When I had my 12 bolt (Built with richmond gears and Eaton Pro posi) apart again for disk brake install, I filled it with Amsoil series 2000 75w-90 GL5 synthetic fluid which is not supposed to need additive for posi rears. It exibited the classic behaviour of a friction clutch posi (sticking, grinding when turning) with no additive. So on Amsoils advice I added their posi additive. What is wierd is that it stopped for a couple of days, then started again.
I don't recall the details, but when it stopped it was cool out, and warm when it started. Is it possible that the 75w-90 is too thin? What is the factory recommended fluid?

Thanks in advance for any advice/insight.

Im using the same 75w90 amsoil series 2000 in my new eaton posi and have had no problems at all, no noises or grinding. Wonder if your package got set up right, I read where the lash settings are very important. I had mine done by mechanic since I dont have that type of tooling. Im sure bigGear head will chime in on this later today.

Ditto click. Eaton posi Amsoil 2000 75-90

i just put a new 12 bolt in my car about 1000 miles ago and also had your same symptoms. until i read a thread on here about doing backwards figure 8s with the car. well bingo problem solved
that was about 500 miles ago and i havent heard a peep out of it since. :D thanks once again to the members at TC

I have sold and installed many cases of Amsoil 75W90 Series 2000 oil. As you know there are exceptions to everything. What works for 99% of the people will not work for others. I had a problem with Amsoil in a rear end that had an Auburn posi in it, but that has been the only one. If you have already tried doing the slow circles in a parking lot and it didn't work then you should probably drain the oil and try the petroleum 80W90 oil with Ford additive M-19546. If you have the 800 pound preload springs then it doesn't matter what kind of oil you use, it will still pop.

Listen to this man...

I just purchased an Easton posi unit for my rear and it came with a tag stating not to use synthetic oil.


AMSIOL synthetic?

Mine did too. Per big gear head I ignored it. Still going strong 1 & 1/2 half years later. I honestly forget the explanation given, maybe Freddie will chime back in.

Originally posted by HO69:
I just purchased an Easton posi unit for my rear and it came with a tag stating not to use synthetic oil.
AMSIOL synthetic? Synthetics and their use in Transmissions and Rear-ends has been discussed on these boards many times.
Even bearing in mind some of the answers are from members whom distribute the products, the overall opinion, and my own based on past results, is that quality synthetics are very safe to use in these applications.
Here is one of the best past threads on this subject - http://www.camaros.net/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=18;t=000021

Here also is the thread that discussed the "fiqure 8" procedure for noisey posi units - http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=18;t=001414#000000

Hope this helps;

John

Good links there John, thanks. Without having to read thru all the chat about this topic, you are welcome too if you have alot of coffee there, here is a quick explanation. You need Micro soft Word to open it.
Synthetic gear oil in Eaton Posi (http://www.brainerd.net/~knudsen/69RS/Eaton%20LSD.doc)

Click did that letter come off of an Amsoil web cite?

It was sent directly to me from Amsoil Tech Mgr.
graemlins/thumbsup.gif

Jim,
I guess I was probably the first to contact Ed Kellerman about this problem. I sent him a coppy of the Eaton card and he contacted Eaton to find out why they included this card with the new posi. He told me the same thing that is in your letter.

Originally posted by click:
here is a quick explanation. Click;

Thank you for forwarding that - very interesting reading!
Knowing how some of the "scientific" test were run, by groups I have worked with :rolleyes: , the "conclusions" don't surprise me.
The offer to back-up the Eaton warranty, in my judgement, says it all about the choice of use of your product in this application.

John

I run 800+ lb pre load and I dont have any problems that are mentioned.

I use Schaffer parrifin based straight 140 wt suspended moly (209), with 1 four ounce bottle for Ford friction modifier......

I have never had a problem with the dreaded pop from friction or clutch pack noise.

Its all a bunch of hooie if you ask me....

**EDIT for spelling

[ 07-02-2004, 02:47 PM: Message edited by: chicane67 ]

Sorry about the error. My dif is an Auburn, not an Eaton (it was 10 years ago that the rear end was built)

I had the rear built by one of the highest regarded shops here in Denver. The owner showed me the pattern on the gears, and the pictures from richmonds instructions, and asked if I was satified. I don't think the lash is wrong.

Per Amsoils tech advice, I am going to add more friction modifier and see if that takes care of it.

After thinking about the problem a bit, it occured to me that the reason it stopped for a while might have been because after first adding the modifier, it was at the right concentration, but after driving it a bit, it mixed with the fluid in the axle tubes, and got diluted to the point that it was no longer enough.

Thanks for the helpful replys.

I usually have to add 2 bottles of additive with the Auburn differentials. They pop a lot more than the Eaton.

Especially with the Auburn 'Pro'........

Originally posted by chicane67:
Especially with the Auburn 'Pro'........ I added another 3oz. and so for so good. Time will tell. If it pops again I'll add another 2oz. and see what happens.

Thanks again all.