Residual Pressure Causing Disc Brake Engagement

[barno68]

I cannot figure this one out; everything works fine when first starting to drive, good movement on brake pedal and no restriction to vehicle movement. After a bit of driving the pedal hardens up and the brakes are not fully releasing causing them to heat up badly. Once this start occurring I have to give it a fair amount of gas to get the car moving it heats up to the point where the rims are hot (all four). I have the pedal rod adjusted to the point that it barely engages the brake switch, which acts as the rear travel limit leaving 3/16" extra space if it needs to retract further. With this extra space I cannot pull back the brake pedal any further, so the rod is fully retracted from the MC.

Here is the setup: LS1 brakes front and rear, 79 TA 4 wheel disc proportioning valve and Wilwood manual 1" tandem MC. Everything, including brake lines, is new except the calipers.

What am I missing? It would seem odd, but does that particular proportioning valve have an internal residual pressure valve? Could it be something internal to the calipers? Any help would be greatly appreciated.

[barno68]

Just got off the phone with Inline Tube, where I bought the proportioning valve. They suggested that I drive the car until the brake problem occurs and then crack a caliper bleeder to release the pressure, then try again and release the pressure by cracking a joint at the MC to try and narrow the problem. I will give this a try, but would be surprised if the issue is a caliper as all four are engaged.

[Vegas69]

Same thing happened to me. If you are using the wrong rod, this will happen. By wrong rod, I mean the type where you pull the c clip and fasten the rod inside the bore.(It's used on the 7/8") You must use a rod that goes down in the bore without fastening it with the clip.

[barno68]

It came with the rod attached, I have never pulled back the rubber boot to see how it is attached to the MC. Are you saying that that, in your case, the supplied rod was the wrong one? Mine is just a simple threaded rod about 4" long. I added a female heim joint to the end and bolted it to the brake pedal arm. I can adjust length with the heim join, but after the last time I just have left is where it is and backed off on the brake switch to give it more room. Here is what it looks like:

https://static1.pt-content.com/images/pt/2011/08/IMG_1548-1.jpg

https://static1.pt-content.com/images/pt/2011/08/IMG_1547-1.jpg

[Vegas69]

I used my rod from my 7/8 bore master and it did exactly what you are describing. It made no sense but I even called Wilwood and they verified that you CAN NOT use the same style rod. If you can't pull the rod towards the drivers seat, it's the wrong rod.

[barno68]

Does that mean that the rod should come off when pulled? What did you end up using instead of the supplied rod?

[barno68]

Ok, I took a look and it has a C clip holding the base of the rod to the MC. I am a little concerned about remove it as there was a bit of brake fluid in the boot when I removed it. What is behind the C clip?

[Vegas69]

Pull the master cylinder off the car. No way you will be able to do it in the car. You need to remove the current rod by taking out the c clip. Then you just need a stock style threaded rod that you can cut to length. You will also need to pull out the center bushing in the master cylinder bore.

[barno68]

thanks for the help, this would be a "nice to know" prior to install;-)