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15/16 Master Cylinder Upgrade for 2nd Gen CRX

Tom Downes 15/16" Master Cylinder Upgrade for 2nd Gen CRX
The 15/16" master cylinder from an 88 Prelude 2.0Si is a nice little upgrade for your worn-out CRX brakes. Don't do this expecting a huge upgrade in braking if your current master cylinder is in good condition, the pedal feel should get firmer.

I did it as a replacement for my old, leaky MC. To get better braking, it should be followed up with stainless steel lines and better pads (and rear discs if you don't have an Si!).

What you Need:
15/16" master cylinder from '88 Prelude 2.0Si
Brake Fluid (at least 1 liter)
Vacuum bleeder (optional)
10mm open ended wrench
14mm wrench/socket
Jack/stands (not necessary but makes bleeding easier)

Removing the Old Part:
Start by taking off the lines from the old MC. You should cover the painted parts of the car in the area, brake fluid eats paint. You can either unbolt the MC from the booster and dump the fluid, or you can use the vacuum pump to suck it dry so it won't drip as much. When you have it out, take some clear hosing (like the stuff with your vacuum bleeder) and connect the two lines to contain drips. This isn't really required but it will keep your alternator/bay cleaner.

Prepping the New Stuff:
First off, clean out the old booster where the MC mounts. Get rid of all the grime and loose rust so the new one will mount on a clean surface. Now take your old MC and separate the reservoir from the top. You will probably want to clean it up a little (the reservoir) before moving it to the new one. Make sure the clamp is tight on the new one. Now take your old MC, rinse it out, and put it in the bag and box your new one came in.

The new part should have come with directions for bench bleeding and some parts to do it. It's pretty simple: connect the plastic fittings into the new MC where the brake lines go, and run the clear tubes into the reservoir. Clamp the MC in a vise facing away from you and fill the reservoir with new brake fluid. Pump the MC in and out smoothly, leaving 10 seconds between pumps, until you don't see any more bubbles coming through the tube. This can take a while, make sure you get all the bubbles out, it's a lot easier to do this than bleeding the whole brake system. When you're done, top off the reservoir and cap it, and there should be some little rubber caps in the kit for the plastic fittings.

If you compare the old and new MC, you'll see that the line fittings aren't quite in the same place for the front one. The CRX line comes out at an upward angle, while the Prelude one is level with the rear line. Getting it in doesn't require too much bending, but it's a pain to get it threaded. If you do that line first, then the rear, then bolt the MC on, it's a lot easier. So remove the caps and screw the lines on, but only finger tight, and then bolt the MC up to the booster. Cover the lines with something and get your helper to push down on the pedal, and fluid will come squirting out of the fittings. This is supposed to keep air out of the lines or something, but it doesn't really (especially if you are struggling with getting the lines in). Tighten it all down while they are holding the pedal still. Bleeding the brakes could be optional, but I would (and did) do it anyway. It's also a good opportunity to flush the whole system, and if you have a vacuum bleeder it's pretty easy. Don't forget to return the old MC for the core, and check again later to make sure you tightened it all down right.
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