Detroit Truetrac?

OK, I mentioned in this thread https://grassrootsmotorsports.com/forum/grm/truck-mpgtowing-question/109527/page5/#post2132827 that the diff is screaming. So, the plan is later this fall to just pull the diff out, stick it on the bench and revuild (with supervision). Now, the truck is an open diff (one wheel peelin' monster) and there's no way I am yanking this thing apart and NOT upgrading to something better than that.

So.. I have come down to the Detroit Truetrac. gear type lsd so takes no additives (like the clutch type) and not overly aggressive. Anyone here had any good experiences? Bad? So so? Should I use a different one? It looks like I can get the TT, intall kit and wheel bearings all from Summit for under $600 shipped.

I'd make sure it's truck capable. Truetrac is like a Torsen, right?

I know a lot of GM truck people seem to like them over the G80 OE clutch type units.

Gear-type LSDs are a nice mild option for keeping the one-wheel-peels in check without causing any nasty handling side-effects or making the vehicle more maintenance-intensive. If you have any problem at all with one of these, it might be that it's not aggressive enough. If you're just towing on pavement I think you'll be fine, but if you're doing any offroading you might want something more aggressive.

Edit: I'm planning to put a gear-type LSD in my Corolla FWIW. The next step up is a Wavetrac, which is a gear-type LSD that can load itself to prevent one-wheel-peeling even if one wheel is completely unloaded.

yeah, this is for the (currently) 1-wd truck that the only "off road" it sees is the 1/4 mile uyp our gravel road and to pull into the yard to grab the trailer. IT's also our "go-to" vehicle in bad weather. Throw in one of those baffled truck bed bladders, add 200lbs strapped down and roll. Adding another wheel to push it would sure be helpful.

It's a Torsen. So not a limited slip diff but a lot more useful than an "open" diff. And no sketchy handling in the wet.

Knurled wrote: It's a Torsen. So not a limited slip diff but a lot more useful than an "open" diff. And no sketchy handling in the wet.

It is definitely a limited slip. Most torsens aren't preloaded though, so assuming a diff with a 4:1 bias ratio, if the left wheel spins once 20 ft lbs are applied, you'll only be able to apply 80 to the right wheel before wheelspin occurs. And if one wheel is in the air, it'll be taking very, very little torque to spin it. So on the other side, you get a 4x very little in this example, which is still very little, hence no forward motion.

Both my vehicles (94 Miata and 96 4-runner) have a torsen rear diff, the 4-Runner is a truetrac. I'm a fan. The 4-runner was perfectly capable off-road with the open diff, but it would happily spin the inside tire in any lowish traction situation. Now with the trutrac it just puts power to both wheels, no fuss.

The biggest difference is in mid traction conditions, such as dirt roads or even pulling into traffic with some gravel in the intersection. I treat it like a fat rally car on forest service roads and with the torsen it is pretty predictable (for a top heavy SUV) and fun to hang the tail out. Honestly for most forrest service or desert road driving (heading out to camp sites) 4WD is unnecessary.

Flip side is when it's icy, the rear comes out FAST. The 4-runner has a pretty short wheelbase, so any tail happiness is exaggerated. In a truck with a longer wheelbase it would be less extreme. As torsens are torque-biasing, lifting a wheel off the ground essentially nets you an open diff. I do very little technical off roading so it's not an issue for me.

Unlike a clutch type LSD, when you lift off the gas it becomes an open diff again. This can be a plus for DD type driving as it should help put the rear back in line if it steps out and you lift. When the 4-runner eventually gets replaced by a newer Tacoma, the locker will be sold & in it's place will go a truetrac

In reply to rslifkin:

The one I installed in a Road Runner a couple years back (Dana 60 rear) was definitely not a limited slip. Zero effort to rotate the wheels by hand with the driveshaft stationary.

In reply to Knurled:

Failing a test that can only check for the existence of certain types of limited slip diffs, not functionality, doesn't mean it isn't still a limited slip. If functionally it is a differential that limits slip, then by definition it is a limited slip differential.

Knurled wrote: In reply to rslifkin: The one I installed in a Road Runner a couple years back (Dana 60 rear) was definitely not a limited slip. Zero effort to rotate the wheels by hand with the driveshaft stationary.

They're exactly an lsd and for a lot of applications, theyre pretty fantastic. They never wear out like a clutch type, theyre quiet, they provide much better traction under 85-90% of conditions. Oems love em because they're a good compromise.

It is still an open diff. It is torque biasing, but it doesn't limit slip. The torque bias may serve to limit slip in practice, but that doesn't make it a limited slip diff.

