Which friction modifier for trac lock rear

[AJV69 2]

There are a few Ford friction modifiers available, which is the correct one for a 3.25 Trac Lock rear on my 69 Mustang M code?

[barnett468 418]

I get it from the gm dealer.

[RPM 1,190]

Ya, pretty sure any would work. That Motorcraft stuff really stinks up the place.

[mustangstofear 608]

We've always used Ford, except this last time we tried the Autozone brand.

[1969_Mach1 333]

16 hours ago, AJV69 said:

There are a few Ford friction modifiers available, which is the correct one for a 3.25 Trac Lock rear on my 69 Mustang M code?

Double check the gear oil you are using.  Some already have friction modifier in it.  If not I use the stuff from Ford.  The GM stuff is very good as well and I have always used that on GM cars.

[Brian Conway 264]

Can't go wrong using a ford product.  Brian

[mustangstofear 608]

The only  time I've  heard from a manufacturer about a specific brand to use is Heidt's. They suggest  Ford only.

[1969_Mach1 333]

31 minutes ago, Brian Conway said:

Can't go wrong using a ford product.  Brian

No you can't go wrong with that.  But make certain the modifier isn't already in the gear oil so you don't double up on the additive.  Then the clutches slip more than they should.  Funny thing is, back in the day and in the late 1970's and early 1980's these traction-lock differentials were fine without a friction modifier.  As best I recall, these modifiers came about in the mid-late 1980's to solve chatter issues with current newer design traction-lock and limited slip differentials.  I may be wrong, but I am not certain it is needed in these older design traction-lock differentials.  Especially if the gear oil already contains it.  Maybe somebody older that worked on these cars when they were new will have more knowledge.

[AJV69 2]

Yes, I remember my father's 63 Galaxie fastback and how it would chatter and my dad always said not to worry about it! Thanks for the replys, I bought the Ford Racing version from CJ Pony.

[1969_Mach1 333]

My first experience with traction lock differentials was back in the late 1970's.  And it was with a Ford 9" unit.  I don't remember friction modifiers available then.  If they were I wasn't aware of it.  It didn't have a chatter issue.  Maybe I was fortunate or simply because I had fresh oil in it.

When I worked as a GM mechanic starting in the early 1980's there still were not any friction modifiers available and we were changing gear oils often to stop chattering, every 20K or so miles.  When the oil was new, no issues.  Eventually the friction modifiers stopped that need for frequent oil changes.

[Brian Conway 264]

In my experience, beginning in the mid 60's of the last last century,  all locking rear ends  required a friction modifier or additive.  Brian

[GypsyR 32]

Years ago the Ford additive from the dealership parts counter was considered so good in the '70's and '80's the GM and Dodge guys would slip in to buy it. Seriously. These days they now have their own additives that work very well. But I know of no others, period. The LubeGard stuff and/or whatever else is at the parts store is crap. Some oils say they have the additive added already. They probably do. But like two drops per 55 gallon drum or whatever the minimum is for them to not get charged with false advertising like they should be.

 Rebuild a Trac-Lok rear. Add the fluid that has the additive already in it.(Flat out lie) Do figure eights. Enjoy the rear chirping the tires and chattering like nobody's business.  Next. Try parts store additive. Repeat. Be annoyed. Add a second bottle. Try again and be disgusted at the wasted money. Wait for Monday when the dealer is open and score a bottle of Ford/Mopar/GM additive. Make a single figure eight and thereafter enjoy a chatter-free rear end.

That's what I did anyway. I kind of prefer the Ford stuff. Because I do Fords and it has a history of being the best. I've also used Mopar and GM bottles and found them to work just as well as far as I can tell. 

If you just change the oil and your clutches already have a bunch of miles on them you can probably get away with using whatever, for a while at least. Rebuild with clutches a little on the snug side (like I prefer) and you'll shortly find out what does and does not work the same as I and many others have over the years. 

I don't know if GM had an additive back in the '70's and '80's. But if they didn't that would help explain why the Camaro guys were in the Ford parts department all the time.