Questions about brake booster swap

I have the FSM for my 1985 XJ and the brake booster swap looks to be pretty straight forward. It appears that I can detach the master cylinder from the brake booster, without unhooking the brake lines that are attached to the MC. Then just unhook the booster from the pedal and fire wall, then do it all in reverse with the new booster. But, here are some specific questions not covered in the FSM...

Do I or do I not need to empty the MC of fluid to do the swap?

Will I loose brake fluid when I detach the MC from the booster?

Will I need to bleed the brakes after the new booster is on and the MC is reattached?

There is no fluid inisde the booster, correct?

Autozone quoted me $78 for a new booster. Am I just as well off using a boneyard part for cheaper?

Anything I should look out for in replacing the booster?


Thanks for any and all information that will assist me in this project.

Cottontail said:

I have the FSM for my 1985 XJ and the brake booster swap looks to be pretty straight forward. It appears that I can detach the master cylinder from the brake booster, without unhooking the brake lines that are attached to the MC. Then just unhook the booster from the pedal and fire wall, then do it all in reverse with the new booster. But, here are some specific questions not covered in the FSM...

Do I or do I not need to empty the MC of fluid to do the swap?

Will I loose brake fluid when I detach the MC from the booster?

Will I need to bleed the brakes after the new booster is on and the MC is reattached?

There is no fluid inisde the booster, correct?

Autozone quoted me $78 for a new booster. Am I just as well off using a boneyard part for cheaper?

Anything I should look out for in replacing the booster?


Thanks for any and all information that will assist me in this project.

Click to expand...

There is no fluid inside a power brake booster. If you find any, it's brake fluid from your master cylinder that has leaked in there, and it means you need a new MC.

Removal of the booster may or may not require you disconnect the MC from the brake lines. It all depends on how much movement you can get out of the hard lines attached to the MC, as you WILL have to move the MC forward some distance to get it clear of the pushrod inside the booster. Since I have never changed a booster on an 89, I am not sure, when when I did it on my 92, there was not enough flex in the hard lines to move the MC forward and leave the lines attached.

If you DO find you need to remove the MC to replace the booster, you will need to bleed the ENTIRE brake system from scratch, including "bench bleeding" the MC first. Plan on buying at LEAST one quart of brake fluid for this task.

A couple of notes of caution:
1. the hard lines where they attach to the MC may be frozen with age, and may twist off when you remove them. Be prepared to possibly have to replace them.
2. getting to the clip that holds the booster pushrod to the brake pedal is a PITA, and will require that you possibly readjust the brake lite switch (which is clipped to the pedal up there) after installation of the new booster.

BTW, if you are going to this much trouble, have you considered the upgrade to the later style dual-diaphram booster? It requires the use of a matching later style MC, but the improvement is boost level and braking power is noticeable.

AZ Jeff said:

BTW, if you are going to this much trouble, have you considered the upgrade to the later style dual-diaphram booster? It requires the use of a matching later style MC, but the improvement is boost level and braking power is noticeable.

Click to expand...

I agree with this statement as well as there are many write ups on the upgrade. It'd be worth looking into, a good rule of thumb is if it's broke upgrade it.

Kinda getting off on a tangent but i decided today to do the 96 XJ upgrade on mine... Ive read all the writeups hereare my only two questions for those in the know

#1 All i need to do is buy metric to standard adaptors for my brake lines right... no new fabricating lines or changing otu the proprotinging valve right???


#2 if i get a new brake peddle.... has anyone tried to use a late model switch instead of modding the new booster ...also what kind of steel is the rod.. If I am going to mod the rod and use my old switch imma be doing it out in the field with out the luxery of my grinder or a vise all i will ahve is my step drill to enlarge the hole and a dreml tool... am i gonna be able to do it with the dremel?

check this out:

http://www.naxja.org/forum/showthread.php?t=54237

I would recommend you replace both unless you are sure the master cyl. is good. Sometimes the master cylinder leaks fluid and it goes into the brake booster, which causes it to fail. If you think this is happening (loosing brake fluid) replace both. No problem w/ a junkyard part just ask for a warranty if it doesn't work take it back. I replaced a master cylinder/booster of a 77 dodge with an upgraded one from a 93 dodge pickup.

wilcharl said:

#1 All i need to do is buy metric to standard adaptors for my brake lines right... no new fabricating lines or changing otu the proprotinging valve right???

Click to expand...

Your current fittings should work - they swapped over directly onto my '93.

wilcharl said:

#2 if i get a new brake peddle.... has anyone tried to use a late model switch instead of modding the new booster ...also what kind of steel is the rod.. If I am going to mod the rod and use my old switch imma be doing it out in the field with out the luxery of my grinder or a vise all i will ahve is my step drill to enlarge the hole and a dreml tool... am i gonna be able to do it with the dremel?

Click to expand...

If your model is 90 or later (IIRC) then the brake pedal should just link straight up. I think the switch is also the same for 90s and up.

I found the booster and MC swap to be an easy mod - the worst part was the bleeding, which just requires you to be patient and methodical.

One thing that you should get is vice grips and a set of the correctly sized brake spanners. They'll make your life so much easier, since it'll help you avoid rounding the nuts off. After completely screwing mine, I resorted to beating my car with a stick out of sheer frustration, Basil Fawlty style! I'd hate anyone else to go there - it's not pretty. :twak: