Hey everyone, I just purchased a 4.27 diff from a 96 SC300 and I’m looking to put it in my 94 SC400. From what I’ve heard, the pumpkin should just bolt right in but I wanted to confirm it here. Does the yoke fit up perfectly and everything just lines up as I thought, or will I need to do slight modifying to anything? If anyone has some insight and could help me out, I’d much appreciate getting some more info while I’m waiting for the diff to arrive.

 

Yes, it will bolt right up. All 1992-2000 SC300’s and SC400’s (and all 1991-2000 JDM RHD Toyota Soarers which are the mirror of our SC’s) use the same 101mm spaced companion flange that bolts to the driveshaft.

All 1993-2002 Supra MKIV’s and all 1991-2005(?) Toyota Aristos and all 1993-2005(?) Lexus GS300’s and GS400’s use a 111mm spaced diff companion flange.

The diff you have will need no modification to bolt up.

To correct your speedometer’s inaccuracy with the 4.27 gear ratio you can use a Yellr Yellowbox V4 or V5. They also give you the option of purchasing an SC/MKIV specific plug-and-play harness for their speedo corrector if you request it at the time of purchasing which I highly recommend.

You use one of the rubber plugged capped off RHD parking brake boot holes in your SC’s transmission tunnel to snake the Yellowbox wires through. You have to note where they are on the Molex connector, carefully de-pin that connector, get the wires through and then re-pin the connector.

They have full instructions that come with it to show you how to program in the speedo correction you’ll need.

 

Awesome, but at the moment I don’t really have the money for the speedo corrector. I’ll probably end up using a speedometer app for the time being lol (assuming that the vehicle won’t encounter any issues by having an inaccurate reading from the vss). When I was checking the yellowbox website, I only saw the v3 and v4 listed under the instructions panel, so I was wandering how I’d receive the instructions for the v5 (and I’ll definitely need them because I haven’t wired anything except for a light bulb to a battery when I was in elementary school lmao). I’ll probably be getting the v5 two thursdays from tomorrow, so I’m not in dire need of the instructions, but I like to plan stuff out ahead of time so I know what I’m getting myself into. Any info would be appreciated.

 

You'll have no issues other than your speedometer reading too fast... and possibly your odometer reading too fast as well but I've never ben able to be certain on that since the SC's odometer circuit simultaneously gets its readings from both the transmission VSS sensor and from one of the front wheel ABS sensors. If you're going to correct out the speedo issue within a couple of weeks you won't have that much of a mileage discrepancy for long.

First off, look at these posts for some Yellowbox install instructions. I made the thread in 2011 and it involves a Yellowbox V4 but the procedure will be exactly the same for the wiring. If you order the SC/MKIV plug and play harness with it (you have to request it with your order) then you will need no extra wiring. All you'll need to do is temporarily de-pin the Molex (connector type) end of that PnP harness to fit the wires through a factory hole in your SC's transmission tunnel. Then you put the wires back into that connector the way you found them and you're ready to plug it in from the cabin!

Part 1 of 2:
https://www.clublexus.com/forums/per...ml#post7250024

Part 2 of 2:
https://www.clublexus.com/forums/per...ml#post7252535

If you email them from their website, tell them your year, make, model and transmission (1994 Lexus SC400, stock automatic transmission) and that you want the V5 model and the SC/MKIV plug and play harness to be sent with your order. They'll take care of it. I believe I paid $111.00 last year for a V5 model and new PnP harness to upgrade from my old V4.

Although just to note their original SC/MKIV plug and play harness from the V4 series plugs right into the V5 model.

The main advantages with the V5 over the previous generation are that there are no dip-switches to set from a calibration table (now replaced with just a couple of buttons that you hit in a certain sequence to adjust your correction factor percentage) and the little electronic brain inside the Yellowbox V5 is a complete upgrade over the V4's brain and much more capable of even greater fine tuning than before.

I just checked and indeed they do not have the V5 instruction manual on the website but they always provide that in paper form with each V5 they send out and they can always email you the PDF version also. The installation instructions for the universal and PnP wiring harnesses are the same for the V4 and V5 since both modules use the same harness and pinout design.

It's really easy to set these things up.

Use this calculator to figure out your speedo error percentage:
http://www.solemnwarning.net/speedo/?

And then use the V5 instructions to adjust the correction for that figure. Then use a Phone GPS app that displays speed in real-time or a Garmin, TomTom or other standalone portable GPS unit that displays GPS-based speed in real time to make sure your speedo correction is basically accurate at various MPH readings (10, 15, 20, 25, 35, 45, 50, 60, 70, 80, 90, etc.).

 

commenting on the odometer thing:

I did a manual trans swap on my 94 sc400, so no VSS is hooked up. Using a GPS speed sensor wired directly into the back of the stock cluster, which means the ODO reads off the cluster.

I didn't have a GPS speed sensor hooked up for the first few weeks and the ODO wouldn't budge, so that brings me to the conclusion that the ODO is affected by the speedometer needle in the cluster.

 

^^ Good info, mr913! Thanks! So this would mean that despite what the SC300/400 electrical TSRM diagram for the odometer might suggest, we DO need to have a three-wire VSS signal of some kind in order for the odometer to function at all and better to have an uncorrected VSS signal hooked up than none at all.

What transmission were you using for your SC400 manual swap? CD009 series?

 

I’m using the 5 speed KA trans from an s13