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M-Series Dodge M37, M42, M43, V41, M601 M37 3/4 ton cargo truck, M42 command truck, M43 ambulance, V41 telephone maintenance truck, M601, and any variants

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Old 09-29-2009, 11:03 PM   #1
Andrew McConathy
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M37 Overdrive

I am looking for an overdrive unit that I can mount om my stock 1951 M37 any ideas? Has anyone on here done this? if so do you have any pictures of the shortened drive shaft?

Thank you

Andrew

Last edited by Andrew McConathy; 09-29-2009 at 11:03 PM. Reason: speling
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Old 10-03-2009, 04:10 PM   #2
Bruce
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Ranger Over Drive

Have you checked out Cabell's page, boat load of info, he posts here from time to time, mostly SS & Joe C's page.

http://www.garbee.net/~cabell/
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Old 10-04-2009, 11:39 AM   #3
Andrew McConathy
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I will give it a go thanks!
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Old 10-06-2009, 09:52 AM   #4
Andrew McConathy
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No luck on a Over-drive for the stock engine and transmission.

any ideas?
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Old 10-06-2009, 11:34 AM   #5
Joe Rokon
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All I can say is drive the truck at its intended speeds. You could change the ring and pinion ratio to 4.89,but I wouldn't want to give up my low gearing.
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Old 10-06-2009, 12:30 PM   #6
W_A_Watson_II
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Andrew,

What is the intent of the Overdrive? Depending upon your desired use of the truck there may be other options. I have no info on it, but there is a Ranger Overdrive that some have installed on the Power Wagons, that I would think might be an option, the only issue is it's not between the tranny and T-Case, it between the T-Case and the rear differential, so it's only good for 2WD.
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Old 10-06-2009, 02:26 PM   #7
MasterYota
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Quote:
Originally Posted by W_A_Watson_II View Post
Andrew,

What is the intent of the Overdrive? Depending upon your desired use of the truck there may be other options. I have no info on it, but there is a Ranger Overdrive that some have installed on the Power Wagons, that I would think might be an option, the only issue is it's not between the tranny and T-Case, it between the T-Case and the rear differential, so it's only good for 2WD.
Actually the Ranger unit (produced by Advance Adapters) bolts between the engine and transmission as an auxilliary unit. The Gear Vendors Overdrive is the unit that bolts to the back of the tcase. As far as I know, its only availble for the newer NP205 tcases, not the Np200 as is found in the M37.
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Old 10-06-2009, 02:48 PM   #8
Andrew McConathy
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I want to be able to travail on the highway to my 4wheel destination at 55mph, then put it in to 4x4 and go up a 60% grade. I love the truck, don't get me wrong, I just want top be able to get to were I am going and still have time to have fun and get back.

So I want a over drive unit that will work on the 2wd behind the transmission.
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Old 10-06-2009, 03:06 PM   #9
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Easiest way would be to swap in a Divorced Np205 from a dodge or international pickup, and then use the Gear Vendors unit behind it.

Here is my 0.02 cents though.

Consider that the 230 might not have enough gumption to push the truck in overdrive along anything but a downhill grade. You may just end up shifting more, and gaining nothing but a lighter wallet.

Also consider the speed at which the truck is designed to operate - 55mph is at the very end of its inteded operational speed. Increased speed will definitley shorten the drivetrain life, especially the tcase, which is prone to overheating.
Its like driving your car with the speedo buried at the end and expecting it to get 200,000 miles of life out of the components. Its not a realistic way to drive.

Leaving 10 minutes sooner would provide the same results, and its basically free, and you could drive the truck at its intended highway speed without sacrificing anything. Taller tires would accomplish the same thing, as the taller tires covers more distance per rotation than a shorter tire. The speedo may read 50mph, but your actually covering distance as you would at 55-60 mph...
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Old 10-06-2009, 04:37 PM   #10
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good point, is the np205 simpler in size to the np200, is it as robust?

Also does the fabled overdrive that bolts on to the np200 made by Denman exist? and were could I get one?

I have looked at my rear end and I think that it will hold up just fine at 55mph I did the calculations on the stresses involved and it is well within its rang ( I think, and HOPE, and pray)

I do agree that the unit what ever it is should be on the 2wheel only and that it should be behind the transfer case. So does aneyone know were I could get a Denman??
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Old 10-07-2009, 05:18 PM   #11
Rodney
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NP 205 Gear Vendors OD

What is the finished length of this OD? Unlike the Warn O.D. for the Jeeps, it looks like this will result in a shorter rear driveshaft and loss of the OEM parking brake assembly. Is this correct?
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Old 10-07-2009, 06:25 PM   #12
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Don't know, does anyone out there have any experience with this??
Good question!
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Old 10-07-2009, 07:39 PM   #13
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I'll try to answer a few questions as best I can, from some of the research I've done over the years

NP205 - Far superior tcase (in any version) to the NP200. Consider that the NP200 is the grandad to the NP205. All the weak links associated with the NP200 have been solved with the design of the 205. The 205 is the strongest tcase ever offered in a light duty vehicle. It is probably found under some medium duty 4x4 chassis' as well. The NP200 is a stout unit, but given a choice between the two - the 205 wins hands down in my opinion.

The Gear vendors overdrive is alot bigger and stronger than the saturn overdrive offered for the jeeps. Where the saturn unit uses the unused rear PTO port on the Dana18 tcases, the GV unit replaces the rear output yoke on the 205, and is built to reliably handle upwards of 1000 HP or so... Its plenty stout. The rear driveshaft would be shortened by about a foot or so, at least judging from pictures. Loss of the rear park brake assy. is definitely possible, but anything can be adapted if enough ingenuity is used.

I've never seen or heard of a Denman Overdrive for the NP200. I'm curious to hear what you've discovered about this unit...

The axles are not really the weak point for driving at 55mph. Its the brake design, and the design of the tcase. I would be more worried about the tcase than anything else. Its design causes it to generate an excessive amount of heat, which breaks down the lubricant and leads to premature failure. Changing the tcase to a centered rear output changes the load on the case and reduces not only the heat buildup, but apparently the noise as well. This is a mod that I'm looking into for mine, using just a machined spacer ring to bolt the driveshaft to the back of the park brake setup. I'm swapping out the axles however to modern units with 4.56 gears - this will allow the tcase to operate at highway speed but at a lower rpm, thus allowing it to run cooler.
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Old 10-07-2009, 08:56 PM   #14
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A note to remember about the Gear Vendor overdrive unit. The GV will not hold back the vehicle while decelerating or going down hill. I have run a GV on a previous vehicle and was really happy with the performance. I've also considered using it in my 1958 D400 with the 5.625 rear ratio but the coasting effect closed that thought. I might be able to run up hill at 55 mph but in a long down hill I'll be back down to 45 at 2500 rpm.
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Old 10-07-2009, 10:24 PM   #15
Andrew McConathy
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Well that solves that, I am not redy to rip up my very stock M37 for a few more MPH, Unless there is a overdrive unit that will take the down hill drag and will work with my Np200 I am going to stay in the right lane. I think I will go to the taller tires tho, thank you guys! This has been a grate conversation, I have appreciated every word of it. My truck is very solid and original but this has me thinking about finding anther to modify full out (when I win the lottery).

Keep on trucking!

Andrew
1951 M37
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