differential - friction modifier?

[ragedracer]

Im replacing the gear oil in my 86 M1009 - 10 bolt rear with gov-loc 10b front - open. Do I need to add any friction modifiers in either diff or is straight 80/90 ok?

Thanks!

rr

 

[Mike D]

If the gov-lock has little clutches in it you need a friction modifier. The friction modifier allows more slip with the clutches ( thus smoother operation on turns ). I believe most brand name differential fluids contain some friction modifier.

 

[6.2Blazer]

The gov-loc does NOT require friction modifier. This is backed up by any owner's manual or factory service manual out there.

 

[AJMBLAZER]

Then why does GM sell the little bottles of friction modifier?

Just curious.

 

[1979jimmy350]

Gov locks contain Friction clutches, they do work better with the friction modifier

 

[dyeager535]

Posi/limited slip diffs. Gov-locks don't lock in corners, meaning you won't get wheel hop without the clutches slipping like you can in spring style LS diffs.

 

[ragedracer]

The gov-loc does NOT require friction modifier. This is backed up by any owner's manual or factory service manual out there.

This is why I asked... The .mil TM does not mention friction modifiers, but I've seen people go both ways on it. Would it hurt anything to put some in just in case??

rr

 

[dyeager535]

It would probably actually help, as they break because the lock up is so violent on them. Being very easy on the diff is the drivers responsibility (if he WANTS to be easy on it lol), if you aren't ever hard on it, you likely won't have problems anyways.

 

[ragedracer]

if you aren't ever hard on it, you likely won't have problems anyways.

LOL - This came out of the Army... I can pretty much guarantee they beat on it.. Although maybe less on this one since it "belonged" to a MSGT. At least I think so - due to the fact that it had "MSGT JOHNSON" stenciled on the front windshield..

rr

 

[dyeager535]

Point being, if it works now, unless you beat on it, it will probably continue to live a long time. I've had three gov-locks, two broken when I got them, one for sure abused, and the third I broke by flooring it coming out of a corner. It lasted YEARS before that happened, but was solely my fault. Bigger than stock tires don't help either.

 

[ragedracer]

Allright, its done.. I went with Valvoline HP 80w/90. It does have some friction modifiers in it already. It took 1 gallon + 1 quart to do both front and rear. Both were full to just below the fill plugs. Front diff looked great. Gear oil was pretty clean. Rear diff, the fluid looked like it might have had a little water in it. It had little like soap bubbles after I drained it all out. The magnets on both had almost no metal on them. Gears all looked brand new with barely any wear on any of the gear faces.

Overall, I would say they maintained these pretty well. I'm eventually going to go with a 4" lift and 33's. I guess I'll see how they hold up. I've broken 2 10 bolts in the past, but both were on a built 400cu engine and I hammered on them with 35's. Maybe this will last me a little longer!

rr

 

[Thunder]

I have never used friction modifier in gov locks. and had fairly good luck with them.
One thing I have found with them is change the lube once a year and check/retorque the pinnion pin retaning bolt. When you run them hard with larger than stock tires. the added stress to the carrier tends to loosen up the retaining bolt. If the bolt falls out ... the pinnion pin falls out and things go BOOM. I have seen a few Gov locks fail that way.

 

[6.2Blazer]

Then why does GM sell the little bottles of friction modifier?

Just curious.

Maybe because the Gov-loc is not the only limited slip/posi they make. Go find me a Camaro with a Gov-loc..........

Regarding some of the other posts, from my understanding friction modifier has the possibility to make the Gov-loc act worse. Ideally the clutches are supposed to grab some and equalize the speed of the tires before completely locking, where if you added modifier they would slip more and thus a larger shock load when finally locking.

 

[dyeager535]

I think the problem is that how some of us drive, and how the rigs are setup, the weight of the "stationary" tire along with the amount of torque going into the diff is just too much, and the lockup is too harsh.

I was playing with my truck in the snow in the driveway, and I could definitely hear it "clunk" as it locked up. Anything that reduces how quickly it equalizes axle speed SHOULD reduce the load on the carrier when it does lockup. Basically, as I see it, the problem is that transition from unlocked to lock is too fast. Slipping would increase the lock time, thus allowing the "stationary" axle to more closely match the spinning axle.

Of course, it also probably depends on the age and condition of the unit, and Eaton has probably made subtle changes through the years that changes the operational characteristics to try and keep up with the habits of modern drivers and the increased loads the axles are seeing both in power input and GVWR.

 

[4by4bygod]

6.2 & Dorian, you guys are pretty on target in your thoughts about friction modifiers.

all I have to add is this..

A friction modifiers role is to manage friction in certain applications..in other words, the goal is to apply the proper amount of friction under a specific load, not just "make things slippery"

Friction modifiers help insure a smooth take up and prevent chatter..

I see the terms "anti wear additive" and "friction modifier" used interchangeably, and that's not quite correct. Anti wear additives ( and extreme pressure additives) prevent the micro welding that occurs during the metal to metal contact seen during boundary lubrication..(that's when the load is really being carried by the working surfaces)

the friction modifiers have a different role as discussed above, but it can be the case that they're preventing wear while they are under load, so maybe that's why they're thought of as being the same.

6.2, that's a heck of a thought about shock loads seen after take up..

shock loads do brush off AW / EP / FM additives, but I never thought about FM additives making the situation worse. Sounds like something worth researching. I s'pose that's why we should defer to the OEM fluid recommendations, eh?