For that matter, a standard open diff also limits slip by its own internal friction. NSU discovered this when they made an open diff that did not use bevel gears at all (it was a ringwheel/cogwheel arrangement) and found that it was extremely easy to get one wheel spinning compared to a "standard" bevel diff. NSU did have a corporate history of trying to reinvent the wheel, which is probably why it ended up getting absorbed by Audi. (I like the engine that used three connecting rods to drive the camshaft, instead of a belt, chain, or gears)

Words have meanings Limited slip diffs have clutches engaging both axles together to limit relative motion. Torsens will happily allow the axles to run at whatever speeds they want, and this is why they work better for 99% of street applications. Let's face it, limited slip diffs freakin' suck, they kill handling, and kill it worse the lighter the car is.

Yes, words have meaning. Limited slips limit slip. Clutch type limited slips do it via clutches. Viscous limited slips do it via a viscous fluid coupling. And helical limited slips do it via helical gear sets.

An open diff transfers power to the wheel that is spinning faster. A limited-slip diff transfers power to the wheel that is spinning slower. A helical limited slip does the latter.

In reply to Knurled:

In this application we are taking about a 19.5' long 5,000 +lb truck. Handling is not a major concern. It already has a 2 mile turning radius.

What I was trying to see if anyone here had good or bad experiences with the TT or there was a better option in similar price range.

https://en.m.wikipedia.org/wiki/Torsen.

I have a TrueTrac in my '77 C10 Shortbox.

I researched all the types (Auburn, clutch, locker, Gov-Bomb), and I've driven the truck with the factory open diff and 3.07:1 gears. For (vague) comparison, my Locost Super 7 has a 2-way clutch.

I decided on the TrueTrac because 1) this is a daily driver, and 2) Canadian winters.

At the same time, I swapped the 3.07:1 to 3.73:1.

In everyday driving, the thing is amazing. It is everything everyone says it is. Quiet, predictable, and I get nowhere NEAR the wheel spin I used to get, despite deeper gears.

In winter, the back kind of has an adventurous mind of its own, but you will always be moving forward (at least, averaging forward), and you can easily and predictably steer with the throttle.

I am completely sold and I would do the same diff again.

Is that more helpful?

Knurled wrote: In reply to rslifkin: The one I installed in a Road Runner a couple years back (Dana 60 rear) was definitely not a limited slip. Zero effort to rotate the wheels by hand with the driveshaft stationary.

That's because there's no preload on it. You're not applying enough torque by hand for it to do anything. A clutch type will behave differently in that situation as there's preload on the diff to make it always capable of biasing at least some amount of torque (a preloaded LSD will still put down some power with a wheel in the air and a highly preloaded one starts to feel like a locker).

In reply to SkinnyG:

That's what I was looking for. I've read similar in other sites but y'all are my default go to.

Anyone use one in a performance application?

My Mustang has a hard time keeping LSD functionality. In 58k miles, burned out the stock clutch, burned out an Auburn Road Race diff, and in one season I am seeing a degradation in the (rebuilt with carbon clutches) stock diff that I put in earlier this year and anticipate having to rebuild it by the end of next year.

So I have been cross shopping a Truetrac, a Torsen, and a Wavetrac. The Truetrac seems to be the cheapest option, so I am trying to figure out if the additional spend on the others is really worth it.

The Wavetrac can apply power with one wheel completely unloaded while the others can't, so those three aren't all exactly the same type. I'd just save the money and go with the Truetrac, your Mustang probably has both rear wheels solidly on the ground at all times, and since your car has a record of blowing up diffs I'd be hesitant to put an expensive one in there.

I prefer the Yukon Dura-Grip from Randy's Ring and Pinion over a Tru Trac. Dura-Grips are rebuildable, TTrac is not. Much better pricing as well.

TAParker wrote: I prefer the Yukon Dura-Grip from Randy's Ring and Pinion over a Tru Trac. Dura-Grips are rebuildable, TTrac is not. Much better pricing as well.

The Yukon is almost $100 more expensive than the TT.

TAParker wrote: Dura-Grips are rebuildable, TTrac is not.

Dura-Grip is a clutch type. So it is rebuildable, because it needs to be. Truetrac is not, because it doesn't.

A buddy of mine has a truetrac in his 1uz swapped Cressida, works beautifully.

I put one on an 06 GMC Sierra when the factory G80 failed at under 100k miles. I sold that truck with 250k miles of reasonably hard use (towing, construction site hauling, offroading) and never had a bit of trouble out of the TrueTrac. It was quiet and very well behaved and always locked up well. I would/will use one again in the future when the time comes.