3UZFE V8 Swapped FRS Part 5: Super Cheap Locking Torsen 3.73 Manual IS250 Differential?!

Added: 2026-05-16

[00:00:00]the ultimate diff. We're having way too much fun in here. That's how you do a torsion dip. It revs to 7,800 RPM.

[00:00:08]>> So, when driving on the highway, the F FRS3UZ system revs out pretty high 3s.

[00:00:15]When you're going about, you know, 60 70 mph, you really don't want to do 80. It gets it gets up there in the rev. So, we solved that problem. We have three differentials that we know fit. Here's what we found from all of our research and what we recommend to do with this is accordingly. The ultimate diff that you can find that just works, plugs and plays, and it's going to be your best bet is this IS-300 manual transmission torsion differential. The 3.73 diff out of a manual IS-300 locking differential vehicle. Very rare. We only found two in America. This one was extremely expensive. We don't even want to share how much we paid for this. it was that expensive. With that said, the little known secret that nobody really talks about, the speed secret we're going to give away today is the IS-250 manual transmission open differential is a 3.73. The reason that these are so cheap is because they're open and nobody uses them. Today, we're going to show you guys how to take the F FRS diff that has a torsion inside, a torsion actual differential center section. We're going to take that out of the FRS dip. We're going to put that inside the IS-250 open diff and make this a locking differential that works inside of that vehicle. All three of these differentials have the same rear casing bolt pattern. They have similar front ears. The bolt pattern is technically the same. The bushings and stuff are a little bit different and the bolt diameter is a little bit different. We can work with all this and get this going. The front flanges are the same.

[00:01:47]The distance from the front flange to the rear diff is the same. The difference between the IS-300 versus the IS-250 and the F FRS is this comes with stub shafts. All of that's not important because we can pop these stubs out and use the F FRS axle. What I will say today is after 3 or 4 months of properly testing this, if you know what I mean, this car has not broken a differential.

[00:02:10]It has not broken a transmission. The transmission might be on its last limb, but it's still intact and it hasn't broken. We haven't broke any parts of the drivetrain. Everything is still good to go. Everybody was kind of really h like skeptical of whether or not this thing was going to hold up over time, but pretty pumped. This this is awesome.

[00:02:28]This is a good setup. Anyway, the the speed circuit for today is IS-250 open diff with the F FRS insides is going to be what we're going to tell you guys to kind of do if you're on a budget and you want to take your existing F FRS diff and get a better ratio on it while still having a a locking center section.

[00:02:47]Little tools list. If you want to come over here, we got we got the pry bar to get the axle/ stubs out. You're definitely going to need this and a lot of force. Most of the fasteners in the back for the lower suspension, 17 mil.

[00:03:00]You're going to need a socket and a wrench for that. The drive shaft uh fasteners are 14 mil front and back.

[00:03:07]You're going to want to use a small extension with a 14 mil um to to if you wanted to use an impact to kind of make it a little bit easier on yourself to knock those out pretty quick. The last one of the last things that's kind of obscure is a 10 mil uh Allen to fill it up once you kind of get the new diff back in. Exhaust off. I'm going to take it all off in one technically one piece from here back.

[00:03:38]This is draining. We're going to go and pop these off. You want to get the pry bar. It's a long pry bar like 36 in. You want to hold the side of the pry bar right here and pop it right here. You don't want to really use the dust cover.

[00:03:50]You don't want to use this dust cover right here as a a part to pry on. You want to pry on the actual machined part of the boot. And it's a lot of force.

[00:03:59]When I say a lot of force, I mean a decent amount of force. And now that it's kind of off, it should pop out with just a tiny bit of There it is. Once you feel that kind of pop with that pin coming out of the uh the splines, it really just comes out pretty easy. Now that it's kind of loose, we need to knock off this 17 right here. This 17 right here. The whole upright is going to kind of come out. That should allow the axle to pop all the way out. Yep.

[00:04:32]Loosen these up and then we're going to go ahead and hit them with the impact.

[00:04:48]close forged uh 17. It's got a 17 hex on the back and an impact grade 17 on the front. If you look right here, these things are cool.

[00:05:00]Like a normal ratcheting wrench wouldn't really fit. Um my ratchet probably would fit on there with this. So, I was able to get that very, very easily. Look at that. He's kind of done.

[00:05:12]Boom. Look at that.

[00:05:18]We got it off.

[00:05:25]All right, guys. We're here with Eric Sunost, automotive specialist, Lexus mechanic of like 15, 20 years. We're taking apart. We're showing you guys what differentials work on the F FRS.

