victorhugo

Hi my names vi tor Since everybody is talking about transmissions well I have a couple question
1 I just bought a 92 sc300 its 5speed but idk if it was automatic before n they swapped n if they did how can I tell?
2 if its stock its a 1 legger I would like to hit donuts or light drift what can I do ?
3 on the freeyway cruising at 65mph im at 5000 rpm is that normal doesnt feel like it to me n if its not normal what could it be im at 8000rpm at 100? Not normal thanks for any info
Not trying to jack any thread

KahnBB6

iTrader: (5)

Hello Victor,

1.) Visually you can tell if your 92 5-speed is original by checking the dash cluster: does it have any "P-N-D-R" vertical column of lights between the speedometer and rpm dials? If so, it was an automatic swapped to manual.
Also, under the hood you should look at the throttle body on the engine: does it have a "TRAC" or "TRACTION CONTROL" logo? Original manual cars did not have an option for factory traction control. Automatic cars *often* came with TRAC but it was an option only on early Base models.
Also, you can bring the car's VIN code to your local Lexus dealer and they can confirm the original transmission.

2.) ALL Lexus SC's were "1-leggers". In the USA none of them had a factory LSD option. There are a few options for adding one but none of them are inexpensive. If you will not be upgrading the engine for more power and want an LSD you will want to read through this thread extensively regarding retaining the stock 4.083 gear ratio or getting a more aggressive 4.272 from an SC300 automatic. Most people want lower, not higher gearing when changing the rear end because most owners are planning an NA-T build or GTE engine swap with far more power that is better suited to a 3.92 (SC400), 3.77 (Supra TT Auto w/Torsen) or 3.26 (GS400/98+ SC400) rear ratio. There are also extremely rare 4.083 and 4.272 LSD rear ends from MKIV Supra NA's but you are unlikely to find one for sale.

3.) If the car is an original 5-speed you should be seeing about 2,800 rpm in 5th gear @ 70mph. This is what the factory 4.083 should give you. Even a 4.272 final drive (not factory on 5-speed SC's) should only be turning 3,000rpm @ 70mph or 3,500rpm @ 80mph.... with an aftermarket speedo corrector. You shouldn't even be able to hit 8,000 rpm which is FAR beyond the stock valve train's safe operating range (redline at 6,800, fuel cut at 7,200). Something is not right with that and I am not sure you're actually turning such high rpm. You should use a portable GPS to determine how fast it says you are going versus what your speedometer is telling you.

This is the only indication to me so far that you MAY have a swapped automatic SC300 with an uncorrected or malfunctioning rpm gauge. If you refer a few pages back into this thread you'll see that if a 5-speed car is used with any ratio other than stock you'll need a speedo corrector like a YellowBox to change the signal back to an accurate reading. And you'd use a portable GPS like a Garmin to measure the actual speed to know what the inaccuracy percentage is.

Here is the page specifically related to installing a YellowBox speedometer corrector should you need it:

https://www.clublexus.com/forums/per...et-swap-9.html

scblackout

iTrader: (2)

I was lucky enough to pick up the tt auto lsd diff on the forums here yesterday and had the exact same idea about using a higher gear ratio that you spoke about. As I have a 96 5sp which is already way to slow I was quite concerned about dropping to the tt gear ratio. Thank you for posting the valuable info on how it works so far for you.

Now I don't want to go and spend another 5 bills to have the gears swapped so I am going to try this myself. Have you managed to find any great how-to guides for swapping gears in the diff, or better yet how to properly rebuild the entire unit?

I've never removed a diff from a car before, but hell it's just bolts so can't be to hard with proper instructions. I'd rather spend the 5 bills on new tools so I can do this myself again in the future.

Question:
Went into Toyota today so I could order any parts I would need when it arrives. The computer said there is NO replacement bushings for the diff and if I wanted them, I had to spend 4500+ to buy a new one.. yeah right...

So when rebuilding the diff what does everyone do to replace the bushings, bearings, etc?

KahnBB6

iTrader: (5)

Congratulations and you're welcome! I always hoped this thread would be of help to anyone else on the fence about gear ratios with an NA car.

I did have the same concerns and since, in my case, the prospect of dropping a 3.77 ratio into an NA car for a period of years until I could get an emissions legal turbo engine swap together wasn't something I was willing to consider.

