DubsackDev

Hey all,

I recently bought an OS Giken 1.5 way LSD and have finally found a shop that can install it into my stock pumpkin but I have a few other questions so I can be prepared. Other than the LSD I also have the SuperPro rear diff mount kit and the SuperPro rear diff pinion mount bushing kit.

https://www.maperformance.com/products/superpro-rear-differential-pinion-mount-lower-bushing-kit-1993-1998-toyota-supra-spf4888k?gclid=Cj0KCQjwmouZBhDSARIsALYcouqvD7cJBwqGoe_o9IfZBl_BtHPDQWfQQEvnTGdGZ303pzClycUL-KQaAmtiEALw_wcB

https://www.enjukuracing.com/products/superpro-rear-differential-mount-bushing-kit-toyota-soarer-toyota-supra-lexus-sc300.html?gclid=Cj0KCQjwmouZBhDSARIsALYcoupRsosRfMKro1n2CoPFwZCfS2GOhbXqWpyrK_xXxiQisW3ba6KsLY0aAgnPEALw_wcB


1. Are there any other parts that I ABSOLUTELY need to install this? Obviously I will need shims as well but will have to wait to hear from the builder on what sizes to get. I also read on another forum that I would need the Driftmotion SC300 differential rebuild kit? Is that accurate?

https://www.driftmotion.com/MK4-SC-Differential-Rebuild-Kit-p/dm3265.htm

2. Are there any other parts that are RECOMMENDED to replace/upgrade when changing out the differential? Anything else you would recommend?

3. Can I use my stock ring gear (4.08 I believe) on the OS Giken differential?

4. I believe the 1994 manual SC300 came with a 4.08 open differential. I only have stock power currently and will probably be at least 1-3 years before I go turbo. Would it be recommended to just use the 4.08 ring gear if possible for now or recommended to go with a different gear ratio?

Thanks in adavnce!

Cheers!

KahnBB6

iTrader: (5)

Excellent purchase! This is pretty much the best LSD you can buy for these cars. Great for street and road racing applications especially.


I don't have a personal opinion on these. I stayed with OEM rubber diff bushings when I set my rebuilt diff up as they were still in very good condition in my case.

Yes, there are. The aforementioned Driftmotion SC300/400/MKIV differential rebuild kit contains all OEM Toyota parts (bearings, seals, etc.) that should be replaced if you're getting a driveline shop to pull out your original open differential and install a new aftermarket LSD.

Also your driveline shop will be ordering from Toyota, after measuring carefully upon installation, what different thickness side carrier shims will be needed. This is essential especially for a new diff install since getting the side carrier shim alignment right and within factory tolerance is key to a healthy diff install that has good pinion gear and ring gear mesh pattern engagement as well as good straight alignment of the diff inside the housing. You never avoid checking this and ordering the right additional shims as needed as not doing so can risk premature differential and gear tooth wear leading to a failure. Doing it right avoids this entirely for the extremely long service lives that SC/MKIV/GS/Aristo/Soarer diffs are known for.

Aside, your OS Giken diff, while being a clutch pack unit, seems to also have a ridiculously long service life once properly installed. I spoke at length with an OS Giken USA representative going over many questions about this very model 1.5-way LSD for my SC (I haven't bought one yet) and other than the regular OS Giken diff fluid change intervals I was informed that the rebuild intervals (with their OS250R fluid) are "almost never" in his words. I pressed further asking if this might best apply to the usual use of these diffs in weekend fun cars and track cars which see fewer mils than your average everyday car and I was told that even under everyday use I would not have to be concerned about this.

Also, I was informed that OS Giken LSDs do not require break-in miles and procedures as some other LSDs do. Call them and verify this yourself but that is what their representative said to me and confirmed again when I pressed him on it.

Just to clean your diff with Simple Green concentrate spray and a plastic scrubbing brush, spray on POR-15 de-rusting solution to get rid of old surface rust in the iron, mask up ALL the areas that have nuts, moving parts, drain plugs, rear output flange and the diff cover and paint it with POR-15 flat or semi-gloss paint. And use 7mil nitrile gloves and a dual-filter respirator mask when doing this!!! POR-15 is a toxic paint to breathe when it emits fumes.

Also use a little cellophane/plastic wrap between the lid and can in order to prevent the paint from hardening the lid and can lip together so as to be impossible to separate again. Keep the lid on as much as you can so as to preserve your reserve POR-15 paint from setting up and drying in the can. Pour a little into a paint tray and work from that with your paintbrush before refilling it regularly as you cover more of the diff. Your paintbrush will be ruined once this process is over with and it dries-- one time use paintbrush.

