Mesican

I am currently trying to build my dif correctly. I'm waiting on my MKIV auto TRD LSD to come in and figured now would be the time to switch up my gears if I can come up with the right solution. I have a 92 sc300 5spd w/ the stock 4.08 gears in it. I was looking into it and noticed the 98-00 USDM Lexus GS300 (auto) has a 3.916:1 setup. small diff and small flange. Has anyone gone with this set or what did you go with? The ring and pinion gear should be direct swap, correct? I'm not sure if I want to keep the 4.08's in there as i'm going single hopefully by spring time. Has anyone ran into any issues w/ this? I've seen where someone recommends boiling the ring gear enough to get it to go on the dif w/ very little effort but there's so many threads on dif's I can't seem to find one similar. (Or maybe i'm dumb and can't search like a pro.) Thanks in advance.

Mesican

I am also considering the MKIV AUTO TT ring/pinion gears @ 3.769:1. I can't find the size of the ring right now but i'm also assuming these will work for my sc300. (I'm searching in between breaks at work at the moment.)

KahnBB6

iTrader: (5)

The 92-97 SC400 rear differentials also use a 3.916:1 ring and pinion. It's the same thing (small 200mm diff). That may be easier for you to source. Take it to a shop with your TRD LSD to have everything installed and rebuilt unless you have experience setting up differential shim tolerances and don't mind waiting for Toyota to order you the shim types you need as per your measurements.

Mesican -- The MKIV TT Auto r&p gears will work in any 92-00 SC, 01-06(?) SC430, and 92-05(?) GS. It's the same size differential casing and internals. Just the rear companion flange is different from the MKIV, GS and SC (you swap over an SC companion flange to your donor differential pumpkin). Also, the MKIV NA and TT Auto rear pumpkin is the same other than that there are cooling fins on the MKIV version. It is the MKIV TT 6-speed rear pumpkin that is incompatible due to it being a larger 220mm design (using the 220mm 6-speed diff requires an entire rear subframe swap).

Mesican

Thanks, Kahn! After further looking, I'm going to give Blumenthals out of OKC a call and see what the availability is for the sc400 ring and pinion. I will look into having someone else do it as I do not have the proper equipment. It's been a very long time since i've done anything with difs. I listened to the instructor half *** 10 years ago when he was talking about differentials. (That teaches me a lesson, right?) I'm going to give Royal Purple 75w-140 a shot as it seems a lot of guys on supraforums are loving it. Thanks again, Kahn!

KahnBB6

iTrader: (5)

^^ Good deal Mesican and you're welcome!

Diffs aren't the easiest to do and getting a shop that deals with them regularly is recommended. Lesson? Eh... I can't remember every fine detail of what was covered in my auto tech courses either (and I wasn't going for a future ASE cert).

Royal Purple is great but it's pricey and despite it working like butter for a while I understand it tends to break down after so many miles (sorry, no figures of the top of my head). Unless I'm mistaken it's a short-duration oil intended for racing applications where normal street use mileage doesn't apply. I believe the differential oil change interval is every 15k miles. I use Redline Shockproof in my TT Auto diff but I am using a Torsen gear-type LSD whereas you will be using a clutch-type LSD. If it's overwhelmingly recommended by SF guys using TRD LSDs then defer to them but I haven't heard that Royal Purple is the best diff oil out there.

I'd also take into account what type of oil (including any friction modifier additives in the formula) TRD themselves recommend for their LSD. Sorry I have no experience with those to offer more concrete advice but some members here have used TRD diffs and might have better advice on oils.

Mesican

I'm not sure about royal purple being the best but most that are recommending it are loving it. They also recommended mobil 1. They said to stay away from castrol and some other brand. The Royal Purple has a friction modifier as does redline. They also recommended redline shockproof or something along the same line. After further investigating what gear set I was trying to get, a couple locations I can get ring and pinions from are telling me i'm S.O.L. Must find this pretty soon. I haven't taken my dif down but I'm assuming and hoping that if all else fails, the ring and pinion are still okay in my dif. And maybe the spider gears are missing a couple teeth.

KahnBB6

iTrader: (5)

What reason do you have to believe that your 4.08 ring and pinion are damaged?

Yes, Mobil1 synthetic gear oil is also very good. I used that in my stock diff and it's also fine to use with the Torsen. I just heard better things about Redline Shockproof. Royal Purple is a very, very good oil. It's just pricey and I have heard the useful lifespan is shorter than that of Mobil1 or Redline. Castrol I wouldn't bother with, sure. Similarly, Redline MT-90 is a highly recommended oil (actually the ONLY recommended oil) for your W58 or any R154 transmission. This being the non-friction-modifier type MT-90.

Don't give up searching for an SC400 differential. They are out there. Have you tried posting a WTB ad in the Clublexus classifieds and your local Craigslist? The 3.916:1 is a common SC ratio and shouldn't be impossible to find. If you were sticking with your twin turbos I'd say keep the 4.08 and install the TRD LSD into that but for a single I agree you'll need the lower ratio.