[00:05:36]Basically, make the gearing and the RPM a little bit more agreeable to highway speeds, 70 mph and plus. What we found from all of our research is the 3.73 or the 3.9 are going to be the most ideal differentials. You want to stay away from this 410. This is an OEM differential out of the F FRS. This is the 410 right here from the F FRS. And this is a IS-250 uh 373.

[00:06:05]So the purpose of this video, what we're going to show you guys is essentially how to take the guts, the torsion portion of this, the iners of this differential, and we're going to try to put it into the IS-250 diff. So, it's not that easy, but it's also not that hard. And that's why we're here. We're going to go ahead and show you the right way to do this.

[00:06:22]>> I mean, I give a pro tip. If you want to change gear ratios in your F FRS, don't buy gears and attempt to put them in your S FRS diff because there's way more setup. You have to set pinion depth.

[00:06:34]There's all kinds of crap you have to set up. Buy the 250 diff, take the center out. If you're not messing with the pinion depth, you just swap the gear over from your 250 diff, from your 250 open diff, the torsson housing from your F FRS to the IS-250 diff, because swapping pinions is a is a pain in the butt. And most people don't have the equipment or the patience to do it. You have to have a dial indicator, hydraulic press. You can only use a crush sleeve once. So once you torque it down, it's done. So you have to assemble it multiple times without a crush sleeve in there to get the D. It's a huge undertaking. Just swap the torsion. Take the ring gear off your IS-250 open diff, put it on the Torsson diff, drop it in, set your backlash, and your your bearing preload, and you're good.

[00:07:17]>> So with that said, we got new bearings, new races, new seals. uh took about a week to get from Lexus. Not a big deal, but this is you need this and the ring gear fasteners. Those are a one time use fastener, but it's an immense amount of torque that goes into those. So, with all that said, we're going to jump right into it. We're going to flip this back over so all the oil kind of settles in this top part and show you guys how to rip this thing apart. Pro tip, flip the diff upside down if it's not fully drained upside down on a bench. All your fluid will sink will settle down because there's always leftover fluid. Even if you take drain plug out, it'll all settle down here. She pop the cover off without making a sloppy mess.

[00:08:02]Couple hits.

[00:08:06]This is the left side, driver side, USDM right side cuz this is upside down. And we're going to go ahead and take this L right here and flip it upside down like that.

[00:08:27]You can't you can't really see this on YouTube, but it stinks so bad.

[00:08:33]>> She's out, baby.

[00:08:37]>> Load on the side.

[00:08:38]>> Sets your bearing preload and sets your uh backlash, your gear backline, >> and they just come out that way. When you do this, you basically pray that the old ones will work properly with the new gears, cuz if they don't, you have to order them. And there's about a hundred different sizes. Oh, that was easy. Wow.

[00:09:02]>> Oh, wow. Okay, it's out, guys. Chat, look at that. 200,000 mi inner dip.

[00:09:27]Oh yeah, that's working.

[00:09:29]Oh, that's definitely working.

[00:09:32]You don't want to hit it directly.

[00:09:34]There's a tiny little edge on the uh side of it. Oh, yeah. It's coming right off.

[00:09:39]So, most people don't realize that gears, ring gears, pinion gears, diff gears aren't actually fully hardened. They can't harden the whole gear because they'll become brittle, break easy. This is a 410. Uh, we're not going to use this for YouTube. I'd like to just, you know, drop it in the garbage. We're here. This is the Torsion inards out of a F FRS. And this thing still worked great. I was able to clutch kick and break both tires free even after 200,000 miles. This is the IS-250 dip. We're going to go ahead and start taking some apart now and flip it over. Pro tip, flip it over so it doesn't leak everywhere. Uh, I'm going to put that back in.

[00:10:27]Y32.

[00:10:29]I don't know the answer to that question, but that's what it is. That's the 373. That's how you can tell it's a lower gear ratio. If I were to go back and do it again, I'd probably do a 39. A 39 in this thing was super sick.

[00:10:49]Oh yeah, that's working.

[00:10:52]We just got that off. Now we got to take this and either weld it or throw it in the garbage. We got this dressed. It's clean somewhat. And we got to pull these gears off right here. And basically, we got new um bearings and whatnot.

[00:11:06]And we're going to go ahead and put new seals and everything. So, we're going to pop these seals off.

[00:11:10]>> If you're doing your bearings, which you should do them before you bolt the ring gear on, cuz you don't want to hit this in the press or chip it, don't chip any teeth.

[00:11:26]Actually work great.

[00:11:33]I will say for the record, buy OEM bearings.

[00:11:37]>> Buy OEM bearings for sure.

[00:11:38]>> There's cheaper options, but the OEM are so precisely machined that you most likely will not need to change the shims. The shims will drop right in and it'll also everything will work.

[00:11:47]>> Seal part number. This is the seal part number here. This is a pro tip. If you don't have a, you know, >> basically to make a to make a sleeve a shim, just press the new bearing in.

