All Wheel Drive experts chime in please.

[Outlaw1]

The shorter tire on the frontend effectively lowered (numerically raised) the gear ratio. When the VC is in 50-50 it puts the car is in a pretty good bind. Imagine putting 4.10's in the front and 3.73's in the back of a 4x4. Even without a bind, you'd be surprised to see how hot diffs get.

It's common practice to weld the VC and the front diff in a DSM. If you ever want to go for a ride in something that will shake, shutter, buck and generally freak out, just throw one odd size tire on it. Within a mile or two there will be some sort of broken drivetrain part.

[mcantar18c]

Irving:
Yeah, like I said dealerships suck. That's why I suggested actually going into a dealership and talking to them... if you put up enough of a stink the service manager will let you do it, and often times just asking will get you in.
What's wrong with your car?

Outlaw:
Different gear ratios will grenade the t-case, but shouldn't effect the diffs themselves.

[Irving]

Outlaw:
Different gear ratios will grenade the t-case, but shouldn't effect the diffs themselves.

This is the way that I understand it.

[Outlaw1]

Outlaw:
Different gear ratios will grenade the t-case, but shouldn't effect the diffs themselves.

I have limited experience with Scubbys, but I know they don't have a traditional T-case. They have longitudinally mounted engine/trans and a center diff that transmits the power to the rear. Sorry if I'm stating the obvious.

Having the drivetrain in a bind with mismatched tires and a locked center differential will affect the whole drivetrain, from one end to the other. IMO, when someone says they 'smoked' the fluid, or 'melted' the bushings, it doesn't mean it got hot enough for the fluid to catch on fire, or actually completely melt away the soft rubber bushings. They might have just been deformed a little and the fluid just smelled. Regardless, you wouldn't know until you drained it. Also, the mounts for the rear diff are on the rear cover, so if the ring and pinion got hot it transferred it right into the mounts.

Heat + drivetrain in a bind = tweaked bushings.

[DFBrews]

I have limited experience with Scubbys, but I know they don't have a traditional T-case. They have longitudinally mounted engine/trans and a center diff that transmits the power to the rear. Sorry if I'm stating the obvious.

Having the drivetrain in a bind with mismatched tires and a locked center differential will affect the whole drivetrain, from one end to the other. IMO, when someone says they 'smoked' the fluid, or 'melted' the bushings, it doesn't mean it got hot enough for the fluid to catch on fire, or actually completely melt away the soft rubber bushings. They might have just been deformed a little and the fluid just smelled. Regardless, you wouldn't know until you drained it. Also, the mounts for the rear diff are on the rear cover, so if the ring and pinion got hot it transferred it right into the mounts.

Heat + drivetrain in a bind = tweaked bushings.

Here is my guess this is based on big trucks so i may be completely off. there are 4 driven wheel ends and normally power is provided to a front wheel end and than the opposite wheel end on the rear. Like a criss cross pattern. there are spiders that allow the axles on the same diff to turn at different speeds when going around corners etc. when you put the smaller tire on the front it made the spiders in the rear diff work really hard trying to provide equal power to the rear to compensate. which made it get hot and start melting stuff and burning fluid.

when i dyno a semi i have to lock in the power divider so both axles get equal power. if i do not BAD things happen

[Outlaw1]

Here is my guess this is based on big trucks so i may be completely off. there are 4 driven wheel ends and normally power is provided to a front wheel end and than the opposite wheel end on the rear. Like a criss cross pattern. there are spiders that allow the axles on the same diff to turn at different speeds when going around corners etc. when you put the smaller tire on the front it made the spiders in the rear diff work really hard trying to provide equal power to the rear to compensate. which made it get hot and start melting stuff and burning fluid.

when i dyno a semi i have to lock in the power divider so both axles get equal power. if i do not BAD things happen

In this case the rear spiders would be take a beating, but they're not having to work the rear wheel tire/tire bias while going in a straight line. The front would have the spider gears working, but they are not in an LSD, so it's not THAT bad on the spiders.

Because of the short tire up front, the front tires are trying to spin slower than the rears with the 50/50 split. The drive side of the ring and pinion in the rear diff was in a serious bind (as well as the coast side of the front diff & the center diff).

[blackford76]

DFBrews gets a cookie!
You have to remember on a Subaru it isn't just a mechanical system, the computer lost it's mind with the odd sized tire and seriously over worked the rear diff trying to compensate. That is why they wanted to add the fuse to disable the awd system.
The whole time the small wheel was on the ground, the computer sensed that one wheel was losing grip, so it sent power to the rear, it uses the abs wheel speed sensors to tell which wheel is "in trouble".

[DFBrews]

DFBrews gets a cookie!
You have to remember on a Subaru it isn't just a mechanical system, the computer lost it's mind with the odd sized tire and seriously over worked the rear diff trying to compensate. That is why they wanted to add the fuse to disable the awd system.
The whole time the small wheel was on the ground, the computer sensed that one wheel was losing grip, so it sent power to the rear, it uses the abs wheel speed sensors to tell which wheel is "in trouble".

Thanks Rob when the hell are we going shooting again


and outlaw no AWD is a true 50/50 split in power... ever

[blackford76]

Thanks Rob when the hell are we going shooting again

I dunno, I have weekends off now, but work nights. We're gonna have to figure something out, I've got 2 new 1911's I haven't shot yet.