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

I just recently completed a final gear swap in my FR-S a couple days ago and have another thread going on that. What I want to do here is give the recipe I followed all in one place.

For reference, when I refer to a "carrier", I mean specifically the whole pumpkin assembly with the actual differential installed in it. Carrier, pumpkin, third member, same thing.

Note for turbo guys: If you're looking to swap to a taller gear ratio, just go get yourself a carrier from an IS300. You want either an M98 (3.9 final drive) or M85 (3.7) code. These are the LSD variants for the automatic and manual IS300, respectively. Both of these are a direct swap into our cars, the only trick is to pop out the axle stubs (the wheels on the sides) as our axles simply spline straight into the carrier. You still may consider overhauling the carrier/differential depending on the condition yours is in, but otherwise you can stop reading here.

OPTIONAL - Donor Carrier
What I did to minimize my downtime was to obtain one of the carriers mentioned in the note above, and had my gears installed in that. Added bonus of having a second working carrier in case something goes Horribly Wrong.

Optional Cost: ~$300 depending on condition

Meat and Potatoes - Ring and Pinion
Give Spence a call at weirperformance.com. Tell him that you want an 8" ring and pinion set for a mark 3 Supra and that you intend to use it in an IS300 or FR-S/BRZ carrier. Then just make up your mind what ratio you want. He also sells a shim kit that I highly recommend for $15. It has all the shims you could possibly need to get the install right.

Cost: $225 for ring and pinion, $15 for shims, plus shipping

Fiddly Bits - Seals and Nuts
For these I just visited a couple different Toyota parts distributor sites. Here's the breakdown of what I got for my installation:

• 90179-20018 Pinion nut
• 41231-24010 Pinion spacer
• 90311-43009 Side seals (x 2)
• 41222-22010 Ring gear lock tabs (x 5)
• 90311-38070 Pinion seal

Note: My carrier was basically brand new so I didn't need to replace any bearings. These tend to be rather expensive (pinion bearing I think was about ~$80, not sure on side bearings). If you think you need to do the bearings, you may as well buy Spence's installation kit. It should contain all of these parts plus the bearings. Not sure on the price there though, but it's on par with acquiring the parts individually.

Other note: If you're looking to make Balls-Out Torques, you may consider getting a solid spacer in lieu of the OEM pinion spacer. Also available from Weir, also part of the installation kit.

Cost: ~$100 without bearings, plus shipping

Putting it together - Labor Cost
4 hours for the ring and pinion install, 2-3 hours for carrier install. I'd recommend a dedicated differential shop for this just because they should be guaranteed to get the setup dead on. Labor costs vary widely, and you could easily save a couple hundred bucks by installing the carrier in your car yourself. I chose to let the Professionals handle it all.

Cost: ~$700 if the shop does everything, ~$400 if you install your own carrier, $0 if you're a Professional

Price Breakdowns

• Bare Minimum (just required parts, all installations done yourself): $350
• Bare Minimum + ring and pinion installed by shop: ~$750
• My Total (spare carrier, no bearings, all installation handled by shop): ~$1100
• Theoretical Max (all parts, all services done by shop): ~$1500

So there you have it! Let me know if you think I missed anything or need further clarification on something. Big thanks to @37, @Jeff Lange and anyone else I may have forgotten for helping me figure out what ratio I wanted and what installation parts to buy.

Excellent post, thank you!

I'm not sure what the pinion spacer is could you clarify that for me? .

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Picture the pinion as the gear on the end of the driveshaft that spins the ring gear. You don't want it pushing off the ring gear and sliding back up the driveshaft. A solid spacer to hold it in place makes that impossible. When I say driveshaft, I obviously mean the assembly in the carrier that the driveshaft connects to, but you get the idea.

I will be doing this eventually. Thanks for the post!

Amazing post! One question though. I live in the Tacoma/Seattle area too and was wondering where you found your carrier at? Local, or did you order online? Thanks!

If you're looking to buy local, do a search on car-part.com. There's always eBay if there's nothing around, but these suckers are HEAVY so shipping will probably be awful.

Ok, cool, I understand that. What's the OEM spacer made of if it isn't solid?

The OEM spacer is still made of steel, but it's meant to be "crushed down" when putting everything back together. Hence the alternative term, crush sleeve. A solid spacer is much more substantial and doesn't deform during reassembly.

Golden thread!

Part numbers are a great help, thanks again

Total noob question, but when searching on car-part does it matter if it is locking or non-locking? Are you able to slap the LSD from your diff into the carrier? If this is stupid sorry :iono:

The carrier itself is identical between the locking and non-locking versions, so theoretically yes, you could take your FR-S/BRZ differential out and have it swapped into an IS300 carrier. However that sort of defeats the purpose of getting the second carrier because you still have to take yours apart; you may as well just install the ring and pinion directly into your carrier. Also I didn't do that, so I'm not 100% on whether that will actually work.

Open differentials suck. You definitely want a LSD version if at all possible.

Great work, this will be very helpful to many (including myself haha)!

I will definitely be doing this as well. Thanks OP for all the info!!

Thanks for the post. Ill be doing this aftet my wheels

Thanks man I subbed to your original post and I am glad that you have done this. This is one of BEST na upgrades you can do. Do you felt like it was a 20 percent increase in torque? Also, could you post some pictures and a videos if you could? Thanks!

Another stupid question. If I have a manual transmission do I have to have a manual carrier?

