Raise the car up, and put it on jack stands, never work with just the scissors jack that came the car supporting it. Remove the wheels. Disconnect the brake hose from the caliper, and plug the hose to avoid loosing to much fluid. Since the caliper kits come with new gaskets, I just had a bolt and nut handy to put onto the banjo fitting, using the old gaskets. It is important that you block off the lines in order to avoid having to bleed the master cylinder. Remove the caliper bolt from the torque plate, and then lift the caliper up, and slide it off the torque plate. The caliper is now free of the vehicle and you can proceed to a suitable work area to overhaul it. Remove the sliding bushing (and clean it), the bush dust boot and the main pin boot from the caliper. Next, using a small screwdriver gently pry the cylinder boot set ring from the caliper, then remove the cylinder boot. You are now ready to remove the piston or pistons, depending on whether it's a single or two piston caliper.
Single Piston Caliper: Remove the bleeder plug. Place a folded piece of cloth between the piston and the housing, and apply low pressure compressed air through the hole for the bleeder plug. It is important that you don't use to much pressure otherwise the piston will come out with a lot of force. Also never try to catch the piston with your hand.
Two Piston Caliper: Remove the bleeder plug. Place a folded piece of cloth between the pistons and the housing, and apply low pressure compressed air through the hole for the bleeder plug. Same cautions as mentioned with the single piston caliper apply. With the two piston caliper, you will find that one piston will probably come out and leave the other one in. In order to get the other piston out, take the piston that has already been removed and push it back in just a little, enough that it seals. Use thin pieces of wood to place between the piston you just pushed back in, and the housing until the wood is snug between the housing and piston. Apply compressed air to the bleeder plug again, and the other piston will be forced out. You should now be able to wiggle out the piston that you earlier pushed back in slightly.
Using a screwdriver pry the piston seals from the caliper cylinder bore. Before going any further check the piston and bore for signs of corrosion, wear, or build up. Clean the pistons and bores, I used carburetor cleaner and they came back looking like new. Wipe off the piston and bore with a cloth, and then blow some compressed through and on them. If the pistons or cylinder bores have corrosion or are badly worn, you should replace them. You are now ready to put the caliper back together.
The caliper kit should have come with a packet of grease (pinkish in color), if it did not you will need to get a lithium soap based glycol grease, do not use just any grease. Use this grease to coat the bore, piston, piston seal surfaces, inside of bush dust boot and main pin boot, sliding bushing, and main pin. Install the bleeder plug. Install the piston seal into the bore, making sure it fits snug in the groove and is level, then push the piston into the bore. If the piston is tight, use a hammer handle or something similar to push it in. Install the cylinder boot, and then the set ring. Install the bush dust boot/ boots into the caliper, and then install the sliding bushing. Put the main pin boot back on the caliper.
Clean the main pin and apply some of the grease that came with the kit (lithium soap based glycol grease). Slide the caliper back onto the main pin until the main pin boot slips into position. Lower the caliper back onto the brake disc (rotor), install and tighten the caliper bolt. I can't give a specific torque value for each different caliper type, but for mine the caliper bolt torque was, front: 27 ft-lb (370 kg-cm, 36 N-m), rear: 14 ft-lb (200 kg-cm, 20 N-m).
Using the new copper gaskets that came with the kit, install the brake line back onto the caliper. On mine the torque for this bolt is 22 ft-lb (310 kg-cm, 30 N-m). Top up the master cylinder reservoir with brake fluid, and bleed the brake system. If you do not know how to bleed the brake system, there is information on this procedure further down. Pump the brake pedal and make sure that there are no leaks, and providing there are none, you are done.
To bleed the system you will need a supply of brake fluid, a long piece of tubing that fits tight on the bleeder plug (preferably clear), and a small container half filled with brake fluid. You will also need someone else to help you with this procedure. Always start on the caliper that is the furthest away from the master cylinder. My car is a right hand drive and as such the reservoir is on the right hand side, so I started with the left rear caliper.
Begin by topping up the master cylinder reservoir. Then connect one end of the tubing to the bleeder plug, then insert the other end into the container with brake fluid, until the tube is submerged into the fluid. Get someone else to start depressing the brake pedal while you open the bleeder plug (by turning it counter clockwise). You should see fluid coming out of the tube, and you should notice bubbles. Have your assistant pump the pedal about three times and tell them to hold the pedal pressed firmly down to the floor on the last pump, then you close the bleeder plug (by turning it clockwise), when it is closed let your assistant release the brake pedal, and pump it a few times. Repeat this again until you no longer see any bubbles. Remember to keep adding brake fluid to the reservoir every couple of times, otherwise you will end up having to bleed the reservoir if it drains during bleeding. Repeat this process for each caliper, working your way towards the caliper closest to the reservoir.
It's a good idea is to replace all the brake fluid. I decided to switch from DOT 3 to DOT 4 fluid, as DOT 4 can handle more heat. To do this just keep bleeding the furthest caliper until the fluid coming out looks fresh, but don't forget to keep adding new fluid to the reservoir. Do the same with all the other calipers, and that's it, you are done.
I recommend after completion of this procedure you drive the car slowly and apply the brakes a few times to make sure the pedal feels firm and not spongy (if the brakes feel spongy, you may still have air in the system, bleed again), and that the car is stopping satisfactory.
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This page was created
by Dennis Heath.
If you should wish to ask a question about the GT-Four/All-Trac, you can join the GT-Four Mailing List, where I, and many others with GT-Four's, might have your answer. For information on joining go to http://www.onelist.com
Please note that I am not a mechanic by trade, and that any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this site, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here.