Stock 1970 Eaton clutch style Posi unit- Will it hold up?

[Markuli]

Hey all,

I picked up a factory Eaton 4 series posi from a guy off Facebook marketplace for 100 bucks. He says it's out of a 1970 K10. Supposedly it was rebuilt in the 90's or some time around then so I'm thinking maybe the clutch packs have been replaced. The guy seemed pretty genuine, he had a bunch of chevy projects and a sweet bracket race Vega... He replaced these diffs with E- lockers when he rebuilt the K10's axles.

So since I'm not changing gear ratios, my plan is to install my original 3.73 ring gear on the unit, shim it up properly, seal it back up and be on my merry way. I may have to change the diff bearings too, methinks.

Now, I do have a ~500hp 406 in my truck, but I'm also running cheap 275's that don't hook. Down the line I'm planning on running a TKO600, at which point I'll do the right thing and buy a fresh Eaton posi, all new bearings, and seals. But for now, do you guys think my cheap Facebook find will let me put two strips down on the pavement without an issue? I know that anything can happen and it's really a crapshoot when it boils down to it, but what's the harm in hearing some testimonies of those with similar experiences, right?

[Mbeef61]

Like you said it’s a crapshoot. My guess is it probably will ok. For how long is the question. Too many variables. Condition of the unit. Your driving style. The tires/traction. Frequency of spirited driving haha. Seems cheap enough to try. And you have your eventual plan anyways so worse thing that happens is the priority of that plan gets moved up.

Ever considered truetrac? Clutchless and doesn’t take special care. I have seen them in big hp setups. I use them in my Jeep front and rear. Don’t know they are there until you need them.

[Markuli]

I'll clean up the diff and take some pics of the clutches when I get home today. From what I can tell, they look like they still have a lot of material left on them.

I was looking at a vid of the truetrac and can't, for the life of me, figure out how it locks the diff under load. Does it just wedge that pinion gear into the housing? Sounds like your housing is your wear item, if that's the case. Of course, it could be 200,000 miles before the diff shows any problems.

Spirited driving and loose tires is the combo. Luckily I have a couple different toys in my rotation, so it's only every- so- often that I get on the juice!

[hjewell2]

I have never had a problem with mine . Running a real snotty small block with a trans brake 4:11 gears 275/60/15 on street and hoosiers on the track , doesn't even whimper oh and using 800# springs in the posi..

[Mike C]

I wore won out and put clutches in it, so I have LOTS of miles on one. The 4 speed and 35” tires in my Jimmy were hard on 12 bolts. But as long as you can avoid wheel hop it will be good. I hit a wet spot in my Jimmy that caused tire spin and then a 3 hop wheel hop that broke the Eaton in 1/2 across the window and the spider gear cross shaft.

Impact loading/unloading in wheel hop is vicious.

[Markuli]

That's good info for people with a similar setup. I realize that I forgot to mention I'm installing this diff in my C10 not a K10, so I definitely won't be running 35's. My current 275/60's are about 28" tall and don't stick too well, so luckily wheel hop isn't much of an issue. If I ever go to slicks it'll be on a rebuilt rear end.

[Markuli]

Here's some pics of the diff now that it's all cleaned up and mostly de- grimed. Ring gear looks great, spider gears look just a little worn, as you'd expect. I have no idea how to tell if the clutches are spanked or not from just looking.

[Mike C]

Clamp one axle vertically in a vise and set the posi on it. Put other axle in top. Use a short “cheater” type bar between a couple of studs and see how hard it is to slip the clutches. Google what breakaway torque should be and see if you think it is close to that parameter.

Most likely it will be OK to run.

[Markuli]

Well after a year of sitting on it, I finally got it installed. Works just fine. Two strips of rubber get left behind now

[Mike C]

Just about my favorite vehicle mod. Glad it worked out for you!

[Markuli]

Thanks for the advice back then Mike, as well as everyone else's input!