Unfortunately I don't really have any pics/video of the installation because I had a shop do everything for me. Differential setup is kind of an art-form though, so if you've never done it before I would recommend having a shop do it for you. As for installing the carrier, that's covered in the service manual and looks to be pretty straightforward, I'm just lazy.

You don't actually gain anything in terms of HP or torque by doing this mod. What you do gain (if you go shorter) is more of your existing crank HP/torque being applied to your wheels. That said, with a 4.88 final drive on the 6AT, it definitely accelerates better. I haven't measured by how much though. It also takes about 500 miles to break in a new gear set so I haven't been able to really get on it and test.

Nope, and not a stupid question. The carriers are identical between the two, the only difference is the ring and pinion installed in them from the factory. Manual has a 3.7, automatic has a 3.9.

I may add onto this for people in other countries.

I'm in Australia and I just picked up my is300 diff. Its labeled as a M22 with a finned carrier (Australia only got auto is300's, firewall build plate says B04B). I opened the back cover and confirmed its a Torsen LSD

Thinking I got the wrong diff I checked out another is300 a few streets away. I did a quick peek underneath and it also had a finned carrier.

Everything else looks the same like the back cover and the top of the diff. ill compare measurements to my 86 when i can.

I've not heard of an M22 coded axle. Searching Amayama, the European-spec IS300 lists 41110-53140 as the part number for the carrier. Comes stock with a 3.5 something final gear. Googling that part number doesn't come up with much though.

This looks like a job for @Jeff Lange: Does this carrier work as well?

so would you say this setup is better/the same as the Cusco ring and pinion set?

It's exactly the same if you get the same final drive ratio, but much cheaper to go this route. Around $325 for parts versus $1000 or whatever the cusco costs these days.

Shameless plug: If anyone wants to buy a 3.9 ring and pinion or a spare carrier, let me know, I'm selling both. :D

Any regrets on the 4.88 ratio? I'm leaning toward 4.56 but 4.88 is a possibility since I have a AT like you.

I also have an AT but went 4.55, how big of a difference is the 4.88?

I'm thinking 4.88 for a manual. *flexes*

Still haven't gotten the opportunity to really thrash on it yet, about 100 more miles to go til we change the oil out. That said, I like it, it was definitely worth it to me. I haven't spun the tires on accident or anything so it's not ridiculous, but it has surprised me a couple times just putting around and getting up to speed faster than I expected. Now 5.71... THAT would be ridiculous.

Hahaha, with the automatic and 4.88, first tops out at like 23 mph. Manual would just be silly. At least I don't have to shift if I don't feel like it.

There's a chart around here somewhere...

I'm actually serious. Think I'm probably going to do it. Eventually.

And yes, first gear's going to be bananas.

I can confirm that the M22 diff thats in the australian/european is300s fit the 86/frs/brz with no issues

Just got the 4.55 gears installed as well. its a good improvement but may look into 4.7 or 4.88 in the future.

so thankyou PantsDants and Jeff Lange for your help on this.

how much u pay for install?

about 1k all up. I had the 4.55 diff gears already that i picked up very cheap from a GA70 supra diff.

Does it really cost that much to install the FD?

Anyone know the going rates in SoCal for FD install? (both gear install and removing&reinstalling of pumpkin).

Tranny Shop recommendations in the LA/OC area welcome :)

Worse comes to worse and if it really costs that much, I think I would just drop the pumpkin myself and just drive it to the tranny shop so they'd just do the install of the gears (but I like the convenience of them having do it all..only if the price is decent of course). I know the actual gear install would cost a bit and requires special tools/skill; but swapping just the pumpkin itself is pretty easy and should only take an hour (or 2 at the very most if you're taking your sweet time). I swapped a junkyard Infinity(iirc) LSD into my S13 before; and I remember it was easy and fast.

It only cost that much as i bought an is300 lsd carrier and paid a shop to setup the diff correctly. I would have saved $500 there abouts if i used my stock 86 LSD instead.

WOW! GREAT post! Saving this for future reference.

Ah, I see. Nice! $500 sounds totally reasonable and like a good price for install labor.

Aside from wheels/tires & coilovers, I think a short FD would be my very first modification. I don't think there's any other better engine/drivetrain mod for less than $1k that would yield such a big and noticeable difference/improvement over stock.

I would recommend it, its a good improvement. I gave the car to my friends to drive without telling them I did this mod and they all noticed the difference.

Thanks for the awesome thread. So much valuable stuff in here.

So, just to confirm.. if we can source the rear differential carrier of an IS300, we can basically swap it with our stock rear differential, yes?

Correct, the only thing to note is that the IS300 carrier will have axle stubs (half-shafts, wheel-looking things) that will need to be popped out. On the IS, the axles bolt onto these, but on the 86, our axles spline straight into the carrier.

...but JUST to make certain, you're talking about just swapping carriers right? Like drop pumpkin #1 from your car, install pumpkin #2 into car, done? If you're talking about swapping the actual differential out of the carrier, I can't say with 100% certainty that that will work. It SHOULD, considering the IS300 and 86 carriers both contain T2 Torsen differentials, I'm just not 100% on if they bolt up the same internally.

@PantsDants what was your reasoning for using he IS carrier? Was it solely to limit down time? It just seems to me if you were paying a shop to do it, why incur the extra cost of the carrier instead of just buying a ring and pinion for the FRS. The setup time for uninstalling and reinstalling wouldn't be more than an extra day or two. Or did you have another reason for doing so?