limited slip

[Nick Triesch]

I have an 85 911. How do I know if I have a limited slip dif? Is there a lever? A switch? I have never felt any kind of wheel seperate movement. Can I use the Kendall limited slip 80/90 gear oil in my car if I do not have it? Thank you, Nick

[Brad394]

Well, i think it is option 220 so if you still have sticker under front hood that would be a starting point.

After that if you put the car in the air and while in neutral turn one of the rear wheels by hand the other wheel will turn in same direction.

as for fluid - my answer would be no - don't mix and match

There are others who can maybe provide more detail.

Brad

[Bill Verburg]

Originally Posted by Nick Triesch

I have an 85 911. How do I know if I have a limited slip dif? Is there a lever? A switch? I have never felt any kind of wheel seperate movement. Can I use the Kendall limited slip 80/90 gear oil in my car if I do not have it? Thank you, Nick

On the bottom of the trans is it's serial #
this is a 915/73 which was used in US 1985 3.2 Carrera

the serial # is 74F 03454, between the type#915/73 and the serial # 74F 03454 is the number 12, This last # indicates that there was a factory installed ZF lsd.


This trans is a 915/63 74C 2459 and had no lsd oem


On a trans w/ a fully functional lsd you can also put the rear wheels in the air and spin 1 of them if the other goes in the same direction there is a functional lsd. This test becomes less useful the more worn the lsd is and is less useful if the lsd is set up w/ a low preload. If you have someone hold the other wheel some sense of the lsd function can be felt, an open diff will have very little resistance, a worn lsd will have a little resistance and want to rotate in the same direction as the driven wheel, a fully functional lsd will have a lot of resistance and again want to rotate in the same direction as the spun wheel

[Matt Monson]

I would never suggest you put in an LSD additive unless you are trying to make your LSD make less noise. LSD additives are friction modifiers, which make it more slippery, which is counter to what you want an LSD to be doing if you are using it as a performance enhancing device. LSD additives are a NVH item, not a performance thing.

[Bill Verburg]

Originally Posted by Matt Monson

I would never suggest you put in an LSD additive unless you are trying to make your LSD make less noise. LSD additives are friction modifiers, which make it more slippery, which is counter to what you want an LSD to be doing if you are using it as a performance enhancing device. LSD additives are a NVH item, not a performance thing.

I couldn't agree more

here's what I use in mine, Swepco in the 915 Delvac in the g50 both w/ lsd that work well

[DRACO A5OG]

Kendell makes straight 80W90 without LSD as well.

Pick up the rear at the engine using a pad or bundle of new papers and spin right rear wheel, If both wheel move you have LSD if not you have Standard Trans

[GaryR]

Originally Posted by Bill Verburg

On a trans w/ a fully functional lsd you can also put the rear wheels in the air and spin 1 of them if the other goes in the same direction there is a functional lsd. This test becomes less useful the more worn the lsd is and is less useful if the lsd is set up w/ a low preload. If you have someone hold the other wheel some sense of the lsd function can be felt, an open diff will have very little resistance, a worn lsd will have a little resistance and want to rotate in the same direction as the driven wheel, a fully functional lsd will have a lot of resistance and again want to rotate in the same direction as the spun wheel

Is that a reasonable way to see if the plates are shot Bill? I was thinking of having it replaced (Guard?) or rebuilt next time the tranny goes in for a refresh. I use Kendall for LSD now after using Swepco for 5 years. Seems to shift with less fuss now but who knows, I tried it on Peter Zimmerman's recommendation..

[Bill Verburg]

Originally Posted by GaryR

Is that a reasonable way to see if the plates are shot Bill? I was thinking of having it replaced (Guard?) or rebuilt next time the tranny goes in for a refresh. I use Kendall for LSD now after using Swepco for 5 years. Seems to shift with less fuss now but who knows, I tried it on Peter Zimmerman's recommendation..

I think so, the factory method is similar and done w/ a torque wrench to put some #s on the test. If you just need a sense for whether it's working or not this is fine.

The ZF in the 915 is set up for nominal 40% and there is a lot more low speed resistance than the motorsports 40/65 in the 993. I assume that is because of preload on the bellville washers.

The ZF is also much more apparent on hard slow speed turns

[GaryR]

Going to be at Limerock April 9th? You can be my LSD wear gauge!

[Bill Verburg]

Originally Posted by GaryR

Going to be at Limerock April 9th? You can be my LSD wear gauge!

Yeah, I'll be there, not driving, just helping the club out.

Looking forward to seeing all the changes you've done.