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Discussion Starter · #1 ·
Just like my other post, there are pics on my school webspace.

Tom Downes
November 2005

_____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 (or better, a flare nut 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.

· Registered
1,707 Posts
Looks good. Can you link the pics in at the corresponding points in the article? That would really help if there was a visual for each step along the way.

I have a 15/16 master cylinder installed from an 89 Accord LXi. It is exactly the same master cylinder as the one from the 89 - 91 prelude 2.0Si. Adding a bigger master cylinder will not improve your braking power, but it is a good step to do before increasing the size of your calipers on the front. (since larger calipers require a larger fluid displacement to function properly).

I also wanted to add one word of caution about disconnecting brake lines. Never use an ordinary open ended 10mm wrench. You will risk damaging the fitting because the metal is very soft. You should always use a 10mm flare nut wrench. The flare nut wrench will grab onto more sides of the 10mm fitting, and reduce the chance of damaging it.

· Registered
9,754 Posts
Discussion Starter · #3 ·
Yeah, I did use a flare wrench, though I didn't put it in the write up. I've taken the lines off before (to replace the alternator) with a regular one and it rounded them a little, I ended up using vice grips. You're right also about the braking power. I did this because my old MC was leaking, and I figured if I'm going to change it I might as well use this one in case I decide to change the brakes up later on. Also I think the feel is better, it shouldn't go as low, since the bore of the cylinder is larger, the stroke will be shorter for the same brakes. I didn't link the pics because they aren't terribly helpful I dont think, I can put them here for now and show you. Also I don't get a lot of space from school, so things are going up and down all the time. That might change soon, my roommate and I just finished a file server, and he owns a domain, so I'll try using that (but I'm kind of computer retarded).
here are the pics:

and yes, I know there's a lot of rust in there, it's the JDM rust performance package, ultra rare, my car is much lighter because of it.
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