Quick Brake Help after 96 swap

[SBpunk]

Did a 96 brake booster/MC swap. Got everything hooked up and bled but  my rear brakes arent working and fronts lock up without releasing. From what I've read the bypass for the height sensor valve might have already been done already since there is a hard line coming out the front of the front brake block. 

 

 

Anyway, I traced the lines back to the rear  and this is what I've got. Any ideas on why I'm locking my fronts and getting nothing to the rear brakes? 

This is what the two lines go back to. 

Plug into this guy 

[SBpunk]

Ok bled  the system and bench bled the MC again. Rear brakes are stopping as long as the clutch is pushed in or its in neutral. Seems normal to me. Front brakes are still locked up. I have the tires off and the front driveshaft disconnected. Is that typical?

[Eagle]

How long was the vehicle sitting? Have the front calipers been serviced?

 

I recently had a front caliper sieze on my wife's 2000 XJ, which gets driven regularly. I drove it three miles to the post office and noticed that it seemed to be pulling to one side. Got there and I smelled the unmistakable smell of cooking brakes. I managed to make it home, but I would not have driven it any farther than three miles like that. Didn't release when it cooled down. I replaced both calipers.

 

Another possibility is that your front flex hoses may have deteriorated internally and a flap of rubber is acting like a one-way check valve.

[LarryH88bt]

I second checking the calipers themselves.  Take them off and use a big ol' pair of pliers to see if they compress.

[1stDeuce]

The distribution valve and all plumbing is compeltely stock looking to me.  :)  

Try putting a tire on and see if you can turn it...  Disc brakes drag some, and you may not be able to spin the rotor by hand, especially if the caliper is a little sticky, per Eagle's suggestion...  If you still can't, then loosen a bleed screw. That should relieve any pressure in the front brake circuit.  If the brake is still difficult to turn, you have a stuck caliper.  (Or two...)

 

If loosening the bleed screw releases fluid and pressure, and frees the brakes, then your brake pedal is somehow pressing on the booster at all times, and not allowing the MC to fully retract...   Did you put in the 1/4" spacer that the XJ used?   Not sure if there's a problem with that on an '89 or not, but it can be critical on some years I think...   If it does turn out that this is a problem, you might be able to use washers stacked on the booster mounting studs to approximate the spacer.  ??   I haven't seen/done this conversion, so I'm gessing there...

Chris

[SBpunk]

The calipers are brand new out of the box. Same with the pads and rotors. 

I used the spacer that came on the 96 XJ booster and everything came within a 1/8th of a inch of the stock set up. 

The old calipers froze up on me to the point where the rims got red hot. Thats what prompted me to replace everything. Front and rear brakes including the hubs in the front are brand spankin new not even a mile on them. Jeeps been sitting for 2 weeks or so while I work on the brakes and rebuild the driveshafts. 

[SBpunk]

So I'm starting to wonder if I cranked my spindle nut down too far when I replaced the hubs. I only had a 150b torque wrench so I maxed it out then hooked a breaker bar up to tighten it down further. 

[HOrnbrod]

So I'm starting to wonder if I cranked my spindle nut down too far when I replaced the hubs. I only had a 150b torque wrench so I maxed it out then hooked a breaker bar up to tighten it down further. 

 

That's way too tight. I don't know the torque specs for a 4WD but for 2WD the specs are:

 

The correct method for the 2WDs is to tighten the bearing nut to 17-25 ft. lbs while rotating the wheel to seat the new bearings/races. Then loosen the nut 1/2 turn and retighten to 19 in-lbs of torque.

 

Someone should chime in w. the 4WD specs but I'll bet your spindle bearings and races are shot now.............

[SBpunk]

Sorry was enjoy some drinks last night. I was referring to the hub nut you remove to pull the shafts and what not. Everything I read was 175 lb torque.

[SBpunk]

Sorry haven't had a lot of time to focus on the truck. We have 2 of our MWD's retiring and its been chaotic at best.

My plan is to check the torque on the axle shaft nut to make sure its at 175lb

Bleed the front brakes again

Pull the guide pins and grease them

Test

Rebleed the entire system including the height sensing valve. I have pieces on the way to make an adjustable arm for it.

Put the tires back on and take it for a slow test drive to see if I just need to hit the brakes a few times while its moving.

 

I figured with the updated brake booster I'd have a lot better stopping power but starting to have my doubts. If all else fails I'll try to get another 1992 front brake block to see if something went bad when my brakes were locking up on me from poor bleeding.

