Brakes

[tugboat95]

My brakes are horrible. They stop it but I've narrowly avoided 2 rear end collisions already when the car ahead of me slammed on the brakes. I actually slow down faster using the gears.

I have already ordered new rotors, pads, bearings and calipers. Previous owner recently replaced the lines. I will have the rear drums replaced (I hate doing drumbrakes). Just waiting to get home.

Is this normal? Do I need to look at master cylinder or booster? Brakes work, just not on par with my more modern vehicles. All most no pedal movement before it bottoms out.

 

89 Comanche

Eliminator

2wd

4.0L

5 speed PukeGoat

Factory Original

 

 

 

[Limeyjeeper]

That is not normal. Comanche brakes should harden up pretty quickly on the pedal. IMHO Comanche brakes are pretty good except for the insane rear proportioning valve which is pretty useless after 30 years on the vehicle.

[jdog]

19 minutes ago, tugboat95 said:

All most no pedal movement before it bottoms out.

 

does this mean they go to the floor? or is the pedal just hard to press?

[tugboat95]

Hard to press. It's not spongy. And doesn't go to the floor.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[jdog]

With your description I would be looking into a booster. With the key off does the brake pedal feel the same? After pumping a few times does it get harder? Holding the brake pedal down start the engine, does the brake pedal drop?

[tugboat95]

With your description I would be looking into a booster. With the key off does the brake pedal feel the same? After pumping a few times does it get harder? Holding the brake pedal down start the engine, does the brake pedal drop?

I'm on the west coast for another week so I can't test it. But the pedal does not drop when I start it.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[jdog]

if thats the case, i would check that the booster is getting vacuum, if there is vacuum there i would suspect a bad booster

[tugboat95]

How hard are boosters to find? Brake parts weren't on the shelves everywhere. I did find them but I had to order them.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[jdog]

https://www.rockauto.com/en/catalog/jeep,1989,cherokee,4.0l+242cid+l6,1179929,brake+&+wheel+hub,power+brake+booster,1884

Its the same as the cherokee and should not be to hard to locate, you may have to order depending on your area. if you replace it be sure to replace the check valve at the same time

[Eagle]

1 hour ago, tugboat95 said:

 

My brakes are horrible. They stop it but I've narrowly avoided 2 rear end collisions already when the car ahead of me slammed on the brakes. I actually slow down faster using the gears.

I have already ordered new rotors, pads, bearings and calipers. Previous owner recently replaced the lines. I will have the rear drums replaced (I hate doing drumbrakes). Just waiting to get home.

Is this normal? Do I need to look at master cylinder or booster? Brakes work, just not on par with my more modern vehicles. All most no pedal movement before it bottoms out.

 

 

What do you mean "almost no peddle movement before it bottoms out"? That's impossible, unless your peddle starts out sitting much too close to the floor.

 

What you are describing is NOT normal. On stock tires, you should be able to lock up the tires easily on dirt, and probably on pavement. It sounds to me like you aren't getting braking on all four wheels.

[tugboat95]

Well my plan is to replace everything on the wheels. They are all original and complete pieces of rust. That HAS to be done. Then do a test. If it not improved I'll change out the booster and go ahead and do the master cylinder as well. If I gotta take it off may as well put a new one back. After reading Rock autos test, I'm leaning towards the booster being bad. But I will check vacuum lines before I spend some money.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[tugboat95]

What do you mean "almost no peddle movement before it bottoms out"? That's impossible, unless your peddle starts out sitting much too close to the floor.

It doesn't hardly move. Clutch goes to floor. Brake is nowhere near it.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[Eagle]

8 hours ago, tugboat95 said:

What do you mean "almost no peddle movement before it bottoms out"? That's impossible, unless your peddle starts out sitting much too close to the floor.

It doesn't hardly move. Clutch goes to floor. Brake is nowhere near it.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

 

 

THe clutch peddle is supposed to go to the floor -- the brake peddle isn't. So your brake peddle is NOT bottoming out, it's building pressure like it should.

 

You said the previous owner replaced the brake lines. My first guess is that he screwed up the two lines to the rear (one primary, one emergency bypass) and you have no rear brakes.

[jdog]

 
THe clutch peddle is supposed to go to the floor -- the brake peddle isn't. So your brake peddle is NOT bottoming out, it's building pressure like it should.
 
You said the previous owner replaced the brake lines. My first guess is that he screwed up the two lines to the rear (one primary, one emergency bypass) and you have no rear brakes.

Or didn't get them bleed correctly

[AZJeff]

I will also add that early XJ’s (and their MJ cousin) don’t exactly have the best boost levels for their power brakes.  The later XJ’s addressed this with a dual-diaphragm power booster, and I would consider this an almost mandatory upgrade when doing a brake system overhaul on these vehicles.

[JustEmptyEveryPocket]

26 minutes ago, AZJeff said:

The later XJ’s addressed this with a dual-diaphragm power booster, and I would consider this an almost mandatory upgrade when doing a brake system overhaul on these vehicles.

I have to say that I disagree with this statement. My trucks brakes (stock) were fine until a rear line ruptured in a panic stop. It still locked up my tires and got me stopped before an accident, but it was time to replace things. Since it was apart I put in the "upgrade" dual diaphragm booster from a WJ. To date I have noticed NO improvement over stock braking.

 

If everything is working correctly the truck should lock the tires up if you put enough force on the brake pedal. If the tires lock up then adding in a better brake booster changes NOTHING. So why bother?

 

OP - Fix the stop brake issue, but don't worry about any supposed upgrades. I agree with the above sentiments, most likely you have a bad booster. Check back and let us know whats wrong.