Do one side of the diff and let it dry overnight, then flip it over to cover the other side before letting it try. Set it on some thick cardboard or even an old shipping pallet to work on and protect your driveway surface from getting POR-15 on it. Once it's on there it's not coming off.

Then once it's fully dry you can finish it off and lock the paint in with the POR-15 Top Coat spray. This protects all the work as a final layer and from any indirect UV light damage. It's an easy last step to do so even for a driveline part underneath the car I think it's worth it to finish off the job for good.

This will make your diff look fresh and new again. It will look good for a very long time after this.

Yes you can. You can use any compatible gear ratio you want when doing this. I had my Torsen LSD diff rebuilt years ago from the stock 4.083 to 4.272 for shorter overall gearing with my NA engine. Then many years later I had the same LSD diff rebuilt again with a 3.769 ratio.

Available ratios for the SC/Soarer/MKIV/GS/Aristo/LS430/SC430 200mm diff housings are: 3.266, 3.769, 3.916, 4.083, and 4.272. An unverified but 99% likely compatible additional ratio is the ring and pinion only from an LS460 diff with a 2.9xx. There is also a super rare European market only 3.54 (I think, for some 200mm diff Euro Supra MKIV TTs). Also the 1989-1995 or so LS400's ring and pinion only can be fitted into our diff housings for a 3.615 ratio.

Whichever ratio you go with should match your intended engine spec. If you've got an NA 2JZ-GE then 4.083 and 4.272 are both good ratios. If you've got a turbo JZ with a W58 or R154 then a 3.916 or 3.769 are good go-to ratios and also the custom-build job 3.615 for a longer ratio. If you have a JZ with a V160/161 or CD009 transmission then a 3.266 is a better ratio. A JZ turbo with a Tremec Magnum is best with a 4.083 or 4.272 ratio. A built A340 4-speed automatic pairs best with either a 3.916 or 3.769 ratio.

Yes, all 1992-1997 original manual SC300's came with open diffs in a 4.083 ratio. No LSD was ever available from the factory and no other ratio was available. In contrast the same exact engine and transmission combination in the 1993-1997 Supra MKIV Non-Turbo 5-speed manual models came in 4.272 ratio from 1993-1996 and in the 4.083 ratio for 1997. And in the MKIV Non-turbo a Torsen LSD *was* optional from the factory, although it was rarely optioned.

As to your dilemma, it's a toss up. I was in the same situation as you staying with stock NA power for several years and given that I decided to rebuild with a gear ratio ideal for NA use since that's what would be most fun for me and useful every day. I went for the most aggressive ratio possible: 4.272

Yes, it costs a lot of money to get a differential rebuilt and yes once I was ready with a turbo engine completed on my engine stand to swap I did have to remove my LSD diff (I had a spare SC400 3.916 open diff handy as a temporary fix to install just to be able to use the car with the LSD diff out for service) and send it out to be torn down and rebuilt all over again with the lower 3.769 ratio.... but I just accepted that this is part of the price of getting a car set up one way for NA and another way for boost later on.

You can certainly get your diff rebuilt with a lower turbo friendly ratio right now and install that but with NA power you will notice that the powerband is long and lazy if you go below 4.083. It'll especially be annoying if you live at high elevation or regularly travel from low elevation into high elevation and back again. If you were to install a 3.266 ratio then I don't think you'd find the car's super long and lazy NA powerband usable at all.

As you can see, this is the one downside to building a nice LSD diff ideally for NA use with the intention to have it done again one more time when you have a turbo engine ready some time later. But if you have a couple of years' gap before you'll even be ready for that then I think you should go for the short 4.083 or 4.272 ratio now so that you can make the best fun use of that awesome OS Giken LSD right way!

You can always pick up an SC400 3.916, SC430 3.769 or LS430/SC400/GS400 3.266 diff (all open type) to keep as your spare for when you are ready to drop in a final ratio to your OS Giken pumpkin.

I can say from experience that I found my bone stock 225hp NA engine with my Torsen 4.272 diff a lot of fun for the years I had it set up that way. Short geared, rev-happy, not any more powerful but a bit more fun from the torque multiplication and each gear as more useful as to usable power within gear gear. Highway speed and fuel economy was acceptable IMO while cruising at 70-80mph on average while highway passing power was noticeably improved.

...

I didn't and still don't regret my choice to build my LSD diff with an NA ratio the first time and again with a longer turbo friendly ratio some years later. I really enjoyed that setup once I had the 4.27 LSD diff, MKIV brakes, full suspension upgrade and meatier wheels and tires installed.

It took me a long time to be ready for the turbo engine so I was happy to enjoy the NA setup at its best until the day came that I began my swap.

