Front Axle ID Challenge

[knobbler]

Hey all! Been a minute since I posted here, but hopefully this is a topic that might be interesting or informative for someone out there. Long/short, got an '85 wagon, front axle is the original (as to the best of my knowledge). Due to some drivetrain failures, I ended up getting a replacement front & rear set from an Eagle of an unknown (at the time) year. Looking under the bird at the old axle and comparing it to the replacement has me a bit flummoxed, though, because I notice the two differ in their mounting bosses.

The old (assumed original) axle bolts up on the passenger side to the hanging bracket as it should on an '85 wagon, meaning there's a passthrough for the connecting bolt welded onto the top side of the axle tube as expected. In addition to this, it also has a tab/mount (for lack of a more specific term) welded to the underside of the tube, to which attaches a length of steel tube with flattened ends that allow fasteners to fix it on one end to the lower mount on the axle tube, and below the starter to the transmission bellhouse on the other. Kind of a stabilizer bar of sorts? My suspicion is that this is intended to partially distribute shock and vibration to the tranny to be absorbed by the tranny mount, taking a little bit of the load off the motor mounts, but I'm no engineer, so what do I know?

In case my vague description isn't enough, here's a bad picture to help make things clear as mud.



Now, I should probably clarify that there's no problem here, per se, except that the diagram for an '85 front doesn't show this lower mount. It's not got the vacuum switch assembly like earlier years, since it's on the fly switched at the tcase (as expected for an '85). Was this an alternate part for a wagon with a towing package, or part of the deluxe trim package options?

Here's the replacement:



As you'll see, it matches the exploded diagram of the axle for an '85, shown in I.S. Note 5E (pg. 7):



In case it might be helpful, here's the diff tag info (don't have the same for the one presently installed yet):

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2.72    49-18
3251266

So the replacement is matching up with the '85 parts listed in the TSM better than the parts I've actually got in my '85! Anybody with a parts catalog or more familiarity with these axles than I do know what's going on here? I'm not too worried about compatibility yet, but if you compare the height of the top mount on the replacement axle, it appears to set both lower than the one on the same that's installed, as well as maybe further inboard? Won't know until I have the current axle pulled (later today, God willing). When that's done, I'll be updating the thread with much clearer comparison pics.

Love to hear what y'all think about this. At present, I'm stumped!

[AMC of Houston]

What you have is a 1980-early 1981 "full-time" axle.   The torque braces were around back then, but only came on the "part-time" axles (the ones with the disconnect box).

[knobbler]

What you have is a 1980-early 1981 "full-time" axle.   The torque braces were around back then, but only came on the "part-time" axles (the ones with the disconnect box).

Ahhh, okay. Thanks for the assist! I only just now managed to finish pulling 'er and came back to post the pictures, so I'll go ahead and add them at the end of this, for the sake of completeness, if nothing else. This is the tag info from the one I just pulled from my '85:

Code: [Select]

8933002629
2.72    49-18
(Yep, the ratio is in fact on the bottom with this tag, versus the one on the replacement, where that info is on the top line)

To make sure I'm on the same page here, are you saying this guy here ("axle 1") is the '80/'81 full-time?



Or is it the new guy here ("axle B")?




EDIT: Pardon my table breaking. I don't remember the BBCODE tags to limit image sizes. I'll fix them once I find the info so this isn't a hassle to browse

[AMC of Houston]

Now I may be slightly cornfused!!   I'm saying the "new guy" axle without a lower torque brace mounting ear is the early "full-time" axle.

The numbers off your original axle tag (33002629) are correct for '85 thru '88 2.72 ratio.   All '85 thru '88 axles were "full-time", and had the torque brace mount ear.

[knobbler]

Now I may be slightly cornfused!!   I'm saying the "new guy" axle without a lower torque brace mounting ear is the early "full-time" axle.

Ohhhhhh, okay I get it now. I think I'm seeing what was tripping me up. My familiarity with the Eagle drivetrain is a really weak point of mine, so I'm gonna need to hit the TSMs and get a better grip on how this stuff actually works.

So if I'm tracking right, Eagles had a few broad iterations of their 4/AWD system over the years:
— Early 80s, 4WD always engaged at both the tcase and front axle.
— Couple years following, switchable between 2/4WD, switched at tcase and via vac controlled engagement fork in the front axle.
— mid-'80s to the end, switchable between 2/4WD, shifted at tcase, front axle always engaged.

If correct, then that means I would be able to install the 998 and 129 I have from an '84 without running into problems with operating between 2/4WD as per usual for an '84 if I were to also install this replacement axle (the one without the torque bracing ear).

Am I following right, or do I need to hit the books harder than I thought?

The numbers off your original axle tag (33002629) are correct for '85 thru '88 2.72 ratio.   All '85 thru '88 axles were "full-time", and had the torque brace mount ear.

Very very helpful there, thanks. Is there a resource I can refer to for decoding those tag numbers? I looked around before, but found mostly stuff for later Dana tag styles that didn't seem to cross correctly.

Thanks again for helping me get this sorted!

[AMC of Houston]

Notes to your notes:

— Early 80s, 4WD always engaged at both the tcase and front axle.
1980 only.  Tho there have been reports of some early '81's like this.
— Couple years following, switchable between 2/4WD, switched at tcase and via vac controlled engagement fork in the front axle.
1981 thru 1984 had the "disconnect" axle.
— mid-'80s to the end, switchable between 2/4WD, shifted at tcase, front axle always engaged.
1985 thru 1988 end of production.

I don't see any issue with a 129 T-case with either axle.  Some folks with the disconnect axle just "lock it" permanently anyway.

[knobbler]

Notes to your notes:

— Early 80s, 4WD always engaged at both the tcase and front axle.
1980 only.  Tho there have been reports of some early '81's like this.
— Couple years following, switchable between 2/4WD, switched at tcase and via vac controlled engagement fork in the front axle.
1981 thru 1984 had the "disconnect" axle.
— mid-'80s to the end, switchable between 2/4WD, shifted at tcase, front axle always engaged.
1985 thru 1988 end of production.

I don't see any issue with a 129 T-case with either axle.  Some folks with the disconnect axle just "lock it" permanently anyway.

Much obliged, sir! Massively helpful.