SRV1

iTrader: (2)

That does not make any sense when it comes to an open diff. I have rebuilt LSD's before so I know all about them. Doing a brake stand on dry pavement with an open diff will always burn one tire with the least amount of traction from what I personally have encountered. I have had many RWD vehicles with open diffs and I have never been able to burn both tires on drive pavement doing a brake stand. Even in my Toyota truck with an open diff so something must be going on in the back of these Lexus's. Heck my 89 non-turbo Supra would only do a one wheel peel doing a brake stand and basically it is roughly the same diff as the one in our cars. Does anyone have any picture of the cover removed? Very curious about this.

Pictures? LOL! The 2UZ hasn't even started in the 93, the 22RE is still in it! The SAS is still on jackstands in my garage and the 4Runner is my daily driver which I do have pics of that! I need to get my butt in gear!

James

PureDrifter

iTrader: (10)

not true. if you have even weight across the rear end and roughly the same grip on both tires, it is possible to spin both tires doing a burnout without an LSD as both will have equal traction (basically what 3uzfte was saying).

i have taken apart a couple LS400 diffs and can assure you there's no factory LSD in any of them.

3UZFTE

Ok. Let's clear some things up. Good to hear your not the type to just have one project, like myself... As far as the 2UZ, Megasquirt that biotch.

Now, back to the diffs. I have done my homework, and will go ahead and share pretty much the almighty knowledge of the A series differential that you will find in a LS400/430, 2nd Gen GS300/400/430, SC400/430, and a MKIV Supra (EXCLUDING Early twin turbo manual diffs), which essentially all share the same drive lines. This makes it very easy swap to just buy an LSD insert, and find your optimal ring gear, and build your own hybrid setup. The smaller diff is used on all RWD Lexus (minus IS300), NA Supras, on the Supra auto TT, and on the later Supra manual TT...IIRC 98+, Soarer, and Aristo.

However, one thing to be aware of is the MKIV Toyota Supra B series, or the one in the earlier, IIRC, pre-98 twin turbo 6-Speed/manual CANNOT be used because it is physically too big to fit inside the A series diff. The reason why I mention that is because those are the one's you will often find on SupraForums, and other sites because there is no use for them. An easy way to tell is A series uses 10 ring gear bolts, and larger B series diff uses 12 bolts. I believe you can swap in the entire B series diff, but you need to buy the axle shafts as they are offset for the larger differential.
Supra 6 speed B series vs. Supra auto A series


Like I mentioned, they share the same parts, but the gear ratios vary between the model lines, so a 2nd gen GS and Supra diffs are interchangeable, but the gear will differ between them. An example would be that the GS3 has a 3.92 ring gear, the GS4 uses a 3.26 ring gear, and a SupraTT (Auto) has a 3.76 ring gear, and even a 4.08 ring gear is available in the SC.

I will make this clear. The ONLY Lexus vehicle to leave the factory with an LSD would be the IS300, which also DOES NOT fit in the LS/GS/SC/Supra chassis. The 89' Supra that you speak of uses a slightly different design, but essentially occupies the same open diff as the rest of us. Notice the axle shafts, diff mounts, and pinion flange, and the overall design is just different.


Now, my personal experience and just some back ground information. I am a Toyota technician, I currently own a 92' LS400 that I turbocharged, open diff and in the process of building a hybrid diff of a GS300 3.92 ring gear w/ Supra LSD insert; 01' GS430, open diff; 89' Toyota pickup, open front and rear diffs(1UZ and SAS this summer), a 64' Ford Falcon w/ a 93' Cobra motor with the usual bolts on through a factory 8" open diff, and a 62' Corvette with the original posi-trac. I can assure you, I also have experience in diffs, especially in our Toyota/Lexus diffs. An open diff will definitely spin both tires, provided traction is similar, you will spin both tires, that is just the shear physics of the open diff.

In the picture you'll see the open diff on the right, which is the EXACT insert that comes in our RWD Lexus vehicles(minus IS300). You will see the splined gears in the side of the diff which power the axles, with 2 "spider" gears that walk around the axle gears. When the pinion transfers power to the ring gear, the ring gear than causes the axle gears to spin. Well, when one axle starts to spin, what stops the spider gears from walking around the axle gears, causing one wheel to spin...? On the contrary, look at the LSD, you will see that there are helical gears with straight gears on the ends. The purpose of these gears is to stop the spider gears from walking around axle gears, and instead it transfers power from the slipping wheel to the stationary wheel, thus limiting the slip of the differential, where are the open diff has nothing preventing the slip.

