Losing my mind setting a gear

[JT351]

Hi everyone,
Ok here is the deal, I've been trying to set up a 3.73 in my red car for almost 5 days now. I am no stranger to setting up gears, I've even done the 4.10 in theThunderstang. No matter what I change, pinion depth or lash I still get the same pattern. Tight lash loose lash it does not seem to make a difference. Anyone else experience this? It is a used gear, is there anything I should know about using a used gear? I checked before installing it and did not see any unusual wear pattern. The other thing I'm wondering is I believe this came out of an 8.8 independant rear suspension expedition. Are those gears different? Any help would be great and thanks in advance.

JT

[Detroit Gearbox]

you cannot change the pattern using a used gear.

[Detroit Gearbox]

use the orginial shim, set the lash @ .008 and let it go

[JT351]

use the orginial shim, set the lash @ .008 and let it go

Thats one of my big problems, I do not have the original shim so I have no idea where to set pinion depth. Right now I have the pinon shimed at .028.

[Detroit Gearbox]

once a gear has a few hundred miles on it, it takes a set. depending on the manufacture of the gear and they type of machinery used to produce it, a new gear usually changes pattern by changing pinion depth and or lash, but this is not the case 100% of the time. some gears you just cannot get a proper pattern out of it.
my guess would be to stick .030 in it, but if all your preloads are correct and your lash is correct, run it.

[JT351]

once a gear has a few hundred miles on it, it takes a set. depending on the manufacture of the gear and they type of machinery used to produce it, a new gear usually changes pattern by changing pinion depth and or lash, but this is not the case 100% of the time. some gears you just cannot get a proper pattern out of it.
my guess would be to stick .030 in it, but if all your preloads are correct and your lash is correct, run it.

Thanks for all the help! +1 for ya

[Pure84GTT]

doing this right is a pain, sure you can just slap it in there with out checking preload or run out but how long is it really going to last. +1 for you for doing it right.

[StanIROCZ]

I've set-up many GM rears with GM gears and never had any real problems getting a pattern to move where I wanted it. Also many Getrag gears, and never had this issue either.

I've set-up ONE aftermarket gear and had this issue. We moved the diff side-to side, pinion in and out, and one side would not move (can't remember if it was drive or coast).

It bothered me and so my buddy was not satisfied. He brought it to a gear shop and paid them $100 do just ignore it and bolt it together.

My conclusion, BAD GEAR. Aftermarket gear quality is poor. Good chance they over-lapped the gearset from the factory. He sold the truck not too long after so I don't know how good are bad it worked.

Are you having problems with the drive side or coast side?

Coast side: as long as it isn't horrible it will probably be ok.
Drive side: you might have some durability issues assuming that this is a car you beat on.

[Sean]

Try Prussian Blue marking compound. that stuff marks alot better. Also make sure to put drag on the ring gear if you are turning the pinion for the pattern and vise versa.

[JT351]

I've set-up many GM rears with GM gears and never had any real problems getting a pattern to move where I wanted it. Also many Getrag gears, and never had this issue either.

I've set-up ONE aftermarket gear and had this issue. We moved the diff side-to side, pinion in and out, and one side would not move (can't remember if it was drive or coast).

It bothered me and so my buddy was not satisfied. He brought it to a gear shop and paid them $100 do just ignore it and bolt it together.

My conclusion, BAD GEAR. Aftermarket gear quality is poor. Good chance they over-lapped the gearset from the factory. He sold the truck not too long after so I don't know how good are bad it worked.

Are you having problems with the drive side or coast side?

Coast side: as long as it isn't horrible it will probably be ok.
Drive side: you might have some durability issues assuming that this is a car you beat on.

Drive side seems to be the biggest issue, and the make of the gear set is Ford. And yes this is a car that gets beat on, trans brake switching to nitrous with the release of one button. I am going to mess with it a little more, worst case I've had my eye on a 3.90 gear maybe I'll just go and buy it.