brake issues

[Manic Mechanic]

ok guys and gals im having brake issues. a little back history i have a yj power brake booster upgrade about 10 years or so ago. last year i replaced the master cylinder along with that i have all new brakes on the front new calipers rotors and pads less than one year old (same time as master) rear brakes a few years older but still in good shape. i have no leaks and the master cylinder is full with clean clear fluid.

now for the problem out of the blue my pedal started going to the floor the jeep would still stop but not the way it should. still no leaks and master cylinder is full of clean fluid. i have no vacuum leaks and the booster seemed to be working. now for the kicker this problem would come and go so sometimes it works great with a wonderful pedal others back to the floor.

now i figured it was the booster so i replaced with one from wrecked yj i picked up for parts for another jeep. low and behold im having the same issues. now i realize it could be a failing booster from the wrecked jeep but i find it very odd that 2 different boosters would have the same symptoms so im asking to see if any of you have any ideas or suggestions to check.

mods feel free to move this if its in the wrong section

 

[Lumpy Grits]

It's the MC.
The isolation seal between the 2 reservoirs, is leaking internally.
LG

 

[Manic Mechanic]

It's the MC.

The isolation seal between the 2 reservoirs, is leaking internally.

LG

I'll look into it but would that cause the intermittent feel that the break booster is not working properly?

Sent from my E6810 using Tapatalk

 

[Lumpy Grits]

Yup-
LG

 

[cglax6]

It's the MC.
The isolation seal between the 2 reservoirs, is leaking internally.
LG

What he said...

 

[Manic Mechanic]

Ok I'll just buy a new one

Sent from my E6810 using Tapatalk

 

[cglax6]

Ok I'll just buy a new one

Sent from my E6810 using Tapatalk

I have a disc/drum MC laying around in the garage if you want it. You pay shipping and it's yours...

I bought it new and used it for 6 months before I swapped in discs in the rear.

No issues with it.

 

[cglax6]

Part # MC1321H Disc/Drum...bought from The Jeep Guy website.

 

[Lumpy Grits]

Use only DOT 3 brake fluid.
LG

 

[Manic Mechanic]

I need the yj one as my brake lines have been rerouted

Sent from my E6810 using Tapatalk

 

[cglax6]

I need the yj one as my brake lines have been rerouted

Sent from my E6810 using Tapatalk

No worries...it'll just sit in the garage...lonely...wanting to go somewhere...anywhere...

 

[Manic Mechanic]

Lol thanks anyway for the offer

Sent from my E6810 using Tapatalk

 

[Manic Mechanic]

ok update i replaced the MC im still having the same issue im going to rebleed the brakes this weekend to rule out any air in the lines as a cause of my problem (yes i bench bled the MC) stay tuned

 

[cglax6]

ok update i replaced the MC im still having the same issue im going to rebleed the brakes this weekend to rule out any air in the lines as a cause of my problem (yes i bench bled the MC) stay tuned

Dang, that sucks...

How exactly did you bleed the brakes? I trust you're doing it right, but I'm stumped now that the MC swap didn't work out as I thought.

When exactly does this happen? Does it happen at a real slow crawl, foot on the clutch, no load? Does it happen at higher speeds...foot on clutch, trying to brake when the engine is revving down?

Do you have a vacuum gauge to check vacuum?

Is the problem still intermittent, or constant?

 

[Lumpy Grits]

Dang-Never had that happen.
May want to look at your p'valve and see if it's leaking.
Bleed into a bottle with a hose, so you have no chance of sucking any air back into the system.
LG

 

[Manic Mechanic]

Lot of questions. Let's see if I can answer them all.

Yes I'm bleeding them properly starting with the one farthest from the MC (right rear) and working towards the closest to the MC (left front) the problem is still intermittent and happens at random times from idle through high rpm driving. One second it works fine the next not so much. With the engine off I get 2-3 pumps before the pedal becomes so stiff I feel like I'm going to break it. Once I start the engine it's anyone's guess as to if the breaks will work correctly or not. Hence why I thought it was the booster at first. There is no vacuum leak that was the first thing I checked after replacing the booster and still having the same issue. There is always the possibility the new MC is bad we all know or at least should know that N.E.W. doesn't spell GOOD.

Sent from my E6810 using Tapatalk

 

[Lumpy Grits]

Who made your MC?
Are you doing the 2 person bleed or using a mechanical bleeder ?
Sure sounds like air trapped in the MC..........
LG

 

[Manic Mechanic]

I'll double check but I'm pretty sure it's Bendix but it's hard to keep track since I buy so many parts for so many different vehicles

Sent from my E6810 using Tapatalk

 

[cglax6]

Sure sounds like air trapped in the MC..........
LG

Like a dumb@$$, I've reconfigured my brake system 3 times in the last year...

The first time I swapped out my MC I thought I bled it enough, but I was getting intermittent braking like you. Instead of taking the MC off and bench bleeding again, I bled it on the booster using a buddy of mine...

My friend operated the pedal, while I cracked fittings. This way is messy, but it got the job done...

I put a bunch of rags underneath the MC to catch fluid...and wrapped rags around the brake line fittings to prevent fluid from shooting all over the place.

As he pressed down the pedal, I'd slowly crack one fitting on the MC until fluid started coming out. When he bottomed out on the pedal, I closed the fitting back up, and then he'd release the pedal. Did that a few times on each and it fixed my problem.

I'd try doing that, and if it still happens, you may have got a bum MC...or some garbage in there fouling the seal.

If you still have your old one, pop the snap ring and take the guts out and have a look.

Something is going on in that MC...either air, or bad seal. Doesn't sound like a booster/vacuum problem to me.

 

[Manic Mechanic]

Yes I still have the old one I will tear it apart after work today and look at it

Sent from my E6810 using Tapatalk