Hey all! I'm new to Cherokee Forum, and wanted to start this thread for help, and hopefully to help others. I've found lots of dead ends on the internet regarding this subject, so hopefully we can figure it out!

I've had brake pulsation from my rear drums since I bought this Jeep 5 years ago. I de-adjusted rear brakes, and drove for 5 years, until this past summer, when I rebuilt rears (for the 2nd time). After Adjustment, pulsation is STILL there. I was a professional mechanic for 5 years, so have a some mechanical experience, but NOT a lot of experience with drum brakes. I've take the vehicle to two shops now who can't figure it out. I've personally spent hours trying to diagnose it. I've read/searched online for hours and hours, and have found many posts with similar problem, but NO ONE posts their solutions (if they even found a solution). So lots of dead ends. I'm committed to figuring this out!

Symptoms:
- When adjusting rear brakes (wheels off ground, turned by hand), you can feel a grab, release, grab, release by hand when adjustment starting to get tight.
- After getting hot, rear brakes pulse. If you've been in traffic, and they are really hot, pulsing is BAD (slower speeds only)
- If they are real hot, you can now hear a mild "squeak, [silent], squeak, [silent], squeak, [silent],".... from rear when rolling at slow speeds.
- Can sometimes feel pulsing just while driving at slow speeds (no brakes)
- Can primarily feel at slow speeds (5-10mph)
- If you press e-brake button and pull up on ebrake lever while driving at slow speeds, STRONG pulsation.
- Pulsing is very minimal and sometimes non-existent when brakes are cold
- No pulsation from front brakes that I can feel, and even had a shop check run-out on front rotors. OK

2012
-Bought jeep 5 years ago, and if adjusted, rear brakes had slight pulsation.
-Replaced rear shoes, hardware, wheel cylinders, and had drums TURNED (All NAPA Premium parts)
--> (front brakes got new pads and rotors at this time too)
-Pulsation was still slightly in rear drums, so I de-adjusted brakes and just drove like that.

2017
June:
- Rebuilt rear brakes with new shoes, hardware, drums, and fluid flush (Advanced Auto Parts Premium shoes/drums)
--> (fronts got new pads and rotors at this time too)
- When adjusting rears by hand (wheels of ground, turning wheels), can feel grab, release, grab, release when getting tight. Not a uniform grab.
- Symptoms same as above. Bad when brakes are hot, can feel at slow speeds (5-10mph), pulling ebrake at slow speeds has strong pulsation.

July
- Removed axles and checked runout: found .005" on both sides. No leaks from axle seals
- Cleaned rears
- NOTICED that leading shoe had a choppy pattern on it. Not smooth & uniform like trailing shoes.
- Adjusted
- Drove great for a day or so until I got them hot again. then pulsation came back.

October
- Took to Brakes Plus. They found slight warpage in rear drums. TURNED rear drums.
- I didn't even leave the parking lot and could feel it still. Not fixed.
- They broomed me - no interest in helping further, and said they didn't know.

November
- Took to a local mechanic (old school guy) who has a specialty in Jeeps
- He couldn't figure it out. Recommended taking a shot in the dark and replacing ABS unit.

I've heard of the ABS unit malfunctions on different brands, and how they can cause subtle pulsing. But considering that I feel the pulse when the car is lifted (engine/key off), and turning rear wheels by hand, it just doesn't seem likely to me. I guess it could be some kind of mechanical malfunction in ABS unit, but I feel like that is a long shot.

If anyone wants to spitball ideas here, I'd love to chat about it, and am happy to try different solves and post results! Hopefully this will be useful for others in the future too.

 

From what you've described it's likely to be the ABS.

Though I haven't worked on ABS in the past and my XJ came with a standard brake system. I have a general idea of how ABS operates.

As you probably are already aware, you basically have a standard braking system of an XJ of which Jeep added ABS to.

To recap your braking system, a standard non-abs brakes for the XJ is divided into front and rear brakes. This is partially for safety reasons in case of front or rear brake failure.

The master cylinder is also divided with a primary and secondary valves for front and rear brakes.

