Please help!!! What master cyl and booster for disc/ disc? On my 66 Wagon.

It was 12" discs up front and 79ish rear discs. I have a 72 Corvette master cylinder and a 69 Grand Prix booster. I have very little brakes and they don't seem to squirt much out when bleeding. We got all the air out but something ain't right. It has an adjustable prop valve to.

My other car is disc drum with a 9" dual diaphram booster and a 69-72 master cylinder with adjustable prop valve and the brakes are great maybe too good they are a little touchy.

Should I go back to that kind of set up for my wagon?

I'm to the point of buying a Master Power or SSB master cyl and booster for disc/disc.

What do you guys think?

Thanks

Can you give us a little more detail on the setup?

What calipers specificly are you running?

Joe

My 66 has 12" rotors up front with 79 Firebird front calipers. I have rear disc off a 98 and newer camaro/firebird. I'm using a 68-72 11" booster with a napa part #39018 master. I have a MP Brakes 4 wheel disc prop valve. My brakes work awesome. Make sure you move your clevis up to the top hole on your brake pedal if your running power brakes, it makes a huge difference. I only use a hand pump bleeder for doing brakes it works the best. MP brakes told me the stock chevelle 11" booster works great for a good street engine. Mine is a 355 with a comp cams XE268H cam. I dont believe in adjustable prop valves. There to sensitive. MP brakes is a big believer in the correct "true" prop valve, so I just purchased one of there 4 wheel disc ones.

What other info do you need?

I'll post it if I know.

Strokd66, you are runnng the clevis in the top (manual brake) hole with power disc? I would have thought that would put the pushrod at a bad angle... though it does give twice as much leverage as the lower power brake hole...

Whittaker, the G.P. booster might have a short pushrod (firewall side) and the 72 'vette master is for a long rod. Make sure they are matched properly. If using a short rod and deep master, the brakes would be very low and not bleed well...
check out
http://ourworld.compuserve.com/homepages/David_Pozzi/brakes.htm#Converting_Drums_to_Discs
for pics of the two lengths and matching masters.
I dunno if thats it, but it's worth checking.

I think the other info needed is what size calipers you are running....

Are the 12" fronts the single piston old style, metric, or newer dual piston?

Originally posted by chevry:
I think the other info needed is what size calipers you are running....

Are the 12" fronts the single piston old style, metric, or newer dual piston? Exactly! smile.gif

What size are you running in the front? That will help us tell you what size MC bore you'll need to run and be able to give you a part number to go off of.

Joe

They are Willwood GM3 single piston calipers.

I think I have this short pushrod issue. They push in then clunck.

Myy friend pulled his off his 67 disc/drum and it worked much better.

So what to do?

You can buy/make a pushrod spacer if that's the problem, or you can change either the booster rod or the master to make one match the other.
The Wilwood 3 lists as having a 2.75" piston, so a 1 1/8 master is plenty big enough. I think Wilwood sells a pushrod spacer...