dott

Maybe this is crazy, but it's rolling around in my head and can't shake it until I investigate.

My '04 Dodge has the AAM 11.5" rear axle with 4.10 gearing and NV5600. It's great for towing. If I never did anything but tow, there would be no issue. Driving unloaded is a pain. To get the best mileage, I have to drive 55-60 mph. I don't want to re-gear (to say 3.73) because it's a standard and the towing would be hosed. Also, backing up is already a little fast, even with the 4.10 gears. Currently running stock size tires.

My crazy idea is to find a 2 speed axle with close to desirable gearing, probably adjust it with tire sizing, then find a way to install it.

Already looked at the Gear Vendors boxes but they are a little pricey and kinda set a budget for any other mods.

Do all vehicles with 2 speed axles use air brakes?

Here is some axle data I found:
GM H15 - Rear Axle
Capacity lb.(kg) - 21,000 (9,526)
Available Ratios (to 1) 3.55/4.83, 3.70/5.05, 3.90/5.32, 4.11/5.61, 4.33/5.91, 4.56/6.21, 4.88/6.65, 5.29/7.21, 5.57/7.60, 6.14/8.38, 6.57/8.96, 7.17/9.77
Ring Gear (pitch dia.) in.(cm) - 16.5 (41.9)

I've heard that the GMC/Chevy Topkicks have a two speed rear as an option. Haven't been able to find any info on this.

It seems like U-Haul trucks would be a good place to look.

I realize there would be a lot of fabbin' to get this to work. I just want to look at the basic stuff first to see if there is any chance of it working.

Any suggestions are appreciated.

dott

Just found this about Topkicks regarding hydraulic brakes:
"The rear axle has a 13,500-pound capacity and two-piston disc brakes."

and

Rear axle ratio, 4.30 - 5.13 available on:
Regular Cab/Crew 2WD
Motor Home 2WD
Commercial Cutaway 2WD

but, that ratio is going the wrong way.

chaikwa

All the 2 speed axles I've seen are almost too big physically to get under a one ton truck. No, they're not all air brakes but I don't know what would have to be done to get your brake system to work with the system on the 2 speed axle. I'd have to think the brakes, lines, cylinders etc., would all be much bigger and I don't know if your master cylinder would work. If you changed your master cylinder, I don't know what would happen to your front brake system. And if you changed the braking system on the new 2 speed axle to something your existing master cylinder would work with, I don't know if they'd be effective.

U Haul trucks typically don't use 2 speed axles because people tend to tear them apart due to not knowing how to correctly use a 2 speed in the first place.

Anything can be done with enough time and money tho!

annabelle

I looked at an 86 (?-not sure of exact year)Ford dully that had a two speed rear axle.

12valve@heart

I recall a mid-70's Ford school bus that used an electric solenoid to shift ratios and used hydraulic brakes. Since the new trucks come with 20" tires already, putting a set of 20's from a bus under there shouldn't be any problem. Oh yeah, aspect ratio.

chaikwa

Does that change when you shift the rear end?

12valve@heart

Depends on what RPM you shift at. High enough RPM and the aspect ratio increases as the tire grows (think top fuel).

chaikwa

That makes sense in a scary kinda way!

dott

Thanks, y'all. I know it's a crazy idea, just thought I'd ask.

olddodgetrucks

Not a stupid idea,had a 70s i.h.c. one ton,gooseneck special ,392,5 spd ,2 speed rear axle with std 8 bolt one ton wheels.