The ABS unit is placed between the master cylinder and the wheel cylinders. Each wheel has an abs sensor that's connected to an ECU of the ABS unit, (which I assume is connected to the PCM?)

* ABS only works part of the time when it's ecu with sensors detect some wheel slippage. When you normally brake often there is no ABS.

If the ABS ECU, it's wires or any of the sensors fail will likely cause problems similar to what you have described.

It's normal to feel some brake pulsation when ABS is active. But not too much and not when the ABS isn't suppose to be active. ABS should only be active when the ECU decides that one of the brakes is locking or is about to lock.

The ABS ECU and sensors monitor each wheel so many times per second. So if something interferes with it's monitoring can potentially cause problems similar or same to what you have described.

I would first inspect all the ABS wiring, connections and it's sensors. Both front and rear. Then inspect all the brake lines connected to the ABS unit, making certain there are no leaks, restrictions, etc.

Also the master cylinder and the wheel cylinders need to be in good working order.

I recently replaced my master cylinder as it was the primary cause of brake problems, once replaced my non-abs brakes started to operate normally.

As for the ABS unit and the ABS ECU I'm not certain without looking at one how I would inspect, test and troubleshoot an ABS unit.

I would probably first remove the ABS unit and inspect any i/o brake lines and any valuing, then I would try to test the ABS ECU to make certain it's working and it's wiring and connections are ok.

I think perhaps the mechanic suggested replacement of the ABS unit as sometimes it's more expensive to repair than to replace or find a rebuilt abs unit.

Note: some XJ owners have removed the ABS. Imo a good working abs produces a braking system with advantages, while lowing braking distances. ABS is suppose to work better than standard non-abs systems in rain, water, dust, etc. decreasing stopping distances, suppose to be better when turning and braking, etc.

So removal is an option, but I don't know if I would recommend removing unless your XJ goes off-road in more extreme environments where ABS may not be needed or wanted.

My XJ doesn't have ABS and I find it brakes ok but I don't think as well as an XJ with working ABS. I often get brake slippage in rain, puddles, dusty roads, etc. and may manually pump the brake pedal to compensate.

 

This is awesome! I really appreciate the detailed response. So it definitely sounds like this is a potential culprit. First thing I'll do is get the visual inspections going (sensors, lines, wires), and then I'll see what happens if I disconnect the ABS ECU. Will do a little digging online about diagnosis, although my gut reaction is that this would be the result of an electrical problem. Although at this point, not ruling anything out!

I've never tested my ABS hard on the Jeep, but I had a VW GTI once with ABS, and for a week decided that every stop I came to would be ABS activated. After I got used to the hard braking, and made it part of my daily driving, it definitely felt superior to threshold braking. Some older vehicles (ie: '96 chevy cavalier) I've owned had some fairly primitive ABS systems, and it felt like a skilled driver may have been able to do better. But I do know that ABS activated braking is supposed to allow you to steer the vehicle somewhat during an emergency braking situation.

Thanks again!

 

Just putting this out there could you have a slightly bent axle ? and to see if it is the ABS just unplug the ABS module and test drive it and see how it doe's .

 

The bent axle was definitely something I considered. I called a 4x4 axle specialty shop, and they said that if my axle seals weren't leaking, and if I couldn't feel any vibration on the road, that they highly doubted it was bent axles. I personally measured axle run-out, and so did one of the shops I took it to. We both found axle run-out around .005", which he confirmed shouldn't be causing issues. The Axle shop on the phone didn't think .005" was a problem either.

I'll definitely try unplugging the ABS unit. The shop owner I spoke to believes that it could be a mechanical failure within the ABS unit as well. Considering that I can feel the pulsation when the engine and key are off (turning rear wheels by hand), I'm guessing that disconnecting ABS ECU won't do anything, but I can try this weekend.

 

ABS stand for anti-lock braking system or anti-skid braking system.

