Hi.

I have some questions about my FC:

1st - How can I check, if the car as a Limited Slip Diferential, and if so, what type? (Torsen, etc)

2nd - How can I change the diferential ratio to a shorter one? Like a 4.77 differential or close? Does it exist?

Thank you.

 

You can check under the car on the diff housing and see if it says lsd. More info will help people help you though. Like if you have an s5 or s4, what do you specifically want from your car etc. If the lsd sticker isnt on the diff housing or not visible you can always do a burn out and if one wheel spins only then you dont have lsd. If you have a TII model it will most likely have lsd (if I'm not mistaken).

For differential and drive train components check out Mazdatrix.

http://mazdatrix.com/g.htm

 

Hum...

I see.
The problem is, if the LSd is in bad condition, I can't reach no conclusion.

the car is a 1986 FC3S NA model. S4 or S5? I don't know!

 

That's an S4 car (86-88). S5's are 89-91

Not all Turbo FC's came with LSD's overseas.

If your diff is in bad condition and wont pass the spinning wheel test, then it's basically a moot question. The diff is useless and acting like an open one.

If you wanted to switch to a drop-in with a higher ratio, certain NA cars came with a 4.3 diff (as opposed to the 4.1 on all other manual cars or the 3.9 in the auto cars). You will need to do some research to find more info (try the stickies for the north american cars on the top of this 2nd gen section).

All S4 diffs were clutch type. S5 turbo differentials are viscous, I assume S5 NA diff's are the same. If you want a torsen diff, you can buy the internals from an early Miata and swap it into the FC pumpkin.

 

4 lug? Peg leg.

 

The burnout test is a bad one. I only once had a problem with only one wheel spinning on dry pavement with my old open diff, and that was when my front swaybar endlink came off.

Basically if it's a stock LSD it's either a clutch type, which wears, or a viscous type, whose fluid degrades, so no matter what it's not going to be that good. You can easily swap in a Miata torsen into an NA housing, or an FD torsen into a Turbo housing, or get an S4 LSD and rebuild it.

If you want a ratio other than 3.9, 4.1 or 4.3 it'll be expensive, as you have to do some custom work on them to lengthen the pinion shaft. An assembled high ratio diff with LSD runs around $2.5k.

 

Mazda Motorsports sells 4.8 and 5.12 ring and pinions. The 5.12 is ~$600, and the 4.8 is ~$330.

 

A ringgear and pinion set does not help a failing LSD, that functionality is in the spider gear portion of the differential.

 

Those are for the short pinion setups. You need to specially modify them to fit in the long pinion FC diff, this involves cutting it and the stock shaft apart and grafting them together. Not something you can do at home.

 

I know!

I have both problems!

I need a ringgear and a pinion set with 4.8 relation, and a good LSD, my favorite is the disc one!

If everything you said, and I believe so, is right, I should have a LSD in my RX7 and a 4.3 dif relation!

My favorite LSD, but I need a shorter dif!

 

I need to replace my LSD, does anyone knows where can I find one (Atanta Rx7 doesn't have it). I found on E-Bay this item :

"OBX Helical limited slip differential. The helical limited slip differential is a torque sensing LSD that features smoothing operation and superior responsiveness. The unit does not require special oil like the clutch type limited slip differentials. "Fitment:

All 85-92 Mazda RX-7 Non-Turbo Models

Utilizes / Specs:
Weight: 11 pounds

Does anyone knows about it, and if I'm going to need additional parts to install it.
Please let me know.

 

that diabeetus avatar is the funniest thing ive ever seen, i broke my rib laughing..