Early 12 bolt/B series LSD vs. Open Diff.


If you really want to find out if you have a LSD rear end, jack up the two rear tires and spin one of them by hand. If it is an LSD it will spin the same direction (Forward/Forward), if it is an open diff, the wheel will spin the opposite way (Forward/Reverse). Seat of the pants is rarely a good testing measure.

Please feel free to correct me if I am wrong any of my posting as I've tried to be as complete as possible. If you really want to start researching, Google is your friend and all you need to type in is GS400 diff, Supra Diff Supra LSD, LS400 LSD, etc. and you will find out almost everything I just told you, if not more. Hopefully I cleared some things up for you.

sdls

Do we know if foreign-market LS vehicles may have had LSDs? I know that in the US, the Cressidas had open differentials but they had LSDs available in Canada. Could it be so with the LS as well?

Raddison

3UZFTE, that was a beautifully written article, super informative, and I'm glad that the community has people like you that research and post really valuable information like this for us all to share.

3UZFTE

I think this is the case with both the Aristo/2nd Gen GS and Soarer/1st Gen SC share that theme, however it doesn't seem that Toyota did that with the LS400/Celsior as it never got a turbocharged motor, which seems to be the deciding factor.

Thank you, I appreciate the kind words, and look forward to helping when I can.

PureDrifter

iTrader: (10)

great stuff

the is300 shares a g-type diff with the ma70 iirc.

SRV1

iTrader: (2)

Well I can tell you that our open diffs are not working correctly if I can do a brake stand and burn both wheels. That is NOT the normal characteristics of an open diff. Like someone mention earlier, maybe a design flaw with the side gears with too much play causing it to **** and put pressure on the side of the case acting like a LSD and I drove and own MANY RWD cars with and without LSD and I can tell you that this is not normal. I do believe you that you say our cars never came from the factory with a LSD but I refuse to believe this is a normal operation of an open diff because it is not.

Also by jacking up the rear end and turning one wheel to see if the other spins the same direction is not totally true. My 96 Volvo 960 had a LSD in it and you can jack up the rear end and spin one tire and the other will go the opposite way. Some LSD's have a centrifugal weight that activated the limited slip clutches and this test method would show that it is an open diff when really it is a LSD.

James

3UZFTE

I see, well you believe what you would like. We can go back and forth all day, but I'm standing by my original statements. If you push enough power to spin the wheels, if traction is equal between both wheels, you with spin both wheels, if traction isn't, like snow, ice, dirt, etc., you will spin just one. I, and other can easily assure our open differential operates as normal. I've driven the last 3 winters cursing out my open diff Lexus's, I just got a 4WD taco. Maybe your lucky and bought a car with an LSD insert, it's not likely, but it's possible.

There's always exceptions to the rule.

PureDrifter

iTrader: (10)

^to clarify i'm 99% sure he means a car in which the previous owner had LSD internals installed into the OEM diff housing (or swapped the diff with one from a supra and used the OEM LS400 diff cover)

3UZFTE

+1 Good catch, I worded it kind of funny.

JBrady

I have a CLEAR understanding of how and why a differential differentiates torque between the two sides. I posted this thread BECAUSE I was originally just like yourself and could not understand why MOST older Lexus LS and SC 400s would spin both tires AKA limited slip.

Limited slip as I described is that the differential has enough INTERNAL FRICTION so that its natural tendency to provide torque equally to both tires is not lost when one side of the vehicle has relatively lost traction. The REASON for limited slip is to allow the differential action in turns where the outside tire must turn more quickly than the inside tire. The most common way a factory limited slip is designed is to install clutch plates between the spyder gears and the case. This creates enough friction between the spyder gears and the case to overcome the tendency of the differential to over power/torque one side causing loss of traction on one side only WHILE still allowing enough SLIP to allow different wheel speed during cornering.

I realize that PURE and 3UZ understand this already and we are all in agreement.

Torsen units are not limited slip. They instead utilize specialized gear designs instead of the traditional spyder gears in an open or limited slip differential. I bought a differential from a 1998 Supra TT automatic that was supposed to be a Torsen unit. It had a different bolt pattern on the cover so I was swapping the cover with my stock cover when I discovered the unit was NOT a Torsen. The seller was absolutely CERTAIN it was a Torsen because it spun both tires at the drag strip. It was not.

