[C2] Having disk brake conversion problem
Thread Starter
4th Gear
Joined: Apr 2019
Posts: 4
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Having disk brake conversion problem
I recently changed the brake system in my '64 from power assisted stock drums & single master to 11-3/4" slotted/drilled disks all around, Wilwood 4 piston calipers all around, all new brake lines, and a 63-66 Dual Master Cylinder conversion from ZIP, that now includes a proportioning valve. I left off the power assist to make room for a future LS swap.
The problem I'm having is that the system now does not work well enough to lock up even the rear tires, no matter how had I stomp on the pedal. I've bled the system multiple times.
Anyone with experience with a similar system & problem, please weigh in. I'm not sure if it's because of the proportioning valve, or that I'm just expecting too much from a disk brake system without power assist. I have a friend who did a similar conversion, has power assist, and has a similar problem.
The problem I'm having is that the system now does not work well enough to lock up even the rear tires, no matter how had I stomp on the pedal. I've bled the system multiple times.
Anyone with experience with a similar system & problem, please weigh in. I'm not sure if it's because of the proportioning valve, or that I'm just expecting too much from a disk brake system without power assist. I have a friend who did a similar conversion, has power assist, and has a similar problem.
Team Owner
Joined: Jul 2001
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From: Various places in Southern California.
Do you know what the bore size is on that master cylinder? If it's the larger 1" bore, it will require more pedal effort than the standard non-power bore of 7/8ths.
Also, on the brake pedal arm there are two holes for the rod going to the MC, one for power brakes and one for non-power brakes. Yours is probably in the power brake hole (lower, I believe). If so, moving it to the other one will help.
Also, on the brake pedal arm there are two holes for the rod going to the MC, one for power brakes and one for non-power brakes. Yours is probably in the power brake hole (lower, I believe). If so, moving it to the other one will help.
Race Director
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What is the size of the caliper pistons? What is the bore of the new MC? Did you move the clevis on the brake pedal lever to the upper hole when you eliminated the booster?
Now that I think about it, I vaguely recall someone on here having a similar problem last year after converting to Wilwood calipers. Turns out the piston size in the Wilwood calipers he used is inappropriately small vis a vis the MC piston size.
Now that I think about it, I vaguely recall someone on here having a similar problem last year after converting to Wilwood calipers. Turns out the piston size in the Wilwood calipers he used is inappropriately small vis a vis the MC piston size.
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You sure it has a proportioning valve? Or just one to control the lights and block off if there is a loss? Is it an adjustable one? Shouldn't need one if the brakes are sized correctly. I have Wilwoods on my car and they stop great with no power assist. I'd double ck master cylinder bore and clevis hole as mentioned.
JIM
JIM
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I recently changed the brake system in my '64 from power assisted stock drums & single master to 11-3/4" slotted/drilled disks all around, Wilwood 4 piston calipers all around, all new brake lines, and a 63-66 Dual Master Cylinder conversion from ZIP, that now includes a proportioning valve. ... The problem I'm having is that the system now does not work well enough to lock up even the rear tires, no matter how had I stomp on the pedal ...
Dan
Melting Slicks
Joined: Jul 2004
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From: Scottsdale AZ
Wildwood 4 piston calipers are a serious racing set up. And you say your master cylinder is a zip conversion set up for stock type brakes. I would suggest you have mis matches components. I would try different Master cylinder's as above go to a smaller diameter
A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid.
A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid.
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Thread Starter
4th Gear
Joined: Apr 2019
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Having disk brake conversion problem
Hi Guys -
Many thanks for the input - all valuable. I'm going to contact Wilwood, as I suspect the master cylinder size I have doesn't play well with their 4 piston calipers. The current MC size is the same as the stock '64 I had. Will also ask if putting the power assist back on will help the problem. Will post what they say.
Many thanks for the input - all valuable. I'm going to contact Wilwood, as I suspect the master cylinder size I have doesn't play well with their 4 piston calipers. The current MC size is the same as the stock '64 I had. Will also ask if putting the power assist back on will help the problem. Will post what they say.