I want to run a welded diff in my FD
 

I have looked high and low and I still dont have a good understanding of which diffs swap to which cars. I do not want a clutch or torsen diff. I have used everything under the sun and welded is the way to go. Im new to this chasis.

My understanding thus far is that I need a series 4 non turbo model open diff. This diff will swap directly into my housing. Is that correct?

Nobody knows the answer or can lead me in the direction to find an answer?

The Non-Turbo diff will not swap in... it's smaller than the FD & Turbo FC Differentials (7" vs 8"). You need a clutch-type S4 Turbo Diff or a Viscous S5 Turbo Diff to gut and weld up for your FD case.

^This is correct.

BUT, in my opinion, I think it's actually easier to have the FD torsen diff welded up than to gut/weld a turbo FC diff. In which case, you have everything you need right now, just have the helical gears welded. I had a welded torsen in my Turbo FC for a bit.


Plus, I would hate to see a perfectly good s4 turbo clutch-type diff go to waste. :)
Not the s5 viscous lsd's though. Nobody gives a rat's butthole about those. Paperweights. Difficult to weld.

Thankyou for the insightful responses. I bought a s4 tII clutch type LSD from a member here for 300 shipped. Do these commonly need built or will I be good with shimming it so it locks hard and keeping the oil fresh?

I "wore" out my stock clutches in a freshly rebuilt S4 clutch type in one season of drifting behind an LS1. I would suggest getting the thicker Mazdaspeed clutch plates (mazdatrix sells them) and possibly restacking the plates in the manner that John Hujiben did in his build thread to give it more friction surfaces.

https://www.rx7club.com/build-thread.../#post11342277

Just save up and get a LSD. If you already paid 300 for a stock one and going to pay 50+ for welding you're already half way to a new one.

Looking at $350 to rebuild an S4 diff. I just rebuilded mine with mazdaspeed friction plates. I haven't had the chance on running it yet.

It doesn't make any since to buy a kazz or cusco when you can get the exact same thing fo 300. I'm going to insect the plates and then order as I see fit. Otherwise I'm just going to shim it to lock harder. Thanks for all the input and ill check out how get got more friction surface in his build thread.

Where do u get the shims and does it work like welded?

If you dont have the money for a 1.5 or 2 way its best to just weld it. I have many years on my s5 lsd welded and know it will never break. I will snap an axle before that happens. Its not worth putting them in just for them to wear out in an event or two just to pull it back out. The lsds when the fluid warms up it doesnt lock for crap and the clutch type will last a couple events but then will stop locking aswell.

So a s4 t2 diff can be welded?

Not completely sure about clutch types but i know viscous lsds can be welded and the 3rd gen torsen diffs can be welded. I would assume the clutch types could still be welded but people pay pretty good money for those cause its a really good diff to run for a street car.

Well I have a s4 t2 I just don't want to pay 1000$ and my friend welds diffs at a shop we just don't know. I have heard u can weld a Mazda 929 diff in t2 pumpkin

2 way

You can pretty much weld anything some are just a little harder then others. If you were a little closer id weld it up for you im in st.pete

i have a welded fd diff if you're still looking for one pm me if you're interested

Its jtp!

For which pumpkin? From your fc?

for FD or FC, will work in both

Pm