Brake issues - soft pedal

[CO_Mini]

Hi all, I'm running out of ideas to get the brakes sorted on my mini. It's an '82 with the front / rear split where the master cylinder feeds directly into the pressure regulator valve. It has discs in the front, although I'm not sure what kind. I left the system dry for several months while I refurbed the radius arms. I also replaced the wheel cylinders, pads, springs, etc.

The car is fairly new to me. I only drove it about 50 miles before taking it off the road to rebuild the radius arms. The brake pedal felt solid, but the brakes didn't have a ton of stopping power. Still, it stopped better with the old partially seized up wheel cylinders than it does now. This is my first classic car so I dont have much to compare to, but even stopping from the top of first gear probably takes a couple car lengths. Note, I'm not driving the car except to test the brakes right outside my garage.

So here's what I've done so far:
- made sure pads are oriented correctly
- made sure caliper bleed nipples are facing up
- tried various settings with the backplate adjusters while the e-brake is disconnected. I even tried tightening it down to the point where the wheel would barely turn, bled brakes, and still couldnt get a good pedal feel or stopping power.
- two person bleed method, but mostly using the EZ bleed system.
- bench bled old master cylinder and re-bled the entire system. No luck.
- replaced master cylinder with GMC227. Bench bled first and made sure the lines are going into the pressure regulator in the correct orientation (ie: reverse of the old factory one). Bled the rest of system. It feels the same as the old master cylinder.

Symptoms:
- pedal can be pressed all the way to floor. There is resistance but it doesnt feel very firm by the end of the pedal stroke.
- If I have the EZ bleed hooked up, the pedal feels as it should. It worked that way for the old master cylinder too. I only pressed it gently a couple times as a last resort. Not sure if that would muck up the seals but nothing seems to have changed.

It's possible air is getting back into the master cylinder when I reconnect the lines going to the pressure regulator, but that seems inevitable. Should I look at replacing the pressure regulator? Any other ideas? It really seems like there's air in the system, but maybe I'm missing something.

Thanks in advance for any suggestions. I'm on my fifth bottle of brake fluid (and patience haha).

[stevieturbo]

If the pedal is going to the floor, either there is air in the system, or there is an issue with the master. Assuming the other blatantly obvious one isn't a huge leak somewhere

It really is that simple.

If you have any flexi's somewhere, you could try clamping them to see if that makes any difference to the pedal which may help locate any air.

[CO_Mini]

Thanks for the reply. I clamped off the flexi hoses and that didn’t change the pedal feel at all so air must be getting trapped further up. No leaks anywhere to speak of.

I re-bled the master and the rest of the system again. It might be slightly better than before. I’d say the pedal stops about 1” off the floor.

I figure if they’re working properly I should be able to come to a screeching stop by standing on the pedal, right? Not being used to old cars I’m not sure what to expect from 40 year old brakes.

[stevieturbo]

Regardless of age, the pedal should not feel spongy, and should not be stopping 1" from the floor before you have functional brakes.

The pedal should feel positive

[Dinlowgoon]

You’ve possibly still got air in the long pipe that goes from front/back (front union to brake compensator). I’d try attaching the Eezi-bleed again and bleed it off at the compensator union. Give it a real good go there,then continue as per normal.

[CO_Mini]

Since my last post I ended up replacing the pressure regulator on the bulkhead (FAM7821) just in case that was contributing to the issue. It doesn't seem to have helped much, if at all.

I also tried bleeding from the outlets of the pressure regulator and that might have helped a little bit. With the bleed screws attached to the pressure regulator, the pedal feels pretty soft for the first part of the stroke and then firms up part way through. I guess that means there's still air in the master or the pressure regulator? Thanks for the suggestion.

[Matt_E_Mulsion]

Could you try back bleeding it from the wheel cylinders/calipers back up to the master cylinder.

[CO_Mini]

I gave it a shot this morning and no luck. Thanks for the suggestion.

[CO_Mini]

I forgot to report back after fixing this. I don’t know if it was the main issue, but I ended up finding a very small leak on the front passenger caliper. It wasn’t much more than a few drops on the floor.

I replaced the caliper, got some new pads, bled with the two person method (I broke the EZ bleed), and the brakes feel good now. The pedal feels firmer midway through the stroke and the car stops much better than it used to. Hopefully that helps anyone else with the same issue.