489 Third member Build - update - Cant set back lash - Need advice

[Weak440]

I am working on building a 489 center seciton with 3.55 gears and a new Eaton Posi. This is the first time I have tried to rebuild one of these so I am taking my time and learning ALOT.

I am working on sitting the pinion depth and have ran in to a couple of issues. The first time I pressed the large pinion bearing on I re-used the .034 shim from the 3.23 gears that came out of this housing. They were waaaaay to deep.

So, I pressed the bearing off and switched to a .024 shim. When I re-assembled it I couldn't get the backlash under .035. I had to take a break for a couple of days.

I came back to it last night and tried to figure out why I couldn't get the backlash set. What I found was that the case on the posi unit was butted up against the inside of the differential housing. In the 3rd and 4th picture you can see where it rubbed as I was rotating the ring gear.

The first thing I did was make sure my caps were on the correct sides. I marked them before I started this project. I know for a fact that they are on the sides that they belong on.

The gears are new (from Doctor Dif) Strange/US 3.55s.

At first I was tempted to pull the posi unit and chamfer the edge of the housing. But, I wanted to ask around before I started widdeling way on stuff.

Has anyone ran in to this before? How should I go about fixing this?

 

[Hipo65]

Yep yer right,you halfta do the very same thing to an 8.25 to get the (newer) aburn sure grips to fit into the housing. In the directions it even told you about how much to grind outta the housing. I havent ran across this yet in the 8.75 but had only ever put in power locks or re-vamped the o.e. cone style sure grip's.

 

[69MOPE]

Yep, the last two I did were that way, get your die grinder out!

 

[Jo Diesel]

Do you have to grind the case or can you bevel the posi unit

 

[SGBARRACUDA]

I have had this problem in the past on 8 3/4's. I ground the the case, problem solved.

 

[rmchrgr]

Shouldn't have to grind on anything.

What tool are you using to set pinion depth? There's good ones and not so good ones.

Gearsets usually come with a specified pinion depth measurement marked on them so you have a good place to start. If you're replacing gears I can almost guarantee the pinion depth on the new set will not be the same as the ones you removed. It's possible that re-using the same shims could lead you down the wrong path to the point where you're at. If it's too deep in the case, try adding more shims and see if it gets you closer to the right depth.

Obviously make sure all bearings and races are fully seated and you have the correct parts in the right place.

Did you tighten down the adjusters on the sides? I don't remember the spec but you need to do that before setting backlash.

Never heard of having to grind on anything to get it to sit in there right but I could be wrong. If you have to though, grind the case, not the diff.

 

[SGBARRACUDA]

Shouldn't have to grind on anything.

What tool are you using to set pinion depth? There's good ones and not so good ones.

Gearsets usually come with a specified pinion depth measurement marked on them so you have a good place to start. If you're replacing gears I can almost guarantee the pinion depth on the new set will not be the same as the ones you removed. It's possible that re-using the same shims could lead you down the wrong path to the point where you're at. If it's too deep in the case, try adding more shims and see if it gets you closer to the right depth.

Obviously make sure all bearings and races are fully seated and you have the correct parts in the right place.

Did you tighten down the adjusters on the sides? I don't remember the spec but you need to do that before setting backlash.

Never heard of having to grind on anything to get it to sit in there right but I could be wrong. If you have to though, grind the case, not the diff.

I believe is because it is a aftermarket SG. I've had to do this before.

 

[Hipo65]

Its the after market center's now days its required to get them to fit.

 

[fishy68]

Its the after market center's now days its required to get them to fit.

Agreed. I just did a Ford 9" for a buddy and had to grind the case quite a bit for clearance. A lot of aftermarket sure-grip's/posi's are beefier so there's times when they hit the case

 

[Weak440]

Update on my progress since my last post. I fired up my die grinder and ground in the case removing enough material to give my posi plenty of room. I cleaned up and reassembled it. With .021 shim I was still too deep. I didn't like my pattern at all. So tonight I swapped the shims for a .018. This is what I ended up with.

I have the backlash set at .008.

I am starting to loose my resolve here. I may try to go thinner on the shims tomorrow night but, I wanted to ask you guys what your thoughts were.

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[Weak440]

Don't know why the pics didn't attach

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[SGBARRACUDA]

Your to close to the face. You shouldn't have to vary that far from your original .034. Pinion is to far away.

 

[Weak440]

Holy crap... all this time I was going the wrong way with the shims! I went back and changed to .037 and it made a world of difference! Thank you so much!

I think it could still use a little more?

Posted via Topify on Android

 

[SGBARRACUDA]

That is looking pretty damn good!