4 Wheel Disks W/Factory Master Cylinder??

[72longbed]

For those of you who have converted your 71/72 truck to 4 wheel disk brakes; can we still use the factory power brake master cylinder? Mine is the 3/4 ton Hydro-Boost master cylinder with a later 73up proportioning valve on it, has the large diameter vacuum booster on it.

Just want to make sure I don't kill myself when I go out on the 'maiden' voyage with the new truck.

Thanks for the info,
72longbed

[truckdude239]

u need to find an mc thats desized for disc brakes disc brakes take more pressure then drums

[FormerMember]

I've run the stock MC with the correct disk/disk proportioning valve.

[75stepside]

Originally Posted by grendel

I've run the stock MC with the correct disk/disk proportioning valve.

I agree... i just finished my 4 year restoration in July and put disc on the rear of my '75 project. The master cylinder and brake booster were on the cab i used, from an '84. i hooked up my rear disc with the stock proportioning valve and had bad results... not enough pressure to the rear... then i put a new disc/disc p valve in the rear... everything works great... put on my first 300 miles this summer - working great!

http://www.inlinetube.com/

http://www.inlinetube.com/Prop%20Valves/PR-101.htm

[FormerMember]

Yep. AFAIK, the bore and stroke of the 1/2 ton MC is the same as many of the disk/disk MC's.

Just that our prop valve has a check valve for the rear drum brake circuit.

[RainFade]

Originally Posted by 72longbed

For those of you who have converted your 71/72 truck to 4 wheel disk brakes; can we still use the factory power brake master cylinder? Mine is the 3/4 ton Hydro-Boost master cylinder with a later 73up proportioning valve on it, has the large diameter vacuum booster on it.

Just want to make sure I don't kill myself when I go out on the 'maiden' voyage with the new truck.

Thanks for the info,
72longbed

Working fine on my 71 just keep an eye on your fluid as the pads wear as the drum resevior is pretty tiny!

I did use the correct combo valve for rear disc and ended up dialing the rear pressure down a bit to keep her from locking when empty on wet roads.

[72longbed]

Thanks for the info everybody! Looks like I need to get that Disk/Disk prop. valve from Inline Tube, just wish I could find one a lot cheaper!

If you all know of the same valve for less $$$, let me know.

Thanks,
72longbed

[dennislbrooks]

I used a 76 corvette mc with good results with a wildwood adjustable prop valve.

[raggedjim]

All you gotta do is ask!

http://www.classicperform.com/Store/...ruck/PVKS2.htm

Same one I have.

Good luck, Rg

[FormerMember]

Bought mine on Ebay. 22.00.

[Oborny71]

also take out the check valve spring in the mater cylinder if converting from drums to discs, both check valves if using front and rear discs. to do this, screw a screw into the flare fitting(s) in the master cylinder, then pull them out. after you get that, out will come the spring, then replace the fitting. this is to keep the pads on drums from backing away from the drums, but you don't want that with discs. as mentioned, use a different proportioning valve too.

[72longbed]

grendel,
thats a good price! What part did you look for on E-Bay for this type application? Was it a private seller or a company?

Thanks to all for the valuable info,
72longbed

[nate68]

i think i used the 76 'vette master cylinder but i can't find my receipt or part number. i tried looking it up online at kragen and autozone and the 76 was giving me weird results.

also using the wilwood adjustable proportioning valve

[Longhorn Man]

Did any of you check the line pressure at the rear with the wrong master cylinder? I can't remember the specs, but disks require much higher pressure.

[nate68]

oh yeah and my master cylinder needs to be replaced and i dont wanna spend a million dollars on a billet one

what kind of price range am i looking at?

[ratrod67]

I have a master from a 74 Corvette from O'Reillys($46) and a Master Power valve($89) in mine.

[drink2mny]

I wanted to give my 2 cents here about the rear disc brakes..

I personnally have installed several rear disc brakes kit ranging from cars to trucks.. 1/2tons to 2 1/2 tons.. I have rear disc on my '72 3/4 ton, had rear disc on my '86 1/2 ton blazer with 36" swampers an 14 bolt rear(sold her)..

Put rear disc on a drag car '70 elkie..

I have never , i mean never need to change out a MC to a disc/disc proportioning..
As you read the post above not even all of you have done the same thing, some still needed an adjustable valve to fix thier brakes to their liking..

We as a company don't offer it because 99% of the time our kits never have an issue..
If someone bought one it would be to there preference to change it out if they thought it needed to be done..

We had 1 customer basically threaten us because we did not tell our customers that they needed a disc/disc valve.. He didn't like the way our kit felt.. his pedal had a different feel to it... well after he *****ed at us and called several "PRO" brake folks.. he bout a disc/disc valve.. guess what.....No difference

He then wanted us to refund him because the kit didn't work... We tried to work with him. offered another kit in return..But he said no..

He went to another reputable rear disc brake kit seller... Guess what... the same....even that company does what we do... not offer a disc/disc valve.. they are almost 100% not needed for our applications...

Everyone has there own choices as to what they are going to do..
I just wanted to let you know....I have never had a problem and neither has any of our customers....

I guess that was more than 2 cents...

[Shane]

Will the 'Vette master cylinders bolt right up to "our" boosters? How about the brake lines ... are the fittings and everything the same?

Basically what I am asking is: Can a guy pull off the stock MC and bolt the 'Vette mc with no mods?

[Shane]

TTT - curious about the Corvette MC bolting up to a stock booster.

[nate68]

yes the vette master cylinder bolts right up (c'mon it's GM, everything interchanges)
i just put a new one on and bled the brakes today.

[Mudder]

My old stepside had drums/drums with a booster. When we put the body on the 77 chassis we used the same 67 set up. A few years later I went to rear disks and kept the same just to see how things worked. They have been on there since about 1997 with no problems. I keep an eye on them, but they work great.

[truckdude239]

wow puled this one from almost in the grave

[LUV2XCLR8]

Subscribing to this thread, so I will have this info later, thanks guys