 

[1stDeuce]

On a 4wd, or a later 2wd that used a unit bearing like the 4wd's, the hub nut can't really be tightened enough to keep the hub from spinning freely.  I pretty much max them out with an impact, so I don't think that's your problem...  On an early 2wd truck with an actual spindle, like a trailer or old muscle car, the nut doesn't get "tightened" per se, but rather all the slop gets removed by hand tightening only, then you back it off one flat or so.  But your truck is 4wd, so that's not your issue.  Don't mess with it.

 

I still say the first thing you should do is loosen a bleed screw to see if that relieves pressure and frees up the brakes.  If that fixes it, something is wrong with your '96 parts, or the way they're installed, and the piston in the master isn't being allowed to retract fully, which will trap some residual pressure in the front system.  (Did you separate them, or did they come together, and get installed that way?)

 

There's no way I can think of to bleed brakes wrong that will make them lock up...  You have something else going on, and a drive may not fix it at all.  

I do recall that if you put post-99 or 00 rotors on a pre-99 XJ/TJ/ZJ, you'll get contact between the rotor and something, and it'll seem locked, and make awful sounds when you drive.   The wrong rotors are full cast, while the correct ones should have a thin (1/8") stamped hat section.     Of course, it's possible aftermarket rotors may be full cast now for even the older trucks... 

 

C

[SBpunk]

On a 4wd, or a later 2wd that used a unit bearing like the 4wd's, the hub nut can't really be tightened enough to keep the hub from spinning freely.  I pretty much max them out with an impact, so I don't think that's your problem...  On an early 2wd truck with an actual spindle, like a trailer or old muscle car, the nut doesn't get "tightened" per se, but rather all the slop gets removed by hand tightening only, then you back it off one flat or so.  But your truck is 4wd, so that's not your issue.  Don't mess with it.

 

I still say the first thing you should do is loosen a bleed screw to see if that relieves pressure and frees up the brakes.  If that fixes it, something is wrong with your '96 parts, or the way they're installed, and the piston in the master isn't being allowed to retract fully, which will trap some residual pressure in the front system.  (Did you separate them, or did they come together, and get installed that way?)

 

There's no way I can think of to bleed brakes wrong that will make them lock up...  You have something else going on, and a drive may not fix it at all.  

I do recall that if you put post-99 or 00 rotors on a pre-99 XJ/TJ/ZJ, you'll get contact between the rotor and something, and it'll seem locked, and make awful sounds when you drive.   The wrong rotors are full cast, while the correct ones should have a thin (1/8") stamped hat section.     Of course, it's possible aftermarket rotors may be full cast now for even the older trucks... 

 

C

I'll give the bleeder screw a shot. The MC and booster came together but I separated them to bench bleed the MC.

The calipers I picked up rom autozone and rotors/pads were a kit on ebay I thought was a good deal at the time. If the MC is bad then its a pretty cheap fix.

 

[Eagle]

The old calipers froze up on me to the point where the rims got red hot. Thats what prompted me to replace everything. Front and rear brakes including the hubs in the front are brand spankin new not even a mile on them. Jeeps been sitting for 2 weeks or so while I work on the brakes and rebuild the driveshafts.

Ah. Are you absolutely certain that you ordered and received parts for your year MJ? There have been several permutations and combinations of hubs, disks and rotors. In general, they can't be mixed. They have different offsets, so mixing them results in no-roll wheels.

[SBpunk]

 

The old calipers froze up on me to the point where the rims got red hot. Thats what prompted me to replace everything. Front and rear brakes including the hubs in the front are brand spankin new not even a mile on them. Jeeps been sitting for 2 weeks or so while I work on the brakes and rebuild the driveshafts.

Ah. Are you absolutely certain that you ordered and received parts for your year MJ? There have been several permutations and combinations of hubs, disks and rotors. In general, they can't be mixed. They have different offsets, so mixing them results in no-roll wheels.

 

Got these guys 

http://www.ebay.com/itm/290974885023?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

and these from AutoZone 

http://www.autozone.com/brakes-and-traction-control/brake-caliper-front/duralast-reman-brake-caliper-front/56704/

http://www.autozone.com/brakes-and-traction-control/brake-caliper-front/duralast-reman-brake-caliper-front/56703_977310_5913/

 

I completely redid my entire drum system and decided to take it out before bleeding the front brakes. Air in the lines ended up locking up the front calipers to the point where the wheel/rim was insanely hot to the touch. Ended up warping my stock caliper. Figured I might as well upgrade to the 96 brakes system while I was at it. I'm worried that I didn't flare the lines correctly (double flare into the front brake block) and it's causing the issues. There is no leaking that I can see tho. 