Essentially ABS tries to determine when your tires are slipping or locking (without normal rotation) and then may or may not apply abs and standard braking to prevent tire slippage and locking up. Once a tire/wheel locks it normally begins to slip over a surface. So an ABS could potentially be referred to as a anti-slip braking system.

Here's an article that I found helpful, for a better understanding of ABS and how it works.

It lists four basic ABS components.

• Speed sensors
• Pump
• Valves
• Controller

Then goes on to explain how ABS operates and the different types of ABS found on vehicles.


https://auto.howstuffworks.com/auto-...lock-brake.htm


I've seen separate abs computer modules for XJ, uncertain if it's the same for all years. New ABS control units for Jeeps I've seen for around $300.00 +/-.


Also some Jeeps with ABS may use a different master cylinder than those without.


However if you can repair the ABS yourself, potentially will save you several hundreds of dollars in parts and labor.

 

If you can feel it when adjusting the brakes then I would think the abs is not the problem the other thing I would look at are the wheel studs if they are centered it would make the drum spin out of round and could the problem .

 

I did a thorough inspection this weekend, and I'm really feeling like it's NOT the ABS as well. I just don't see how it would cause the out-of-round feelings when turning the wheels by hand when the vehicle is lifted. On that note, I inspected the tone rings, sensors, and wiring, and found no obvious problems.

I did notice that when the drum is placed on the wheel studs, that there is a small amount of rotational play on the studs. I can slightly turn drum forward or backward about a half millimeter or full millimeter. Although, I wouldn't expect this to cause the on, off, on, off grabbing.

When spinning the wheels and looking in to the inspection ports on back of drums, it appears that there was a TINY TINY amount of out-of-round in the drums (or something), as I can see the drum get just a hair closer to the shoe, then move away a hair.

In the end, I'm really starting to think that I've just had ****ty drums the entire time. The fact that it gets worse under heat makes me think that maybe the cheap drum material is deforming, which causes more rubbing, and more heating, and more warping (dog chasing it's tail). I'm thinking now that after having them recently turned, that they then deformed under heat. I'm considering taking the drums in to have them checked again, and possibly buying a new set of drums from somewhere other than Advanced Auto Parts.

 

On another note - does anyone know what the purpose of this vacuum line is (coming out the top) on the rear brakes? Looks like it is going in to the top of a distribution block for the rear hard lines. It then goes in to the frame.

 

I had a pulsation a while back in my 2000. Had the drums cut, still pulsated. next time I needed rear shoes, replaced the drums. No more pulsation. I would lean towards your drums being the problem.

ABS is only working when your hard on the brakes potentially causing lock up. If you have your Jeep up in the air, and just rotating your tires and you can feel random drag that's not ABS.

 

That's the rear axle vent. It's not related to the brakes at all. The drum having that slight play back and forth on the studs is normal.

 

The hose coming out of the rear end is a vent line for the rear differential . See if you can find a place that will warranty drums for you , that way if you have any problems you can get them replaced or you can step up to a better drum .

 

Another option..?

Pick up a used rear axle from a local boneyard and swap it in?

At this point that's what I would do.. Weekend project. DON'T use any parts off the original axle except for the wheels.

 

I was gonna say, just replace your drums. They're relatively cheap and easy to change. Definitely not ABS related.


As others have said, it's a vent tube for the rear axle/diff. What's confusing about it is it's attached to the same block that serves as a T connector for the rear brake lines. I've not pulled it apart to verify, but it would appear the brake line part is machined separately from the vent portion.

 

Thanks everyone. I'll post back if I end up going with updated Drums.

The Brakes Plus store near me is connected to an Advanced Auto Parts (AAP) store. They said that they had to stop using drums and rotors from AAP because the majority of them were out of round when new. Shop said that they got to the point that they'd just throw new AAP rotors and drums on the lathe right out of the box. Brakes Plus says that they use another brand now (can't remember name), and have had great results. $200 for a set of new drums.

Anyone have recommendations on drums? I'm not doing any towing, although do live in Colorado and the car sees mountain driving (think 5,000 ft in elevation to 12,000 ft in an hour, then back down), so some beefier brakes are always nice. Thanks!