LSD acts like open diff?

Joined
May 19, 2018
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98
Location
CT
'03 Tundra w/about 108k miles. When backing slowly up my packed gravel driveway the other day wheelspin resulted in only one hole being dug. Was told when I bought it last year the diff was an LSD and it does have LSD sticker on it.

Is it expected to start slipping with age, or should I try a fluid change? I'm not sure if it has ever been done. I know the Vette will dig two holes if I'm over aggressive backing up, but it has much less mileage.
 
Drain old fluid out and see how it looks. Metallic? Might be clutch material. If fluid doesn't look too bad, refill with synthetic GL-5 gear oil. You might try putting a heavier oil in it. Most synthetic gear oil already has the friction modifier in it. Worst case you have to replace the clutch packs in the differential.
 
Not all limited slip differentials are the same. Even if your truck and your Corvette are both plate-type LSDs, they will likely behave very differently based on the applications. The Corvette is going to be way more aggressive than the truck.

There are three tunable pieces to a plate LSD: Break-away torque (preload), the ramp angle, and the total locking force.

Break-away torque is the measure of required torque to initially allow spinning from side to side. If you were to jack up the vehicle, hold one tire stationary and attempt to rotate the other side, the point at which rotation happens is the break-away torque. This is primarily for low speed turning. If the break-away torque is too high, the rear tires will chirp and squeak in parking lot-type maneuvers as they lose traction before the break-away torque is reached. Bigger tires, heavier vehicles, and stickier tires can get away with more break-away torque.

Ramp angle is how aggressive the LSD action is. As torque input increases (more power!) and/or wheel speed from side-to-side increases (wheel slip), the mechanism that applies pressure to the clutches rotates. Think of this mechanism like an eccentric cam: The more it's rotated, the tighter it gets. The eccentric can be a different shape, more or less angle, and that determines how aggressive that pressure is applied.

Total locking force is exactly what it sounds like: How much total force is applied to the clutches.

The LSD in your truck is almost guaranteed to be less aggressive than one in a Corvette in every way: Less preload, less aggressive ramp, and less overall locking force. I assume you weren't making a conscious effort to tear up your gravel drive, so you probably just didn't have enough input torque or wheel speed differential to really ramp in the LSD. You probably weren't tearing up the driveway with the Corvette either but it likely just has a higher preload that couldn't be overcome on a loose driveway.
 
^ Great info thanks.

It could be the above, it could be fluid, and it could be that your LSD is worn. (also could be that someone put the LSD tag on the outside of a regular diff....but that's unlikely)

I'd jack up the rear and turn one rear wheel. If the other side turns the same way your LSD is still working and MrHorspwer's info will apply. If not, then it's time for some investigation.
 
People always expect way too much from factory limited grips.

I don't know how Toyota's perform when new, but at 108k I'd expect worn clutch packs. However even with new clutch packs it may not do a lot. Engineers err on the conservative side because a diff "locking" too much in slick conditions on the road will cause the typical driver to go off the road and/or cause understeer.
 
Drain old fluid out and see how it looks. Metallic? Might be clutch material. If fluid doesn't look too bad, refill with synthetic GL-5 gear oil. You might try putting a heavier oil in it. Most synthetic gear oil already has the friction modifier in it. Worst case you have to replace the clutch packs in the differential.

I will probably start here and change the fluid. It certainly can't hurt anything. Will any synthetic GL-5 gear oil be acceptable, or should I err on the side of caution and go with genuine Toyota fluid from the dealer? Do different brands use different amounts of friction modifier, or is there a standard they all have to meet?

Not all limited slip differentials are the same. Even if your truck and your Corvette are both plate-type LSDs, they will likely behave very differently based on the applications. The Corvette is going to be way more aggressive than the truck.

There are three tunable pieces to a plate LSD: Break-away torque (preload), the ramp angle, and the total locking force.

Break-away torque is the measure of required torque to initially allow spinning from side to side. If you were to jack up the vehicle, hold one tire stationary and attempt to rotate the other side, the point at which rotation happens is the break-away torque. This is primarily for low speed turning. If the break-away torque is too high, the rear tires will chirp and squeak in parking lot-type maneuvers as they lose traction before the break-away torque is reached. Bigger tires, heavier vehicles, and stickier tires can get away with more break-away torque.

Ramp angle is how aggressive the LSD action is. As torque input increases (more power!) and/or wheel speed from side-to-side increases (wheel slip), the mechanism that applies pressure to the clutches rotates. Think of this mechanism like an eccentric cam: The more it's rotated, the tighter it gets. The eccentric can be a different shape, more or less angle, and that determines how aggressive that pressure is applied.

Total locking force is exactly what it sounds like: How much total force is applied to the clutches.

The LSD in your truck is almost guaranteed to be less aggressive than one in a Corvette in every way: Less preload, less aggressive ramp, and less overall locking force. I assume you weren't making a conscious effort to tear up your gravel drive, so you probably just didn't have enough input torque or wheel speed differential to really ramp in the LSD. You probably weren't tearing up the driveway with the Corvette either but it likely just has a higher preload that couldn't be overcome on a loose driveway.

Thank you for taking the time to share. Very informative.

^ Great info thanks.

It could be the above, it could be fluid, and it could be that your LSD is worn. (also could be that someone put the LSD tag on the outside of a regular diff....but that's unlikely)

I'd jack up the rear and turn one rear wheel. If the other side turns the same way your LSD is still working and MrHorspwer's info will apply. If not, then it's time for some investigation.

I will definitely test this by jacking up the rear before I change the fluid.

People always expect way too much from factory limited grips.

I don't know how Toyota's perform when new, but at 108k I'd expect worn clutch packs. However even with new clutch packs it may not do a lot. Engineers err on the conservative side because a diff "locking" too much in slick conditions on the road will cause the typical driver to go off the road and/or cause understeer.

This makes sense. You wouldn't want the back end to come around on you too easily, and they may be trying to play it on the safe side since unloaded there really isn't much weight over the rear in a pickup. Perhaps if I was driving in snow it may have been enough to spin both rear tires, or as was suggested the clutch packs could also just be worn.
 
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