I am partially into the Rich Downing 4-wheel disc conversion detailed on David Pozzi's site and am now concerned about master cylinder & booster selection. http://ourworld.compuserve.com/homepages/David_Pozzi/12_corvette_brakes_on_fgen.htm

I want to install mid 90's Camaro rear discs, and early 90's Corvette 12" front discs. I have purchased the four rotors and front caliper brackets, but not yet the calipers.

Now on to my question.... The Rich Downing info addresses manual boosters in 15/16 cylinder diameters from late model autos. I would like a M/C & booster combo that looks more original to my car, a '69 Camaro.

Would a '79 Trans-am 4-wheel disc M/C mate to a '69 Camaro booster? How about an early 70's Corvette M/C with the '69 Camaro booster? Or, would the complete '79 Trans-am 4-wheel disc M/C and booster assy work? How about the brake pedal clevis and linkage? Also, do these late model calipers require a quick take-up master cylinder? I would rather stop now before I can't later.

My rolling body came with no brake components other then the rear drums and the front rotors, so I am pretty well starting from scratch. This is my first time attempting a project such as this and my inexperience shows.

Thanks in advance for any assistance offered.

Here's the master/booster I used on my 4 wheel disc brake setup. It's not a GM master but it looks real close. I got it off Ebay but I checked a couple of the brake company sites and there are a lot of subtle differences between master cylinder applications. I can't remember the exact details on this setup but I think it was the 1" bore master specifically for 4 wheel disc brakes. My car had full front rotors on the front and back and it stopped awesome. Go to the Master Power website and look through the different master cylinders.

http://cjcfo.fbody.com/members/jeffhansbury@comcast.net/68LT1/68LT1-8.jpg

With the front/rear PBR caliper setup and vacuum assist you will want a maximum 15/16" piston bore. A 7/8" would be better. NAPA has catalogs that you can paw through that list model, piston size, and line size.

I had a 1" bore PBR setup on a 12" disk (like yours) using a large diameter stock booster. The engine made 12-13 inHg. There was not enough assist. The large stock booster provided more assist than the aftermarket small diameter setup.

I really like the later model alumunum MC's. They shed a lot of weight from the front end and have many piston sizes available, but they do not look even close to stock. Here's some additional MC info. The 13" PBR caliper is the same as yours.

http://www.geocities.com/torkerscamaro/torker.html

The chevette P/B had a 7/8" 1 piece cast master. I dont know if the ear spread or rod hole was the same, and you'd have to remove the drum residual valve, I think.

Ford Grenada with 4wl disc was 15/16" cast. It is a little big without more boost and/or performance friction. Even the 7/8 might be a tad big if it was manual brakes.

Master Power Brakes recently told me that four wheel discs require additional volume, and the 7/8" or 15/16" wouldn't be large enough. The conflicting information is puzzling.

A friend of mine converted his '66 Chevelle to 4-wheel discs and used the '79 trans-am 4W/Disc master cylinder mated to a '72 buick booster. He says it does a nice job. The entire '79 T/A assy looks like it might fit well, other than the clevis attachment to the brake pedal. I don't know what the piston diameter is, but I suspect no smaller than 1".

I printed the torkerscamaro info and had planed to pretty much duplicate his set-up, but want to go in another direction with the M/C.

Please keep the suggestions coming.

volume boils down to cylinder ratio... master vs slave.

also playing a role is pedal ratio and booster, and to a lesser extent, rotor size and pad coefficient will effect the amount of pressure needed.

if the 66 chevelle's calipers are the same as yours, you can use it as a comparison. I believe it has the same pedal ratios.

the calipers you are using may be low drag, which require more volume, such as from a quick take up master. A larger master can make up for the volume, but it cannot produce as much pressure with the same input.

What is your caliper configuration and piston sizes, and I can give you some hard #s to give to MP as comparisons.

I have yet to purchase the calipers, but they would be the same as on torker's web site.
http://www.geocities.com/torkerscamaro/torker.html
Maybe someone can advise us of the cylinder diameters.

Here's an interesting option, the seller has advised me that the cylinder has a 1" bore, which based on the information above still may not be powerful enough.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7939288910&fromMakeTrack=true
Looks like the amount of available vacuum is really a key factor here.

That link says he is using a 15/16" step bore with hydroboost, and he specifies not to use a 1" or larger.

I was wrong about the disc/disc Grenada, I think it uses a 1".

Here are some examples of cars with similar brakes that I know the sizes of:
88 olds cutlass:
15/16 master
front: 41mm dual floating
rear: 34mm single floating

1990 300zx/fi:
7/8 master
front: 40mm 4 piston fixed
rear: 38mm 2 piston fixed

1990 300zxTT:
15/16 master
front: 43mm 4 piston fixed
rear: 38mm 2 piston fixed

yours:
master?
front: 38mm dual floating
rear: 43mm? single floating

hope this helps. you probably need a step bore.

I don't trust most of the aftermarket brake companies. One of them supplied a 1 1/8" MC for use with PBR calipers. There is no way a 1 1/8" MC will work with the PBR caliper + a vacuum booster. I doubt it will work with a hydraboost unless both legs are used. The president of the company tried to convince me it was a volume problem. Yeah, right. He did not want to believe me when I presented him the hard facts (engineering calcs.) A smaller MC fixed it.

Many aftermarket brake companies do not have the expertise to properly design a brake system. The only one IMO that offers a performance aftermarket brake system done correctly is Baer. If you look at their kit they supply a 15/16" MC, but the older kits were 7/8". The 7/8" are getting harder to find.

The 15/16" on Torker's site is a quick take up. The working part is still 15/16" so the effective pressure is figured from there. Mine is from a Cobra Mustang, and has what I believe to be a 1" MC. Both use a hydraboost.

The hydraboost supplies more assist than a vacuum booster. Hence a smaller MC may be required.

The NAPA catalog list the MC's as Drum/Drum, Disk/Drum, and Disk/Disk. Most of the older disk/disk setups use a caliper with a larger piston than the PBR, so there will not be a volume issue.

If you are using the PBR caliper with vacuum assist I'd recommend staying away from anything larger than 15/16". If a med-large cam is involved a smaller MC may be needed.