Alternatively you could see if anyone on Supraforums is selling a 3.769:1 TT Auto open-diff pumpkin. Not sure what those price at but in case you'd have a chance at sourcing one of those faster it's another option to try. Just remember that your SC companion flange (or any SC companion flange) has to be swapped over. And there is a procedure for that too using a dial-torque wrench.

gerrb

iTrader: (34)

OP, KahnBB6 said it right... an SC400 diff ring/pinion will be your best instead of the MKIV AUTO TT ring/pinion if you want to lower your gears. The latter are hard to find and they are sold for an arm and a leg now.

PM me , I have 3 SC400 diff but I am not shipping the whole diff ..lol.. I hate shipping big and heavy stuff. Too much hassle.

KahnBB6

iTrader: (5)

The irony: I have a 3.77 ring and pinion set aside for my swap but the swap isn't ready yet.

gerrb, I never noticed the sheer number of built JZ cars you have. Holy moley that's an impressive list!

I also agree about not mailing an entire diff. They're about 90lbs fully assembled. You'd have to tear into it though :/

gerrb

iTrader: (34)

Thanks KahnBB6 . Well , as they used to say , it is a desease. You are never satisfied . My local forum member friends who go to my place every now and then just shake their heads when they see my 2jzgte cars...... got that serious 2jzgte bug I guess for now . But it will pass am sure just like my obsession in other vehicles before. One day , I will just have maybe one 2jzgte car or not even one maybe .

Hold on to that 3.76 ring & pinion. They are getting harder to find. Well if you find them, they are pricey. And true , not worth paying for shipping for a full SC400 diff. I don't mind taking the ring & pinion for the OP. It is easier to pack and ship. I will just toss the pumpkin to the trash after.

Mesican

Kahn, I am hoping that my spider gears are what took a crap. I'd imagine so from the symptoms. Drive straight, no clunk, turn left or right and it feels like the axle and wheel just broke off. I couldn't figure out what it was. Tranny mount, busted axle, or dif were my guesses. Got to the point where I was pissed off enough to put it through some hell. Dumped it around 6k and it held together for the next 100 yards. Came to a stop to get back on the highway and turned right. It literally felt like my rim snapped off. I pulled over and checked it out. Nothing. Got back on the highway and it was good to go all the way home w/ no crazy clunking. LOL.. So i said F it. LSD time. After more thinking about it, I figured 4.08's might not be good for a built single setup. I don't want this car to be a 1/4mile car honestly. After all this is over with I will know that my only weak links in the rear now are my axles and struts for now. Coil overs and AEM next. I need to look into the shockproof dif oil now that you mention it. I am running mt90 in my w58 and will run it with my r154 setup.

Mesican

Got the diff out last night. It was pretty simple actually. Removed the cover and the spider gears are destroyed! I'm going to degrease everything and power wash it here in an hour or so. While i'm at it, i'm going to put my new BV solid dif/subframe bushings in. One bushing on the dif was in pretty bad shape for a 104k mile car. I still don't know when my TRD dif will be in. :/

KahnBB6

iTrader: (5)

gerrb -- I'd hold onto at least one of those cars since you like them so much. They'll be considered pricey classics before long once parts are harder to find in 10-12 years. Yeah, I will keep the 3.77 R&P. They were removed from my TT Auto LSD rear to have a 4.27 set installed (no turbo) but the idea was always to rebuild the diff a second time once the engine is swapped or converted. The 3.92 ratio has also intrigued me though because I'll be on a stock USDM twin setup and probably won't do more than 15-16psi when all said and done. Such demanding goals, lol. I have been impressed with the big difference between the 4.08 and 4.27 in all driving situations given the NA output. I've wondered if the 3.77 vs 3.92 would be a similar comparison with turbos or if it's far better to just use the lower ratio.

Mesican -- That's not good Yes, it's time to rebuild. It seems the car has forced your hand now. Do the 4.08 ring and pinion still look good? If you're lucky it's just the open differential that is blown and the rest of that diff is still good. Definitely now is the time to locate a 3.92 ratio set for the rebuild or entire SC400 diff to swap in. TRD parts being on delay doesn't surprise me. The guys at Carson Toyota have been having some trouble getting responses back from TRD Japan in the last couple of months for parts they have on order from customers. I think everything is just delayed a bit with them at the moment.

wanganstyl

iTrader: (5)

Here are some photos I took when setting up the unit for my swap. The toyota factory service manual has the proper procedure for heating up the ring gear to fit - Follow the factory instructions or hire a professional shop to do it for you

sc400 unit (3,91) + TRD LSD

KahnBB6

iTrader: (5)

OP, I hope this isn't too off-topic but since you're installing one of these soon I figured it would be okay.

Wanganstyl, I've got a couple of quick questions for you: How many miles have you put on your TRD LSD? Also, do you anticipate having to tear it down and service the clutch packs at some point? I've always been curious about the service life on the TRD units. Thanks!