Project Silvia’s Girlfirend Part 2: Making it Handle

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Here you can see one of the clutch packs in its natural habitat. Half the discs are tabbed on the ouside, so they rotate with the housing, while the other half are tabbed on the inside so they rotate with the side gears.  When the car is going straight, the side gears and housing rotate at the same speed, but when you turn, the outer wheel’s spider gear will spin faster than the diff housing and the inner one will spin slower. This is where the clutches get to do their job.

This mystery diff has four clutch discs per side, normally stacked in an alternating inner-outer-inner-outer pattern to get the most torque output from the clutch stack when the wheels start going different speeds.

In this original configuration, the diff chattered and bucked in low-speed corners (intersections and driveways and such), and the car tended to push into understeer when you rolled on the throttle in a corner. Classic symptoms of a diff that’s too tight for the car. To reduce the torque bias and loosen up the diff, I simply re-stacked the diff plates outer-inner-inner-outer. With the two inner discs next to each other, there’s no resistance between the middle two plates. I can’t remember exactly how much this theoretically reduced the torque bias, because it depends on whether the end plates are up against surfaces that turn with them or not. Anyways, it’s a lot less…

BRAKES:

We had a free 4-wheel set of Z32 brakes on hand, so they were an obvious choice. Z32 brakes are a straightforward bolt on at the wheels (if you have the Z32 rear uprights and 5-lug hubs all around), but we also wanted to get the hydraulics right. Many S13 owners report Z32 brakes feeling wooden and unresponsive when paired with S13 hydraulics. We pulled both the master cylinder and booster from the Z32 so that everything could work together as a system.

Looking at the difference between S13 and Z32 boosters, its no mystery why the Z brakes feel heavy in an S13. The thicker Z32 booster looks to be a dual-diaphragm type that will add a lot more vacuum assist. Naturally, swapping boosters isn’t nearly as easy as it should be.

The long studs of the Z32 booster are too long for the S13, so they must to be trimmed to length.

The other issue is one I ran into when swapping master cylinders on Project Silvia too. Some of Nissan’s ‘90s master cylinders used inverted flares, while a few used bubble flares. I think the difference has to do with the specific master cylinder supplier being used that week. (By the way, I’d like to thank the internet for this copyrighted, almost-in-focus picture that I stole from a website that stole it from somewhere else. Go internet!)

Look closely at the brake line ports on this master cylinder. The outer two ports have cones sticking upward, ready to mate with an inverted flare brake line. The middle one has a concave cone and requires a bubble flare. I have no idea how one master cylinder ended up with both fitting styles, but look closely when swapping master cylinders!

Luckily, this inverted flare is achieved with a little insert that’s supposed to be down in that port. Here’s an insert fitting snugly with its inverted flare brake line. (Perhaps the insert somehow fell out of the Z32 master?)

Getting that insert out of a donor master cylinder without damaging it was no small challenge. First I had to cut down to somewhere near the insert without actually hitting it with the saw.

Then I had to use caveman chisel technology…

Then I had to use it some more…

and FINALLY, the right hit form the right rock released the little bastard. After a quick squirt of brake cleaner, the insert dropped right into the Z32 cylinder and all the brake lines fit.