If I could have done a simple 1JZ swap within a much shorter timeframe I'd have avoided the diff rebuild entirely and swapped it as is very close to the time my new engine would go in. So far it's been about 3.5 years since the diff swap and I'm still collecting parts for my turbo engine. Driving on a 3.77 while NA for all that time would have made me miserable.

My gearset swap and rebuild ran about $450 through a specialist Driftmotion contracts to. It can be more but I consider that a good deal and it's their reputation I trusted. Years later it's fine.

I haven't found but a couple of extremely truncated guides on the process of installation. The first thing is you'd want the Supra MKIV TSRM handy for all the specs and basic procedures. More than that, however, is how precise setting up a differential needs to be.

Toyota will sell you the seals, bearings and shims needed to do a complete overhaul but you have to use a micrometer and Prussian Blue to measure the runout of the ring and pinion and their alignment to be EXACTLY within the specified ranges the TSRM states.

And do to that you have to assemble the diff with the new gears, seals, etc, measure how much shimming is needed and then order those shims from Toyota's parts dept. Then you have to install the new shims and you'll want to double check again.

I have NEVER done this and I don't recommend this at all unless you know what you are doing. If you set up a differential the wrong way it won't take long for you to start wearing it out very quickly and harming the ring, pinion and possibly the LSD itself.

Someone else will have to add more detail on how to do it yourself. I'm not the person to ask or recommend you try it... unless you already know how. It HAS to be done right the first time.


Now this isn't hard and anyone can do this. Again, have the TSRM handy.

Also, refer to the truncated details on Page 2, Post #95 of this thread.

You need to properly jack up the rear of the car in a SAFE and secure way and roll under the rear. The diff needs to be supported by a Jack and possibly with one that has a plate or wood spacer. You don't want it topping over on you (100lbs!!).

The axles need to be undone by having the parking brake engaged and I believe it's a 10mm or 12mm hex bit that is required with a socket wrench. Six axle bolts on each side which are supposed to be torqued to (IIRC but please check the manual) 64 ft-lbs when they are put back in. You rotate the axles every 2-3 bottles for optimum angle with your socket wrench by disengaging and re-engaging the parking brake.

I found that for a couple of axle bolts on mine they were torqued to as much as 100+ ft lbs. I don't know if this was due to settling because of age, factory error or a previous mechanic's mistake over the years. Nonetheless you should order a few new of the factory axle bolts to have handy because you may have to ruin one or two to get them out if you are similarly unlucky. Usually this will not be the case though.

There are some vertical bushings connected to the aluminum carrier cover and the two big bolts at the differential "ears".

Then there are the three bolts connecting the diff companion flange to the drive axle. I don't remember the torque specs for anything but the axle bolts so please refer to the TSRM.

Remember to have the diff supported on a jack securely and the car jacked up safely and securely!

Once you have all of those out, you can gently get the diff to lower down and let go of the axles. Please do this carefully and with help.

To install another SC diff is the exact reverse procedure. To install a GS or Supra MKIV diff requires removing the companion flange from an SC diff, removing the companion flange from the GS/Supra diff and swapping on the SC companion flange. A dial-torque wrench must be used for this to secure it at (IIRC, please check the TSRM!!) 35ft-lbs. You need the dial torque wrench because a normal torque wrench will over torque and there is a procedure in the TSRM for this. Under-torquing or over-torquing the companion flange can affect the precise alignment of the pinion gear and thus it's meshing within spec to the ring gear inside the diff.

Now all of that said... most of us here on CL can follow the manual procedure and do a diff removal, companion flange swap and reinstallation.

However in my case I had Driftmotion not only rebuild but swap the companion flange for me even though I looked up the procedure and bought a dial torque wrench to do it myself. They were doing the rest anyway so why not?

That sounds about right for new old stock. There are two ways to replace bushings and neither is available from Toyota:

Aliga occasionally has polyurethane sets for the ears and rear subframe made available for around $140 or so but only in batches.

Then there is this that recently became available:

https://www.clublexus.com/forums/per...-vs-solid.html

I can't recommend solid bushings unless you're strictly building a track car with a stripped shell and a racing seat.

As above, I highly recommend finding a reputable shop that knows how to do this. But the seals, bearings and shims plus aftermarket poly bushings are all available. The shims have to be ordered specifically based on your micrometer measurements though which is probably going to be taken care of by the diff/axle rebuilder.

I hope this helps!

