Here's the deal, I've had a 94 3.9 L 5 Speed forever, and I'm getting my 92 3.9 Automatic on the road (or trying to). Both are 2wd extended cabs. The 92 automatic feels like it has no stones off the line. Seems to have adequate power for an extended cab V6 automatic at speeds over 15 mph. The only other difference between my two Dakotas is the 92 automatic also has the LSD. So my question is, is 1st gear in the 42RH that testicularly-challenged and that's just the way the 3.9 automatics are? Is there something wrong with my LSD (I did change the fluid, and put in the additive before I got it on the road)? Cat was rattling when I got the 92, but I took care of that. I used to work in a shop, but it's been years since I drove any 3.9L Dakotas. Any input from anyone who's had or has both an auto and a stick would be appreciated. I don't feel like chasing ghosts, but it's really annoying me I live on a very busy road in a traffic-congested area, so it's a bit of an issue.

 

When you replaced the cat., what about the rest of the exhaust? New muffler or the old one still on there? I'd do a vacuum check on it make sure the muffler hasn't rusted inside and collapsed. I bought a '93 Dakota Sport new back in '93 and it had all sorts of pep. Just ask that State Police officer.

 

Do they both have the same rear gear ratio? IMO a stick "feels" quicker, due to being able to get the rpms up to launch it. I would not suspect your exhaust if your problem is from 0 to 15 mph.

 

What 93 ragtop said.

I'd check the rear end ratios.

Let's also look - the AX15 has a 1st gear ratio of 3.83:1, the NV3500 is 4.016:1, and the 42RH is 2.74:1 ( the 46RH is 2.46:1).

Try comparing the manual 2nd or 3rd gear launch also; that's closer to what the automatic has for final if the rear ends are the same.

That extra on the manuals helps the 3.9 launch; it needs some revs to get up to where it has some grunt. Now the torque converter helps offset that some; but they're actually fairly tight from the factory, so they don't help that much.

RwP

 

Grouch, I checked vacuum before I fixed the cat, and after. Definitely looked normal after I fixed the cat, but that was before I got it registered and on the road. I'll check it again in the next couple days, see if some rust or a chunk of converter shifted around after actually driving it on the road and is plugging something up, again.

Ragtop, I checked, peppy 94 manual has 3.2, slowpoke 92 auto has 3.5. I always get confused on gear ratios, but I did some googling to refresh my memory, and what I found would seem to suggest that the 92 auto with the 3.5 ratio should be quicker off the line, at least differential wise. Is this correct?

 

Holy crap Ralph, that looks like a big difference in gear ratios between the ax-15 and 42rh. Maybe that's just it, the auto does almost feel like when I do a California stop in 2nd gear in my 5 speed. .

 

Differential wise, yes.

But.

If you have the AX15, the 94 final ratio will be (3.2 x 3.83) or something stiffer than 12.26 (the 3.2 is missing the last digit; I don't know what it is, it's not in my books at a super quick glance). The 92 final is 2.74 x 3.54 (THAT ratio I know!) or about 9.7 (!!!) And THAT is what the math says. Same size tires on both, the stick will have a lot more out of the hole, due to being close to 30% stiffer than the auto.

RwP

Addendum: Saw it after another glance. That's a 3.21 . Why don't they list the last digit on the tags? Dunno, you'd have to ask Chrysler Corp; but I bet so that 3.54 and 3.55 both could use the same tag; or say 3.21 and 3.23 or any other pairing close as that between the 7.25, 8.25, 9.25, and various Dana axles used over the decades by Chrysler. It barely changes the final numbers, though.

 

I don't care why Chrysler left the last digit off the diff gear ratio, I want to know why they gave the 42RH such an anemic 1st gear ratio! Argh LOL. Thanks all 3 of you for your responses, pretty sure I have my answer now, even though I don't like it. At least I know I'm not going crazy and imagining my automatic's lack of oomph starting out. Guess it's time to gather a spare AX-15 and pedals and what not...

 

Could always regear the rear, or, put in a different torque converter with a higher stall.

 

Just for consideration, are there any bolt-in Dodge rears with a ratio greater than 3.5? I am not comfortable rebuilding a rear, I worked in a shop 10+ years, never had to do it. I've heard that even guys with some experience screw it up sometimes, especially setting the pinion depth.

On the torque converter, where would one find said torque converter with a higher stall speed?

I'd consider either option, getting older and grumpier with bad hips, bad back, and bad right shoulder. My 5-speed days are probably going to be in the rear view soon. It's a shame, the dingbat I bought it from actually told me it had a bad transmission and was slipping between 3rd and 4th/overdrive (I never got it past 15 mph on "test drive," he had no plates on it or insurance). Manual shift linkage was hopping around from bad front cab mounts and ripped engine mounts. Trans has not slipped on me once. Shifts so well I'm almost thinking it's been replaced at least once with 178,000 miles. Just a crappy design. For right this second though, I'm going to stop chasing ghosts. It is what it is.