Friction modifier for TBD?

sbmackie · 01-14-2016, 02:34 PM

Hello,
Goldcrest is doing my 915 box with a Quaiffe in it. I use the Kendall dino. Any reason to put friction modifiers in for a torque style slip limiting differential?

T'anks
Scott

Matt Monson · 01-14-2016, 03:16 PM

No. Friction modifiers are for clutches not gear driven diffs. They will also hinder the shift quality of your synchros.

sbmackie · 01-15-2016, 03:54 AM

Thanks Matt.

uwanna · 01-15-2016, 05:09 AM

Quote:

Originally Posted by Matt Monson

No. Friction modifiers are for clutches not gear driven diffs. They will also hinder the shift quality of your synchros.

Matt,
I have a 915/70 with factory LSD. I have been using the Kendall W/friction modifier gear oil.
LSD seems to work just fine and the synchros appear to work just fine as well as it shifts into any gear with no problems, even first while in motion. Shifts "like butter"
Should I continue to use friction modifier lube, is it really needed?

KTL · 01-15-2016, 06:10 AM

The friction modifier induces more slip between the friction plates and thereby reduces the effectiveness of the limited slip diff's function. It's often used in diffs to reduce chatter & noise. But if you want the diff to perform best, and not wear out prematurely, you don't want a gear oil with the FM additive. In all honesty if your LSD has never been rebuilt, it's probably well worn and doesn't provide a lot of limited slip/lockup effect.

Matt Monson · 01-15-2016, 06:48 AM

Quote:

Originally Posted by uwanna

Matt,
I have a 915/70 with factory LSD. I have been using the Kendall W/friction modifier gear oil.
LSD seems to work just fine and the synchros appear to work just fine as well as it shifts into any gear with no problems, even first while in motion. Shifts "like butter"
Should I continue to use friction modifier lube, is it really needed?

My advice frequently comes with a racing bias attached. Since I knew Scott was auto-xing his car, I felt I should mention the shift thing.

On a street car I don't think it matters as much. Many people report that when they use oils with friction modifiers their cold shifting gets better, which make sense since it's more slippery. And I don't think most street car guys get things hot enough in there to hit the other end of it where the hot oil is so slippery that there are shifting problems like we see in racecars.

On the oem ZF LSDs some people feel like they chatter and some don't. I think a lot of it does have to do with how worn it is. Really a personal thing.

On my LSDs I tell people to never use a modifier for the reasons KTL describes. I'm dealing with a situation this morning where one of my LSDs got passed through to a few different people without proper care and feeding instructions and it's wearing really quickly. I'm 90% sure it's got Redline Shockproof in it, which is probably my single most hated oil ever made.

uwanna · 01-15-2016, 07:30 AM

Quote:

Originally Posted by Matt Monson

My advice frequently comes with a racing bias attached. Since I knew Scott was auto-xing his car, I felt I should mention the shift thing.

On a street car I don't think it matters as much. Many people report that when they use oils with friction modifiers their cold shifting gets better, which make sense since it's more slippery. And I don't think most street car guys get things hot enough in there to hit the other end of it where the hot oil is so slippery that there are shifting problems like we see in racecars.

On the oem ZF LSDs some people feel like they chatter and some don't. I think a lot of it does have to do with how worn it is. Really a personal thing.

On my LSDs I tell people to never use a modifier for the reasons KTL describes. I'm dealing with a situation this morning where one of my LSDs got passed through to a few different people without proper care and feeding instructions and it's wearing really quickly. I'm 90% sure it's got Redline Shockproof in it, which is probably my single most hated oil ever made.

Matt,
My 915/70 LSD was brand new in the crate when I bought it in 1992 to install with my 3.6 transplant motor. It only has about 40K easy miles on it in the subsequent years, used to be DD, but now pretty much a garage queen. Just put the Kendall LSD lube in it about 1500mi ago. I think I'll go back to Kendall non LSD within a few months per you folks counsel. Question is, after 40K miles is the LSD probably still pretty much functional and how do I assess whether it is?
Thanks,
Grant

KTL · 07:58 AM

Whatever do you mean Matt? What's wrong with running liquid pink lipstick in these transmissions?

I had my own experience with that stuff when I got my "new" '79 SC racecar on the track for the first time in 2010. It runs a slightly modified '84 915/68 with a billet LSD (apparently a knockoff of Guard's, unfortunately)

Shifting was pretty clunky and I would get blocked out of 3rd more often than not. Decided to start with the oil to see what was in there. I found the pink goop. Shouldn't have been surprised since one of plastic totes that came with the car (guy selling was getting out of the hobby and gave me quite a few spare parts, etc.) had 3 qts. of Redline shockproof in it. Screw that. I put some Kendall in it and voila'magic shifting fix. But wait.........

Ran the Kendall for a while and changed it, find a bunch of fuzz on the drain plug. That's not good...... Even when the pink goop was in there, there wasn't THAT much fuzz on the drain plug magnet. The Kendall I used was their "Special Limited Slip" formula. Ah crap I just put a bunch of wear on my limited slip discs!!!! So I put some Swepco 210 cherry pie filling (it's crimson red) in it and now I think it's got an oil in it that's not doing the trans any harm. Latest oil change when I tore the whole thing down showed very little fuzz

So take that for whatever its worth.

Matt Monson · 01-15-2016, 07:46 AM

Street driven? Your LSD is probably fine. It's not 100% accurate but you can jack up on wheel, put it in neutral and put a torque wrench on a lug nut to see what it takes to break it loose.

If it were me I wouldn't waste the money on changing your gear oil again. I do my own every 10-12k or every 2 years, whichever comes first. Way more often on cars that I track.

KNS · 01-15-2016, 08:04 AM

Matt,

You have a PM.

winders · 01-15-2016, 08:48 AM

Quote:

Originally Posted by KTL

So I put some Swepco 210 cherry pie filling (it's crimson red) in it and now I think it's got an oil in it that's not doing the trans any harm. Latest oil change when I tore the whole thing down showed very little fuzz

So take that for whatever its worth.

I use Swepco 210 in my race car. It works great! I like how the transaxle shifts better than with Swepco 201, and my transaxle builder says the wear is better with Swepco 210.

Matt Monson · 01-15-2016, 09:10 AM

Quote:

Originally Posted by winders

I use Swepco 210 in my race car. It works great! I like how the transaxle shifts better than with Swepco 201, and my transaxle builder says the wear is better with Swepco 210.

When 3R used to run Cup Cars they would buy nothing but 210 for them. Swore by it. I think it's a great race oil.