Master Cylinder?? What to upgrade to/Brake booster upgrade

[Rokhound]

Is there an o-ring that goes between the booster and the master cylinder? I am trying to get my brakes to work on the MJ. I have an 8.8 in the rear a XJ pop valve up front. I can bleed the brakes and will have great brakes until I start the truck then they go clear to the floor. While I am bleeding the brakes there is something up front that sound like it is sucking air but I am not losing any brake fluid. So what gives??

[HOrnbrod]

Is there an o-ring that goes between the booster and the master cylinder? I am trying to get my brakes to work on the MJ. I have an 8.8 in the rear a XJ pop valve up front. I can bleed the brakes and will have great brakes until I start the truck then they go clear to the floor. While I am bleeding the brakes there is something up front that sound like it is sucking air but I am not losing any brake fluid. So what gives??

 

Got your check valve and vacuum hose hooked up to the booster?

[Rokhound]

i have the big hose hooked up i no that i will have to check and make sure that i have all the other lines hooked up.

[offroader461]

your booster may have a leak...i kept hearing a hissing sound when i stepped on the brakes...booster was bad

 

if its a sucking sound the seal around the valve on the booster could be bad??

[Rokhound]

could this all be why my brakes aren't with a $#!&

[87manche]

could this all be why my brakes aren't with a $#!&

 

yes, a booster that isn't getting proper vacuum will not provide power assist. Leaving you with a rock hard brake pedal.

 

there is a seal between the master and the booster, but I think it's more likely a problem with the booster itself.

[Rokhound]

i can get a brand new boster and master for 90 or do I upgrade to a junk yard part and if so what?????

[offroader461]

a 90 booster is not an upgrade...its just a replacement...i would do the 96 swap or the 99WJ swap to upgrade the brakes...i plan on doing my 90XJ when my lift/tires go on..I'm doing it the same way i just did my MJ

[Rokhound]

a 90 booster is not an upgrade...its just a replacement...i would do the 96 swap or the 99WJ swap to upgrade the brakes...i plan on doing my 90XJ when my lift/tires go on..I'm doing it the same way i just did my MJ

 

What i might is that i can get a BRAND new reman for $90.

 

If i go with this do i need the bake pedal as well

 

http://cgi.ebay.com/ebaymotors/97-01-Je ... dZViewItem

[1999MJ]

u should be able to use your pedal. It all bolts in the same location

[Rokhound]

u should be able to use your pedal. It all bolts in the same location

 

99 thanks

 

do you think that is a good price.

[CEThomas]

We have the same problem after the 8.8 & XJ pop valve switch. And the breaks worked fine prior to the switch :nuts: We replaced the booster last week after we put the auto in and I just got the new front lines on last night so I will bleed them tonight and let you know what I get. I am thinking it mat be traped air in the line somewhere that will have to have a vac pulled to clear it out :roll: Most of the time when the booster goes you get a hard pedal, but this is like mush which is air most of the time :nuts:

[oldjeep]

I'm not sure if the XJ/MJ and YJ use the same booster, but if they do then a 78 Mercury marquis MC is a great upgrade. Moves a lot of fluid, is set up for front and rear disc, and costs about $30.

[BARILLMS]

Junkyard for $30?? Is that whay you mean? I'd like a new one... where did you buy a 78 Mecury Marquis master cylinder?

They had 4 wheels discs in 1978?

[oldjeep]

Brand new at O'reillys for $13.99 + $10 core.

Cardone part # 10-1603

Yes in 1978 some of the big cars had 4 wheel disc brakes.

 

Very common swap for people with YJ's and Explorer 8.8 rear

 

Junkyard for $30?? Is that whay you mean? I'd like a new one... where did you buy a 78 Mecury Marquis master cylinder?

They had 4 wheels discs in 1978?

[Rokhound]

We have the same problem after the 8.8 & XJ pop valve switch. And the breaks worked fine prior to the switch :nuts: We replaced the booster last week after we put the auto in and I just got the new front lines on last night so I will bleed them tonight and let you know what I get. I am thinking it mat be traped air in the line somewhere that will have to have a vac pulled to clear it out :roll: Most of the time when the booster goes you get a hard pedal, but this is like mush which is air most of the time :nuts:

 

here is the thing i can here an air being sucked in from some where so i am going to go get one fromt the junk yard and put it on and see what happens.

[CEThomas]

If you here air then it must be the booster seal.

[Rokhound]

If you here air then it must be the booster seal.

 

can this be replaced or do I need to buy a new booster

[CEThomas]

Get a new / new used one.

[pingpong]

I say find a mastercylinder from a newer 1 ton truck that has 4 wheel disc brakes, and make it work. I know the big three all offer 4 wheel disc brakes, and some even offer the hydrovac sytem as well.

[Rokhound]

Ok I am going to the junk yard to get a new to me booster should I go with a ZJ or just a 95 and new XJ booster. I am running stock D30 and 8.8 with disc brakes.

 

Thanks

[DansGreyMj]

Brand new at O'reillys for $13.99 + $10 core.

Cardone part # 10-1603

Yes in 1978 some of the big cars had 4 wheel disc brakes.

 

Very common swap for people with YJ's and Explorer 8.8 rear

 

Junkyard for $30?? Is that whay you mean? I'd like a new one... where did you buy a 78 Mecury Marquis master cylinder?

They had 4 wheels discs in 1978?

 

what if you did that swap and still ran rear drums?

[oldjeep]

what if you did that swap and still ran rear drums?

 

I doubt that it would work very well. Disc brakes need high volume, which is why a drum brake MC doesn't work very well with rear discs. Drum brakes need high pressure. Best bet is to be using an MC that was designed for the type of brakes you are running.