My final gear swap project
 

EDIT, 10/17:
For the list of parts and relative costs of this swap: http://www.ft86club.com/forums/showthread.php?p=1275527
(By the way, everything actually worked!) :D

I read the thread about the Cusco 4.556 final drive gear kit and how it is a god-send for those of us who intend to stay N/A. What I took from that was that the Cusco kit was simply re-boxed Toyota parts with an insane markup. So that got me thinking: Why don't I just source my own parts? And why not go bigger (shorter)? So here's the fruit of a few weeks of research hitting various forums and vendors!

According to @Jeff Lange, the rear differential carrier out of an IS300 is a direct swap into our cars, and the T2 Torsen LSD inside it is identical to what our cars have. So my first step in this project was to source one, because I liked the idea of minimizing my time without my car, with the bonus of having two fully functional carriers in the end. You could definitely just swap the ring and pinion into your stock differential, but since I'm kind of being a pioneer (read: guinea pig) here, I decided I didn't want to risk having everything apart and have something not fit.

There are two versions that come with an LSD and there are two that are open differentials. The ones we want (LSD) are marked with axle code stickers M98 and M85. The M98 is from an automatic IS300, and is a 3.9 final drive ratio. The M85 is from the manual and is 3.7. I managed to source a basically brand new M98 from a major auto recycling company out here.

With that out of the way, I needed to figure out what ring and pinion kits are actually compatible with this carrier. After trolling various IS forums, I found that ring and pinion sets meant for a North American MK3 Supra (8" or 205mm ring diameter) will fit, but the pinion seal will most likely not. (The pinion seal for the IS300 from Toyota is 90311-38070 and is like $9 online.)

Spence over at http://weirperformance.com/ sells ring and pinion kits specifically for the Mark 3 Supra in a wide range of ratios, including the 4.556, for $225. I spoke with him on the phone specifically about using one of his kits in the IS300 carrier, and he told me that he's had a few IS guys buy from him for this purpose and no one has called back to say the parts didn't fit. He also sells installation kits, which include bearings, adjustment shims, solid spacer, etc. The price on that will vary depending on exactly what you need. At the very least, you'll need the shims, pinion nut, and spacer, as well as the IS300 pinion seal but he doesn't sell that. There's probably something else I'm forgetting here but he'll hook you up.

I haven't ordered my gear kit yet simply because A) I'm heading out on a road trip in a week and B) I haven't quite decided on the gear ratio I want to run. That said, I THINK I'm leaning towards a 4.88 or 5.29 final drive.

"THAT'S CRAY HOLY CRAP YOU'LL BE CRUISING AT 8K RPMS" you might say. However, my car is an automatic. The difference in 6th gear between the automatic and manual in this car is huge: .582 on the auto, and .767 on the manual. Using a gear calculator app, (I used this one: http://pw1.netcom.com/~sgalaba/mph.htm) I figured out that with stock tire sizes and a final drive ratio of 5.29, I'll be running at 2500 rpm at 60 mph. I am more than willing to live with that. I even tried holding my car in 4th at freeway speeds just to see what the sound levels were like around those revs and didn't detect any audible difference. Granted, I've not done anything with my exhaust yet, so I may live to regret this decision, but I feel like for the money I'll be putting into this project, I may as well go big.

For the price breakdown, here's what I'm looking at:

• $400 for the IS300 carrier (they can be had for as low as ~$250 from a scrap yard/eBay, but this was basically brand new so I jumped on it). Again this is optional.
• $225 for the ring and pinion set
• ~$150 for the installation bits (this is just an estimate really; the full installation kit they sell is ~$300 but I don't need the expensive parts, which are the bearings)

So rounding up, that's around $800 in parts, about a $200 or more savings against the Cusco kit, BUT, that's with buying a whole other carrier.

If you're just swapping the parts into your own carrier, worst case scenario, you're looking at around $500 if you need the full installation kit, ~$400 if you only need the essential bits. That's a helluva deal compared to the Cusco kit.

For labor, I was quoted $400 for the ring and pinion install, and about $250 for swapping the carrier into my car. So the grand total for me is going to be around $1500. Again, this would be even cheaper if you don't buy a separate carrier.

Questions? Comments? Concerns? Please note that I have not actually done this yet; I plan to order my ring and pinion after I get back in a couple weeks and get the install done ASAP after that. I will update this thread with my progress, positive or negative, and any pertinent details I can glean from the shop as they do the install.

Edit, 8/26: Full list of installation parts (everything besides ring and pinion) can be had here: http://www.ft86club.com/forums/showp...5&postcount=45

You should post some of this info in the final drive thread. I've seen the Cusco 4.56 for under $900 here in the US. But I like your deal much better. Hmmmm maybe they gave automatics that ratio to keep them slower than manuals... hehe... just kidding...?? Thanks for the info.

Hahaha, my guess was fuel economy, but you're probably right.

I did mention Weir Performance in that thread. Spence sells the shims in his installation kit. I can throw down some more knowledge in that thread, but I'd feel more comfortable AFTER I do my install and verify I'm not full of crap. :D

Alright, I'm confused. Where did you get the 4.88 and 5.29 numbers from? Is that what the IS300's 3.7 and 3.9 equate to in our cars?

Level 1 Noob

Great legwork! I was >hours< away from ordering the Cusco kit! (I still might do it but this is great research).

Well looks like we've been thinking the same thing in part. I got in touch with Spence a couple of weeks ago and am ordering my 4.56 final drive kit from him today with a solid pinion spacer. All of it shipped for under $350. Granted I still have to get shims, pinion bearing, and pinion seal, but still way better than paying the ridiculous mark up on the Cusco rebranded parts.

very much subscribed

4.88 and 5.29 are final gear ratios that Weir Performance offers on their Supra ring and pinion kits; it'll make sense if you check out their site, they have a wide variety of final drive ratios available. The ratio is based on the number of teeth on the ring gear divided by the number of teeth on the pinion. So basically, they're just gears with the same dimensions as our ring and pinion but varying numbers of gear teeth.

Oh. Yeah, I completely miss understood you then. I thought these were IS300 gears. But I guess you were just talking about IS300 LSDs?

So what exactly would I need to buy to make a Supra 4.88 work in my car? Explain it to me like I'm retarded because, well...

No. He is swapping the ring and pinion gear so the 3.7 and 3.9 ratios that come from the factory on the IS300 didn't really matter to him. With his new ring and pinion he will have a 4.88 or 5.29.

Just curious, why didn't you buy the shims and pinion bearing from him as well? Markup? He also told me to replace the pinion nut, FWIW.

The IS300 part of this equation is actually unnecessary to get this done. Theoretically, you can just swap one of these ring and pinion kits into your FR-S/BRZ carrier and be done with it. Again, theoretically. I didn't want to give my car to a diff shop for a few days and have them take my carrier apart and realize something was missing or wouldn't fit. That's why I got the IS300 carrier, so that they could install the ring and pinion in that without taking my car apart, and then when that was done, swap the entire carrier into my car.

So, for the FI guys, would the IS300 carrier be a direct swap FD and all, so we can run the auto LSD and get down to a 3.9 FD without any other changes?

So...

- Ring
- Pinion
- Shim
- Carrier if you don't want down time

That's it? I don't care about down time, so could I just buy the 4.88 ring and pinion, find a matching shim, and go to town?