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Brakes not working after bleeding and new Master cylinder/booster

Tiny
CJA31186
  • MEMBER
  • 1983 JEEP CJ7
  • 6 CYL
  • 4WD
  • MANUAL
  • 111,000 MILES
I recently installed a new master cylinder and power booster, and one new set rotors, one set of new bearings, one set of new calipers, and 1 set of new brake pads on the front brakes for my vehicle. I bled the master cylinder, and bled all the wheels in the proper way. Bled each wheel eight times in the correct order from farthest to closest to the master cylinder. I also used a clear tube immersed in brake fluid to watch for bubbles, and a partner pumping the brake. Kept master cylinder topped off, and bled each wheel until no more air was coming out of the lines. Pumped three times, on the third time, partner held, I loosened bleeder valve, then shut the valve before the brake pedal stopped moving down to the floor.

My problem is that the brakes still do not work. I noticed that when I am not moving or only edging forward, I have a mostly solid pedal and the brakes work. However, as soon as I start moving at driving speed the pedal loses pressure and goes to the floor. Do the lines need to be bled again? I cannot imagine there is any air in the system.

I also checked the power booster for the right adjustment length on the push rod, and it is correct. However, when I put the master cylinder back on, it seemed like the booster was not working as well either. Everything was put back the way it was found, but now it seems like the pedal is harder to push. There are no vacuum leaks in the booster. I checked. What is the problem here?
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Thursday, October 19th, 2017 AT 5:40 PM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,536 POSTS
It sounds like your rear brake shoes are way out of adjustment. How it your parking brake? Also when you bleed the brake do you "pump" the pedal becasue this will allow air into the system also did you bench bleed the master.

Here are some guides for you to go over and then get back to me.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

and

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

and

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Please let us know what happens so it will help others.

Cheers, Ken
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Friday, October 20th, 2017 AT 2:18 PM
Tiny
CJA31186
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  • 89 POSTS
I did bench bleed the master cylinder. When I bled the brakes, I had an assistant pump up the pedal, on the third pump they held it down. I then loosened the bleeder screw to let fluid come out, then tightened it back up before he let pressure off of the pedal, and before fluid stopped flowing, and before the pedal hit the floor. Parking brake seems to be ok.
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Friday, October 20th, 2017 AT 5:18 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,536 POSTS
We need three clamps gently squeeze the rubber brake hoses closed, this should make the pedal not move hardly at all if the hydraulic part is okay. If okay then the problem is in one of the wheels.

Please let me know what happens.

Cheers, Ken have a good weekend
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Friday, October 20th, 2017 AT 8:53 PM
Tiny
CJA31186
  • MEMBER
  • 89 POSTS
I clamped one of the hoses as I only have one clamp available right now. Pedal got a lot stiffer. Seems it could be with the calipers or wheel? I read somewhere that another person had a similar problem and they bought the wrong calipers. When they changed the calipers to the correct ones the problem went away. They mentioned something about having either 2 bolt or 6 bolt calipers. They didn't even give me that choice when I bought the new calipers, but could this be the issue?
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Saturday, October 21st, 2017 AT 11:59 AM
Tiny
CJA31186
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Another thing I just remembered is that the calipers were moving a little when the brake pedal was pushed during bleeding.
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Saturday, October 21st, 2017 AT 12:11 PM
Tiny
CJA31186
  • MEMBER
  • 89 POSTS
Another update: when turning sharply in reverse the jeep stops moving as if the brakes are depressed. It also appeared to be under some type of a load when I put in 1st after it was struggling to move in reverse. Did not have this problem before I replaced everything. Wheel is not rubbing. Could it be that the axle nuts were tightened too tight? That's the only thing I can remember that might have been off. There's no air in the lines. Master cylinder appears ok. There's no leaks in the calipers. Everything was installed the same way as beforehand except maybe gen axel nuts might have been tightened too tight. Not sure if these are symptoms of that though.
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Saturday, October 21st, 2017 AT 2:10 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,536 POSTS
It sounds like you have a caliper flex hose that is twisted, can you double check the flex hioses on both side and send a picture so I can see please?
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Sunday, October 22nd, 2017 AT 5:43 PM
Tiny
CJA31186
  • MEMBER
  • 89 POSTS
So I took the front wheels off today and found the driver side brake pad came out of the mounting groove. It was bent from pressing the brake and not being seated correctly. Got new pads, and now seem to be better. However, still don't have a decent pedal. It now takes a couple pumps to build up the pedal. Lines have been bled countless times. Only other thing I can think of now is the master cylinder and brake booster are defective. Tested the brake booster by pressings brake before jeep was started. Held pedal as it started and pressure did not change. It didn't get any easier to push it down compared to before I started car. What do you think?
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Sunday, October 22nd, 2017 AT 7:18 PM
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Correct way to test booster is to pump pedal engine off until all vacuum is expelled, that is the pedal is hard, keep foot on brake and start engine, if the brake pedal sucks down a little the booster is working.
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Monday, October 23rd, 2017 AT 5:02 AM

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