So, my 1973 911S with LSD has been feeling like I have the 4WD on while I’m making slow turns. Obviously it doesn’t have 4WD but that’s what it feels like. There is a binding sensation much like when the front diff is enabled on pavement in a four wheel drive vehicle. I raised the rear end and the wheels seem to move independently from one another sometimes. I’m not sure if that is normal for the LSD. Any thoughts?
Last edited by METAVINYL; 04-22-2020 at 06:56 AM.
What kind and brand of diff do you have?
It’s the original transaxle. Are there factory variations?
Last edited by METAVINYL; 04-22-2020 at 09:42 AM.
Factory ZF diffs, will make noise slow turning. They also break the undulated pressure lamina at the outer extremes of the plates. Almost all were set at 80% and should in neutral, up in the air, have a fair amount of tension when holding one wheel and turning the other. If not a rebuild might be in the offing. They can be updated, the % can be changed. I’ve run factory diffs for decades, they always barked a little on slow turning. I’ve just run my first Guard diff, 40-60%, completely transparent and quiet. is the trans type# still readable (915/xx. G
Thanks for the response. This is my first experience with LSD. (Couldn’t resist). I’m going to try some Kendall in there. That should tone it down a bit, but it’s sounding like it’s a normal artifact of the diff.
Does the owner’s manual call for a limited slip gear lubricant (i.e. contains a limited slip additive)?
Peter Kane
'72 911S Targa
Message Board Co-Moderator - Early 911S Registry #100
It’s just the standard ‘73 manual. I don’t see anything specifically about an additive but it does call for different fluid than the standard gearbox. M 2 C 28 B as opposed to MIL-L-2015 B. I ordered the Kendall LSD GL5 from Pelican.
Here’s some product I found online that actually mentions the Ford M2C-28B spec...
https://www.usteile.ch/Zubehoer/Rekt...-Kanister.html
I had never seen that spec before. I guess that’s what was available back in the day for this ZF application. Let us know if the Kendall product fixes the problem.
Peter Kane
'72 911S Targa
Message Board Co-Moderator - Early 911S Registry #100
Very interesting. Thank you for the link. Last night I dug deep and was reading through the maintenance record. I discovered that the a previous owner put the Kendall LSD gear oil I just ordered in the diff some 30 years ago. I’m sure it’s due for a change. If it was recommended then and now there must be something to it! I will report back one I change the fluid.
The LS additive allows the clutch plates in the differential to “slip” rather than “stick”. If they stick too much, you get the roughness you’ve encountered. Great discussion topic!
http://www.181spirit.com/menu/techni...F/ZF_SA_01.jpg
Peter Kane
'72 911S Targa
Message Board Co-Moderator - Early 911S Registry #100
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