KahnBB6

iTrader: (5)

scblackout,

One more thing. I want to be clear that my TT Auto diff ratio swap is in no way going to give you the improved acceleration any turbo engine will give you (with a lower ratio). But it is far more suited to aggressive driving and it is a bit faster, using the power band far better than before. The only price is shifting more. If you must stay NA you would do well with either the 4.083 or 4.272. The 5-speed ratio will feel too docile as always while the 4.27 makes the 220hp power band much more useable and 2nd and 3rd right in their sweet spot for curvy roads. 5th becomes more useable at highway speeds with a small price to pay in slightly higher rpms. But it's no different than what MKIV NA's cruise at. You shift a bit more with the aggressive ratio but it makes the NA engine as useful as is possible without boost.

It is not comparable to boost but it's a very strong improvement for natural aspiration, especially with the LSD. If you still want (or can easily switch to) turbo horsepower, stick with the 3.77 ratio in that TT diff.

Also, speaking from experience, even though an R154 technically improves acceleration ever so slightly it is better to pair the 4.27 with the lighter W58 gearbox. Not because of shift qualities so much as that the bigger gears inside are overall better matched to the turbo engines they were designed for. High speed highway driving is better, in my opinion, with the 4.27 + W58 than the 4.27 + R154. My installation of the R-series transmission was part of a staged path to going turbo of course.

scblackout

iTrader: (2)

After reading your info and a GREAT pm I got with detailed instructions, I think that first I am going to shop around for a good shop that has actually worked on Supra lsd's. The shop I currently go to mostly does bmw, mercedes, audi, but I am still going to ask their opinion. I would hate to do something very basic the wrong way and create a 1k paper weight.

I'm staying NA for now because honestly there are so many different ways to boost the car that I am unsure how I want to go about it. Besides, at that point I am committed to the car, where at the moment I am still not sure if it is what I want to drive. Either way, the car needs an lsd, and going down in gear ratio is not an option as the car is already way to slow. I'll add a complete writeup to my build thread next week when I get it installed. For now I am going to Toyota to order everything the installer could ever need to do the job so I don't have to wait on parts.

KahnBB6

iTrader: (5)

Looks like you've got a sound plan ahead.

Ordering the parts (apart from shims) now is good no matter what. If you do decide to do it yourself I know there are a few members here with experience rebuilding diffs who can help (and one already contacted you). Yes, you just want to be very sure of measurements being within spec if you do. No matter who rebuilds your diff, do keep the 3.77 ring and pinion wrapped up safely for future reassembly. They are not easy to find now.

I agree with you holding off on boost until you're sure of what you want. Getting into an engine build does change your commitment but also depends on how crazy you go. You'll have a lot of fun with an LSD. Keep the rolling diameter of your tires closer to SC300 OE to maximize your acceleration potential.

KahnBB6

iTrader: (5)

I thought this might be of interest for comparison. Today I just helped a friend buy a 1995 Mercedes 300D (OM606 I-6 diesel, sometimes referred to as the "2JZ of diesels") and got curious about LSD options for her Autobahn econocruiser since it shares the same chassis and suspension compatibility with the much faster Merc 500E with a 322hp V8.

http://mbworld.org/forums/e-class-w1...ls-w124-s.html

What's important to glean from that thread is how just the same as with our cars it is crucially serious to set up a rear diff the right way. Not to mention how few LSD options there are for most vehicles.

KahnBB6

iTrader: (5)

Minor update for YellowBox correction factor info for anyone this helps:

Coming from an original 5-speed car which expects:

W58 gearing
4.083:1 final drive
215/60R15 tires

to:

R154 gearing
4.272:1 final drive
255/40R17 (rear) tires

...I have recently rechecked (with a Garmin GPS) the calibration of my YellowBox corrector which intercepts the VSS signal from the transmission. Over multiple low and high speed runs I've locked my speedo correction factor at a flat 18% (over-read before any correction). I do remember a very slight over-read when the car was stock but this could have been as little as 3-5mph off. Perhaps not even that much.

Note to anyone using the YellowBox (2020 edit: any model through V4 but the newer V5 model may not require this) that you must shut off the engine and ignition EACH time you make an adjustment. This comes straight from Yellr's instruction manual.

Once again, this is an easy to use guesstimator for what your correction factor will be, however the more driveline changes you have made I highly suggest the GPS verification method to determine your car's actual speed at a given speedometer reading.

http://www.solemnwarning.net/speedo/?

And for redundant reference, a link to Yellr's site with downloadable PDF instruction manuals for each of their speedo corrector models with complete correction tables. This comes printed out with every unit.

http://www.yellr.com/yb_inst.htm