[1stDeuce]

I've said it before and I'll say it again... air in the lines or "bad" bleeding does not, cannot cause the brakes to lock... you have or had something else going on...

[SBpunk]

I wonder if its the stock forward block then. Would that being faulty cause the front brakes to drag/lock up? Sorry I'm not doubting you just covering every angle.

[ParadiseMJ]

My experience with rotors between my 88 and my 90...the rotor was completely different.  The 88 was much thicker...that the NAPA guy gave me for the 90... and it was cast. The 90 was considered composite and the "hat" was much (almost 1/2 inch) taller.  I don't remember if the disk itself was thicker. 

 

I can think of 3 reasons for the caliper not compressing besides a faulty caliper.  1.  Hanging up on the slide 2. Disk too thick  3. Hat too tall (aka the disk itself is backset)...if releasing the bleeder doesn't produce a "spurt", try to work the caliper piston with a C-clamp and see what happens.

 

Have you followed the bleeding procedure for the height sensing valve on the rear diff?  Adjusted the rears?

[SBpunk]

My experience with rotors between my 88 and my 90...the rotor was completely different.  The 88 was much thicker...that the NAPA guy gave me for the 90... and it was cast. The 90 was considered composite and the "hat" was much (almost 1/2 inch) taller.  I don't remember if the disk itself was thicker. 

 

I can think of 3 reasons for the caliper not compressing besides a faulty caliper.  1.  Hanging up on the slide 2. Disk too thick  3. Hat too tall (aka the disk itself is backset)...if releasing the bleeder doesn't produce a "spurt", try to work the caliper piston with a C-clamp and see what happens.

 

Have you followed the bleeding procedure for the height sensing valve on the rear diff?  Adjusted the rears?

I won't be able to mess with it until tomorrow. I'll give the calipers a shot also in the morning. 

[SBpunk]

Ok so the wife gave  me the ok to mess with it a little tonight. 
Topped off the reservoir
Put a bleeder bottle on the front passenger side  bleeder (has a speed bleeder on it too)
Cracked it open and  fluid started come down the tube. 
Can free spin the rotor with a little muscle. 
Moved over to the other  side and did the same thing

After that I went back to the passenger side and cracked it open again.
This time I pressed  the brakes 4 or 5 times and shut her. Rotor still spun
Did the same with driver side. 

Now the only thing that looks like is happening is the brakes need to wear themselves down a bit. I started her up, jumped inside, dropped it in first and let the backs spin a bit then hit  the brakes. Did this  a few times  then jumped out and checked the rotors. Still about the same resistance. Looks like whatever it was its not a problem now.

 

Tomorrow I'm going to bleed the system again including the rear load sensing valve and try to get it adjusted with some steel hanger until the pieces get it so it won't move. Hopefully that'll just be a day or two. Then I'll finish putting these drive shafts together and take her for a test  spin around the base (max speed 15mph so pretty safe).

 

 

[SBpunk]

So I did a proper brake bleed but I couldn't get the brake light to turn on. It's not burnt out since it comes on with the e brake. I'm hoping the sender for it just isn't working. I'll be testing it out this weekend since I finally got my front driveshaft rebuilt as well. A couple more things and she'll be back on the road.

[gogmorgo]

The brake lights (on the back of the truck) shouldn't be coming on with the parking brake. The brake warning light on the dash should only come on with the brake pedal if there's a problem with the brakes... you shouldn't see it once the brakes are properly bled.

[SBpunk]

The brake lights (on the back of the truck) shouldn't be coming on with the parking brake. The brake warning light on the dash should only come on with the brake pedal if there's a problem with the brakes... you shouldn't see it once the brakes are properly bled.

Everything I've read said that once you open the front bleeder, leave it open, open the rear bleeder with the load sensing valve in the down position and have someone press/hold the brake down the 'BRAKE' dash light should come on.

http://comancheclub.com/topic/40428-brake-bleeding/

 

 

 

[1stDeuce]

I didn't read that other thread bit the differential pressure switch that you are talking about only activates if there is pressure in one circuit and none in the other. With both bleeders open, you won't build pressure in either circuit, so no light... if you leave the rear bleeder closed for the brake apply, then the light will come on like it is supposed to... then you open the rear bleeder...

 

How are your brakes working anyway? Hope you are driving the truck by now!! :)

[SBpunk]

_{Breaks are working decent for now. I'm still getting a weird clunk from the front right caliper but hasn't effected performance at all. Back has been locking up decent when need be. Going to do the adjustable rod modification to it when I get time. She rarely see's over 25 mph specially since the front needs a new seal and leaking diff fluid.}