I just installed a third member with 4.88 gears and detroit locker in my 86 pickup. It all went smooth but I have questions.
If I grab the drive line and twist it, it rotates approximately 45* before the gears mesh, in reverse 45* till it meshes with the coast side. (the diameter of the seal protector is aprox 11" round and it turns 1.5" till gears mesh) (Tranny in neutral and emergency brake on.)
It seems to have too much back lash and kicks when I start letting the clutch out resembling a bad u-joint. Am I correct in my assumption? Will I hurt it driving it this way and what parts do I need to fix it? Well the supplyer want the third back to correct the problem or have me find a local mechanic to fix it?

Ive also developed a vibration since the swap. It starts at 55 and stops at 60. Could the problem be related or should I look another direction to find that problem? I did get new tires about 100 miles ago and dont recal having the vibration but......... Might be something for me to look at?

The U joints arent new but they are in good shape.

 

My buddy has an 87 pickup and in neutral with emergency brake on, his drive line only turn about 5/8 of an inch till gears mesh. He still has factory 4.11 with 200k miles.

 

The backlash is excessive. Does it make any noise??
That much play between the pinion and ring should have been easy to see before you put it into the truck.
If you paid any substantial price for the unit, I would send it back.
If it was cheap and runs quietly, I might try to run it for a while.
Should have never been installed in the truck like that IMO.

 

I did pinch a finger turning it before installing it but it apeared to be right to me. only after installing it did I see how much it turned. Ill be completely honest though, I have very little experience with loading gears or how to inspect them. My automotive classes never went into gears but only motors and thats been 30 years ago.
Yeah, it cost me $1300 delivered. So its safe to assume that I'll be dropping the old member back in till the company fixes it?
Is it something that just needs adjusting or have the miles Ive put on it already during break in going to screw me?

 

There are several places that lost motion can occur in a final drive. Some are of less concern than others.
It may be possible that not all of your motion is attributable to backlash between the ring and pinion gears.
Maybe you should get an opinion or two about where the play actually is from folks more familiar with gearing.
It is possible that the ring and pinion are correctly set and that the play is elsewhere in the rear end.

 

at $1300 it sounds like you bought a new diff - it should be spot on, at least that's what I'd expect. which company?

if you haven't already, i would disconnect the rear driveline and try to spin the pinion flange to see if you still have the same play, just to help diagnose exactly where the problem is coming from. if it's not the diff itself, then look to u-joints next.

 

The detroit locker will have much more backlash than a normal open diff will. That could be a big part of your issue. Also, it will make more noise, clicking and clunking, etc.

If you disconnect the drive shaft and carefully rotate the pinion flange, you should be able to feel where the pinion gear is picking up the ring gear, and then where the ring gear is rotating the locker into engagement. The motion between ring and pinion should be fairly small, as noted in previous posts, but the locker itself will have a lot of slop. 45 degrees at the driveshaft translates to about 10 degrees at the locker itself, which I don't think would be considered unusual for a detroit locker. Detroits are strong, but probably among the most clunky and road-unfriendly auto lockers out there.

 

Ive had several Detroit lockers. Some auborn lockers in my gm trucks but I think they are the same company. I dont recal having this much slop. Although they had automatic tranny's too so that would keep pressure on the gears?
Maybe my setup is right? Will thepinion bearings loosen up enough to ppossibly keep the gears from running against the coast side when im braking with the clutch disengaged? That would reduce the degree's a little?

 

Well, you really need to sort out whether the slop is in the locker or between the ring and pinion. The test I suggested can give you an idea, but to really know you'll need to pull the third member and check the ring and pinion backlash with a dial indicator. To do this, lock the pinion flange, set up a dial indicator perpendicular to one of the ring teeth at the outer circumference, and rock the ring gear by hand. The total tooth motion should be around .008", not more than .011". If it's more than that the gears aren't set up properly and the unit should go back for sure.

I don't have any information on expected backlash for the detroit locker, but I'd guess you could find it on their website.

 

Thank you. That is making sense.
When I took the third out of the package it still had marking grease on the teeth and the patern it made looked just like the pictures ive seen on the computer. I think the gears are meshing proper (my feeble opinion). Lce is checking into it for me but I'll take it to the guy installing my front gears and let him look at it. He installs 10-12 sets a year so he should know what to look at. Thanks again.

 

Looks like your right. The ring/pinion are set close and the extra play is in the locker. I will get used to it in time and it will become habit to take up the slack before letting the clutch out. Driving it just now, it seems better today than yesterday. Im guessing things are wearing in. Thanks.