Brake master cylinder

[firehawk]

With a larger diameter master cylinder, you will be moving more fluid with the same pedal travel, which translates to longer piston travel at the caliper. So the pedal will be harder to push and there will be less transition between "slowing down a bit" and "dropping the anchor". Not very nice for a street driven car, but for driving on a track or racing, where most of the braking is of the latter kind, it may be worth it. Shorter pedal travel for same braking effect may also be useful when rev-matching using heel-and-toe.

Of course, when using brake calipers which have a larger fluid volume than the original ones, a larger master cylinder is quite necessary as the original one would result with a spongy pedal feel and perhaps even worse braking performance than with all-original brakes. MR2 Turbo twin-piston calipers with a stock AE82 FX-GT master cylinder was absolutely rubbish to drive and hard braking required the pedal to be put all the way to the floor.

Naturally, a full pedal box would fix all the problems and offer a multitude of adjustments for pedal travel/position and brake bias but they are quite expensive and in most cases on the street and in some racing classes, not allowed.

[Ivan141]

I'll agree that it helps if you have calipers with more volume capacity, but for the stock system it's just taking away some of the maximum force you can apply to the brakes, assuming that your brake system is in good shape, eg. pedal wont go to the floor if you brake hard.

I'm not saying this to nag on your project, but I think a word of warning is needed before other people start thinking bigger master cilinders are better for regular ae86's.

[firehawk]

You're absolutely right - the engineers at Toyota certainly knew what they were doing back when the car was designed so there's no real need to use a larger master cylinder if there isn't a need to displace more fluid. If the stock brake system gives a bad pedal feel, it's most likely that it's just that the fluid has absorbed too much moisture and needs to be replaced.

Oh, and I'm using the 90-91 SW20 master cylinder which is the same size as the AE86 one. I just had one laying around and since it was in a lot better shape than the original one, I cheapskated my way from buying a MC rebuild kit.

[robokill]

Top thing for Abe.... I never noticed this ..... Its pretty good to see but I wonder what it will do.

Maybe on my racer I wil ltry an MR2 one..

[Ivan141]

I bought 2 restored (like new) AE86 master cilinders on ebay for 10 dollars each. Lucky me I guess, the mr2 master cilinder sounds like a worthwile replacement part for stock hachi's.. at least you can find those any time you want.