Disc Brake Conversion Issues

[70BuickSkylark]

I purchased a disc brake conversion kits from Jegs. The mechanic who is installing it as been having all sorts of traouble with the proportioning valve installation. He tells that when he installed the kit that the pedal will go all the way to the floor. However, if he pinches off the brake lines going to the rear brakes, then he will get pressure in the brakes.

In a nutshell, the mechanic is saying that there are issues with the proportioning valve. Has anybody else ever ran into issues like this installing a disc brake conversion kit on a Skylark?

 

[LARRY70GS]

The proportioning valve you are using is actually a combination valve. It combines a hold off valve, proportioning valve, and warning light connection. The purpose of the hold off valve is to hold off the front brakes until pressure is built in the rear. This is because disc brakes inherently apply instantaneously whereas drum brakes have clearance between the shoe and drum, and must overcome spring pressure to apply. On stock 70 disc brakes, the hold off valve is separate, and is mounted up near the master cylinder, but in later years, OEM used a combination valve. Being you have a conversion kit, you probably have a combination valve. For the stock system, the service manual instructs that when you bleed a disc brake system, you must depress a pin in the combination valve (hold off valve pin). It is located under a rubber boot on the stock valve, but I don't know what you have.

Also, it is very important that you bench bleed a new master cylinder before installation. You did get a new master cylinder, right? A disc brake master cylinder is different than a drum brake master.

 

[Ehartlieb]

Are you still having the issue I am installing it on my Chevelle I have the same issue I find if you loosen or remove the caliper bolts the problem goes away for some reason when I fully tighten the bolts the caliper bracket flexes twisting the calipers enough so on the first stroke of the pedal there's nothing but then after that its good. Let me know if u fixed it and what u did to fix the problem I'm still currently working on this problem
Thanks
Eric

 

[mackyyy20]

hello wellcome to this forum,Being you have a conversion kit, you probably have a combination valve.
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