Ford 9"

Kputz · #1 (**permalink**) 08-21-2002, 12:24 PM

Most Ford 9" rears are lubed with 80/90..whatever..and then the "additive". Most cars equipped with a 9" for racing purposes (and they are legendary) don't run with the additive. Aside from the considerable noise generated running sans additive the difference seems to be that they hook up better, the running life of the rear end doesn't seem to be the issue. I know guys that change out trannies in A Sedans twice a year that haven't touched the rear in years.
The question begs itself....what does the additive really do? It obviously supplements the lube for a purpose, but is this purpouse to thicken the lube to prevent the noise?? Any FoMoCo wizards out there know the skinny?

427sharpe · #2 (**permalink**) 08-21-2002, 08:15 PM

I saw your post, didn't know an answer so I called my FoMoCo Motorsports Rep, and HE says the "Friction Modifier" is a compound agent (which means he doesn't know what the he!! is in it either) to lessen gear chatter and reduce NVH (noise, vibration and harshness) as well as to displace moisture, which can cause trouble in locked or posi rears. He said this was a real problem a few years ago w/ trucks that lowered boats into water (imagine that!). He said a lot of the race teams DO use it in the 9" Lockers, but he said most don't because they either change the fluid or the pumpkin between each race. An interesting aside is that Ford requires it at differential service intervals to maintain warranty.

Kputz · #3 (**permalink**) 08-22-2002, 07:35 AM

NVH...interesting acronym. It would seem that the only function it has then is to silence an otherwise noisy rear end. I wonder why they just don't go with a thicker lubricant. Anyway, I thank you for your research, and I'm impressed with your sources. The next time mine gets to chattering I'll dump in a bit more "modifier".

cwmcobra · #4 (**permalink**) 08-22-2002, 10:07 AM

The friction modifier is actually used in limited slip differentials, not locking differentials. Lockers have a mechanical locking mechanism that solidly locks the axles so that both always turn until they are unlocked. The limited slip differential has a disc pack that acts like a clutch. It never totally locks up, but does transfer some of the torque to the non-turning axle when the driven axle (wheel) starts to slip. The friction modifier is to keep the disc pack from partially locking when you don't want it to, like when you go around a corner. You might have experienced an occasional "chirp" when turning corners with a LSD. This is when the discs start to lock due to friction among them. The friction modifier is intended to help this situation. It doesn't totally eliminate it, but it helps.

My company makes these differentials, so that's my source, but its a layman's view, since I'm not an engineer on these products.

Chuck

427sharpe · #5 (**permalink**) 08-22-2002, 10:25 AM

cwm: My Ford Motorsport Detroit Locker came with a reminder tag requiring use of friction modifier as well...

Campy · #6 (**permalink**) 08-25-2002, 06:32 PM

I have a Ford 9" as well. I do not use any other lubricant other than the 80/90EP gear lube. I have not any issues with excess vibration or noise. You should be aware, however, that in the Cobra, you’re sitting just 12 - 18" from the rear end and you will hear a little more than in other vehicles.

On a side note: When I was in the build stage, I purchased the entire 9" rebuild kit with new gears, etc. I seriously considered doing the job myself. That was at least until I did some reading and discovered how critical gear lash tolerances, end play and other adjustments can mean the world of difference. Especially in the longevity and quietness of your finished differential. I located a local shop that specializes in all types of rear ends. $125 later I had a like new, freshly painted setup. So far I've got 2500 miles on it and it actually quieter that when it was first installed.

cwmcobra · #7 (**permalink**) 08-25-2002, 08:34 PM

Robert,

Sorry if I misspoke. I should have added that my response relates only to Eaton differentials, since that's the product I'm familiar with. I haven't studied how the Detroit Locker and other locking differentials function, so I have no experience with them.

I've just got to get Eaton to make one for the Ford 9"!

Chuck

Excaliber · #8 (**permalink**) 08-25-2002, 09:21 PM

Those rapid starts and the feel of the tires breaking loose and the a$$ end sliding around have taken their toll. To late for "friction modifier" for me, my "limited slip unit" acts more like a one legger these days. I think I broke it..........

Ernie

Wayne Maybury · #9 (**permalink**) 08-26-2002, 08:09 AM

When I was putting my car together, a good friend of mine who has done a lot of drag racing, suggested that I put in 1/2 container of the additive. If I wasn't satisfied, I could always add the rest. I put in half and it seems to be fine. I do get some gear noise but I guess that is normal.

Wayne