[00:11:59]Just cut the cage off the old bearing with some good side cutters. And there's your shim.

[00:12:05]>> You press it right on. Boom. Let's go.

[00:12:08]>> Straight.

[00:12:08]>> And you make sure you're wearing eye protection, PPE.

[00:12:15]Only reading about one ton of pressure.

[00:12:18]That should be enough.

[00:12:20]>> There it is, guys.

[00:12:24]And you guys got right in. Yeah, we got right in.

[00:12:29]>> Can't drop the ring you're on because you can only guess where the holes are going to be. And if you drop it on, it sticks. You can't move it.

[00:12:35]>> So, you got to do this.

[00:12:36]>> Are you saying it's an obscure bolt pattern? It's not all >> No, it's just they're super super accurate. There's There's no give in these holes.

[00:12:45]>> Dead nut.

[00:12:47]>> Yeah.

[00:12:49]And really, you're supposed to put the ring gear. Do they want you to put the ring gear in boiling water?

[00:12:53]>> We can do that >> to expand it.

[00:12:55]>> You want to do that?

[00:12:56]>> It's if you have to put a ton of pressure on them, it's a bad idea, but these usually slide right on.

[00:13:09]All right. 72.

[00:13:17]Start.

[00:13:23]Definitely want to do this slowly.

[00:13:26]We'll just start cranking down. Let the gear pull on.

[00:13:41]So, what we're doing is we're measuring this because we didn't touch the the pinion bearings. We just want to measure this for documentation what we're starting with. So, we're starting with basically 1 inchb of rotational resistance and bearing preload.

[00:13:55]So, then we're going to drop the the actual diff in.

[00:14:02]Once we put the diff in, we'll measure the bearing preload again because that's going to give us our total preload at the pinion. Um, which on the 220s, we generally add 12 basically 12 inchbs once the diff is in.

[00:14:16]So, we should see about 13 inchbs of rotational resistance at the pinion once this is all assembled.

[00:14:24]But be very careful with this cuz as I said before, if you if you chip the chip the teeth, your ring gear is basically useless.

[00:14:34]>> It'll grind itself into oblivion.

[00:14:37]>> Did you put the shims in or that's what we're doing right now?

[00:14:41]>> All right. Dial indicator.

[00:14:47]>> I have a set of brass strips that come really handy for this. Yeah.

[00:14:51]>> 63 >> 63 foot-lb.

[00:14:55]>> And this is where it gets tedious because we may have to take it all back apart again once we measure everything because we use the shims that came out of it. Hopefully not.

[00:15:07]Okay. So, it's actually really good.

[00:15:10]It's about 11. That's That's really really good. With new bearings, you want about 17 inchbs of preload. with used bearings, especially with these, God knows what the miles is, old IS-250 diff, they're so broken in, you're not going to get any preload. Like, if you were to change the front seal, you might put a little bit of bearing preload on them, but you're you're going to measure almost nothing. So, this one measured 1 inchb.

[00:15:35]Now, the the the the total assembly when you turn the pinion with the diff bolted in, you want to add 11 to 13 inchbs to your total rotating resistance. So, right now, we're getting 11. So, I mean, we we added another 10 to it. So, I'm perfectly happy with that. To try and we can spend another 3 hours changing shims to get two inch pounds of preload. It's not worth it. So now we need to check the backlash cuz backlash feels good.

[00:16:05]Back backlash should be 2 to 5 lb. With new bearings, you want 17 inchbs of bearing preload. So you want to torque everything down to where the bearing has 17 inchbs of resistance going this way.

[00:16:17]Either way really new bearings, you're going to have almost nothing. But we took our measurement before it was 1,000 of preload. So now we need to add um 10 to 13,000 of preload for the whole assembly including the diff with the diff bolt in. Now rotating it. It's right at 11,000.

[00:16:43]It's right 11 about about 11,000.

[00:16:46]>> And then we're going to measure the soy Toyota wants 2 to 5,000 of bearing backlash of gear backlash which is almost nothing.

[00:16:57]And you can see that this has got the optimal amount of backlash right here.

[00:17:01]>> Literally 5,000 >> 2 and a2 thousand. Yeah, >> actually it's about three.

[00:17:07]>> Two and a half, maybe three. That's perfect.

[00:17:09]>> So this is dialed in literally.

[00:17:12]>> That's what happens when you use factory bearings and put the shims back where they belong.

[00:17:17]>> So you start at zero.

[00:17:19]>> Unless you're going with a Cass or an aftermarket diff, you're going to be really close and put everything back.

