8 3/4 rear end assembly question

[Chris]

Got my 8 3/4 489 3rd member back packed with 3.55 gears and a true trac. Upon re-assembly is there anything I need to do specifically to ensure I don't f...k up this expensive hunk of steel?

Is it as simple as:
Gasket for third member
Bolt on
slide akles in
bolt up

Is a quart og gear oil enough?
Do the axles(Moser) lock in in any way...
DO I grease the axles or bearings?

 

[Cranky]

Normal is 2 quarts. What bearings are on the axles? The Green setup?

 

[Meep-Meep]

I fill to the bottom of the fill plug and that seems to be about 2 qts. As pointed out above, if you have the OEM bearings you will need to set or at least check end play and grease the bearings. If you have the greens then they just go in but they are not nearly as good as the OEM setup.

I don't know what a tru-track is but the power lock (OEM 4 pinion carrier) has these buttons in the center that are the thrust for the axles. If your carrier is new and professionally built I'm sure all that is taken care of.

Are the gears new? If so you will need to break them in. Basically take short trips to avoid to much heat build up. You might want to check with the gear manufacturer for details.

 

[Chris]

Thanks guys,

Set up is brand new. Gears are 3.55s with Moser axles. I am re-building the drums as well. It should be alot better than the original 2.97 open rear I had...

 

[Cranky]

The True Trac is an Eaton/Detroit limited slip differential and it is a helical gear unit and I doubt it has any center thrust button/block in it so the axles probably have the Green bearings. If so, just stick them in. The bearings are sealed. I like to do a couple of heat cycles on new gears before I hammer them but many do not. Being a machinist, I learned to check anybody's work when I put something together a long time ago.....food for thought....

 

[Chris]

Great,

What do you mean by a heat cycle?

 

[Meep-Meep]

Great,

What do you mean by a heat cycle?

If I may...I will interpret "heat cycling" as time to allow the gears to lap together under light loads - not allowing the temps to get too hot - and do this as several short trips (heat up; cool down) before you hammer them. The tooth contact pattern will get bigger as the gears wear and that will increase the load carrying ability of the tooth by not punching through the film strength of the oil. It's all about surface area and film strength to maintain a happy mechanical device.

 

[Meep-Meep]

The True Trac is an Eaton/Detroit limited slip differential and it is a helical gear unit and I doubt it has any center thrust button/block in it so the axles probably have the Green bearings. If so, just stick them in. The bearings are sealed. I like to do a couple of heat cycles on new gears before I hammer them but many do not. Being a machinist, I learned to check anybody's work when I put something together a long time ago.....food for thought....

Thanks for the clarification.

And myself being a tech / shade tree machinist I completely understand where you are coming from!

 

[Cranky]

If I may...I will interpret "heat cycling" as time to allow the gears to lap together under light loads - not allowing the temps to get too hot - and do this as several short trips (heat up; cool down) before you hammer them. The tooth contact pattern will get bigger as the gears wear and that will increase the load carrying ability of the tooth by not punching through the film strength of the oil. It's all about surface area and film strength to maintain a happy mechanical device.

Yup....just driving normally works fine.

 

[scotts74birds]

RE: Anything I need?
This may be the dumbest thing I typed in a while, but I think I remember that GMs needed a bottle of Posi Additive for them to work well. Is it the same for Mopars?

 

[Meep-Meep]

As long as you use a gear oil that's compatible with limited slip you should be fine. I put some additive in the 9" trac lok in my Ranchero but those use clutches with friction material (C4 clutches as a matter of fact) and MoPar's don't - that I have seen.

 

[Cranky]

What does Eaton/Detroit say about their units? I have a crappy Trac-Loc unit in my Durango and the additive doesn't do very good for it but STP does. Go figure.

 

[Meep-Meep]

What does Eaton/Detroit say about their units? I have a crappy Trac-Loc unit in my Durango and the additive doesn't do very good for it but STP does. Go figure.

I don't know about Eaton/Detroit but the 9.25 limited slip carriers I looked at don't have friction material clutches like a Ford Trac Lok. I'm sure I have the same LS carrier in my 02 Durango as you do. Mine has the 9.25" with 3.55's. The main problem with that unit is the half round shims that act as a buffer between the clutch steels and the carrier case break and the loose pieces fall out and/or scrub on the inner carrier bearing cap. I think the solution is to replace the carrier with an Auburn style cone clutch unit.

 

[5.7 hemi]

aren't the plates in the sure grip called clutches?

 

[Cranky]

The Power Loc Sure Grip has clutches but the Auburn style Sure Grip has the cup and cone clutch setup.