Fitting KJ Liberty rear disc brakes to an XJ Cherokee 8.25 axle

[sprintagogo]

This is my write-up about how I installed a rear disc brake set-up from a 2003 KJ Liberty/Cherokee with a Chrysler 8.25 axle onto my XJ Cherokee with a drum braked 29 spline Chrysler 8.25.

I bought the parts from a breaker that was advertising parts from a crashed 2003 Liberty (Cherokee here in the UK). I told him how to remove the axle shafts and to make sure he included the wheel studs, the back plate studs and the handbrake cables. When the parts arrived I was surprised to open the box and find that he had removed all the hardware from the backing plates.


I’ll go through the bits in the picture-
1, Backing plate studs and nuts
2, Wheel studs
3, Handbrake shoe springs (1 still hiding in the box, I did find it later)
4, Handbrake shoe adjusters
5, Handbrake shoe retaining clips
6, Part of one of the handbrake cams
7, I didn’t use these, presumably they are for the brackets on the handbrake cables?
8, Calliper bolts (the long one was a poor replacement for one that must have been lost at some point, fortunately they are the exact same size as the front calliper bolts and I have plenty of them!)
9, Didn’t use these either, perhaps some additional supports for the handbrake cables?

This is a picture of the bare backing plate. As you can see the plate is made of two parts which can move out of alignment, the calliper bracket and the dust shield. The two parts are held together by one pop rivet so I added two more because I am petty like that!


And here is the assembled backing plate once I had worked out how it all fitted together and with the extra pop rivets. You have to counter bore the hole for the rivets so they have somewhere to go when the plate is bolted to the axle.



As you can see the discs were quite rusty but in otherwise good condition so I decided to refurbish them on my patented disc turning rig.


By bolting them to the drum and setting the axle turning in 1st gear I could clean the braking surfaces with a course 4½” sanding disc in a grinder. This worked a treat and gave the surface a nicely machined finish.



Other than checking the calliper bleed nipples were ok that was about all I could do in preparation and now it was time to start dismantling my Cherokee. First job is to raise the vehicle onto a good pair of stands and remove the road wheels. Then I removed the diff cover and pulled the C-clips so I could pull the axle shafts out. This now leaves the old backing plate with all the hardware in place and it sure looks crowded compared to the KJ back plate.



In the second picture you can clearly see that there is some thread left exposed on the back plate studs but I wasn’t sure this would be enough to work for the thicker back plate of the disc set-up so I went ahead and used the much longer studs from the KJ.


It’s a straight swap from the drum back plate to the disc back plate, there’s no need to enlarge the centre hole like the common ZJ disc swap. Just undo the 4 nuts, the hard line and disconnect the handbrake cable at the splitter/adjuster. Then swap to the longer studs (I put some copper grease on the studs to help them slide into place) and bolt on the KJ back plate.


The longer studs are excessively long but this doesn’t interfere with anything so they can be left as they are. From this point on it all starts to go back together, first job is to swap the wheel studs so the shafts can be refitted and the diff cover sealed up. I hit a snag with the wheel studs as although they are longer to compensate for the difference in thickness between the drum and the new disc, they are also fatter at the shoulder where they press into the axle shaft so would not fit. I was lucky and got round this by knocking the wheel studs out of some old front hubs I had lying around.


The stud on the right is the original from my Chrysler axle, the one in the middle is a stud from a front hub upto 1999.5 (I think the studs in the 2000/01 hubs are even longer) and the stud on the left is the KJ one that wouldn’t fit. In the picture you can just see that the base of the studs I used are not as thick as the KJ one so the effective threaded part of the studs is almost identical. I pulled the studs into place by putting the shafts into a drum and a wheel and tightening each stud so I could make sure they all were fully seated.

Once the shafts are fitted back into the axle it’s time to fit the discs and callipers. HINT – you need to put the top calliper bolt in before offering the calliper up to the mounting as the leaf spring prevents the bolt from being fitted in-situ. The KJ flexi hose is crimped onto the hard line so you have to use the entire line to the splitter on the axle. I ran the hard line behind the U-bolts and along the top of the axle to avoid the risk of damage. The flexi hose can be mounted by using the KJ bracket cut and welded to the axle tube as in this picture.


The bracket is indexed so it will only fit the hose one way but with a little filing you can adapt the hole to fit any way round. The long hard line has a rubber sheath which is just in the right place to fit into the original brake line clamp on top of the axle. I cut the clamp down so it only had 2 claws (you will understand this when you see the bracket!). The hardest part of the entire job is getting the hard lines adapted to fit the splitter. Unfortunately, when Jeep switched from the XJ to the KJ they swapped the brake line fittings from imperial to metric so the hard lines won’t fit. This isn’t a problem though as the lines are a little too long anyway. I got round this by cutting the fittings from the old hard lines that went with the drum brakes and taking the callipers with the new lines attached to a shop that could re-flare the pipe with the old imperial fittings in place of the metric ones while reducing the length at the same time. The new lines are black coated so that needs scraping off for a few inches to allow the imperial fittings to slide on.
Final jobs are to bleed the brakes and fit the handbrake cables. The KJ cables work perfectly with the XJ splitter and the long side is just a couple of inches too long which is fine. However, as the KJ cables are both the same size this means that the other cable has to be looped round on itself which isn’t ideal but seems to work ok. If this gives me any trouble in the long term I will have to think of a better solution then.

