Lucas is not a syn diff oil, it's dino oil with some stuff added in.

There was a sticky link to an Amsoil diff oil study a while ago on the forum, but they're a sponsor so take their word with a grain of salt. Not a bad read though. See what Dino oils they tested. If I recall correctly, Mobil 1 syn was the best mass available syn that they tested.

 

There seem to be a lot of good oils but they are all synthetic. Thats why I'm hoping to find the best non synthetic. I like Amsoil and have used there stuff for a while in bikes but I like Royal Purple better. Thats just a personal thing though.

 

The thing I read on Dodgetrucks.org about the Auburns liking the Ford or GM modifier says to use 3 oz. of friction modifier for every quart. Since the Ford ones come in 4 oz. bottles do I just want to add 2 of these? That would be 8oz. and doesn't it take about 2 and a half quarts of fluid?

I got some Ford friction modifier and some Lucas 80w90 heavy duty oil. I don't know what the heavy duty part means it's just what it says.

 

I use Mopar non synthetic 80W90 with Ford friction modifier per recommendation from Auburn. Also saw this (see pic) on DTO that agreed with what Auburn told me. I used Mobil 1 synthetic in the front diff, but Mopar non synthetic in the rear. Right now, it has something in it from the shop that changed the gears. When I do the 500-1000 mile fluid change, i'll probably go back to non synthetic Mopar gear oil and the Ford friction modifier.

[IMG]local://upfiles/9095/519E3CDD600E4BFAA5D9C8EDB2E8BE3B.jpg[/IMG]

 

Wow that seems like a lot of FM.
I don't think I have ever added more than 4oz to a diff.

 

I put 2 bottles of Ford Friction modifier so 8 oz and used Lucas gear oil. I then used Royal Purple in the front. I might should have used the Mopar brand gear oil but I didn't even check on it maybe I will next time. How much is it a quart?

 

That seems like way to much FM.
Will it cause a problem? Who knows?
The way I understand it the FM makes the oil more slippery so there isn't any noise or chatter when turning. but there is a point where if it is too slippery the posi clutches won't hold properly during low traction. I think that is why most manufacturers don't recommend synthetic axle lube with aftermarket LSD.
According to a few guys I respect on BITOG they recommend adding 4oz and test driving. If there is no chatter leave it alone. If there still is some keep adding 1oz at a time until it (chatter) disappears.
Apparently adding too much FM actually degrades the oil over time.

 

Silver said he used the same amount. I also figured it would take about 2 and a half quarts and with 3oz of fm treating 1 quart of fluid according to what Silver posted. I'd seen that anyway before that over on DTO. That leaves me with 7.5oz. I figured that was close to 8 so I went ahead and added 8 oz since it was 2 bottles. Turns out it took more like 2 1/4 quarts. It didn't take half a quart of the 3rd bottle like I thought it would. I might have a tad much but it's what Silver is running too. Should I not add as much when I change it next time? I'm thinking I will change it in another 8k miles. I originally planned to change it at 10k from when the Auburn was put in but since I did it now at 2k I'm thinking I will do it again in 8k miles.

 

I know that's very close to what Auburn recommends.
It just seems like a lot to me.
My own experience with auburn hasn't been great but I doubt it has anything to do with too much or too little friction modifier.
Time will tell I guess...

The only reason I use the Mopar fluid is because I used to get it free and still have a small stash.
And you know how I feel about free

free.....

 

Every time I have done my rear diff, I go through this calculation, and I have tried to carfeully mix to the exact fluid recommendations, and everytime, I come out to just barely under 8oz by time i'm done. I have actually asked Auburn about this directly a long time ago, and they said there is no issue with having a little extra in there if it should come out that way. If you have too little though, you can have clutch chatter.

You have to be careful with the Ford modifier though, because they actually make two kinds. Ones is a super concentrate and is in a 4 oz bottle too. I recall that the fluid is red in color. The one that is not concentrated is also in a 4oz bottle, but it is blue colored fluid. Either can be used, but you wouldn't want to put 8 oz of the super concentrate. The other thing I don't like about the Ford friction modifier is that it smells like you pissed on a cat and then lit it on fire. It's aweful. The concentrate version is even worse.