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was in a friends m37 and at 50mph I thought the engine was gunna blow....the rpms were high......I know the gearing keeps top end speed down....how can I either increase speed or keep the rpms down in 4th at 45-50 mph......since most of my driving will be on concrete roads I'd like to maintain 50mph without burning up the engine.....will have a freshly rebuilt 230 put in.....

bobcat,

You're asking for a lot........these trucks weren't designed to run continuously at 50 mph. There are lots of options to improve the situation, such as 4.89 gears, bigger tires, etc, etc...but probably your best bet when all is said and done will be a re-power and driveline change. That 230 just won't like running at 50+ mph all day with anything close to the original driveline. Heck, M37 wheels aren't even balanced.

But you're in the right forum with that question.....there are folks on here that have been there, done that.......and you'll benefit from all those lessons learned. Sorry I can't be of more help.

regards,
bob

Bobcat,

If the engine is in good condition and running strong, they will survive with the 5.83 gears and 39" tires for about 55 MPH, but that is best case. I've got 39" on my 46 PW with a Plymouth 218 (rather than the correct 230) and it struggles to hit 50 and sounds like the engine is turning 4K, but is actually having a hard time hitting 2,800.

Even with the 4.89's and 39" the engine better be a strong one to prevent it from bogging down.

With stock tires and gears the engine is doing about 2,885 RPM at 50 MPH.

I've briefly been to 50 in mine with everything stock except the tires (STA Superlugs) and that was all I could stand. I normally cruise at between 35 and 40 and then I use earplugs. I just don't see a reason to push the engine any harder than that. I will ride around my neighborhood at 30 if there is no traffic.

I have run my truck down the 4 lane highway a couple of times, for about a 20 mile trip. I am happiest running it at 40-45 mph max. I don't have the guts to try 55 mph. I think the engine will grenade!

4.89 gears, 38" tires and a diesel engine. Talk to Charles Talbert at M-series. With mine the top of the power curve is about 50 but I can push it to 62 with the diesel. I wouldn't do this unless I had balanced tires and 4 wheel disk brakes and tight steering. I normally cruise around 45- 50 on local roads. Only place I push 60 is on the interstate and then just to blow out the cobwebs. If no one is on local roads I enjoy poking along at 35.

Whats max RPM for the stock engine?

carolinamv wrote:Whats max RPM for the stock engine?

The maximum governed speed is supposed to be 3,400 RPM per TM 9-1840A.

But the old flathead doesn't seem very happy at that speed.

thanks for the info, I'll look for 4:89 gears......guess that's the best I can do without taking away from the original look/equipment.....

bobcat,

I believe the only supplier of the 4.89 gears is Vintage Power Wagons. They started re-making them this past summer.

regards,
bob

How much low end crawl do you loose going to the 4.89 gears? I have the stock 5.83 gears, and in high range I start in second and top out at 45 mph and wish I had another gear. 4.89 gears seem like they'd be great for every day driving, but how are they on rocky, ledgy 4x4 roads?

I have 4.89 gears and 38" tires with a Hercules diesel. Unloaded on flat ground I still start in second. During a parade I put the M37 in first gear normal range and can walk faster than it will idle down a flat road. The diesel gives me plenty of low end grunt.