Disc brake conversion problem

[dpdmw]

Guys,

Purchased a 71 Super that had a front disc conversion, brakes were great. Just completed a body off restoration and along the way replaced the MC and all brake lines. I cannot seem to get a good firm pedal now. I have tried another MC with no success. I have bled and bled until I bleed using a pressure style bleeder connected to the MC reservoir. If I clamp the front two caliper rubber flex lines shut, I get a great pedal. I clamped them closest to the caliper to eliminate them from the equation. I removed and opened up the calipers to check that both bleed ports were open, all is good. I have bled using only the top bleeder screw but have also used the bottom as I am grabbing at straws here. Using a new Raybestos 2 port MC. Do not have the MC that was on it when I purchased it. Any help is appreciated. Dennis

[V8Nate]

I had a similar issue with my cb disk brakes. I had to unbolt the caliper and rotate it on the disk so the nipple was as exactly 12 o clock. I was also told to bleed the fronts then the rears due to internal valving in the Mc. Hope that helps

[dpdmw]

Thanks, I will give that a go and see what happens. Currently hard steel line to caliper from flex hose so will need to get some longer flex hose to accomplish this. On a side note, are you using residual valves on front disc or rear drum?

[V8Nate]

I have 4 wheel disk, cb recommended the residual valve for the rear so I installed it, didn't fix the problem, then stared at it till I figured out I had a huge air pocket but it is still installed on the car

[Ol'fogasaurus]

Try bleeding them manually; not using the pressure bleeder. Sometimes, for any of several reasons, bleeding the whole system manually works better than using a bleeder.

Not sure why but sometimes this way seems to work better.

Lee

[H2OSB]

You know, i didn't even think about it when I first read this thread, but I had the same issue with my 4 wheel CB disc brake conversion, with stock MC. I was using a 1 person manual bleeder, even though my adult son was helping me. It was at night, so I couldn't call CB to ask, but in desperation, we did the fronts first and it worked.

I will tell you this...those brakes were amazing once dialed in. My son and I autocrossed the car together several times where we swapped in and out one run after another and they stopped on a dime every time, with no fade whatsoever.

H20SB

[V8Nate]

You know, i didn't even think about it when I first read this thread, but I had the same issue with my 4 wheel CB disc brake conversion, with stock MC. I was using a 1 person manual bleeder, even though my adult son was helping me. It was at night, so I couldn't call CB to ask, but in desperation, we did the fronts first and it worked.

I will tell you this...those brakes were amazing once dialed in. My son and I autocrossed the car together several times where we swapped in and out one run after another and they stopped on a dime every time, with no fade whatsoever.

H20SB

I agree I drive my bug very hard(on the street) and the brakes do fantastic!

[Ol'fogasaurus]

Its been a long time but in an old time open system you usually bleed starting at the cylinder farthest away from the MC first then work forward but I seem to remember that with residual pressure valves (they are for the front brakes and located on the front brake side of the brake line Tee. Their design is to either hold 2#s or 10#s of brake pressure) can change the bleeding method so you do them first.

Turning/cutting brakes, mounted higher than the MC such as on the tunnel for example, also changes how you bleed the brakes.

Lee

[Ol'fogasaurus]

Has anyone come up with a dual chamber Master Cylinder for early VW bugs. That might be a way out of the problem with residual pressure valves.

Lee

[V8Nate]

Has anyone come up with a dual chamber Master Cylinder for early VW bugs. That might be a way out of the problem with residual pressure valves.

Lee

I'm running a dual circuit Mc that I got from cb with a 67 reservoir. If memory serves me correctly 67+ had dual circuit

[Ol'fogasaurus]

Thanks! I got a MC later model VW MC too but the angle of the mounting plate is wrong so the reservoir is angled. Since I only have rear brakes on both my buggies now I haven't worried about it but the question seems to be relevant now days.

Lee

[dpdmw]

Thanks to all - thus far no success in getting any improvement. I did as suggested and removed the calipers and rotated to better get the bleeder valve at a 12 o'clock position and then played around with different positions, no help. In the meantime I will try the manual bleed process and see if any air gets pushed out. I have also ordered a M/C that VW used when the vehicle was factory front disc. It is a 3 port, with one independent line going to each front caliper, which makes sense give the extra volume needed for disc brakes. Will keep you posted and also appreciate any new suggestions.

[Ol'fogasaurus]

I have also ordered a M/C that VW used when the vehicle was factory front disc. It is a 3 port, with one independent line going to each front caliper, which makes sense give the extra volume needed for disc brakes. Will keep you posted and also appreciate any new suggestions.

That sounds like the best plan. I had forgot about the three ports in the dual chambered units as it has just been a looooooog time since I have played with them .

I hope it is the solution to your problems. Good luck and on to the next problem .

Lee

[Bruce2]

I have also ordered a M/C that VW used when the vehicle was factory front disc.

No such part exists today. All you can get today is a generic one-size-fits-all dual cct MC to use with drums or discs. The number of ports is the same for disc and drum cars. It has nothing to do with flow volume.

Two tips:
Try taking your caliper off the spindle and tying them up high above the level of the MC. Place a 5/16" shim between the pads and attempt to bleed them.

Remove the bleeder screw and liberally coat it with anti-seize compound. It is most likely that air is being drawn in around the outside of the bleeder screw through the threads.

[Ol'fogasaurus]

I did a search and got this: https://www.bing.com/search?q=dual%20ci ... 38F2C9F152

I do question what is said in searches at times but because what Bruce2 said surprised me so I did a search myself and got this. Again, it is a search and this is what I got as a starting answer.

Lee