jbrob007

Guys, Got a few observations & questions on LSDs. My car has the manual tranny and does NOT have the 220 option code although I THINK I have a 40% LSD... am not sure.

I was under the assumption with a standard differential that if you turned one rear wheel by hand it would turn the other side wheel in the oppoisite direction... and visa versa... correct?

I was also under the assumption that turning a rear wheel on an LSD it would turn the other side wheel in the same direction... correct?

With my 86.5 / Manual tranny up on jack stands, in neutral, you can turn the driver side OR pass side rear wheel by hand without turning the wheel on the other side (at all) in either direction. Strange...??

When put into gear, if you turn one wheel by hand it will turn both wheels in the same direction...

Needless to say, I'm confused... which isnt saying much... Any thoughts on what kind of differential is in the car?

GregBBRD

Open differential. No limited slip.

Ducman82

^^ what he said.

jbrob007

O.K. I'll take it as gospel, but... how??? Ya know, so some other guy doesnt have to ask the same question... yeah, thats the ticket... so someone ELSE doesnt have to ask it...

GregBBRD

I've tried three times to start and try to explain this....but it keeps tuning out too complex. Part of the problem is that what you have claimed is happening is impossible....unless the clutch is also depressed, when the transmission is in gear.

Here's the best way to understand the one data point that told me you absolutely didn't have a limited slip

If you have a limited slip that works, both axles will turn in the same direction, if the transmission is in nuetral. The two axles are "joined" by friction discs and will turn together, with a limited slip, until the friction between the friction disc is overcome and one or the other "slips".

The fact that one axle turns and the other doesn't, with the car in nuetral, actually tells you a couple of things. It tells you that the axles have nothing connecting them (no limited slip)....otherwise they would turn together, in the same direction. It also tells you that there is less resistance to turning the entire differential, ring gear, and pinion shaft, than the differential simply turning the other axle.....in the opposite rotation. To me, that means a brake is dragging or the axles are dry and resistant to rotation.

The problem with your second data point is that you say that if the transmission is in gear, the axles turn in the same direction.

If the transmission is in gear, the pinion shaft can't turn, unless the engine turns or the clutch is pushed in. If the pinion shaft can't turn, neither can the ring gear. That means the differential "carrier" can't turn. Consequently, the only direction the other axle can turn, regardless if there is a limited slip or not, is in the opposite direction.

I suspect that you must have the clutch pedal depressed or have something disconnected, when you have it in gear. This allows the entire ring gear and carrier to rotate, turning both axles in the same direction.

jbrob007

No brakes dragging... but axles dry and resistant to rotation is a definite possibility. I'll look into it... Thanks for the tutorial - I learn more everytime I log on here... again, thats not saying much

FiveElements

Here's a relative question...

I have an 88 Trani that I'm putting into my car soon. It has 110K miles on it. Should I rebuild the LSD (if it has it) and how do I know if it will need the rebuild?

DougM

Just jack the car up in the rear and open the fill plug and have a peek with a flashlight. There is quite a significant difference of what you will see in the differential between LS and non-LS. Pictures are on here somewhere in some past threads.

Dave928S

I think it's worth checking the LSD while you have the transmission out, to check the friction surfaces, which are very likely to have some wear. You can check how well it's working before you pull it apart by doing a torque test, which is checking the torque required to overcome the frictional resistance of the plates to get one axle rotating relative to the other. It's in the WSM, but basically you lock one axle, and then with a torque wrench and adapter you check the torque to overcome the resistance of the friction plates and get the other axle to turn. Edit: For this method, of locking one axle and torquing the other, the trans needs to be in neutral because the spool will turn when the break through torque is exceeded.

The pics are in this thread .... https://rennlist.com/forums/928-foru...questions.html

GregBBRD

Check it.

Put the transmission into gear and turn one of the flanges with a torque wrench. 7-25 pounds is the specififcation for your differential. Start with low torque and work you way up with the torque setting. Since the bolt torque is 32 ft lbs, the opposite flange should turn before the bolt gets too tight. Less than about 10 ft lbs.....it needs attention. More than 25 ft lbs...you've got some serious grief.

IcemanG17

Okay I don't know much about transmissions....or LSD's........................but what I DO KNOW is Doc Brown does know!!!! My freshly rebuilt transmission in my race car is WORLDS better than what I had before.....I can actually floor it mid corner and the car accelerates.....before it was an endless 1 tire smoke show....sometimes at 90+ mph.... Here is a video of my worn out LSD

depami

And it will turn in the opposite direction, correct?