[00:17:23]You hold the front pinion bearing and you just try to rock this thing back and forth to see how much lash there is. And that is that's exactly what you want. That's it, guys. Going Toyota to Toyota, you keep the shims you took out. Toyota stuff is machined so precise, it's most likely going to be within spec when you put it back together with everything right where it came out and used factory uh bearings. It's It's going to be good.

[00:17:48]All right, that's all you need. Not more, not giant globs. It's a quarter inch bead and it's still going to blow out the sides everywhere.

[00:17:57]>> And Fippage is different colors for different things. This is a lot thicker of an oil. They use the orange specifically for this.

[00:18:04]>> Yes.

[00:18:04]>> Uh as opposed to the black. The black is what you would seal up a motor.

[00:18:17]>> There it is.

[00:18:20]>> You don't need much. Fortunately, I say as soon as I torque this down, it's going to glob out everywhere. Anyways, >> 14.

[00:18:25]>> It's perfectly machined surface. So, there's there's no space in there for a lot of silicone. If you put more, it's going to end up getting trapped in your it's going to end up in your diff, getting trapped in some of the oil passages, getting trapped in your pinion bearings.

[00:18:45]Don't be that guy. Don't be a silicone monster.

[00:18:50]It's going in real easy.

[00:18:53]So, another video in the works.

[00:19:01]That's how you do a torsion diff in a IS-250. You have an IS-250, you want a torsion diff, grab an F FRS. Watch this video. Boom.

[00:19:11]And these are IS-300 stubs. You can use these. Look at that. Look at how cool that is.

[00:19:22]Boom.

[00:19:25]Took those to 56 footbs. Once we're done with that with that, these go to 70 footbs right up here. These front ears, 70 foot-lb, 56 in the back. And I usually just do German tight on these right here.

[00:20:05]Two.

[00:20:10]Uh, getting these in without damaging the boot is tough. I got a a dead blow. And then I got this big ass set of channel locks. I grip onto this little There's like this little like recessed machined area right here. I grip onto it as hard as I can.

[00:20:26]Pro tip.

[00:20:33]>> Yep.

[00:20:45]All right, guys. Uh, Eric basically knocked out this IS-250 diff. It's a manual IS-250 diff, 373 uh, gearing, and we just put that F FRS torsion inside on it. This is the equivalent of an IS-300 manual torsion differential, which is extremely rare and super expensive. I saw one on car dash part go for $2,500.

[00:21:10]And to be honest, that's not a bad price for something so rare that you will almost never see in the wild. So, we basically made the same thing for at least 1/4 the price. All OEM parts. Uh you look at the price tag for the parts just for the bearings and seals. $198.

[00:21:30]It's got new bearings. The lash, we checked the lash has a little under 3,000 of lash and uh what the rolling resistance is like 11,000 >> 11,000 >> or 11 inch pounds or whatever. It's it's crazy. This is this is like the best way to do a manual 373 diff for the 3UZ FRS.

[00:21:53]I feel like this is the proper diff.

[00:21:55]It's either this or the 39. The 39 is probably the next best thing. I will well I will say when you're done especially on a tourin you don't need fancy oil you don't need red line or Lucas or whoever you want to use a lot of their additives will actually start to separate under hard use and especially with the torsson the gear shearing will actually cause the the additives to separate and you'll get a white funky buildup in your oil passages >> it's almost like a grease it's almost like like a lithium grease um and it's not good for the diff mobile mobile gear oil is all I use in every diff I build. Um 7590 GL5 for a factory tours in anything else I'm doing a clutch type I might use 75140 because they do get hotter and you do get more it does quiet them down but mobile one is all I use in diffs and it works fantastic you don't need the overly priced fancy crap you just don't need it.

[00:22:49]>> This is it guys. Um I feel like this video was a win. We went ahead and installed that IS-300 torsion diff in the car. We've been driving it for about 200 miles at this point. It's awesome, man. I'm I'm 2,800 RPM at 70 m an hour.

[00:23:03]I did not have to do anything on the link ECU or any part of the car. The ABS system kind of picked up the recctor from the front wheels or whatever. It just went ahead and automatically fixed the speedo. So, that that car is a proper daily driver now. You can drive on the highway. You can drive anywhere.

[00:23:21]It still burns out in first gear without touching the brakes or clutch kicking.

[00:23:25]It's It's awesome. It is a good set of headers away from being a finished car in my opinion. Stay tuned for the next video. We got a lot of stuff, a lot of new stuff coming up. AC lines, other stuff like that. Just go ahead and uh hit the like, subscribe. Big thanks to Eric Sunost Auto Specialist. And big thanks to you guys. Keep those comments coming in. What do you guys want to see next? You guys want to see boost? You guys want to see flat plane crank? What do you guys want to see? Let me know in the comments. flat plane crank UZ.

[00:23:55]>> That would be rad.