M1009 Gov-Lock Sometimes Not Working?

[RickTheEngineer]

Hey all, I decided recently to try to test out the rear traction device that the M1009's are known to have. I saw a video online once on how to test a G80 (and I figured the test should probably work for my truck) which was the jack up both rear wheel and spin one by hand one way (the other wheel will start to turn in the opposite direction) then suddenly jerk the wheel you're spinning really hard and then the locker will kick in and the wheels might jerk the opposite way again. I tried this and it was a success. It felt a little soft, almost as though something was slipping a bit, it was not the violent jerk they are known for causing. Then last night I was in a high flex situation when my rear driver tire was having very low friction on what was essentially frozen turf. The tire started to spin slowly, while the passenger rear tire was planted. I slowly accelerated thinking the gov-lock will engage and it did not until the wheel was spinning considerably quickly. (I am running 33's by the way). I hit the brakes and brought the wheel to a halt. I try again, no luck. One final time and it engages!

Curious, I try to test it again, and under the same circumstances, I more or less could not replicate my results. I recently changed the diff fluid, and it definitely looked kind of neglected from the previous owner, but I filled it up with 80w-90. Should I be concerned? It definitely does not seem straight up broken or anything, and I am wondering if there is any way I could "exercise" it or service it. Thanks!!!

 

[cucvrus]

After driving M1009's for 20+ and new Chevrolet pick-ups. (my 2014 has an Eaton locker) I have had the situation you described. I have off roaded my M1009 very hard working and playing and I think that the rear has a safety built into it in so it does NOT violently lock and engage. It would make sense. But I know that they can take some abuse but I never blew one apart in over 20 years. 1 time I failed to replace the lock pin bolt and the center pin came out. That was not the rears fault. I have had them lock on loose stones at intersections and get the locked diff effect. So my experience has been without going wild and spinning madly they seem to work. But others have bad experiences with them. I know every new Chevy truck I owned had and still has the same Eaton locker in it and they never failed me. Everything has a breaking point. Good Luck. Have you checked the magnet? Was it minor metal particles? If so that is normal.

 

[RickTheEngineer]

The magnet had minor particles, no chunks, or anything above what you might consider iron dust... I tried it at all different RPMs, from the one tire just barely moving, to fast enough to sling a bit of dirt. I never touched the diff as far as parts go, only replaced the fluid and everything seemed normal in there. Granted, it wasn't as shiny as a new diff, had some minor oxidation on the surface but still seems like it could take another 30 years if maintained. Just so I understand a little better, is it normal for it to be a bit finicky to work? Does it need a rebuild?

 

[Chaski]

One of the GM promo videos for "G80" said that it needs 120 rpm difference between the two axleshafts.

Maybe more skinny pedal is needed?

 

[RickTheEngineer]

I had spent some time thinking about that, but 120RPM is 2 turns per second, and I definitely was doing more than that at one point. Certainly faster than in any product video I saw for it haha. The only time I got it to work was after I braked, then slowly turned the wheel (maybe like 80 RPM). Couldn't replicate it though.

 

[cucvrus]

I say if it's not broke don't fix it. I had mine clunking and grinding a few times in Terminus M1009. 10 minutes later it worked like a champ. So I cannot say what the issue is 100% but when I changed my fluids everything looked great inside and this was a plow truck for 20 years. So I know it was abused. The right axle was snapped off inside the center carrier splines. like I said everything has a breaking point. And it would have to be finicky or as soon as one axle would spin that thing would lock and all 7734 would break loose. And I am sure that is what happens when you get an inexperienced driver behind the wheel dead set on ripping and spinning and not using common sense. Anyone can spin the wheels and break things. Good Luck. I think you are fine. Happy Holidays.