outasite
outasite New Reader
6/26/15 7:36 p.m.

My recently acquired 99 Miata equipped w/Torsen differential is doing something I have never experienced w/other limited slip, posi, etc. differentials. Accelerating through a sweeper, disengage clutch to shift and the front end makes a move to the inside of the curve. Is this normal??

Junkyard_Dog
Junkyard_Dog SuperDork
6/26/15 8:12 p.m.

It sounds like every one I've owned or driven. The CTS-V rear I put in mine fixed it. Clutch type iirc.

DCharger68
DCharger68 Reader
6/26/15 8:13 p.m.

Weld the diff

Keith Tanner
Keith Tanner MegaDork
6/26/15 8:58 p.m.

Wouldn't that be standard weight transfer? Weight shifts from the rear wheels to the fronts, front gains grip and tightens up the slip angle.

Mr_Clutch42
Mr_Clutch42 SuperDork
6/26/15 9:15 p.m.

Don't shift mid-corner?

yamaha
yamaha MegaDork
6/26/15 10:19 p.m.

Torsen, quaife, mFactory, wavetrac, etc are not limited slip differentials, they are active torque bias units(ATB) They still slip one side more than the other. Is that possibly what made your car do that? Yes. Is it possible its just weight transfer? Yes. Hell, it could be as simple as an alignment issue.

outasite
outasite New Reader
6/26/15 11:13 p.m.

In reply to yamaha:

I just did a 4 wheel alignment after it happened the 1st time. Every thing is preferred specs w/0 thrust angle. I also increased caster more positive. Seems like the differential wants to go straight under power and front tires gain traction when power is disengaged. Only noticeable on sweeper coming out of town. Guess I will stop racing bubba trucks.

SkinnyG
SkinnyG Dork
6/27/15 12:00 a.m.
outasite wrote: Seems like the differential wants to go straight under power and front tires gain traction when power is disengaged.

That sounds reasonable for a traction aid device.

sesto elemento
sesto elemento Dork
6/27/15 10:29 a.m.

If you had more power you could ask the rear tires to not have traction when the traction that they're having is bothering you. Just a thought

codrus
codrus Dork
6/27/15 12:06 p.m.

If you take a sweeper going the other way and do it again, does it still pull to the inside or does it always pull to the left (or right). If it's always to the inside, then it's an LSD/traction/weight transfer behaviour, if it always does it to the left/right then it's caused by something asymmetric in the rear suspension (alignment, bushings, tire pressures, etc).

outasite
outasite New Reader
6/27/15 1:06 p.m.

In reply to codrus:

Yes, still pulls to inside, thus my question about Torsen. Car has 56,000 miles and I did an inspection before I aligned it. The differential and transmission had a heavy gear lube in them when purchased. I drained and changed to synthetics. It took a while before transmission shifting improved. Wondering if I run some skid pad circles both directions to work unit gears and lubricate w/new fluid may help. Been driving and wrenching lots of cars since early 60s and never had this happen.

T.J.
T.J. UltimaDork
6/27/15 1:11 p.m.

For some reason I first read the thread title as "Torsen differential equation" and was interested to learn something new.

Knurled
Knurled UltimaDork
6/27/15 5:04 p.m.

+1 to Yamaha - Torsens are open diffs with a variable bias. The torque being applied to each wheel is NOT even like an open diff. What you are probably feeling is an understeer from torque being biased towards the inside rear tire (turning slower, more torque for the same power due to diff's internal gear reduction/splitting) and then when you lift off the throttle the understeer goes away.

You should see what happens if you drive with a good limited slip or spool. I've only had chance to spend a lot of time in my RX-7 with one of each (they act the same) so I can't say for everything, but it DIVES to the inside of a corner when under power. Not in a powerslide tail-out way, it feels like the Hand of God is pushing the front bumper to the inside of the corner. Very useful but spooky if not expecting it. This is probably the opposite from the issue you have, since the tires can't differentiate, they always scrub in a corner, so off throttle the outside tire scrubs slower than actual speed, but on throttle the inside tire scrubs faster than actual speed, so the OUTside tire is doing most of the thrusting under power. Only way I can explain what is going on there.

Mr_Clutch42
Mr_Clutch42 SuperDork
6/27/15 10:43 p.m.

In reply to Knurled: What good limited slip or spools have you driven?

outasite
outasite New Reader
6/27/15 11:35 p.m.

In reply to Knurled:

That was my theory as well when I researched Torsen operation. Just never experienced this in any muscle/performance car I have owned or driven. Wanted to know if this was normal Miata handling.

Knurled
Knurled UltimaDork
6/28/15 5:20 a.m.

In reply to Mr_Clutch42:

See above - my RX-7. None of my other cars ever had anything but open bevel diffs. I had one with switchable locking diffs but it didn't make enough power for any weird effects to be noticable.

T.J.
T.J. UltimaDork
6/28/15 7:29 a.m.

In reply to iadr:

Nice!

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