 15/16" master from a G-body, and some using a 7/8". Where do the 7/8" masters come from?
I will be using a vacuum pedal, I can adjust the pedal ratio as needed, not sure if it has the manual hole. My PM pedal is going in my brother's cutlass along with the hydroboost. I don't feel safe going 150+ and if the engine dies, I will have no brakes.
I went out and bought a 1" wilwood when i had 4 piston in the rear and stock calipers in the front.

I know this isn't the exact answer you are looking for, But my honest advice is to buy a brake pressure gauge and verify what type of pressures you are running.

I guess right off the bat, I am going to try the master off the vacuum set up off the Cutlass. It should be the 15/16 bore.
1978-1980ish Malibu, El Camino, Cutlass, Grand Prix, Regal, etc came with manual brakes from the factory. They come with a 7/8 inch bore. If buying one of these from the auto parts store, measure the bore to make sure they are selling you a 7/8 inch (0.875”) bore and not the power brake version with the 24mm (0.944” or 15/16 inch) bore. Buy new, non clearance priced master cylinders, because the rebuilt master cylinders may be hit or miss in quality and functionality (not work when installed).

Even though the g-body from 1982 to 1988 did not come with manual brakes, all vacuum boosted power brake models will have the pedal with the manual brake hole.

I don’t know which caliper you are using with the Wilwood setup, but most dual piston calipers have approximately the same area as a stock g-body caliper, most times even less. A smaller diameter bore master cylinder will allow more fluid pressure at the caliper which helps the clamping force of the caliper. Up to a certain caliper piston area, a smaller bore master cylinder is best.

I don’t know what year cutlass master cylinder you are using, but newer models had step bore master cylinders. Do an internet search on these master cylinders. In my opinion, these master cylinders are problematic because they are harder to bleed and the built in by pass valve could fail (especially on rebuilt ones). They are needed for low drag calipers which you do not have with the Wilwood units. Strait bore master cylinders are almost always a better choice.
I have a brand new Mopar 7/8 master if your interested. $85 shipped.
Yes Mike, I am interested. I like the look of the chrysler masters over the GM ones. PM me payment info. Thanks.
I have to remove some weight from this pig. It is getting a 10 point CM cage this winter. I figure I can drop 200lbs, and hopefully only get 100 of it back with the cage.
The Mopar piece is a nice choice. I believe if you go that route you will need an aftermarket adapter plate. If you use a GM style, the original powermaster adapter works great. Another option might be to slot the holes, not sure never tried.