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Posi (Limited Slip Diff) for your RX ...


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I'm posting in the Gen II Forum also in case those folks don't look in the Gen I Forum. 

It seems there was/is a mythical Unicorn among RX's.  In the early model years there was an optional Torsen posi-traction rear differential.  I'm very keen on finding the parts to make that happen in a 2009 RX 350.

So I went looking in the Toyota parts stream. I was searching the parts at a web site called Toyota Parts Overstock, or something similar. I was looking to see if some, or all, of the internals from an earlier rear diff would fit in a latter one? So I concentrated on the center section (the casting that carries the ring gear) P/N 41311J in the diagram. As I honed in on that part, I got a parts diagram with notes that that listed the years and models.

The internals seem to be an 8" 2-pinion (spider gear) "V-6" diff that was commonly used on most everything: TOYOTA: 7 models, 305 variants between 1982 and 2010. Fits CAMRY, CELICA, HIGHLANDER, PREVIA, RAV 4, SIENNA, VAN

And on page 1 at the bottom are some variation notes about the shape of the spider gears. And under that is a note about the model RX300 ... The rear end in a Lexus RX might be designated as an MCU15 ...

Tthis is not conclusive proof of course, but aken all together, it seems to indicate that minus some variations in attachment, rubber isolation supports, and spider gears; this same rear end (internals) have been used in RX's from day one through some time in 2010. So the idea of finding a rare early RX 300 posi rear diff is possibly a good one. And with changing the external bits that make up the year model mounting variations, might actually fit a Gen II RX 350 ...

I have to do more research, and prolly digging at Pick-&-Pull looking at Highlander and RX models from various years. But if what I'm reading is true (?), we could use the RX 300 Torsen posi in later models ...

The trick will be to get a VIN number from an early vehicle with a Torsen factory installed. And use that VIN number to order the internal parts through Toyota's various web sites to build up a modern version (housing & mounts) to fit the vehicle of interest.  Or rebuild the one we have with selected new internals.

See attached for info:

Lexus RX Rear Axle Housing.pdf

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  • 3 weeks later...

Is there an issue that you are having with your present diff that has prompted you to go down this path? - just curious.

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Yup.  I'm coming from a full boogie Big Bronco 4x4 with Lo-Range, manual locking hubs, and Posi out back.  That truck has 230K and is really too big for our retired life-style.  Pain to get in and out of back seat, pain to park in modern parking spaces, rough riding, very fuel inefficient, etc ...

I'm working on a book about WW-II training areas in the desert south west that my mom started (WW-II WAC Vet.) before she passed ...  I need to visit and photograph a few hundred locations.

The desert does not hold any surprises for me.  I have been all over the routes I will traversing with my wife and a bunch of camera/gps gear, etc.  The trick is to have reliable 3-wheel drive.  There are enough obstacles (small rock ridges and swales or ditches that must be crossed diagonally due to terrain limitations) to stop forward progress by biassing the suspension such that opposite corner wheels become unloaded. One, or both, will spin and throw a little dust and you go no-where.  In the old days (before the RX) I would adventure in in 2-wheel drive, and if I got stuck, put it 4-wheel drive to get out or keep going (SOP).  With the RX I do not have that option ...

I have already located an OEM Lexus Torsen LSD rear diff used from a salvage yard.  I'll prolly pick it up Saturday.  The rubber boots on my new-to-me RX300 rear struts are cracked and broken.  I do not want those struts to go bad prematurely (~$1,100 each for true Lexus versions).  The back end will be getting torn down anyway to put in new boots, and the Posi can go in at the same time.  Aussies and Englishmen have reported that TRAC and VSC seldom engages with a Posi installed, and their vehicles have excellent grip, so I'm going this route.

There are other folks who are acquiring older RX's as toys for adventure outings.  Yeah, I get that they are not true 4x4's.  But may still be quite capable in mild off-road scenarios.  If a KIA Santa Fe will go, so will a Lexus RX - just in way more style and comfort 😄

Plus it will be very helpful in getting our outboard up slippery boat ramps, or the little day sailer 🙂

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  • 1 month later...

Well I found one in Oregon with 158K on the ODO. Seller (B&D Auto Wrecking) confirmed that it was/is a locker. So after the previous three vendors failed to check well enough and either sent the wrong part, or just refunded my money after double checking, I pulled the trigger and got it. Yup, it's a Toyota OEM Limited Slip Differential carrier complete. Raining right now, so don't want to open it up, but will in a few days.

Looks like the right rear stub axle seal was weeping, so before it goes into my RX, I'll have the shop install all new seals and double check the lash. I don't want a noisy one replacing a dead silent existing one...

So I got a photo of the "Build Plate" off the drivers door jam (sticker) from the donor vehicle (Highlander) :
_highlander_lsd_build_plate_7fc77d8630dfdbf90958eafed47c6e4c57927a32.jpg
So you see the axle data in the lower right hand corner? It says -04A for this axle. My existing one is a std open diff (-02A). It's the thing you are looking for when out shopping. -04A is the axle code to look for in the field when hunting for one of these.

I have seen one door sticker with an -03A on it, but was not able to get any more info about what axle that might be ...

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