How-To: Change final drive ratio (relatively) cheaply

[PantsDants]

Originally Posted by fooddude

I thought I read somewhere that only JDM IS300's have the 4.56 in certain models and none of the USDM IS300s had 4.56; hence, you won't find any 4.56 pumpkins in american junkyards. I could be wrong though or may have thought incorrectly.

I don't know anything about the JDM IS (Altezza) models having a 4.56 from the factory. What I DO know is that the 4.56 ring and pinion pair was used in a JDM-only model of the Supra, the GA70. Thing is though that the carrier assembly from one of those won't work on an 86; you'd be looking at installing those gears in your existing carrier.

As it stands, I don't know of any carrier that has a 4.56 pre-installed that will just drop into an 86.

[fooddude]

Originally Posted by PantsDants

As it stands, I don't know of any carrier that has a 4.56 pre-installed that will just drop into an 86.

This is the unknown golden-secret as it stands I guess. Probably the best bang-for-the-buck mod out there once found (as junkyards usually let them go for $300ish)

But there gots to be a 4.56 Torsen LSD pumpkin out there somewhere, that will directly bolt/swap into the 86 (axle/driveshaft flange bolt patterns and all) . And once that secret is out, the junkyards are gonna be getting a lot of phone calls hehe

More research on the usdm IS300 (and/or old Supras or other Toyota cars?) might be of use:
- Which are 4.56
- Which have Torsen LSD
- Carrier bolt/hole-mount placement
- Driveshaft flange bolt pattern, size and type (holes or studs)
- Axle flange bolt pattern, size and type (holes or studs)

[ed1117]

Do you have any noise after swap from the FD?

[fooddude]

Originally Posted by PantsDants

As it stands, I don't know of any carrier that has a 4.56 pre-installed that will just drop into an 86.

^^^ the only thing I care about is this discovery (if it exists)

[PantsDants]

Originally Posted by ed1117

Do you have any noise after swap from the FD?

I don't think I do, no.

That said, the diff shop guy did tell me I could expect some, based on how these cars are shaped and how short the FD ratio is. His advice to me was if you have some whine right after install, it's probably fine. If that noise changes though, then you should be concerned.

[kodyo]

Thanks for the tips! Picked up my diff today for $250 to start the project:

[Dipstik-sportech]

3.73 ratio works great with boost. Highway cruise is way quieter as well

[Brody602]

Would anyone be interested in buying a brand ring and pinion set for an M85 differential? I was going to swap the stock differential ring and pinion but found a good deal on an M85 diff.

[M23]

Any recommendations for good dedicated differential shops in socal?

[Top-Secret]

this thread seems pretty dead lately. has anyone done this 'WITHOUT' replacing the pumpkin yet?

[kodyo]

Originally Posted by Top-Secret

this thread seems pretty dead lately. has anyone done this 'WITHOUT' replacing the pumpkin yet?

Why would that make a difference?

Unless you have any of the following, I wouldn't recommend doing it yourself:
1) Good public transportation
2) Walking distance to work/grocery store
3) Access to carpool
4) Spare pumpkin to work on

Either buy a pumpkin and prepare for the agony of doing it yourself, or take it to a shop.

[Top-Secret]

Originally Posted by kodyo

Why would that make a difference?

Unless you have any of the following, I wouldn't recommend doing it yourself:
1) Good public transportation
2) Walking distance to work/grocery store
3) Access to carpool
4) Spare pumpkin to work on

Either buy a pumpkin and prepare for the agony of doing it yourself, or take it to a shop.

None of that is an issue, I just want to know if someone has done it in the 86 pumpkin instead of buying a spare from an IS300. That's money I'd rather save

[Dipstik-sportech]

Originally Posted by Top-Secret

None of that is an issue, I just want to know if someone has done it in the 86 pumpkin instead of buying a spare from an IS300. That's money I'd rather save

Buying new gears, bearings, seals, and having a shop install them would be probably twice what you'd pay for a whole is300 pumpkin. So I fail to see the benefit unless you want a 100% new rear end

[Top-Secret]

so its just cheaper to go with the is300 then?