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Rear Disc Brake Conversion from a late model Jeep to early model Mopar 8.75 rearend.
By Mike Lavigne
I am going to give the "411" on the disc brake conversion process on a 8.75 Mopar rear end using late model 1998-99 Jeep Grand Cherokee rear disc brake hardware. You can find these setups in the salvage yards for around $50- $100. Look around because there are a lot of these Jeeps popping up in the salvage yards these days since they are already 10+ years old. Many of you are thinking why don't you just buy an after market setup from Wilwood, Stainless Steel Brake, or another supplier. Well I have installed these setups in the past and found that they are not any easier to install. The down side to most of these after market setups are getting replacement parts. Take the Stainless Steel Brake kit for a 8.75 rear end. They will sell you the kit, but will not give you the application list for replacement parts if you need to items in the future. Some of the parts are machined or modified for this application so you would need to get the replacement parts only from that supplier. Also in most cases a 14 inch wheel will not fit with some of the after market brake systems. This Jeep setup will allow you to still run a 14 inch wheel for the stock look if desired. You will need to get a Mopar wheel that was for a disc brake application which are common on the early 70's Chrysler products, since front disc brakes were becoming a standard option. These wheels have a different back area that allows clearance for the brake caliper. Well with the Jeep brakes you can get all the parts from any auto parts store and you don't have to wait a week for the replacement part to arrive. I have listed the steps below to guide you through this conversion. You will need to have machine work performed on a couple of items to make this conversion successful. You will also need to bend new solid brake lines or modify the original drum brake lines. I have also included some pictures to use as reference for your conversion project.
Steps:
1) You will need to locate the rear disc setup from a 1998-99 Jeep Grand Cherokee or Jeep Liberty. You want to obtain the setup that has the brake caliper located towards the rear of the vehicle. Look for items that are in good condition because this will save you from having to buy a lot of replacement parts. You still should replace the brake pads and have the rotors machined. The rear brakes from a Dakota or Durango will also work but the rotors are 6 lug instead of 5. You will need to pull all the brake hardware from the Jeep rear axle tub. This includes the brackets, backing plates, calipers, rotors, emergency brake cables, and rubber flex brake hoses.
2) Next you will need to get new axle bearings for this project. You can either go with the replacement green bearing or stick with the original style that has the spanner nut for the end play adjustment.
3) You will need to take the Jeep disc brake bracket assembly and drill out the rivets that are holding the brake caliper bracket and backing plate together. There are 2 rivets that will need to be removed so the assembly will come apart.
4) The Jeep brake caliper bracket will need to have some machine work performed. The center opening where the wheel bearing will pass through will need to be enlarged. Also you will notice that the Jeep bracket only has 4 bolts holes that mounted the assembly to the axle tube. The bracket and backing plate will need to have the 5th hole drilled in the 6 O'clock position. This will be the lower hole were one of the rivets that held the assembly together was located. When you take your brackets in for machining be sure to also take your new bearings with you so they can be used for reference on the openings size.
5) If you are using the original emergency brake cables on your vehicle, you may also need to enlarge the cable mounting hole in the Jeep brackets to allow the older cables to be used. You will need to test fit the cables to see how much the hole may need to be enlarged. You can also have your machine shop perform this if you don't have the tools at hand.
6) Remove the axles and old drum brake assemblies from you 8.75 axle housing. You will need to use a couple of items from the old drum system for this conversion.
7) The axles will need to have machine work performed also. So to save some money go ahead and remove the old axle bearings. These bearings are pressed on so the old ones will need to be cut off. Once the bearings are removed go ahead and clean the axles. You will need to have the bearing stop/shoulder machined on the axle. This is the shoulder that the bearing is pressed against to seat the bearing in the proper location on the axle. You will need to have the machine shop cut out 3/16th of a inch from this shoulder. This is done to compensate for the additional thickness of the new Jeep brackets and backing plate which will allow the axle to return to the original location in the axle tube and also allow you to use the original end play bearing adjustment if desired. This is also needed to allow the brake caliper to have plenty of travel so it doesn't have contact with the brake rotor when the brakes are not applied. If this wasn't done the outer brake pad would contact the brake rotor and would not release because the caliper would not be able to move far enough on the bracket. Go ahead and have the new bearing pressed on at this time also.
8) The next thing to do is make your emergency brakes work on the Jeep setup. You will notice that the Jeep emergency brake cables have a square loop on the end that is connected to the hook on the end of the emergency brake arm on the Jeep brake assembly. You will need to modify this Jeep arm to be able to use the older style brake cables that have a ball on the end of the cable. You will need to remove the emergency brake arms from the old drum brake assemblies and the arms from the Jeep assemblies. You will want to cut off the lower part of the drum brake arm about 1 inch from the bottom. This will be the end that looks like a fork. This end will need to be welded onto the Jeep arm so you will need to also cut off 1 inch on the hook end. The Jeep arm is the same for both sides of the vehicle, they just flipped them to be used on the other side of the vehicle. You will need to take this into account when modifying the arms because you will not be able to just flip them once the old fork end is welded into place. You are now making a specific right and left arm. You will want to make sure that when the new modified arm is assembled the fork is on the upper side of the arm. This will ensure that the cable will not become dislodged from the brake arm. Look at the pictures for reference.
9) Next you will want to remove the studs from the 8.75 axle tube ends and replace these with 1 ½ x 3/8th inch grade 8 bolts. This is done to ensure that the amount of threads are sufficient to hold the new brake assemblies in place. You will need to grind off one side of the bolt head to allow the bolt to slide into position from the backside of the axle tube end. You can use the original studs as a reference to perform this process. Also make sure that you use a self locking nut for the reassembly, since this is also holding in the axle as well. If you use a lock washer it will burr the bearing retainer flange and cause you to have problems pulling it apart in the future if needed.
10) Now that all the machine work and modifications have been completed it is time to assemble everything. Place your new brake bracket in place on the axle housing. Make sure you use some sealant between the axle tube and bracket. This will keep out dirt and water from the bearing area. Next slide your backing plate into position also using some sealant. Next side the axle into place and bolt it down using your new locking nuts and the bearing retainer plate. You can now assemble the rest of the brake hardware at this time.
11) Next you will need to make some brackets to hold the rubber brake flex hoses in place on the rear end hosing. You can use some steel flat stock from any hardware store and make a bracket to weld to the rear end housing. This will mount the one end of the rubber brake line in a stationary location. Make sure that the brake caliper can travel freely and not put a lot of strain on the rubber hose which could cause the hose to rupture or break. Also make sure that the hose does not interfere with anything which could also cause the hose to fail. Then you will need modify or bend new steel lines to connect to the rubber hoses and the brake line "T" on the rear end housing. I also flipped the right and left rubber hoses to the other sides. This helped in mounting the solid brake line connection to the new brackets that were made of flat stock and welded to the rear end housing.
12) In some cases you may need to enlarge the lug stud holes on the Jeep rotors slightly. You will notice that the older Mopar lug studs have a shoulder on them. This will cause the Jeep rotor not to seat properly against the axle flange face. You can enlarge the stud holes on the Jeep rotor using a 5/8" drill bit. This will then allow the brake rotor to seat properly against the axle flange face.