So, back to my ORIGINAL post with the REAL reason for our older differentials becoming limited slip. The surfaces between the spyder gears and the CASE wear into each other and provide ENOUGH friction to RESIST allowing one side to get more torque than the other. Under turning the friction SLIPS to allow differential wheel speed hence LIMITED slip. Now, clearly this is NOT the intended design of the differential. It is an unintended consequence of wear inside of our differentials. I never stated that it is equal to an factory designed limited slip but it DOES improve traction and is FREE as stated. Rarely is a failure so helpful.

SRV1

iTrader: (2)

Basically you just summed up what I just said but a clearer explanation. Also I assume that if any of us were to add a LSD, we would have to disable our traction control or would it still work correctly?

James

SRV1

iTrader: (2)

For those who do not understand still, here is a good video of how a differential works. It is old but the principle does not change:

http://www.youtube.com/watch?v=K4JhruinbWc

JBrady

Theoretically you are correct and if traction is equal both tires will continue to get equal torque.

In actual practice under MOST circumstances open diff vehicles with sufficient torque will spin one tire (provided sufficient torque). From a start on even ground this is due to the rotational force the engine places on the chassis. This rotates the chassis lifting the right side and compressing the left side. This reduces the load on the right side and increases the load on the left. When this happens the right side is unloaded reducing its traction relative to the left and it can begin spinning. My 99 LS400 did exactly this with under 60k miles at the dragstrip.



Good picture, I will use it to help explain further.
First lets get the components named correctly.
PLEASE SEE BELOW... I have attached a PDF of the Toyota Service Manual below and the breakout is on the second page.

The main components are...
Using the common and then the (Toyota) names:

Pinion Gear (Toyota calls Drive Pinion) which the driveshaft powers from the transmission.
Ring Gear (Toyota calls Ring Gear) which is turned by the Pinion Gear
Carrier housing (Toyota calls Differential Case)
Center Shaft or Spider Spindle (Toyota calls Pinion Shaft)(differential gear shaft is more accurate)
Spider Gears (Toyota calls Pinion Gears)(confusing at best as they are differential gears)
Axle Gears or Side Gears (Toyota calls Side Gears)

Power flows from the pinion gear (not shown) to the ring gear (not shown).
This turns the carrier.
The shaft through the carrier turns the spider gears.
The spider gears turn the axle gears.

In the picture the open diff carrier is on the right.
The ring gear would bolt to the outside edge with all the bolt holes.
The shaft that holds the spider gears is barely visable on the left edge of the carrier.
The spider gear shaft transmits essentially all of the power from the carrier to the spider gears.
I say "essentially" because that is the design. In practice the spider gears/washers also touch the carrier and there is friction between the two components.
There is also some friction between the axle gears/washers and the carrier housing as well as with the spider gears.
More on this in a moment.

I find it VERY telling that Toyota states that during assembly and testing the differential gears SHOULD rotate freely in the carrier.
If they do not Toyota specifies to change the thickness of the thrust washers.
So, it appears possible to set up a stock diff as a limited slip if you use tight thrust washers!
This is also probably why Totota has frequent diff oil changes on the schedule as not doing so results in an apparent increase in friction (good for us!)

In addition to the above the size of the differental gears (spider and axle) seem relatively larger than the GM and Ford diffs I grew up with. This larger size may have a similar function to a clutch disk where the larger the disk the larger the friction surface and the higher the torque capacity. Friction between the differential gears is exactly the way a conventionally designed clutch type and cone type limited slip works... by causing friction between the gear and carrier to prevent differential action with the exception of limited slippage in cornering.

Furthermore, as the power is transmitted to the spider gears the bevelled interface between them and the axle gears forcing them to press outwards into the carrier case. This increases the friction between the parts increasing the resistence and reducing the free ability of the differential gears to rotate.


Actually the Torsen is NOT a limited slip.
It does not have spider gears.
It is an ingenius design that engineering claimed impossible prior to the inventor creating it.
The internal gears of which (some parts of these gears are visable in the picture) continuously mesh and allow one wheel to turn faster than the other but the action is not the same as a standard differential.
It uses worm gears in a very interesting way.



It does not use friction to stop the differential action as power is never uncoupled from either wheel regardless of traction and therefore no slipping is needed (no limited slip).