Brake issue *soft pedal* after caliper and MS replacement. - NON-ABS

Questions:
- Is there anything *different* or troublesome about the system (non-abs)
- is there a disti valve or proportioning valve that can get air stuck in it.
- is there a very specific method to priming the master cylinder? (I have seen some cars that have bleed valves, etc)
- Any other advice
- Could it be the push rod behind the MS needs to be adjusted? I left the same setting it was on before. But the symptoms are the same regardless.


First and foremost.....

- Replaced defective master cylinder
- Replaced defective rear passenger side caliper
- bled the ENTIRE system
- NON ABS
- Issue that existed before both replacements still exists.


Issue: Engine on, pedal is soft and can go to floor, there is resistance but still travels too far. With the engine off the resistance is much greater and it does not go to the floor but you can tell it's not resistant enough. Also Ebrake can be pulled all the way to the limit, any less and you can spin the wheels, whereas before it was fine.

Backstory: I bought the car about a year ago, the fluid was low and I filled it and it seemed fine until recently then the master cylinder started leaking, I never let it get empty but I did fill it a few times. I was already working on one car so I couldn't work on the P5. The last time I drove it on my way home to work the pedal went soft, the car would stop but the pedal was pretty much at the floor.

Repairs:
- Replaced the master cylinder as it was obviously leaking from the rear seal.
- as I went to bleed the 4 corners I spotted the rear P/S caliper obviously leaking as it was covered in fluid.
- Replaced the caliper and bled the entire system, lots of air bubbles at the rear.
- Thought all was good and put the wheels back on started it up, and their soft.
- Rebled the rear caliper that was replaced to to make sure I got all the air out.


Today I'm going to re bleed all four calipers, I realize the obvious go to here is that there is still air in the system, but that's why I'm asking if there is something I could have missed.

Did you bench bleed the new master cylinder before installing it? I would start there after bleeding all 4 wheels, it sounds like it could either be air in that new master cyl (or a faulty new master cylinder, wouldn't be impossible to have a defective one out of the box, however unlikely).

If none of the above works, I start looking at the brake booster. It could be a bad vacuum line or vacuum check valve or the booster itself. I'd also recommend checking and replacing all the rubber brake lines at the wheels with stainless steel braided lines.

I doubt it's the booster because if it were to fail I would have the opposite effect.

I did bench bleed it. But it's possible I didn't do it right or that isn't trapped.

The Master Cylinder HAS to be bleed FIRST before bleeding each wheel, otherwise you will forever be pushing air around your brake system and not get the air out - hence a soft pillow.

What are the condition of the brake lines? Are they original? The lines could need to be replaced. Old lines will cause brakes to be soft.

Also, yes there is a method for bleed the MC. Usually the MC will come with 2 plastic lines with fittings. The MC gets mounted to the brake booster, the plastic lines and fittings get attached where the hard brake lines go, you then loop the lines back into the MC bowls, add fluid. Make sure the lines are below the brake fluid level...begin to pump. When the MC feels solid, the MC is good to go. Hook up the brake lines and begin to bleed the passenger rear, then the driver rear, then the passenger front and then finally the driver front.

You still have air in the system. Any problems with the hoses would have been evident prior to the master cylinder failure.

Are you closing the bleeders before releasing the pedal? You need to, or it'll suck air past the bleeder threads and you'll be chasing your tail.

Try opening the bleeders and letting it gravity bleed for a while, or borrow/buy a vacuum bleeder.

Have you adjusted the new rear caliper?

JDM323J48 said:

Have you adjusted the new rear caliper?

Click to expand...

^^ what he said...
Your e-brake handle should click 5-7 times. Adjust that first then check your brakes again.

(your brake piston could be floating way back, taking up all kinds of brake pedal movement)

JDM323J48 said:

Have you adjusted the new rear caliper?

Click to expand...

Didn't think about this, but the rear brakes set your pedal height, so their adjustment is very important.

The rear calipers should self adjust as they do with pad wear. I've always just backed the piston all the way in, put in new pads, and never adjusted the pistons back out.

I think the reason he's stroking out his parking brake lever is because there's no pressure to push out the rear caliper pistons so the parking brake can adjust. His problem still lies in an unbled system.

Either way, he needs to set his parking brake.

If her reused his old pads the piston has further to move...

Apparently you can push the brake pedal hard then pull the p-brake lever a bunch of times to operate the adjusters one click at a time until they are set instead of turning the adjuster screw.

Unless he has a bad new caliper where the adjuster doesn't work. (happens a lot...)

Hey guys, didn't mean to ditch out on the thread, I apologize.

So I may have found the *current* cause:
faulty caliper assembly on the replacement caliper.

I noticed that even light presses on the brakes (motor on or off) that the replacement caliper was rotating as if the lower side pin was hanging. After checking it turns out they used the wrong length (plus maybe wrong diameter) To test this theory we swapped the lower pins on both calipers, sure enough the rotating followed the pin.

Somehow I deleted the images I took yesterday. If I remember I'll take new ones when I pull the caliper to return it.

You may want to bring a wrench and an Allen key to test the adjuster on the new caliper.

One guy had to have three brought up to the front before he got one that worked.

Hey guys, I'm back.

got the new caliper in, and adjusted both.

I think air is still in the system somewhere as mentioned above. i think it's time to start over with the bleeding process. I'm going to pick up a BM bleeder and do it over, then rebleed all 4 corners.


When attempting to get the caliper adjusters to move via brake pedal and ebrake movement nothing was happening at the caliper (even after adjusting), it leads me to believe that maybe there is too much compression in the MS to the rear calipers, thus pushing the brakes down isn't moving anything.


I gravity bled both sides a couple of times already so I know there is fluid back there.