1J7FT36E8KL607378

[WAEMID IV]

1989 Jeep Comanche

 

2.5L / AW4 / 2wd / Dana 35 /  Short Bed

 

Current Location: Nekoosa Auto Iron and Metal (Wisconsin Rapids)

 

Status: sawed in half at a junkyard

This yard has 4 MJs. I shall add them to this registry for documentation purposes. This is MJ 4, which according to all known laws of MJ should not exist. The VIN confirms:
>It is a 1989
>It is a 2.5L
>It is equipped with the AW4 4 speed automatic

If you put that VIN into the build sheet generator on Jeep.com, it confirms it had an 18 gallon fuel tank, which was only available on the short beds. Because it was a short bed, we know it had a Dana 35 rear axle. It's a column shift with door pockets, an intact door sticker, and a very custom looking coil spring job in the front. The bed and rear frame have been cut off and are long gone.

What I find strange is the build sheet declares this Jeep had a 3.47:1 gear ratio. As far as I know, not only does that ratio not exist for the Dana 35, but it's mathematically impossible. The closest I can get via estimating the teeth count on the ring and pinion gear is 45/13, which gives a 3.4615384615 (which would round down to 3.46, not up to 3.47). I would of course just open the differential and count the teeth to see for myself, but as noted, the entire back half of the truck is not there and it is 2wd so the front axle can't help us.

Another thing is, I've only heard of 2.5L + Automatic during the renix years to be a 1987-only thing. I have heard of a handful of *specifically 1987* XJs and MJs with a 2.5L mated to an AW4, but never, not once, a 1989 with this drivetrain configuration. It is considered "known" that the 2.5L didn't even have an automatic option for 1988-1993, with the Chrysler 30RH returning in 1994. This truck existing implies the AW4 stuck around until at least 1989 behind the 4 cylinder - a late 89 at that, manufactured on June 3, '89 brings this MJ close to the last known model year 1989 Comanche (that I'm aware of) which is June 29, 1989.

 

[fiatslug87]

1 hour ago, WAEMID IV said:

Another thing is, I've only heard of 2.5L + Automatic during the renix years to be a 1987-only thing. I have heard of a handful of *specifically 1987* XJs and MJs with a 2.5L mated to an AW4, but never, not once, a 1989 with this drivetrain configuration. It is considered "known" that the 2.5L didn't even have an automatic option for 1988-1993, with the Chrysler 30RH returning in 1994.

We actually have 2 '89s (now 3) and 2 '90s in the registry that are 2.5L AW4s

 

[WAEMID IV]

I have been looking through the registry spreadsheet for the past few hours now lol. These are all very interesting trucks
I notice there are 5 times as many 87s as there are 88-90, which would explain why some people (like myself) thought it was only a thing for 87
One thing nobody can agree on is the gear ratio. The Jeep.com build sheet generator says 3.47, The MJ build sheet generator says 3.55, owners themselves say 4.10 and commenters who think they know everything say 4.56. I must find one with a rear axle and count the teeth myself.

[fiatslug87]

Did you confirm the ratio in the ‘87 you found?

[WAEMID IV]

I was not able to yet. This yard doesn't allow you to jack up vehicles for liability reasons, so I have to make an appointment to have a guy come out with a forklift and get it off the ground so I can get the axle un-buried from the sand. I will report back once I have confirmed the ratio.

(I also contacted Dex Jeeps to see if he had any renix 2.5L + autos, and he doesn't have a single one. That shows how rare they are.)

[eaglescout526]

If I remember 3.47 is a reused code that’s for the modern Jeeps with the D44’s. 3.55 would be damn near too low for the AW4. 4.10 would be about correct and maybe 4.56 but 4.56 was found with the Chrysler 900 series 3 speed. 
But then again we are talking about AMC, where my 84 XJ has 3.55(front and rear) 5spd manual NP207 and it can keep up, but can be a smidge slow. 

[WAEMID IV]

This may be a controversial take, but I don't think there ever was a 4.56 ratio from the factory in an XJ/ MJ. I've been looking through all sorts of pages on here, forums, facebook posts etc ever since I made this post 4 hours ago, and not once has *anyone* actually been able to confirm they had 4.56 gears ((unless they re-geared themselves)). The Novak page, wikipedia, and vast amounts of uninformed commenters claim 4.56 exists, and only with the 2.5L + Automatic, but not a single one of these sources can back up that claim with actual evidence. No build sheets, Factory service manuals, differential ID tags, or axles listed on car-part.com across the country have ANY 4.56 ratios. For comparison, I can find 3.31 without any issue, and I know those are rare.

4.56 with a 2.5L just isn't possible, especially with the tiny 195/65R15 tires they usually came with, the RPM would be ~3,500+ at highway speeds, even with the AW4's overdrive. I think 4.10 sounds reasonable, and even then you're at what, 3,000 RPM at 70mph. I'm sure someone who can speak math will correct me

I got to drive a 2000 2.5L Auto XJ (3 speed) recently, and confirmed it had 3.55 gears in the axle. That thing had a 0-60 time of 26.5 seconds, *literally* slower than a semi truck. I would guess a 2.5L Auto (4 speed) should have either 3.73 (haven't found any evidence for that) or 4.10, but most certainly not 3.47, which isn't even mathematically possible unless you have 52 teeth on the ring gear and 15 on the pinion. I'm not sure if such a thing would fit in a Dana 35, but I'm not an expert in axles.

Like you said, this is AMC, they're not exactly known for doing things that make sense.

I have discovered a rabbit hole so deep I am actually losing sleep over this at 2 AM on a wednesday

[Pete M]

4 hours ago, WAEMID IV said:

I got to drive a 2000 2.5L Auto XJ (3 speed) recently, and confirmed it had 3.55 gears in the axle. T

 

3 speed?  in 2000?

[89 MJ]

2 hours ago, Pete M said:

 

3 speed?  in 2000?

Probably. YJs and TJs had 3 speed autos up to 2002. 

[89 MJ]

@GonzoTheGreat, can you confirm the ratio in the rear of your 2.5L auto truck?

 

Disregard, I saw his comment on this thread.