Bolt On Subaru Master Cylinder Upgrade

[Crow Horse]

Just a couple of items that need clarification before I get into the nitty gritty…

 *This upgrade is not my brainchild. This is Yankee Tim & Yankee Bob’s baby. They “discovered” it and made it work so the credit that is due is theirs. I am merely the beneficiary of their research, testing, and generosity. I’m only documenting what I did for others to see. That said, thank you to Yankee Tim & Yankee Bob……

*The specific year/model Subaru isn’t cast in stone as of yet. From what I’ve found so far on Napa’s site is that a 1998 Legacy with ABS appears to be an exact match to the one I’m using. I’m sure there are other models/years that will work as long as it has a 1 1/16” bore.

*If you have the original brake proportioning valve, you might want to consider replacing it. I've had used a few "good" used ones, but they eventualy leaked. After all, they are nearly 20 or more years old. I once did a "autopsy" on one and discovered that they can leak internally for quite some time with no external sign of the leak. I replaced mine with a new one just to be safe.

A couple of items you’ll need:

Subaru master cylinder (1 1/16” bore for ABS) as compared to Suzuki's 7/8" bore

Subaru master cylinder wire connector Master cylinder to booster gasket (or RTV silicone)

Small tube bender

6mm x 1.0 bolt, app. 50mm long (grade 8.8 or better)

The swap:

Remove original master cylinder. Save gasket if possible (use old gasket as a template for a new one).
Reach into booster and remove the booster push rod.
Remove the “tip” of the pushrod.
Cut the head off the new 6mm bolt.  Clean up threads by “chasing” with a die.
Round off one end with a grinder to make the new booster push rod tip. As an option, you can use a 6mm acorn nut, grind off the corners of the hex, then loctite it on.
The original push rod length was too short, so the new push rod will have to adjusted to the proper length. There needs to be zero tolerance between the tip and it’s mating surface inside the master cylinder. This will take a couple of minutes to adjust properly.
If the Subaru master cylinder doesn’t have an “O” ring on it, swap the Suzuki one onto it.
Once the pushrod is adjusted properly, Bolt up the master cylinder after you’ve bench bled it. Use the gasket you cut or RTV.
Using a tube bender, bend the brake lines to mate to the new master cylinder.
Splice in a connector (Subaru) to the Suzuki wires.
Bleed the brake system.
Enjoy the improvement in braking.

[Crow Horse]

More pics of the swap almost finished.

The last pic is of a 2005 Impreza master cylinder.  Looks very familiar......

[n0lan]

great info as always crow!


Thanks!
Nolan

[crapurai]

could u please explain how this improves braking? i dont quite understand.

[Zippy]

The Suby MC increases the volume of fluid being pushed to the brakes.  The stock MC has a bore of 7/8" and the Suby one is 1 1/16".  The bigger bore is really important when you have rear discs or larger calipers on the front.

Kevin

[Yankee Tim]

*This upgrade is not my brainchild. This is Yankee Tim & Yankee Bob’s baby. They “discovered” it and made it work so the credit that is due is theirs. I am merely the beneficiary of their research, testing, and generosity. I’m only documenting what I did for others to see. That said, thank you to Yankee Tim & Yankee Bob……

Brain child!?!?  HA, more like brain-fart.  We do that alot.  Glad you like it, and sorry for the loooooonng delay in *finally* getting that M/C to you.

[Crow Horse]

Brain child!?!?  HA, more like brain-fart.  We do that alot. 

Well, if that is true, I'd like to have you and Bob over for dinner.  The menu - beans, beans, and more beans.......

If you can fart like this, be my guest and fart away!

Thanks!

[Crow Horse]

FYI........

The wire connector I used was from a Nissan.  Many models use the same connector as does Subaru.......

[zuku26]

Is this more of an offroad upgrade where you need the better braking to stay put on rocks and such? I find that on the road especially wet or slightly wet pavement my brakes lock very easy sending me into a slide. Wouldn't stronger brakes sending me sliding ever easier? I'm sure a better wet pavement tire would increase my stopping...is it possible to be too light!?!?

[RazorRodent]

I swapped on the whole booster,  mc assembly from my 4dr kick donor. It much larger and has the same bolt pattern.

[Crow Horse]

I swapped on the whole booster,  mc assembly from my 4dr kick donor. It much larger and has the same bolt pattern.

And the results are?........

[RazorRodent]

Oh it fits like it was meant to be there, I havent tried it out yet though since I'm still in the process of rebuilding the zuk

[Crow Horse]

Keep us posted on the results......  Pics too if you can....

[Yankee Tim]

I swapped on the whole booster,  mc assembly from my 4dr kick donor. It much larger and has the same bolt pattern.

  Do you have the M/C diameter from the Kicker M/C?  The number is underneath it on the end on the M/C.  I think it's only 1".

[zukiowa]

kick m/c looks to be 1" w/o abs and 15/16" w/ abs according to parts store
but booster might have bigger diameter so more assist