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Old 12-28-2019, 05:27 PM   #1
fleetw00d
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SUSP : Master Cylinder Rebuild

If you're so inclined, the brake master cylinder can be rebuilt.

Tools needed:

Snap ring pliers
5 mm Allen wrench

Parts needed:

Rebuild kit. I got a 15/16 inch (LX, DX) Raybestos kit from RockAuto; I haven't found a 1.0 inch kit for the EX/SE (ABS) master cylinder.

Procedure:

- Remove the master cylinder (I already had one of questionable function; I rebuilt this one so I could immediately install it when I removed the one from the car)
- Remove the rubber seal from the depression in the brake booster

- Remove the retaining ring from the push rod end of the cylinder

20200104_125722 by Paul Kemme, on Flickr

- Remove the primary piston (it should come out easily)

- Compress the secondary piston some, then remove the stop screw from between the two ports. There is a steel sealing washer on the screw.

20200104_125914 by Paul Kemme, on Flickr

- If you knock the cylinder against a bench, the secondary piston should come out (I rebuilt the one I took out of the car, had to pull on it some to get it out)

20200104_130955 by Paul Kemme, on Flickr

- Clean the cylinder bore, inspect it for scratches or corrosion. If clean (like mine) proceed to the next step. If scratched, you should be able to hone it slightly to clean it up. For the second one, there were a few marks where the secondary piston had hung up when removing it (photo I tried doesn't show it well). I used a piece of 2000 grit to "hone" the top end of the cylinder. The marks were beyond where the primary piston seal would run.

- I removed the reservoir to clean it thoroughly

- If you're going to install the MC on the car in short order, lubricate the bore with brake fluid. If you're going to wait, I used just a little spray lubricant (MotorKote spray) to lubricate it. If it sits with a little brake fluid in it for a while, it may absorb water and cause the bore to corrode.

- Install the new secondary piston

- Compress the secondary piston some, then install the stop screw (the kit came with a small copper washer, but it didn't look substantial, so I reused the steel washer)

- Install the primary piston

- Install the retaining ring

- Install the reservoir if you removed it.

- Bench bleed the master cylinder to remove the air

- Install the booster seal disk on the piston rod

- Install the master cylinder

The picture shows the MC with the new parts already installed as well as the old pistons.

20191223_110412 by Paul Kemme, on Flickr

Because the only air I might have introduced into the lines was immediately at the tube connections, I remove the front wheels and compressed the front caliper pistons to push fluid and the air back into the master cylinder. I alternately pivoted each front caliper up and slowly pumped the brake pedal to extend the piston some; then compressed it again to push fluid back into the MC and push any air in the cylinder back into the reservoir. I then bled each caliper some to make sure there wasn't air there. After reinstalling the calipers and pumping up the brakes, I have a VERY solid pedal.
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Last edited by fleetw00d; 01-11-2020 at 06:57 AM. Reason: Correcet the title to proper format
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Old 12-28-2019, 09:49 PM   #2
Crankshaft
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I tried rebuilding aluminum calipers but i managed to break pieces while trying to remove the cylinders off the calipers so i gave up. I simply did not have the patience to keep trying since only one piston would pop out on the multi piston caliper design.
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Old 12-28-2019, 10:39 PM   #3
fleetw00d
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The seals in the MC are nowhere near as tight as caliper piston seals.
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