Swapping MC and BB

IronMonkeyL255 · Post by **IronMonkeyL255** » Fri Jul 22, 2005 9:36 am

Would a newer Impreza master cylinder and brake booster work on our cars?

I was thinking, and I think that if they would work, they might enhance brake feel and response more than other options.

I have already done pads and adjusted the pedal. I replaced my leaking proportioning valve so that's not a problem.

I have bled the lines numerous times, but am still not satisfied with overall brake feel. The brakes in my mom's '03 Legacy wagon feel MANY times better than the ones in my SS.

What do you guys think?

BTW, I found the master cylinder for $35 and the booster for $60.

scottzg · Post by **scottzg** » Fri Jul 22, 2005 10:07 am

yes.

GC non abs imprezas have a single stage booster too

vrg3 · Post by **vrg3** » Fri Jul 22, 2005 3:15 pm

What generation of newer Impreza? I would expect any of them to bolt in, but I've only actually done it with GC/GF Impreza parts and with BD/BG Legacy parts.

I'll assume you're talking about a GC/GF/BD/BG single stage booster:

You'll definitely appreciate the feel. It's a lot nicer than stock.

You don't actually need to swap the master cylinder. Your stock one bolts right up.

If you do swap to the master cylinder that came with the single stage booster, you'll have to plug two of the ports since it was meant for a non-ABS car. You'll also end up with lower pedal effort and longer pedal stroke, because the bore of the cylinder is 15/16" as opposed to our stock 17/16". If you want to replace your master cylinder I would actually suggest a remanufactured stock-replacement unit rather than the Impreza one.

Those are pretty good prices.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sat Jul 23, 2005 3:01 am

What did the single stage booster come in?

Those were prices pulled off of carpart.com for a local JY for WRX parts.

vrg3 · Post by **vrg3** » Sat Jul 23, 2005 4:45 am

Don't know exactly, but I think it came in 93-97 non-ABS Imprezas and 95-99 Legacy Brightons.

WRXes have tandem-stage boosters. They may provide lower assist than ours, though.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sat Jul 23, 2005 5:18 am

I just really hate the squishy brake pedal.

vrg3 · Post by **vrg3** » Sat Jul 23, 2005 5:46 am

If you still have your original master cylinder, that may be causing some of the squishiness.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sat Jul 23, 2005 7:06 am

Yup

Is there a master cylinder rebuild kit or something available? I don't want to spend alot of $$ if I don't have to.

vrg3 · Post by **vrg3** » Sat Jul 23, 2005 2:35 pm

Yes, you can get rebuild kits, but I don't think it'll be cost-effective. For example, last time I priced 'em out, Advance Auto Parts could get me a rebuild kit for 65 bucks or a remanufactured master cylinder for 60 bucks.

A professionally remanufactured unit's preferable to a home-rebuilt one, anyhow. For one thing, if your cylinder bore is scored badly there's not much you can do about it. For another, they probably do a better job honing the wall down than you'd do. And they give you a warranty.

Even if you find a cheaper rebuild kit, I'd recommend dropping the extra cash for the peace of mind, if nothing else.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sat Jul 23, 2005 5:24 pm

I may do that soon, since it's so cheap.

How do you bench bleed the cylinder?

vrg3 · Post by **vrg3** » Sat Jul 23, 2005 10:15 pm

First, you place the master cylinder in a vise (carefully and in such a way that the bore of the cylinder has no chance of deforming). Then, you fill the reservoir with brake fluid. Then, you place your gloved fingers or something over the ports. You fully depress the cylinder with a wooden dowel or something else that won't damage anything, remove your fingers for a moment to let the pressure out, and repeat.

It's basically the same as bleeding any brakes except 1) the wooden dowel replaces the brake pedal and 2) your fingers replace the bleeder valves.

You don't necessarily have to bench-bleed the master cylinder. Both Josh and I installed dry master cylinders without doing so. He was able to bleed the whole system just from the periphery by running the engine so as to have the brake booster assist him in applying pressure. I used a homemade vacuum bleeder.

IronMonkeyL255 · Post by **IronMonkeyL255** » Sun Jul 24, 2005 3:02 am

I have a vacuum bleeder I can use.

Most of the time, I hear people say that you have to bench bleed a MC or you won't ever be able to get all the air out of the system.

vrg3 · Post by **vrg3** » Sun Jul 24, 2005 3:53 am

Yes, that is indeed what people say. I used a pretty powerful vacuum bleeder, though; I was using a refrigerator compressor to pull the vacuum.

Now that I think of it, I didn't bleed only at the periphery; I have the standard Nippon ABS unit so I was able to bleed there, which isn't very far from the master cylinder. Maybe that had something to do with it too.

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Swapping MC and BB

Swapping MC and BB