New diff issues - 1.5-way LSD
 

A lot of chatter and scrubbing on the Tomei diff. I've done figure 8 for about 15min, drove straight for a bit, did some more figure 8s. It's still locking up and won't unlock when coasting through a turn. The car is off the ground, in neutral, I can't get the wheels to spin independent of each other. As I lay under the car, shouldn't I be able to rock the wheels back and forth to unlock them? It's bound up like it's welded. Straight out of the box setup, I haven't adjusted the plates.

Sounds totally normal. Welcome to the world of budget steel plate clutch type diffs. Unfortunately its never going to "unlock" and act open with the wheels in the air. The breakaway torque is much higher than you can duplicate with your hands. The chattering is how you know its actually allowing some slip...each pop is a slip, then locks again until the breakaway force is reached. Also, when you just coast doing your figure 8s, the popping and locking should become much more subdued. Another way to ascertain that it is actually working as intended.

You may try different combinations of fluid and friction modifiers to quiet it down, but Ive never found those to calm the true nature inherent to a given differential design. For example nothing I could do would quiet down my Cusco RS...that diff is so tight at 80% you may as well be driving a spool (which isnt always a bad thing btw). Id image its nearly the same with the Tomei. I run an OS Giken now, and although its night and day in terms of breakaway torque and turn-in performance, I do still miss that "tight" feeling of the Cusco RS. Believe it or not spool differentials have always been, and still are, a real thing in racing.

Even Tomei themselves advertise the "high initial torque" as a feature on their diffs. Great for drift and high grip and hp applications, but youll find that lower hp grip cars tend to need more "nuance" from their differential performance. Which is usually what separates the value oriented diffs from the pricier ones. Your best bet is to open it up and re-stack the clutch plates to the lowest engagement possible if you want to make it streetable. And if you have it open you may as well see about getting a thinner cone spring washer which will also help. That or just sell it and get a Torsen style, which is usually what is recommended for primarily street driven vehicles as they are MUCH more seamless in operation.

Thanks for the info. Yes, it does get noticeably quieter while clutched in. However, one side makes more noise than the other. Is that typical? Will it break-in eventually and act more symmetrical? Will it loosen up over time at all? I really don't feel like pulling it out again to restack the plates.

I may smooth out ever so slightly after it gets some miles on it, but it likely will remain as unruly as it feels now. Re acting asymmetrically, I wouldnt worry its probably more your perception and car setup, tires, conditions, etc.

Not sure if the Tomei comes set at 80% or 100% on the clutch packs, but dropping it to 60% and getting thinner cone washers for each side is going to be your best bet to make it as livable as possible. This will reduce the breakaway torque and decrease the overall lock to the extent possible on that diff. Iirc the tomei doesnt use any springs on the pressure plates, so there is no tunability there.

Otherwise get used to explaining why your car sounds broken, and the rear end kicking out on the street through turns when you roll on the throttle. Though, mount some stickies and get on track, suddenly it all makes sense.

What fluid are you running?

Sorry to hop in, does the Kaaz act in the same manner ? (most I know have taken it down to 60% too).

Yes it will definitely be similar since it is almost an identical design. Though plate material treatment and design can make noticeable improvements in noise and harshness.

Thanks. Tomei stock fluid. Haven't flushed out the first fill, yet. Getting my suspension swapped. What do the cone washers do?

They reduce preload on the assembly at static, before throttle is applied. I believe they sell a couple of thicknesses for the tomei, they are the "spring disc kits" here:

http://www.tomeiusa.com/_2003web-cat...pair_parts.htm