Once it was all buttoned up I couldn’t wait to see how the new discs worked. I wasn’t expecting miracles as many people have commented that rear discs only work as well as well maintained drums and my drum brakes were in tip top shape. After I had done about 10 miles with plenty of braking to bed in the discs and pads I could feel a distinct improvement and when really stamping on the pedal the rear wheels just start to skid. They don’t lock up uncontrollably but they are definitely working harder than the old drum brakes ever did and the Jeep stops more positively than it ever did before. This is good as improving the lacklustre braking was one reason for the project.

The two other reasons for ditching the drum brakes was the habit of the rear braking function sometimes disappearing when driving in heavy rain and the huge benefit of the callipers ability to retain the axle shaft in place should I ever snap it. This will hopefully allow me to limp off the trail and call out recovery without losing a wheel!

[sprintagogo]

Thought I should just update this thread with my solution to the extra long handbrake cable that had to be looped around on itself to fit. While it worked fine I wasn’t happy to leave it be so decided to find a firm that could shorten it. It took two attempts to get it right as the first time they did it they made it the wrong length, pure and simple ****-up on their part which they readily admitted.

Here is a before and after shot of a standard cable against the shortened one. It loses over a metre in length.


I had it made so the outer casing measured 670mm from arrow to arrow and this leaves plenty of slack for suspension movement.


Once fitted it clearly makes the routing look like it came from the factory. I even got them to fit a piece of foam sleeving I removed from an old XJ cable so the new item wouldn’t rub the underside of the spring.

[justanotherjpr]

Looks really nice.

[CDX74]

looks good, how much did the KJ brakes end up costing you?

[LilRedDakota]

Of course UK prices won't help us much, I too am curious. Now that mine is my DD I really don't want to go back to the Neon and would like to upgrade cuz I drive 75 miles a day,mostly highway.

[sprintagogo]

Originally Posted by CDX74

looks good, how much did the KJ brakes end up costing you?

The whole conversion was incredibly cheap. I don't know if I struck lucky with the breaker I bought all the bits from but the cost (UK £'s/Sterling) for all the bits including the wheelstuds I didn't use, the handbrake cables and delivery was only £100. On top of that was gear oil for the axle, a little brake fluid and then £35 for the handbrake cable modification that wasn't strictly necessary. I was a real cheapskate and reused all the friction materials (pads & shoes) as they were in reasonable shape, cleaned up the rotors and simply checked the calipers moved freely.

It would have cost more if I had rebuilt the existing brakes with new drums, shoes, springs and cylinders.

[Carves]

Originally Posted by sprintagogo

The whole conversion was incredibly cheap. I don't know if I struck lucky with the breaker I bought all the bits from but the cost (UK £'s/Sterling) for all the bits including the wheelstuds I didn't use, the handbrake cables and delivery was only £100.

Over $600au just for used KJ bits here ...

Another worthwhile mod that wont be happening to mine ...

[srb43]

Nice work,and from a KJ,I would have never thought of that.And love the brake disc turner!

[60driver]

Do the axles have to be pulled to do this? I feel like I'm missing something here. Then again I am completely new to this kind of stuff but I want disc brakes instead of drum brakes and I found a 2005 liberty at a junk yard here that I can get the parts off of. Anyway you can make this any more Barney style (big purple dinosaur) for inexperienced guys like me?

[justanotherjpr]

Originally Posted by 60driver

Do the axles have to be pulled to do this? I feel like I'm missing something here. Then again I am completely new to this kind of stuff but I want disc brakes instead of drum brakes and I found a 2005 liberty at a junk yard here that I can get the parts off of. Anyway you can make this any more Barney style (big purple dinosaur) for inexperienced guys like me?

You will have to pull the axle shafts out so you can get the old brackets off and the new brackets on.

[BRad704]

So the XJ axles are or are not reused? I have a 96, which means 27spl 8.25... and I might be able to do this if I don't have to buy axles as well...

[justanotherjpr]

Originally Posted by racefan318

So the XJ axles are or are not reused? I have a 96, which means 27spl 8.25... and I might be able to do this if I don't have to buy axles as well...

You re-use the axles in your XJ. The axle shafts in the donor ZJ are not used. You may have the 29 spline, you'll have to pull a shaft and count.

[BRad704]

Originally Posted by justanotherjpr

You re-use the axles in your XJ. The axle shafts in the donor ZJ are not used. You may have the 29 spline, you'll have to pull a shaft and count.

But either way 27 or 29, the brake swap is do-able with my axles?

[justanotherjpr]

Originally Posted by racefan318

But either way 27 or 29, the brake swap is do-able with my axles?

Yes, you will keep your stock axles in your XJ.

[Khary23]

I planning on doing this swap. I just wanted to make sure I read correctly that I can use the front wheel studs from another XJ to make up for the difference in length at the rear.
thanks