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Hey, I'm looking at trying to get custom gearing for our 9 5/8" difs. Preferably in the 4.56 range. Does anyone know of any places that do such work.

I called Bob Stahl about 2 weeks ago and he was out of 4.89s, I haven't called vpw yet about their's but I want the numerically lower gears so I can get it up to a cruising speed easier and with less drive train stress.

I'll ultimately be running 35.5" interco tsl bias

4.89 gearing is the only choice.

Any particular reason? I know the calculation doesn't account for available horsepower and torque, but are these flatties that anemic? Or are you saying it because that's the only other option put out by Bob and VPW?

Literally, 4.89 option is THE ONLY CHOICE. There is nothing else made that will fit the Dodge diff except the original 5.83. So yes it is the only option put out by anyone today. It was a factory option in civilian trucks, but all M37's had the 5.83 ratio. Very few power wagons got them it would seem, we've never had one here that had the 4.89 gearing originally installed.

Is it too high for a 230, you will shift into 3rd gear more often, especially if you operate in hilly terrain. A good condition engine will support them fine; but if your engine is getting tired, you may be disappointed. It can be a border line situation. I really love them in the Cummins trucks, and likewise generally speaking with a good 230.

The original tops out about 45 to maybe 50.. What's the top end for the 4.89 set?

-jim lee

jim lee wrote:The original tops out about 45 to maybe 50.. What's the top end for the 4.89 set?

-jim lee

It will raise ground speed by 10 MPH. Whatever the RPM is at 45 now, it will be that at 55 with 4.89 gearing.

Thanks! That's exactly what I've been looking for. Just enough to get on the freeway and get somewhere. 45 is a little too spooky.

-jim lee

That's my main reason as well. I'll just start setting asside money for a few things down the road after my PCS.

Please be careful in your thinking that you willingly want to drive the old M on the freeway. These trucks do not like the speed and the steering and brakes if stock are marginally up the their tasks. I would be very uncomfortable driving next to a hundred vehicles at speeds approaching 55 mph. I would run my truck on side roads to that speed but I also had disc brakes on the M37 to enable it to stop in a resonable time frame and stop straight without swapping the ends around. There are lots of people who will try and tell you shouldn't drive these trucks like that but please start out slowly and work up to the freeway after understanding the M's handling and quirks. I loved driving mine around but other people don't understand your in a 60 year old vehicle and treat like you every other driver and these trucks can be a handful to drive. Terry

All systems certainly need to be up to the task.

If they are rebuilt and upgraded correctly, they will handle 75 MPH like a dream; but you can't have that safely until you start at one end and come out the other rebuilding all in between the best it can be.

Its not so much "I need to go fast now!" Its more, "I'm glad there is a path I can take if and when the time comes." Right now the engine is getting rebuilt. So it should be able to pull the speed. But, before trying the new gear sets, I know I'm going to need new brakes & steering. After we get the ground work finished, we can try upping the gear ratios.

-jim lee

jim lee wrote:Its not so much "I need to go fast now!" Its more, "I'm glad there is a path I can take if and when the time comes." Right now the engine is getting rebuilt. So it should be able to pull the speed. But, before trying the new gear sets, I know I'm going to need new brakes & steering. After we get the ground work finished, we can try upping the gear ratios.

-jim lee

Not to worry; the 230 engine the best it can be will never take you to ride at 75.

Trust me, I hit the brakes wall tonight with mine, the rears wont bleed under pressure even after cleaning the bleeders, and the M/C has no resistance in its stroke. I'm honestly just going to replace the lines and M/C, the wheel cylinders look decent though. So many things. The wiring is an issue as well.....