master cylinder for 4 wheel disc

[Budweis]

asked this somewhere else but never quite got an answer. i had 4 wheel drum and now having 4 wheel disc and was unsure on master cylinder to use. someone else was saying you need corvette master cylinder but i was planning on using existing one. do i need a different master cylinder? if so does anything have to be modified to bolt on a vette master cylinder? also i have a 77 vette master cylinder in the garage , will it work if i need to change over?

[Deuce]

You do need a different master cyl. If you can find a copy of the new "Classic truck Magizine" it explains the different components of the braking systems for drum/drum, disc/drum and disc/disc.

[Grim Reaper]

Well since your starting froms scratch then yes get a master from a vehicle that had 4 wheel disc.
Good canidate would be some of the early 80's Formula Fire birds and Trans am's ran 4w disc as well as some early 80's Cadilacs. A Disc drum master can be made to work. I put Disc's on my 75 Jimmy and still runnign the stock master and have really good brakes now considering the 35's that it wears. Here is a write up I did on that and hopefully you can gets some answers your looking for.

http://coloradok5.com/atrondiskbrakes.shtml

[Budweis]

ok, guess ill dig out the vette master cylinder and see if it will fit, i got a old vette proportioning valve i guess ill throw on it too(hopefully i can find in mess in garage) i think i heard something bout this elsewhere talking bout how drum brakes like constant pressure and disc prefer no pressure less under load. if anyone has this article would greatly appreciate posting as cant get this magazine round here i doubt as have hard time even getting car craft mag locally.

[Grim Reaper]

Originally Posted by Deuce

You do need a different master cyl. If you can find a copy of the new "Classic truck Magizine" it explains the different components of the braking systems for drum/drum, disc/drum and disc/disc.

If his truck was like my 70 it was a single piston system. To get the 4 wheel disc to work he is going to have to deal with some bias problems and that would be a bit easier on a dual piston master. Also the dual piston is safer then a single. It's rare to loose both systems at once on those.

[FormerMember]

Proportioning valve is more important...

I used a # 1257225 (proportion valve...)
it's from a P30-60 truck that was a one ton ether lunch or utility truck and had 4 wheel disk brakes.

Mounts on the frame rail

[Budweis]

ok thanks gonna check out your article must have posted at same time as me on my last post. meanwhile heres a pic of the vette vs existing mc. can i take the c clip off and switch out guts on end of mc as the rod goes way in on old one but not on vette one.

[Budweis]

found the vette proportioning valve so gonna try using it. only prob i have now is how to adapt the vette mc above to the old rod off the booster. any ideas? gonna go out back and see what the rod on the vette booster looks like i guess, maybe i can just use a rod off a vette booster? garage is like a vette junkyard so rather stay with all vette stuff since its free

[Budweis]

ok got it figured out now, found the rod off the parts vette in pic below and all i had to do was turn down the piston area where arrow is below a few thousands and it all fit right in and looks like should work fine. now think everything should be a breeze to go together and i think the vette proportioning valve should work fine. thanks for the ideas.

[nate68]

if you have problems with the backs locking up too soon (which will most likely happen) you will need to add an adjustable proportion for the rear brakes. this does not replace the regular proportioning valve. it goes after the regular prop. valve so you can lower the pressure to the back brakes

[Budweis]

ok thanks for the info, this will at least get me going and i can figure out from there. if i need to put one in for back i think ill mount inside like grim reaper did so can adjust from cab.

[skid]

If you look at your pictures, you will notice that the Vette m/c has much larger reservoirs than the truck. This is because as the disk brake pads wear, oil is used to fill the void as the pistons push out further as the pad wears. 4 wheel disks should have large reservoirs front and back like the Vette.

The stock disk/drum proportioning valve is designed to keep slight residual pressure on drum brakes (or in the case of drum/drum m/c, residual pressure on all four drums). This will cause unnecessary friction on the rear disks. Use a 4 wheel disk prop valve like what comes with the Vette.