My brakes are crap

[xjklmnop69]

99 XJ

Jeeps been sitting all summer as I've replaced floor pans and rock sliders. Came back to her with no brakes

Pedal goes to the floor with minimal resistance, brakes were never excellent before but they'd hold enough to spin the rear tires

A few years ago I did the Liberty rear disc swap and the pedal feel got much stiffer over the drums although it stopped about the same

After this summer hiatus I came back bled all four corners with no air or improvement. I was hoping all the welding boiled some fluid in the hard lines. Went for the master cylinder after that. Bench bled until I saw no bubbles. Installed the new unit then bled all four corners again. Slightly better feel.. I think it was mental. Check all four calipers. Pistons go in and out easily, no leaks. Slide pins are working. No visible leakage anywhere in the system

If the Jeep is off, brake pedal feels excellent. Once I start her up, the pedal goes soft again. I started on a few other forums but never read any good final conclusions

The only parts still in question to me could be all the brake hoses, but I don't see any brake drag. I have one at each rear caliper, the hose from body to rear axle (a few years old), then the two front hoses. A lot to potentially go wrong and all at the same seems unlikely. Fluid is also going though the ABS module but not functioning (wasn't working years ago when I did the rear disc swap either). Is air getting trapped in the ABS?

Brake pedal feels like the lines are full of air when the engine is running but are rock solid when off

Any sugges0tions? :dunno:

 

[Anak]

Get rid of/bypass the ABS module.

If that doesn't make a difference get someone to at least watch each hose while you pump the pedal (or simply replace hoses with new).

 

[RCP Phx]

First, I'm surprised the Liberty brakes fit since you have a Dana35! The mc, proportioning valve, and the ABS can be hard to bleed so vacuum bleeding can help. SS hoses work better than rubber but try to keep the length as short as possible. Are the calipers installed so that the blenders are on top? Your D35 may also have excessive end play eating up pedal travel, I ended up shimming my 8.25 for less pedal travel.

 

[xjklmnop69]

Thanks for your suggestions!

Get rid of/bypass the ABS module.

If that doesn't make a difference get someone to at least watch each hose while you pump the pedal (or simply replace hoses with new).

Replumbing all those lines does not sound fun so I'm trying to avoid that until its the last option. I did watch the hoses as the brakes are pumped and I didn't see anything swelling up.

First, I'm surprised the Liberty brakes fit since you have a Dana35! The mc, proportioning valve, and the ABS can be hard to bleed so vacuum bleeding can help. SS hoses work better than rubber but try to keep the length as short as possible. Are the calipers installed so that the blenders are on top? Your D35 may also have excessive end play eating up pedal travel, I ended up shimming my 8.25 for less pedal travel.

Opps.. Forgot to mention since its been in there so long but good point. It is a Chrysler 8.25 rear end. That is why the ABS isn't functioning. My buddy has one of those mityvacs, I'll try to borrow that. Stainless hoses are well worth it! Bleeders are facing up. I was hoping I did something simple like that. Maybe I'll end shimming later on to get a better pedal feel

We'll get it eventually :banghead:

 

[RCP Phx]

Also check your unit bearings and all your brake hardware. Anything that would cause slop in the calipers including inspect the glides for ridging.

 

[RCP Phx]

Add any rotor run-out to the list.

 

[xjklmnop69]

Also check your unit bearings and all your brake hardware. Anything that would cause slop in the calipers including inspect the glides for ridging.

I had one of those while you are in theres during this brake job and welded some material back to the steering knuckle where the front pads slide. The pads were starting to get a taper. Regreased all the slide pins and boots too. Once I get this hydraulic issue figure out its going to be like a brand new ~300K+ Cherokee

 

[ljobbins]

Leaking or bad brake booster will make your brakes go away when the engine is running. My old xj had liberty disks on an 8.25 and I swapped the booster for an “WJ upgrade” and swapped the proportioning valve guts for Wj guts and I immediately had a huge upgrade in my brakes but one day on a trail I lost all my brakes and it ended up being a vacuum leak in the new booster. When I fixed the leak the brakes were back to excellent.

 

[xjklmnop69]

Leaking or bad brake booster will make your brakes go away when the engine is running. My old xj had liberty disks on an 8.25 and I swapped the booster for an “WJ upgrade” and swapped the proportioning valve guts for Wj guts and I immediately had a huge upgrade in my brakes but one day on a trail I lost all my brakes and it ended up being a vacuum leak in the new booster. When I fixed the leak the brakes were back to excellent.

Did the booster have an internal leak or vacuum supply? I was considering the booster also, so I disconnected the vacuum supply from the intake manifold. My pedal felt stiff but was ineffective at stopping. When I swapped over to the disc I went to install the Liberty prop valve internals but the cap was a different thread pitch than the XJ, and the spring was a different diameter so it didn't sit properly to the XJ cap. The WJ was a direct swap?

 

[RCP Phx]

On my 2000 with WJ fronts and Liberty rears I run a Durango mc but the booster and proportioning valve are factory stock.

 

[xjklmnop69]

I borrowed a vacuum bleeder setup. Tried a few different bleed methods with little improvement. Initially I started at the furthest corner and worked forward just trying to maintain vacuum with the bleeder open. Next I found and read the mityvac recommended way of starting at the closest bleeder and working backward for ABS systems. Never heard of doing that but tried it anyhow. Next I hooked up the vacuum pump at the furthest bleeder pulled vacuum then opened the bleeder and closed it before the vacuum dropped off

Brakes work well enough to do brake torque burn outs and lock up on dirt roads (forwards and backwards) but I still don't think the pedal feels right. I have someone else that is looking for a scan tool that'll actuate the ABS module to try to bleed more air out of the system.

I'm starting to think I just expect more out of my brakes than what they are capable of after having a luxury summer driving a 23 year old truck

When do your brakes start to work? Pedal travel wise?

 

[RCP Phx]

Mine are 8yrs old and the rotors need re-surfacing but right now it's about 3/4" freetravel before any engagement with another inch to lock-up. When they were new I only had about 1/4" freeplay with another inch to lock-up.

 

[xjklmnop69]

I got a OBD scan tool that would to ABS. Found three fault codes, LR and RR wheel sensor open circuits then ABS Pump circuit fault (09). I found the old rear wheel speed sensors from the D35 and plugged them in hoping the pump error would also clear but it didn't. Wasn't able to successfully run the ABS bleed function due to the pump. The pump voltage is low relative to the battery and doesn't cycle. If the electronics don't clean up or can't jump enough power to run the ABS bleed I'll try to get to bypassing the ABS all together and doing it the right way that I've been avoiding. We are expecting a nice 45 deg F heat wave this weekend early December :yelclap: