I have terrible brakes, but why

Oh joy. This doesn't sound very fun at all.

Is this a good time to upgrade the braking system, since I'll have to have everything taken apart anyways?

Before I jump into something that will take me forever, because i know it will, how do I know for sure that the MC and/or booster is bad? Sounds like this may be somewhat easier if the truck is up on a lift; then there's no prezel-ing in the cab.
 
Well....... to play Devil's Advocate, I put a 95 dual chamber booster & M/C on my 94 (was single chamber) in a morning. That includes bending up new lines, and mounting an adjustable prop valve as well. This particular swap really didn't require any fab work.

I'd suggest that you really consider a dual chamber swap.
 
I might have access to a 97 with a booster and MC. I haven't done a lot of searching on the subject, but swapping that 97 into my 88 will require some work, right?
 
I think so. The usual swap for an early XJ or MJ is for a 95 or a 96 booster.

Personally, I bought a new set, I wasn't interested in getting a set from a junkyard where I wouldn't have any idea if it was functional.
 
A hissing sound will also be heard when depressing the pedal from a leaky master cylinder gasket. Take it off the cover and hold it up to light to make sure you have no pin holes in it. A hole can actually put air into the system. The system was made to be air tight & a hole in the gasket can cause issues.
 
bigalpha said:
The rotors are still very thick as are the pads.
I performed a full fluid flush.
Click to expand...

I HATE when people come into my shop and say that....happens almost daily!! I'm not trying to be mean, but listen to what you're saying....you DO NOT have a calibrated eye, you NEED to measure the rotors with a micrometer as stated below. You cannot with your eye, tell if they are thick enough, especially when you're talking about thousandths of an inch!!!

winterbeater said:
Brake pulsing varying on vehicle speed is rotor thickness variation and possible rotor runout or rear drum out of round. .........check the rotor thickness for variation with a micrometer.......
Click to expand...
 
bigalpha said:
Oh joy. This doesn't sound very fun at all.

Is this a good time to upgrade the braking system, since I'll have to have everything taken apart anyways?

Before I jump into something that will take me forever, because i know it will, how do I know for sure that the MC and/or booster is bad? Sounds like this may be somewhat easier if the truck is up on a lift; then there's no prezel-ing in the cab.
Click to expand...

It is easier if you pull the front seat out. The problem is the stuff you need to reach to disconnect is on the firewall interior, up under & behind the dash. And the front seat limits your wiggle room. I am a big guy with a big arms and hands now, so it is harder for me. When I was 20, I did pretzel jobs in my sleep.:D

Lifting it is no help. In fact it would make it harder. If you pull the front seat out first it is not as bad. I am just lazzy, and leave the seat in there so I can bitch about it.:D

If you hear any kind of sucking sound when you apply the brakes the Vac BB is shot. The rest of what you posted, and my recent experience with about 6 POS rebuilt MCs, tells me your MC is shot too. In fact with the Vac BB shot, a good MC would be very hard to push period, and yours is not!

I just wish I had done both, and used new parts, 3 times ago instead wasting time and money piece mealing it with so called rebuilt junk.:rattle:

I would not replace the Vac BB with out installing a new MC. I got both parts at Autozone, for about $130 total, IIRC. I would install a new MC only, only if the Vac BB was still good.

Don't let my colorful painful descriptions scare you off. It is nothing like doing a head gasket.

Oh, and the fun part is after your done, when it works!:D
 
Yeah, I'm going to look into doing an upgrade with a newer year BB and MC since it'll be taken apart anyways. At the very least, these components are 20 years old so they need to be replaced even if they are not bad right now.
 
So what is the big deal with the newer double D Vac BBs? I have noticed that the newer systems seem to have smaller MC reservoirs, that are made of plastic and have aluminum bodies, which does little looks wise to attract me to them as an upgrade. In fact the MCs look flimsy to me. The DD Vac Boosters are another story, but they are useless if the MC fails and kills the Vac BB anyway. So am I missing something here?
 
bigalpha said:
The double D systems are supposed to provide better stopping power due to a better design.
Click to expand...

My question is what is the better design, why is it better. Also that better design still depends on the rest of the system, including a leak prone rebuilt MCs, and reported problems with the rear drum system and rear drum adjusters.
 
Alright.

After some quick research, it looks like I can swap the BB, MC and PV from a 99 into the 88 with minimal work. Looks like the hardest thing is going to be getting the old rod into new system.

After that, it should be fairly straightforward to get the lines to fit properly between the MC and the PV and get it all bolted up.

Did I miss anything important here?
 
Unless I'm missing something, you'll need line adapters on the M/C to connect with the existing prop valve lines. Through 94, they were SAE thread, 95 and newer are metric threads. I've heard that some of them are bubble flares and not double flares.
 
bigalpha said:
The pedal wouldn't do anything until halfway to the floor then they'd feel all spongy and crap. So I just bled the whole system, front and rear. The fluid that was in there was dark and nasty; but full. The pads/rotors, shoes/drums are all in good condition with plenty of meat left.
Click to expand...

My 91 MJ is much the same. Nothing until half way down, then ok. My guess is new MC\booster and full fluid flush.
 
ChiXJeff said:
Unless I'm missing something, you'll need line adapters on the M/C to connect with the existing prop valve lines. Through 94, they were SAE thread, 95 and newer are metric threads. I've heard that some of them are bubble flares and not double flares.
Click to expand...

Even if you replace the PV, BB and MC?

The only things that would be different would be the connections from the lines on the truck to the new installed system.
 
CROSBIKE said:
when you pull the booster vacuum line be ready to throw it in park very fast as it is near impossible to stop it after it gets going.
Click to expand...
:huh:

Are you suggesting that someone pull the vacuum line without plugging it off causing a very high idle, then going for a drive without power brakes? I think what everyone else is suggesting is that you test it in the driveway unless I am missing something?
 
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