8” IFS Clamshell w/FRS Torsen

In my quest to build an AWD Taco, I wanted to upgrade the front drivetrain with a non-selectable traction option for several reasons. Everyone reading this is probably aware of the ADD diff’s needle bearing vibration issues, and research there shows that the open unit’s cast spider gears just aren’t a good fit at all; so I started looking for a Torsen unit. If you’ve found this post you might be searching for the unicorn, too. Many will say that it simply doesn’t exist; I’m going to try and prove them wrong.

In searching through many resources currently out on the interwebs, I found that the Land Cruiser’s front diff shares carrier bearings with older Supras and the newer FRS/BRZ/86 cars. The dimensions of those bearings are very similar to the 8” IFS Clamshell’s, and as luck would have it, the FRS cars come with a newer style torsen from the factory. Many google image searches later I felt pretty confident that the FRS torsen unit looked to be similar in dimensions to the 3.91+ carrier found in the AWD FJCs.

I asked @ZUK what he thought about test fitting the FRS torsen unit into an FJC clamshell and he said I might be onto something. I was able to find both an FJC 3.91 and an FRS torsen on eBay for $400 shipped, each, and placed my orders.

Today I disassembled both diffs and attempted to swap the ring gear from the FJC open unit to the FRS torsen unit. The ring gear fits quite nicely, except the bolt holes on the FRS torsen unit will need to be opened up a bit to fit the larger bolts from the FJC. Now I’m just waiting for @ZUK to agree to rebuild the front and regear the rear for me If he agrees, I’m sure there will be more than enough pictures to make up for my lack thereof.

Here are a couple money shots to hopefully makedo in the interim. The FRS torsen unit is on the left with the non-ADD intermediate shaft seated nicely inside.

 

Interesting...

 

Very cool. I've had thoughts of an AWD Taco float through my head a time or two but haven't moved on anything. Are you still on the stock Tacoma transfer case or have you swapped it?

What size are the bolts in the FRS diff vs the AWD FJC diff? Could you machine or have machined spacers to fill the gap in the FJC ring gear bolt holes to fit the FRS bolts? That might be easier/cheaper than drilling/tapping the FRS diff for larger bolts.

 

I'm still on the stock transfer case, but will be going with the electronic unit unit from a T4R/470 as it has the locking center separate from 4LO. I'm not sure what the exact sizes of the bolts are, but I can snap a pic later to show the difference. I'm no engineer, but I think drilling the carrier out will be easier and more secure than a spacer and the smaller bolts from the FRS unit. I actually think you could probably just run a tap through the bolt holes of the FRS unit and the bolts from the FJC would pass through.

Another reason I'm looking to go AWD is because of rear driveshaft vibration woes. I think a T4R/FJC front AWD shaft will likely fit our trucks with the AWD transfer case and a custom length, two-piece, double-cardan rear shaft will seal the deal.

 

Cool. My thoughts were to use the manual trans FJC AWD case which is manually shifted. I haven't come across any information though as to what that case's input shaft diameter or spline count is. I know the auto trans FJC transfer case bolts right up to the R155F that is used in the 4x4 2.7L trucks.

 

I am not sure I follow what you are doing with the two diffs in your picture. Are you trying to mount the ring gear on the right diff onto the left diff? it's difficult to be sure from your picture, but the ring gears look to be opposite rotation. Is that an issue, or is that what you are trying to accomplish?
Interesting idea you have going here. Good luck with your project!

 

Yes the ring gear from the right diff does fit on the left diff, aside from the bolt holes being too small for the bolts to secure the ring gear. The diff on the left is a rear diff from a Scion FRS, the diff on the right is a front diff from an FJ Cruiser and yes the rotation is reverse because of this.

 

This is awesome! So the question is, will the FJ bearing fit, right? Have you pulled the bearings and taken measurement?

 

So another option I just verified is using the reverse cut gears from a Land Cruiser 100 series, since it uses the same ring gear bolts as the FRS. I will likely go with this option instead of drilling out the carrier's bolt holes to fit the larger FJC bolts.

 

Which bearing are you talking about? From setting the FRS carrier bearings inside the clamshell, they are definitely the same OD, but I already knew that from here.

 

Is there a place for the CV circlip to lock into place on the other end?

 

I have so many questions. Front is reverse rotation, does this work in reverse rotation?

Edit:
I'm reading torsen works in both directions, that's promising.

 

The FRS uses CV axles in the rear, so yes our front CV axles will also work.

The torsen unit is a type 2.

 

OMG, this is almost perfect

 

Me being lazy, does the 100 series come 4.10?

Edit:
I'm reading 03+ got a 5 speed with 4.10:1 gears

 

And you said you've placed this in the FJ diff and it closes up without binding or hitting anything? It fits?

 

Awd taco is fun. That’s what my truck is. You will need the T4r front shaft. The Tacoma one is not long enough because of the center diff

 

I have not completed the swap and closed everything up yet, but everything appears to line up as necessary. The key pieces being:
1. The carriers having the same dimensions, which you can see from the picture they do.
2. The carrier bearings fit into the clamshell; which isn't pictured, but I assure you they do and can be verified from documented bearing dimensions.
3. The axle shafts fit into the carrier, which you can also see in the pictures above.

I'm going to pack up the diff and send it off to be rebuilt, and once it is there will be plenty more pictures to confirm all of this. I'm feeling 99.5% confident at this point.

 

Thanks for contributing to my hopes of completing the project! From your build page it looks like you are using an ADD diff instead of the AWD diff. Is that true?

 

That's great man, I wish you luck and am seriously considering this myself. I have an aussie locker but rather have this. I'm trying to find a 4.10 gear that will work for my truck. This is exciting.