Ring Gear and Differential M38A1

Bob_C · Post by **Bob_C** » Sat Jun 14, 2014 2:34 pm

Hi all,

I haven't posted in a while with any kind of regularity. I've been checking in from time to time though.

Anyway, I have a question for any folks that have done this before. I restored my m38a1 a few years ago now. Long story short, I noticed small metal flakes in my rear differential oil. Pulled the cover off, and noticed right away that the ring gear is quite pitted from corrosion. I'm thinking this is from years ago (before I owned it). The previous owner replaced the original differential unit with a trutrack positraction (brand new) unit, and I don't think I spent much time in the rear differential because of it / didn't notice it.

So, my immediate problem is I need a new ring gear. I also am leaning towards popping open the trutrack unit to inspect it now, as I have found out that the posi doesn't seem to engage. If I stick with the trutrack, I may need parts...and to tell you the truth, I don't even know if they are still in business. Like I said, the few times I've needed it to engage, it hasn't, and so I'm leaning towards ripping it out and putting the original one back in. However, my original differential, of which the ring gear came off of, is also pitted in similar fashion. If I go this route, I'll need a whole new unit. I'll also need the original spindles, as the trutrack makes use of different spindles ( similar to ones that are in the front.) I'll also need the original axles (trutrack has a different spline).

The laundry list is getting long, as you can see. Thus, I am thinking of using the trutrack still. Does anyone else have any experience with these units? Is it worth keeping? Curious as to why the posi didn't engage. Like I said, this was installed years ago by the previous owner...not sure if it a matter of some adjustment being missed, etc

Anyone have a favorite source for ring gears? I rebuilt my transmission and ordered parts from Novak a few years ago, but I'm not sure if he deals in this sort of thing too.

Post by **wesk** » Sat Jun 14, 2014 3:58 pm

I'd go straight to the horses mouth:
http://www.drivetrain.com/parts_catalog ... ction.html

913A589 53080 Dana 44 Rear 3.73 & Down 30 $567.65 $681.18 $113.53

http://www.eaton.com/Eaton/ProductsServ ... 264#tabs-2
http://www.eaton.com/ecm/groups/public/ ... 128302.pdf

1964 - 1970 Dana 44 8.5" 1.25" 19 3.73 & dn 19961-010
3.92 & up 19960-010

Note the Eaton Pubs say no fancy synthetic gear oils. Mineral oil only!

Detroit Truetrac
A quality petroleum (mineral) based oil is recommended. Synthetic
oils and friction modifiers should not be used, as they will decrease
overall performance.

Some places to go and look:
http://buildingdifferentials.com/

Download the TrueTrac owner's manual:
http://www.eaton.com/ecm/groups/public/ ... 087652.pdf
or
http://www.eaton.com/Eaton/ProductsServ ... /index.htm

dago_red · Post by **dago_red** » Sat Jun 14, 2014 9:05 pm

loopbackzero wrote: I'll also need the original spindles, as the trutrack makes use of different spindles ( similar to ones that are in the front.)

If you have Dana 25 type spindles on your rear axle, sounds like you have a full floating conversion there. They're an interesting mod; I plan on doing one to my '54 A1. If it is a full floater, you should check on the spline count, etc, as an original 10 spline axle shaft won'tl be in there. It would have been replaced with a 19 or 30 spline and the true trac would reflect that.

Post by **wesk** » Sat Jun 14, 2014 10:57 pm

The truetrac would have come in a 30 spline configuration and loopback mentions the odd spline count and free floaters in his original post.

Bob_C · Post by **Bob_C** » Sun Jun 15, 2014 7:56 am

Correct, they are floaters with the Dana 25 spindles. And yup, they are thirty count axles. I thought it was a neat mod at the time, and thus didn't change it.

Thanks for the link Wes. I don't know why I didn't see this originally. I guess I wasn't looking at eaton. The original paperwork I have on it from thirty years ago lists it as a Detroit trutrack I think.

As I said earlier, I found fine metal in the oil, I suspect mostly from the pitted ring gear. I'm not sure yet if this has damaged the trutrack itself in any way. Looked at the prices for a new one, and they look steep. I had the m38a1 out at a small airport out here during the winter driving on the taxiways before they plowed the snow, and the trutrack didn't seem to be working very well. I'd often get into situations where one wheel was spinning.....just driving on a flat snowy surface.

In any case, I guess I should price out the original configuration. I have some spare parts that were given to me, but I've found in the past many of these parts are well used and abused.

Post by **wesk** » Sun Jun 15, 2014 10:42 am

Don't overlook my comment on the correct oil. If you are currently using synthetic 90-140 GL3, 4 or 5 oil then that's part your problem.

Eaton still labels your diff an Eaton Detroit TruTrac.

Bob_C · Post by **Bob_C** » Sun Jun 15, 2014 1:38 pm

Thanks. And I'm aware of the oil recommendation, it's on my old documentation too. Not using synthetic anything in the jeep. Pulling it apart later today.

dago_red · Post by **dago_red** » Mon Jun 16, 2014 10:15 pm

wesk wrote:The truetrac would have come in a 30 spline configuration and loopback mentions the odd spline count and free floaters in his original post.

If he dumps the true trac, original axles wouldn't do him any good. As you know, original are tapered and he'd need a new set of 10 spline axle shafts made up for the full floater set up (that would be strictly custom as nobody sells a 10 spline axle like that). He could still use the spindles as they have been bored out for the 30 spline shafts. 10 spline are smaller diameter so they would pass thru ok (besides they are made for 10 spline).

Dana 44 from a M38A1 never had spindles originally. The first post was a tad confusing but I think I see what loopback was getting at.

By the way, I never did see the reference to a full floater in his first post; you sure it's there?

Loopback- are truetracs rebuildable? Might want to check on that too.

Carry on.

Post by **wesk** » Tue Jun 17, 2014 6:46 am

That is what he realizes. He will basically need a complete A1 44.

And yes he mentioned the floater by this reference to spindles which should have read hubs in his first post:

I'll also need the original spindles, as the trutrack makes use of different spindles ( similar to ones that are in the front.)

Bob_C · Post by **Bob_C** » Thu Jun 19, 2014 7:18 am

Hi all,

Sorry for the confusion with some of my terms. I was typing the original posts on an iPad, and I tend to get a little sloppy on it. My apologies.

I think I have the axles and appropriate hubs from a spare rear end I have. I took the spare apart to see if I could use the differential itself, and it is in rough shape (corrosion). The axles at first glance look fine, and the hubs just need a little bit of sand blasting.

I have two differential cases with pinion gears for the D44. On both sets, the pinions look rough. Anyone have a favorite source for rebuild kits for these?

willysmjeeps.com

Ring Gear and Differential M38A1

Ring Gear and Differential M38A1

Re: Ring Gear and Differential M38A1