[Eagle]

1 hour ago, AZJeff said:

I will also add that early XJ’s (and their MJ cousin) don’t exactly have the best boost levels for their power brakes.  The later XJ’s addressed this with a dual-diaphragm power booster, and I would consider this an almost mandatory upgrade when doing a brake system overhaul on these vehicles.

 

Like JustEmptyEveryPocket, I also disagree with this statement. I don't regard the change to the later booster as being at all mandatory. It's an option if you want to run larger tires, but IMHO completely unnecessary with any stock size tires. The original brake system on the older XJs and the MJ was completely capable of locking up all four wheels, and that's all the braking you need.

[tugboat95]

Yeah mine is all stock and will stay that way. I will do the wheels first and check vacuum. Then go from there. After some online reading I'm almost convinced its the booster/vacuum issue. I'll find out when I get home next week. (Depending on wife's honey do list). Great thing about my job....every 21 days of work, I get 21 days off.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[tugboat95]

Yeah mine is all stock and will stay that way. I will do the wheels first and check vacuum. Then go from there. After reading here and other online sources, I'm almost convinced its the booster/vacuum issue. I'll find out when I get home next week. (Depending on wife's honey do list). Great thing about my job....every 21 days of work, I get 21 days off.

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

89 Comanche
Eliminator
2wd
4.0L
5 speed PukeGoat
Factory Original

[AZJeff]

9 hours ago, Eagle said:

 

Like JustEmptyEveryPocket, I also disagree with this statement. I don't regard the change to the later booster as being at all mandatory. It's an option if you want to run larger tires, but IMHO completely unnecessary with any stock size tires. The original brake system on the older XJs and the MJ was completely capable of locking up all four wheels, and that's all the braking you need.

Its interesting you say that, because my 1992XJ had HORRIBLE brakes, even after I rebuilt the drums in the back and replaced the calipers up front back when it was about 10 years old.  I literally could stand on the pedal and not lock them up.

 

I was new to the XJ/MJ chassis at the time, and read up on how Jeep had created the improved dual diaphram power booster and MC.  I decided to put that in my XJ, and the improvement was quite noticeable.  It's possible I had a bad booster before, but it didn't show any symptoms when I did the classic booster function test.

[Eagle]

28 minutes ago, AZJeff said:

Its interesting you say that, because my 1992XJ had HORRIBLE brakes, even after I rebuilt the drums in the back and replaced the calipers up front back when it was about 10 years old.  I literally could stand on the pedal and not lock them up.

 

I was new to the XJ/MJ chassis at the time, and read up on how Jeep had created the improved dual diaphram power booster and MC.  I decided to put that in my XJ, and the improvement was quite noticeable.  It's possible I had a bad booster before, but it didn't show any symptoms when I did the classic booster function test.

 

I can't lock up the brakes on my '88 XJ now, either. But it's on 31" tires. I bought it new, so I know I could lock 'em up when it was new.

 

It doesn't apply to the MJ, but much of the bad rap the XJ brakes get is due to the proportioning valve getting gummed up and not allowing the brakes to get full (or any) pressure to the rear circuit. The corollary in the MJ is when people work on the rear brakes and then don't bleed the rear circuit properly. When (if) I get the old XJ back on the road, a high priority will be to open up the proportioning valve and clean out the gunk.

[AZJeff]

41 minutes ago, Eagle said:

 

I can't lock up the brakes on my '88 XJ now, either. But it's on 31" tires. I bought it new, so I know I could lock 'em up when it was new.

 

It doesn't apply to the MJ, but much of the bad rap the XJ brakes get is due to the proportioning valve getting gummed up and not allowing the brakes to get full (or any) pressure to the rear circuit. The corollary in the MJ is when people work on the rear brakes and then don't bleed the rear circuit properly. When (if) I get the old XJ back on the road, a high priority will be to open up the proportioning valve and clean out the gunk.

I dunno.   My first XJ sat on stock wheels and about the biggest tire I could fit without a lift, but I don't remember the exact size.   That beast could NOT lock up it's brakes until I did the booster upgrade.

 

I know your experience on the XJ/MJ chassis exceeds mine from the days when I lurked on XJ forums.   None the less, there must have been a good reason Chrysler upgraded the booster design, and that is why I did it to my MJ when I got it.

 

 

[derf]

I suspect that people replacing a worn out booster for a new dual diaphragm booster attribute much of the improvement to the fact that it's the newer booster.  When in reality, the old worn out booster was the problem and replacing with an OEM style replacement would have given you a lot of the same improvement.

 

It's like anything else.  On the full size Jeep groups there is a common upgrade to the Ford TFI ignition system from the older style Ford ignition.  So you do new plugs, wires, cap adapter, rotor, and coil.  A lot of people say it was a night and day difference.  Of course, their 30+ year old plugs, wires, cap, rotor, and coil were completely shot.  Replacing it with factory parts would have made a huge difference too.

 

Sure, if you're replacing a part, it doesn't hurt to upgrade if you can cheaply.  But really, as long as you have new factory spec parts you should get at least "decent" performance.  I'd replace the booster with a dual diaphragm since you can get "cheap" factory replacement parts.  But there's nothing wrong with factory replacement part on a mostly stock MJ.

[JustEmptyEveryPocket]

When did rear discs replace rear drums? Would make sense if it was around the same time they went to a dual diaphragm booster.

 

Anyways, apologies for the highjack here OP. Let us know if your wife lets you work on your jeep next week.

[AZJeff]

37 minutes ago, JustEmptyEveryPocket said:

When did rear discs replace rear drums? Would make sense if it was around the same time they went to a dual diaphragm booster.

 

Anyways, apologies for the highjack here OP. Let us know if your wife lets you work on your jeep next week.

Rear discs never appeared on the MJ nor the XJ during it's production runs.

 

Rear discs first showed up on the ZJ, and were back compatible to the MJ/XJ chassis due to extreme similarity.