Brake Booster Something Malfunction

[kazam]

Greetings,.

 

I have a mostly '87 Comanche with a 150 c.i. engine (I-4).

 

The idle had been a bit high recently; I did not find any broken vaccum lines; et cetera; I looked for problems.

I am a Mechanic with training, credentials, and experience, and looked for simple soulutions; besides that I have worked with the XJ type much and this MJ for about ten years with various time allocated.

That said, as a Mechanic, I am up to learning more about some specifics.

I do not know every thing.

 

The Idle had been high, and today the brake pedal stuck.

The brake booster seemed to be working when not-requested.

 

I pressed on the brake pedal (today) and the pedal moved to the floor/firewall on its own.

I disconnected the vaccume line to the brake booster assembly.

And I plugged/sealed that line with what I had available.

It was a surprise to me when the brakes locked up today.

 

So I may have to replace the brake booster assy.

Before I order parts I posted this message asking:

Is there some other part that could be (Likely) causing this propblem.

 

Maybe a something that the brake-booster assy. interacts with like a sensor?.

It seems to me like the brake booster I have may have an internal diaphragm failure, or something.

It also seems like that is a sealed unit that I do not work on  standardly.

 

I am not attempng to change out parts without a reason to.

My next step with the Comanche brake situation is to chcek this forum this weekend.

And I will likely replace the brake booster assy.

 

I thought to ask for some helpful perpective.

 

 

Thanks very much.

 

 

 

 

 

[Pete M]

look into doing the double booster installation.    It's one of the most worthwhile mods you can do to any MJ.  

[kazam]

Greetings, 

 

Thanks for the reply.

I did a quick search for a "double booster" upgrade and am not sure what the parts change would be.

'Any more information available on that?

 

Thanks very much.

[cruiser54]

Get a booster/master from a 99 to 04 grand cherokee. be sure to grab the lines exiting the master cylinder.

 

"booster upgrade" would be better search term. 

[schardein]

What you are looking for is a "dual diaphragm vacuum brake booster".  1996 Jeep Cherokee (XJ) is another source for a dual diaphragm booster that can be adapted to the older XJs/MJs.

 

The early XJs/MJs use a single diaphragm.  The dual unit simply has more surface area for the engine vacuum to work against, so you get more boost.

 

The next step up in brake booster performance would be a conversion to a Hydroboost unit, which uses hydraulic pressure from the power steering pump to provide the boost instead of engine vacuum.  Commonly found on GM 3/4 and 1 ton trucks, also older Astro vans.  Much more work involved than going to the dual diaphragm unit.

[Pete M]

there should be links to writeups in the link in my sig  

[tom_echo]

A 99-04 grand cherokee swap is great, I've done it on my MJ.  It really helped braking and wasn't really all that difficult.  There's a bit of grinding and drilling to adapt the rod to the brake light sensor (newer jeeps don't have that but my '87 and yours will too).  Also you have to run new brake lines but that's not a big deal.  Total cost for me was $36 for the booster/mc from an '04 jeep grand cherokee wj, $5 for new bolts for the back of the booster, $10 on misc brake line parts (metric fittings and the lines).