4-wheel disc conversion, no pedal. HELP
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Fleet Mechanic
Joined: Jun 2019
Posts: 1,899
Likes: 236
From: Southern California
4-wheel disc conversion, no pedal. HELP
Full disclosure, I'm working on a customers Chevy truck and am in a pickle. I'm here all trhe time, over in the 61-66 area and this forum has some of the most knowledgeable folks on the internet so I ask you.
So this is a 53 C pickup on an 80's C-10 chassis with four wheel disc brakes. Single piston calipers all around, nine inch booster, an unknown chev master with big/little reservoirs like you see on disc drum setup, and an adjustable valve for the rears. My customer bought it like this and his story is that he lost brakes, was out of fluid. I told him fill it up, pump it, and see if he can drive it or tow it to my shop. He drove it, said after doing as I told him, it stopped ok. I checked the calipers, hoses and lines, no leaks. Pulled the master and saw brake fluid coming out the back. Got a master cyl, bench bled, flush and bleed entire system, pedal i8s nearly on the floor and it does not stop for ****. Compared to my 4-wheel manual drums on my slick this thing is scary. I tried putting on a master for 4 wheel disc with a larger, 1.250" piston and its no better. Any ideas?
TIA, Dan..TK65
So this is a 53 C pickup on an 80's C-10 chassis with four wheel disc brakes. Single piston calipers all around, nine inch booster, an unknown chev master with big/little reservoirs like you see on disc drum setup, and an adjustable valve for the rears. My customer bought it like this and his story is that he lost brakes, was out of fluid. I told him fill it up, pump it, and see if he can drive it or tow it to my shop. He drove it, said after doing as I told him, it stopped ok. I checked the calipers, hoses and lines, no leaks. Pulled the master and saw brake fluid coming out the back. Got a master cyl, bench bled, flush and bleed entire system, pedal i8s nearly on the floor and it does not stop for ****. Compared to my 4-wheel manual drums on my slick this thing is scary. I tried putting on a master for 4 wheel disc with a larger, 1.250" piston and its no better. Any ideas?
TIA, Dan..TK65
Thread Starter
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Fleet Mechanic
Joined: Jun 2019
Posts: 1,899
Likes: 236
From: Southern California
Wrong master cylinder. I ended up getting a master cylinder with a larger piston, 1.5" I think. Not sure about the application, I went on Summit Racing and looked at specs, picked one, and called my local parts source and had them cross the number. Brakes work fine now.
Mountain Pass
Joined: May 2006
Posts: 194
Likes: 31
From: Summerfield
Make sure you are using a 4 wheel disc master cylinder along with a 4 wheel disc proportioning/combination valve. A 1 1/8" bore master cylinder should be fine or at the very least a good starting point, the larger the bore the more assist you will need and/or a harder than ideal pedal will result. The bigger the bore the LESS pressure you will have at the calipers for a given input pressure as compared to a smaller bore MC, although the bigger bore MC will have an increase in fluid volume.
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