Help - new brakes not working

Looking for any advice or ideas:

So, my new brakes are very soft and not stopping the car ('77 308 GTB) well at all.

I had a leaking rear caliper so I had all four calipers rebuilt by PMB. New rotors from T Rutlands, and new pads from Superformance UK. System was bled using a Motive Products pressure bleeder and I am not seeing any bubbles.

Here are the symptoms and my observations.
- Brake pedal is firm with engine off but if you keep pushing it will slowly sink a bit.
- Brake pedal is very soft with engine running.
- Front caliper pistons retract enough that pads are visibly clear of the rotors.

PMB Brakes FAQ talks about having to "hyperextend" the pistons due to the new bore seals pulling the pistons back. http://www.pmbperformance.com/faq-common-questions.html#169964
So, I may jack the car back up tomorrow and try that. Unfortunately, the hose on my power bleeder broke tonight so rebleeding with it may have to wait. At least the oil is changed and belts done.

Anybody got any other ideas. I am hoping it is not a master cylinder issue.

 

Albiet we used GyroD systems (w a manual/modiefied system) and we had really soft response on pads and pedals for a couple days. Drove brakes hard and they seated and after heating up good a few times they starting biting hard and the pedal stiffened nicely.

 

Make sure you have the calipers on the right side the bleeders should always be at the top. I did a rebuild on a jeep one time and had the fronts reversed and had the same symptoms ???
Hope this helps

 

If you start out with a hard pedal but the pedal starts to depress with constant pressure that sounds like the master cylinder.

Another point to confirm is that you gapped the rear pads to get the proper clearance between it and the rotor. There is a mechanical adjustment to achieve this.

 

I also had my 4 brakes done by PMB and experienced the same symptoms. I kept bleeding (pressure bleeder and banged on the caliper with a mallet to dislodge any bubbles) but hardly any air came out. Eric gave me the same explanation so I bedded the brakes and slowly, over a week or so, the pedal got better.

My brakes were working before I sent them off, so I figured, as well as tested, that the brake booster and vacuum was fine. The only thing that changed was the calipers and bleeding these brakes is as basic as it gets.

Just use caution and plan some extra distance for a few days. Mine did get better.

Also, take the time to accurately adjust your rear brake pads to get the emergency to work. You just spent all that money so all the mechanisms to adjust both brake shoes will work with precision. Just make sure the emergency brake cables and pulleys are lubricated and move freely. Your car left the factory and had a working emergency brake. Rebuilding the mechanism and using the factory specs and adjustment procedure does work. When I park mine, I just put it in neutral and put on the e brake (however if I was in San Francisco, where my car was sold originally, I would put it in gear and turn the wheels).

 

All,

Thanks for the tips and it is good to know that I am not alone in these symptoms (Joe). I will rebleed, check the rear pad clearances (currently set to .004"). Rear runout is a little large at .003" so I may just tighten the rear pad clearance a little. Parking brake locks solid at 4 clicks on the handle. I will also try the PMB hyper extend procedure as well. Brakes were good prior to pulling the calipers.

I just hate having to jack up the car again, LOL. Need a lift.

 

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Well, followed PMB's FAQ and hyper extended front caliper pistons and then rebleed using my pressure bleeder at 25 psi. Much better. Now, I just need to be the new brakes in and should be much better.

 

Update.

Bedded the brakes in and it stops very well. Pulls to the left on hard braking and locked left front caliper. Decided to swap the pads from side to see tonight to see if problems followed pads. Hit them with a little 220 grit as well.

As I was doing this, I noticed that the right front flex line looked a little twisted. Loosened it up at the caliper fixed line and untwisted it. I am thinking that the slightly twisted line was reducing brake effectiveness.

Raining outside here so will try to get it out to bed the brakes again tomorrow.

 

Do we assume you replaced the rubber brake lines with new lines

 

Rubber lines were replaced with stainless flex in 2011. I managed to twist one of the lines while reinstalling the calipers.

 

Curious to see if that makes a difference.

 

Just need the roads to dry out around here.

 

Update. Success. A least a major improvement.

Bedded in again and the major pull is gone. Sometime get a little pull, but I think that is more related to worn suspension bushings and road condition. Will drive some more and see how it goes.