...

The 4.08 ratio will feel just the same as it does now acceleration-wise in each gear and as to highway revs but with the OS Giken LSD you'll now have a very different sensation pulling smoothly going straight AND in the corners.

Similarly these effects are amplified when using the same LSD on any turbocharged SC with whatever ratio is appropriate for its setup because the LSD just does a much, much better job than the stock open diff at distributing power upon acceleration and in curves and keeping all the turbocharged torque and horsepower from making the car feel excessively wild and difficult to control under load (boost). A turbo SC with an open differential requires FAR more steering correction even in a straight line than an LSD-equipped turbo SC does.

In an NA SC with an LSD you can feel all the same benefits. There is less power and torque and both are delivered very differently but the LSD does transform a naturally aspirated SC300 or SC400.

You're welcome! Ultimately you'll have to decide for yourself which ratio you want right now vs what you'll grow into later but I hope this has helped you make a better informed plan of action. You're going to love that LSD once it's installed!

Cheers!

DubsackDev

Thank you for the reply! I appreciate all of your insight!

I bought the Driftmotion kit, took to my driveline shop and everything was I installed in about 4 days. I did speak with OS regarding break in and they reported there is a 500-1000 mile break in period where yo should not do burnout, dyno, etc so I can only assume that means no sliding as well until the break in is over.

One question which I did not get answered very specifically from them and wondering your opinion. They have a list of approved fluid that you can use for break in and then they recommend to switch to their OS gear oil specifically for their LSD. Do you think I should use their gear oil for the break in as well? If you think one of the approved fluids would be fine what is your opinion between the Motul Gear Competition 75w140 and the Motul Gear 300 75w90? The SC OEM diff calls for 75w90 I believe so I'm not sure if it would be better to stick to that or go with the thicker oil as I believe the OS gear oil is like 80w250 or if it really doesn't matter for that few of miles?

I definitely plan to clean the differential before I put it back in the car but I may hold off on the POR for when I have to rebuild it in a few years when I go turbo as the differential currently is not very dirty or rusty as the car only has about 75k miles on it. I am just anxious to get it back in the car and get some miles on it before winter as it does not see the snow.

I did end up just sticking with the 4.08 as I could not find just a ring and pinion gear for the 4.272 without buying or sourcing an entire auto differential which would be another $400 or so from what I could find.

Thanks again for all your help, I am very detailed oriented so I like to k ow as many specifics as I can and don't want to screw anything up.

Cheers!

KahnBB6

iTrader: (5)

Hey-- I'm glad the rebuild went quickly and smoothly for you! And thank you for relaying that OS Giken *does* recommend a break-in period of 500-1000 miles (I'd do 1,000 to be safe personally). It makes sense and I was a little skeptical when one of their reps told me otherwise a couple of years back. I would consider this to mean to just drive the car "normally" without getting aggressive, power sliding, doing burnouts, etc. much as you would be gentles for the first 1,000 miles during an expensive clutch break in period.

As to alternative diff oils, they do have at least one alternative oil brand, weight and viscosity that they approve of for use in their diffs but it's not said to be as ideal as their own unique OS250R diff oil, pricey as it is. From what I understand it is that unique oil that is the special ingredient that works the best in their designs both for overall performance and quietness. It's exactly the kind of thing you'd expect a company offering a pricey product to say ("Please use our own oil as well!") but there is something to it in their case.

I would look into forum threads about OS Giken LSDs and their fluid on Supraforums, a big Miata forum, BMW forums, etc. and see their reviews as well.

If you go onto the OS Giken USA website there are downloadable PDF tech pages on all of their products in English translation including their LSDs.

I am sorry I cannot be of more help with direct experience! I'm still saving up for one of their LSDs myself! I know there are a few members here and on Supraforums who run that 1.5 way LSD with the pricey pink fluid and they love them.

From my notes after talking with the OS Giken USA rep a couple of years back:

The TY-031-HA Super Lock 1.5-way LSD is a "negative preload diff" which according to them is actively trying to stay unlocked... until it needs to lock up. They describe it as acting like an open diff during "regular" driving (I'm assuming this means when just cruising along without much load applied with the car going straight). Fluid changes from the rep whom I spoke to were deemed to be once a year under daily or semi-daily driving conditions or basically just follow Lexus' factory manual diff fluid interval changes. He said the main thing is to make sure the fluid is still "gold" in color.

Again... I am just relaying what I discussed with the OS Giken representative so I cannot back this up from my own personal experience. Take it as you will and augment it with the information that you have gathered in your research to date.

I know you'll have a good experience with this once you get it installed and broken in!