Disclaimer This rear-disc modification was done specifically for intense off-road use only. For standard road use this modification may not pass certification in all provinces or states. Therefore, we recommend that the owner have his or her vehicle certified for road use to meet the regulations pertaining to that area. All liability in the installation and usage of these component parts are at owner's own risk.

Home-Grown Samurai Rear-Disc Brake Conversion

April 10, 2000

By Robin Schmidt and Dave Hrdlicka

After dealing with poor braking performance and having gone through 3 sets of rear brake shoes in 6 months, we finally decided to do the rear disc brake conversion on our 1985 Suzuki Samurai.

Parts Used for This Modification 2 Samurai rotors 2 rebuilt Samurai calipers 2 Samurai caliper mounts 2 upper caliper mounts 2 rear drums 2 rear backing plates 2 front brake lines set of front brake pads 10 wheel studs from a Sidekick front-end 12 1/2 inch grade 8 washers 4 grade 8 bolts with lock washers and nuts proportioning valve 1 ft steel brake tubing transfer case mounted e-brake (stock on our '85).

When we bought our Samurai, it came with a spare front axle complete with calipers, rotors, etc. The axle housing was bent pretty badly but everything else was fine. This spare front axle supplied us with the rotors, calipers, caliper mounts, and the brake pads that we needed for the conversion.

Before You Begin

In order to mount the rotor you will have to get your rear drums machined at a local machine shop.

1. Hammer the wheel studs out of the rear drums, these will be replaced later with the Sidekick front wheel studs which are longer by about 1/4 inch.
2. Have the rear drums machined so that you're left with a round disc that has an outside diameter the same as the inside diameter of the rotors.
3. Once this is done, hammer the front wheel studs into the newly machined disc. The front wheel studs are about 1/2 inch longer than the rear ones and will compensate for the extra width of the rotor.

Stock drum on left, newly machined drums at bottom center

Final machined disc with wheel studs inserted

Installation

1. Loosen the rear tire lug nuts.
2. Jack up the back of the Samurai and place it on jack-stands.
3. Remove the rear tires.
4. Remove the rear drums.
5. Remove all the brake parts including the brake shoes, springs, self-adjuster, etc.
6. Remove the brake lines from the wheel cylinders.
7. At this point you will need to mark the backing plate so that it can be cut out later in step 10. Scribe the backing plate from the inside side of the vehicle to mark where the axle flange sits against it.
8. Remove the 4 backing plate bolts and pull the rear axles out.

   (Side Note: It's best to replace the wheel bearings while you've got the axles apart but if you want to re-use them then cover the wheel bearings so that no metal filings get into them.)

9. Cut the backing plate so that you're left with a square the same size as the axle flange. We used an angle grinder with a cut-off wheel to do this. This will be much easier if you are having the bearings replaced because you can have the backing plate off of the axle so it (the axle) won’t be in your way when cutting.

   Cut-out Backing Plate on the right, Final cut-out caliper mount on left

   (Side Note: We also chose to have the backing plate piece removable so we cut 2.5 inches out of the bottom to allow it to slip over the axle (not shown in picture). This makes it easier to replace and carry spare axles since we won’t have to carry axles with the backing plates attached).

10. Cut the caliper mount brackets so that you can slide them over the axle housing and set them flush against the inside of the axle flange. (see picture above 'disc-brakes-003.jpg' to see final cutout caliper mount)
11. Use vice-grips to clamp the mounting bracket where you want it to sit. We chose to mount ours at the 10 o'clock position (when facing the axle from the passenger side of the vehicle) although it may be possible to mount the brackets in the straight up and down position.
12. The bracket will need to have two new holes drilled into it so mark the positions through the holes in the axle flange.
13. Remove the bracket and drill the holes to the proper size.
14. We chose to weld the bracket onto the axle housing as well as bolt it. (see picture below to see the welded bracket from the inside)

    Caliper bracket welded in place

    (Side Note: I wouldn't be too confident on just having the bracket bolted so would suggest that you weld it as well. I would also suggest that it be welded while the axles are not in place since the heat from the welding may damage the wheel bearings. Also be careful not to heat the axle tube up too much as you will melt the oil seals).

15. Slide the axles in and using a hammer, lightly tap in the axle until the bearing is fully pressed in.
16. Put the modified backing plate on and bolt it using 2 of the grade 8 bolts and 2 of the stock backing plate bolts.
17. Bolt the newly machined rear brake drum onto the axle.
18. Temporarily bolt the rotor onto the modified brake drum.
19. Assemble the rest of the caliper mount by bolting the upper caliper mount to the caliper mount on the axle housing.
20. To get the upper caliper mount to sit evenly over the rotor you may have to shim it out a bit. This is what the grade 8 washers are used for. We used 3 washers for each bolt to shim the upper caliper mount towards the outside of the vehicle by about 1/2 an inch. Once the caliper mount is all bolted together and the rotor turns properly without touching the mount you can put the rest together. (see pictures disc-brakes-006a.jpg and disc-brakes-008a.jpg below)

    Using washers as shims to get proper spacing

    Another View

21. Put the brake pads on.
22. Using the front brake lines, attach them to the existing metal lines and then to the calipers. (see picture disc-brakes-004.jpg below)
23. Bolt the calipers on. (see picture disc-brakes-005.jpg below)

    Steel brake lines hooked up

    Calipers bolted on

24. Bleed the brakes starting at the wheel furthest from the brake booster.
25. Put the tires back on, jack it up, remove the jack stands and fully tighten the lug nuts.

Proportioning Valve Install

Proportioning Valve Installed

I won't go into the details of the proportioning valve setup as there is an excellent write-up at http://www.izook.com/tech/discbrakes/discbrakeinstall.htm that explains the proper way to do this. Currently we have our proportioning at 50/50 and it seems to work fine. I've heard that most others run front/rear proportioning of 60/40 or 70/30 but so far we've found 50/50 to be best. We've had it in slippery snowy conditions and have done some hard braking to test it with no scary effects at all. You're probably thinking that we could have tested the braking performance with the stock proportioning valve first, and then decided if we needed an adjustable valve; that would have saved us $100 CDN). That's a perfectly valid point. On the other hand, the adjustable valve has allowed us to test various proportions to see which gives us the BEST performance. If you're going through the time and effort to install rear disc brakes, it only makes sense to make sure that you're tuning it to provide maximum performance and safety, right?

Testing Your New Brakes

Double-check to make sure that all nuts and bolts are tight and take your rig for a test-ride. Please make sure that your testing is done in an area away from other cars. Make several quick emergency stops under wet and dry surface conditions to insure that the rear brakes aren't locking up before the front brakes and that stopping occurs in a controlled manner. If you've decided to put in a proportioning valve, adjust it slowly until you get the proper brake biasing for your vehicle's setup.

Resulting Impressions

At the time of this writing we've had the Samurai off-road over 9 times. It has been driven to and from the trail, through snow and rock covered trails, driven through deep water, mud etc, and the performance is awesome. I would definitely recommend doing this modification, the difference over the drum brakes is phenomenal.

Just to re-iterate our disclaimer: we are providing this article for your interest. We are not professional mechanics nor do we claim to be (we can provide a long list of friends who will attest to this). Therefore, we advise you to seek help from a professional mechanic prior to doing any kind of modifications on your vehicle that could affect its safety.