I completed the Front disc brake conversion on my 49 3600. Brake kit was from TSM. It came with a combination valve which has been properly installed. After a couple of short test drives in the neighborhood I noticed a puddle of brake fluid beneath the left rear wheel. Removed the drum and could see that the leak was coming directly from the wheel cylinder. Took the wheel cylinder off and inspected it, was older And a slight bit of roughness, not really pitting, on the inside. Ordered and installed two new rear wheel cylinders and when bleeding the brakes, had the same problem, the new wheel cylinder on the left rear began leaking. Took it apart and inspected it, cannot visually see any issues whatsoever with the wheel cylinder.
Questions:
1.) My initial thought is that there is excessive pressure going to the rear brakes causing the leak. When I installed the disc brake kit I was told that the combination valve has a built in “proportioning valve“ that reduces pressure to the rear drum brakes. Is this so? I’ve also read that it only functions in a hard panic stop and otherwise allows the same pressure to the rear brakes that flows to the front disc brakes, which I understand require more pressure than drum brakes. But, it seems odd to me that the pressure to the rear brakes would be so high that it would cause fluid to bypass the rubber cup and the piston in a way that caused a rather significant fluid leak, especially since the leak occurred during the bleeding process. Any thoughts or input on this?
2.) my current plan is to install a true proportioning valve in the rear brake line in an effort to reduce pressure to the rear brakes. In my research I can’t determine if proportioning valves vary in the amount of pressure that they will permit. For example if brake pressure in the amount of X psi is excessive for the rear drum brakes, it seems I would want a proportioning valve with an upper limit less than X. Does this make sense? I’m the first to admit that my knowledge in this area is extremely slim.
3.) Does anyone know of any other possible causes of the leak? It seems a little hard to believe that my new wheel cylinder is defective especially since I can perceive no issues with it upon visual inspection. I have read that with a disc brake conversion a supplemental proportioning valve is a must but have also read other threads saying that it is unnecessary and that the combination valve is sufficient to reduce pressure to the rear brakes. I’m kind of lost here, any help would be greatly appreciated!!
4.) As Long as I have your attention I attempted to bleed the brakes using my new Capri vacuum bleeder but all my efforts were somewhat disastrous. It mostly just sucks air and I tried numerous pressure settings between the minimum of 40 psi and over 100 psi. I wrapped the bleeder fitting with so much Teflon tape I could hardly start it by hand and had to wrench it most of the way in. Also tried fewer reps of Teflon tape but found the Capri bleeder to be wholly ineffective. Eventually went to the classic pump and bleed technique and that is when the leak appeared. Any similar experiences or any recommendations? Thanks, you guys have always been a such great help with my questions don’t know what I would do without this forum.
