Best Rear Axle Ratio

[KE964CUMMINS]

Hi there! I am new here and the reason I am here is because I finally got the 1st Gen. Dodge Cummins 5.9 12v that I was looking for. The truck is actually in great shape with 144k on it, it drives extremely well, but I noticed that the 3 speed auto trans it's kind of rough. I want to upgrade several things on this truck, but I think it is needed to start with the transmission and transmission axle. Regardless, what I am looking to get from this long question is:

1. What is the best upgrade on my 3 speed transmission:

• I want to keep it automatic
• I want for to have more gears (6 at least)
• Not too worry about MPG but I would like to get to 80 MPH with no struggle

2. What is the best rear end ratio with an upgraded 3 speed auto transmission?

• I have seen a lot of conversations about Dana 70,80, but I am not too concern about disc brakes
• I want to be able for the 2 wheels to spin
• I want for the rear axle to respond well to the transmission and engine, while maintaining towing capacity high

3. Lifting the truck:

• I would like to lift the truck but not too much, maybe 4 inches
• I want for the front and rear to look the same
• I want to add air bags without too much modification on the rear axle
• I want to be able to run wider tires

Thank you in advance for all your help.

 

[petersonj]

I want for to have more gears (6 at least)

What is the best rear end ratio with an upgraded 3 speed auto transmission?

These two statements conflict.

What is the axle ratio of your truck?
2WD or 4WD?
What is the long term intended use for the truck?

The three speed automatic transmission without converter lockup placed behind the Cummins 5.9 diesel engine was absolutely the worse decision that could have been made. I am still amazed that Cummins even allowed the deal to go through.

If you are set on an automatic transmission for that specific truck, then I would look into an Allison 5 or 6 speed with converter lockup in every forward gear. It would be expensive, but by comparison it would perform very well and you probably would not need to change axle ratios.

- John

 

[KE964CUMMINS]

The truck it’s a 2WD and thanks for your reply.

 

[AnonEd]

Lifting the front four inches would be a challenge...I've only seen coils to 2.5"...it's probably easier to lower the rear. But if you're trying to make a desert go-fast out of it and stick on 33s or 35s that might be custom work. If the rear airbags are additional there's a few options not too expensive, but if you're thinking air/link to replace the leaf springs that'll get spendy.
Your truck has a Dana 70 in back, ratio could be ~3.07:1, 3.54:1 or 4.10:1. With a six-speed automatic (or anything with overdrive) and standard-height tires it'll do 80 with any of those ratios. @petersonj is correct about the transmission, but some might recommend a properly built Ram 4-sp auto for a lot less $.
Tire size will depend on what wheels you use, how much the bump stop is lowered and how much you want to trim the fenders.

 

[RWherley]

As far as I know if you have the 3 speed auto then you automatically have the 3.07 rear gears, and I'm pretty sure that is a special version of the axle know as Dana 71 and the housing will only work with 3.07 gear ratio, but double check me on that. As far as transmissions go Jon is on the right idea if your dead set on having a six speed but, the 1000-2000 series Allison that you would be using is physically much larger and is going to need a different engine adapter plate to mount to and a custom cross member and rear mount and may require floor pan modifications to fit. The 4 and 5 speed autos with OD from the 92-93 or 94-97 trucks work just fine if they're rebuilt and upgraded to handle the power level you want and are much easier to fit in the truck. As far as lifting the front end, I don't know of any bolt on kits for the 2wd trucks, but I will tell you the factory ball joints don't like excessive angle and you have to watch them, I had one tear in half on my 93 while driving and it caused a lot of damage to the truck when it did. That said from factory the truck should be pretty close to level if everything is right, if your truck is sitting with the noise really low compared to the rear the front coil springs are probably worn out. Circling back to your rear gear question, once you have OD I like running 3:54 gears, they give you good cruising speed and don't kill your low end for towing

 

[RedD250]

If you want to lift your 2wd that much, the only way I have seen after extensive research is to go this route: https://farfromstockstore.com/colle...cts/72-93-axle-swap-coil-kit-2nd-3rd-gen-axle

It will require extensive work, and you'll need to source a 3rd gen front axle. I'm sure the labor will be at least as much as the kit, if not more, unless you have a good shop to work in and plenty of good tools, time, and know-how. Probably looking at $10-15,000 to have it professionally installed. Might as well buy a 4x4 truck. BUT, the advantage to that route is it'll ride exponsntially better than the 1st gen could ever hope to. My 2wd rides like a bus on solid rubber tires. I had to get a new travel mug with a closing flap for the drinking hole because my tea would come flying out and splash all over the place 4 or 5 times every night on the way to work when I hit bumps that I never even notice in my Elantra.


They sell an air kit for the back too: https://farfromstockstore.com/colle...suspension-1g-w-3rd-gen-4th-gen-aam-11-5-axle

 

[KE964CUMMINS]

If you want to lift your 2wd that much, the only way I have seen after extensive research is to go this route: https://farfromstockstore.com/colle...cts/72-93-axle-swap-coil-kit-2nd-3rd-gen-axle

It will require extensive work, and you'll need to source a 3rd gen front axle. I'm sure the labor will be at least as much as the kit, if not more, unless you have a good shop to work in and plenty of good tools, time, and know-how. Probably looking at $10-15,000 to have it professionally installed. Might as well buy a 4x4 truck. BUT, the advantage to that route is it'll ride exponsntially better than the 1st gen could ever hope to. My 2wd rides like a bus on solid rubber tires. I had to get a new travel mug with a closing flap for the drinking hole because my tea would come flying out and splash all over the place 4 or 5 times every night on the way to work when I hit bumps that I never even notice in my Elantra.


They sell an air kit for the back too: https://farfromstockstore.com/colle...suspension-1g-w-3rd-gen-4th-gen-aam-11-5-axle

Yes to both "will be extensive work" and "my 2wd rides like a bus on solid rubber tires". Honestly, I have noting agains the 1st gens, I really like the looks but I am realizing they are a pain in the ass to be honest. Nevertheless, it is my pain in the ass now and I love it. Regardless, going back to the extensive work, you are absolutely right. This weekend I spend sometime online watching a few videos and it looks complicated. I would not be afraid of doing it with my dad around, but he doesn't live near by. Also, it seems like it will be cheaper to simply buy another truck, but I was thinking about it simply because this truck is very clean. Will continue to look at different options (not that many out there, but I might just do a few things here and there, like upgrade the transmission, it sucks!). Thanks!