disc brake conversion
#1
Senior Member
MASTER BUILDER
Thread Starter
Join Date: Apr 2009
Posts: 175
disc brake conversion
I bought a 70 chevelle from racing junk last year and I am just now putting it on the road. The question I have is the guy I got it from put disc brakes on the front (not power disc) The pedal is rock hard. Does the proportioning vavle needs changed? I'm not sure whats wrong.
#2
Senior Member
RACING JUNKIE
Join Date: Sep 2007
Posts: 4,137
Probably the wrong master cylinder.
If the bore is too big the pedal will be hard as a rock.If they are manual brakes find a master cylinder with a bore no larger than 1". I just went through this last summer. A 1.125 bore MC made my pedal rock hard...going to a 1" bore cured it.
Another just FYI ....drum brakes have risidual valves to keep the springs from forcing fluid back to the master cylinder, they must be removed when you go to disc. I think they are usually in the master cylinder itself but I think some had them in the distribution block...if they are left in they can make the calipers drag the rotors
If the bore is too big the pedal will be hard as a rock.If they are manual brakes find a master cylinder with a bore no larger than 1". I just went through this last summer. A 1.125 bore MC made my pedal rock hard...going to a 1" bore cured it.
Another just FYI ....drum brakes have risidual valves to keep the springs from forcing fluid back to the master cylinder, they must be removed when you go to disc. I think they are usually in the master cylinder itself but I think some had them in the distribution block...if they are left in they can make the calipers drag the rotors
#4
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RACING JUNKIE
Join Date: Sep 2007
Posts: 4,137
I went on NAPA Auto Parts web site and started poking in old Cars at random until I found what I was looking for...their website lists the bore size. I was working on a Nova with Wilwood brakes but ended up using the master from a 68-72 corvette I think it was...It has a 1 inch bore...it was made for 4 wheel disc brakes but as long as you instal a risidual valve between it and the rear drums it will work...I didn't need one for some eason but have only ran it once so far.
#6
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MASTER BUILDER
Join Date: Aug 2007
Location: Iowa - USA
Posts: 218
I thought the residual valve on drum brakes was to prevent fluid drain down. In other words, if I was told correctly, if that valve is not there, the first time you kit the brake pedal, the pedal wll go to the floor. 2nd time is ok.
#8
Senior Member
RACING JUNKIE
Join Date: Sep 2007
Posts: 4,137
Originally Posted by jreiley
I thought the residual valve on drum brakes was to prevent fluid drain down. In other words, if I was told correctly, if that valve is not there, the first time you kit the brake pedal, the pedal wll go to the floor. 2nd time is ok.