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Project Tundra: Getting More Grip with an Auburn Gear HP Limited Slip Differential

by Mike Kojima

Supercharging Project Tundra is one of the best things we have ever done to any project vehicle in the MotoIQ fleet.  The TRD supercharger has proven to be totally reliable in thousands of miles from towing up hill in blazing heat to driving all over the place.  It has also proven to be economical as our normal driving gas mileage has not changed at all.  If anything, the large amounts of power have had only one negative effect on the truck: no traction.  To help deal with this we obtained the only limited slip diff on the market for late model Tundras, the Auburn Gear HP Limited Slip Differential.

Traction was a big issue with Project Tundra.  Our engine could easily break the big 295 Nittos loose from a roll all the way up to 50 mph.  The wheelspin was so violent, the truck's traction control, stability control and electronic Limited Slip were going crazy.  Not programmed for so much power and big grippy tires, the truck would sometimes get into violent oscillations where the electronic nannies fought to control the power to no avail. It was scary, your options were to let off the gas or crash.  

Since the stability control and electronic Limited Slip work by using the brakes to either add understeer or slow the rear tire spinning faster than the other, the added power and the fact that the electronics were coming on all the time were killing the brakes, especially the rear brakes.  In addition the electronics were causing irritating things to happen like what we would call Auto Bog. This is when you stepped on the gas hard to make a right or left turn with oncoming traffic.  You would gas it to speed up and the truck would shoot into traffic, only to have the electronics bog the motor and the truck would just sit with no throttle control as on rushing traffic would come closer and closer.  This was not only annoying but potentially dangerous.

The spinning tires would also generate huge amounts of wheel hop when the electronic LSD would try to vary the torque from side to side.  Not only would this affect traction but the pounding was putting a lot of stress on the drivetrain.  Now the stock truck is affected by all of these issues as well but the addition of the supercharger with its big injection of power and torque makes it much worse.

We figured an LSD Differential would help all of this and after doing some research we were surprised to find that only one company made an LSD for late model Tundras.  Auburn Gear has an HP model differential that fits all Tundra's from 2007 on up.   We obtained one of these diffs and proceeded to install it.

 

The Auburn Gear HP Differential fits the Tundra's huge 10.5" ring gear.  We think this is the beefiest differential of any 1/2 ton truck on the market.  The diff has a strong cast nodular iron case with precise machining for easy setup as we found later.
The Auburn Gear HP diff is very different than your typical limited slip that usually uses clutch packs loaded by cross shaft torque.  The Auburn HP Diff uses the side gears which are machined with cone like backs to provide locking torque.  The side gear cones are forced into the differential case by these springs and retainer plates when the rear wheels start to turn at different speeds.  To us, this seemed like it would not have very much lock up.  Would this diff be able to lock up with our big tires and 500 plus hp?  Read on.
Our Tundra is so big, it won't fit on our lift so Howard Watanabe had to work on the floor with jackstands.  The first step is to remove the wheels.

 

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Comments
Mike Kojima
Mike Kojimalink
Monday, February 23, 2015 11:23 AM
No love for perhaps one of the best additions to a Tundra!
Burninator
Burninatorlink
Monday, February 23, 2015 2:11 PM
Glad to hear it worked out. Especially for such an inexpensive diff. I figured you'd be pointing out flaws while examining it, and that it wouldn't work well. Glad to know I was wrong. It really is nice to hear that you don't have to shell out 2 grand for a diff to not be crap.
rhocken
rhockenlink
Monday, February 23, 2015 3:28 PM
Is there any special coating on the conical section and the housing it mates with? Given it is is tapered, the axial force produced by springs is magnified into the radial direction (like driving a wedge). Also I think the spider gears also push the conical section axially as well (so more torque results in stronger lock). Such a high radial force that slips I'd be concerned about it galling - curious if that is the case and anything special was done in the design.
Mike Kojima
Mike Kojimalink
Monday, February 23, 2015 3:37 PM
When looking at the diff, I was almost sure it was not going to work too well due to the small overall area of the clutch cones and the limited tension of the 4 springs. The wedging action is probably part of what's going on and the spider gears probably provide a small additional outward force component which probably peaks right before they start to differentiate a lot. The cones have some grooves for lubrication but I don't think they are coated other than perhaps a slight phosphate coating. This diff is awesome, it predictably transfers over 400 lb/ft of torque, locking hard even with huge tires, yet is as smooth and quiet as a torsen or viscous LSD. Don't let the simplicity of the design or the low price fool you.
Supercharged111
Supercharged111link
Monday, February 23, 2015 5:29 PM
For perspective, GM half tons come with an 8.5" ring gear and the Fords an 8.8". GM will give you a 9.5" differential with the top of the line tow package, but 10.5" is only for 2500HD+. I'm betting your brake pads will last a lot longer now that TC isn't kicking in as much too.
Burninator
Burninatorlink
Tuesday, February 24, 2015 9:28 AM
Am I wrong to guess because of the design that there is the same lockup under decel as under accel?
Van_1986
Van_1986link
Tuesday, February 24, 2015 11:47 AM
Love the drivetrains in these Tundras, I just wish they weren't so incredibly massive. Its fine if its just a weekend tow rig but having lived with a previous gen Tundra daily, I wouldn't want anything bigger. Now if we could just shoehorn the supercharged 5.7L/10.5" diff into a Tacoma...
Mike Kojima
Mike Kojimalink
Tuesday, February 24, 2015 1:19 PM
@burninator, I think the lockup under decel is less due to lack of wedging action of the spider gears. The diff doesn't seem to contribute to turn in understeer and doesn't rachet at all. It does chirp the inside tire a bit when throttling out of tight turns. Now that I turned up the shocks compression damping and am poking the limits I am scaring myself. This thing seems to corner well but I am scared how far I can push it before it flips over.

@Van_1986 I agree, I love this truck but finding parking places for it and going in parking structures is a bitch.
Burninator
Burninatorlink
Tuesday, February 24, 2015 2:53 PM
I live in Montana, everybody drives trucks all day every day. Driving one around daily would be no issue at all.
Burninator
Burninatorlink
Tuesday, February 24, 2015 2:55 PM
In a pinch I've used my '94 1-ton (long box, 4-doors) as a daily driver while my other car was out of commission. Some drive-throughs are tricky, but other than that it's not a big deal. Also, we don't believe in parking structures in Montana.
SM_Clay72
SM_Clay72link
Wednesday, March 04, 2015 10:43 AM
I was driving one of these trucks for a while. a lot of the time on gravel roads where it would try to correct your intentional oversteer in part by braking the outside front tire and attempting to send you off the outside of the corner! It is possible to turn off both Trac and ESP, but only with the truck in park (and maybe nuetral?). It involved holding down the button for 5 secs or so. Can't remember, but I am sure it is Googleable.

You probably know this though.
Mike Kojima
Mike Kojimalink
Wednesday, March 04, 2015 11:49 AM
Yes we know that but it doesn't turn all the way off. It also defaults to on and for everyday driving it's better to leave it on. It's better to make the car behave with the electronics on
Blenton
Blentonlink
Thursday, March 08, 2018 10:38 AM
Synthetic gear oil??? Auburn is adamant about using ONLY conventional gear oil in their LDS units, but I see you used full synthetic. Synthetic has a great deal of benefits, but I'm curious as to why you made that choice? I'm also curious to see an update on the longevity of the Auburn unit after thrashing on it.
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