M38 Speed with Overdrive

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.
Marty, SoCal
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Re: M38 Speed with Overdrive

Post by Marty, SoCal » Tue Oct 11, 2011 5:12 pm

I'm happy cruising the SoCal freeways at around 60-62 MPH with the overdrive in my GPW. No, I wouldn't drive it in the snow or rain that fast, but on a straight freeway, usually with a friend driving behind me in a modern vehicle running interference, it cruises happily at that speed. I've had is up to 72 mph, verified with a GPS, but it was a bit squirrelly with the NDT's at that speed. In my opinion, it's safer to at least drive at a speed close as possible to the rest of the traffic, than to go too slow for traffic conditions. Seems like many of the MV fatal accidents lately were caused by driving too slow for traffic conditions.

The overdrive lets you split gears, helping to keep you in the powerband for hill climbing, 2nd, overdrive is just about in between regular second and regular third. A small hill is usually no problem if I'm over 45 mph, if not, I drop it back unto direct drive 3rd, or on realy steep hills, second OD. RPM's at 62 are roughly the same as at 45 mph without OD, the engine is a lot happier even at slower speeds in overdrive. It just puts along. Usually, I'll start out in regular first, then go to regular second, then OD second then OD third. Level ground, you can use overdrive third above about 40 mph, no problems. Here's a link to my post of the Overdrive installation in my GPW:
http://www.g503.com/forums/viewtopic.php?f=10&t=164205" onclick="window.open(this.href);return false;

The M38 with 5.38s and 700x16s works out to be about the same relative rpms as my GPW with 4.88s and 600-16s.

My buddy took this pic on the 10 Freeway near the Morongo Casino last November from his TJ:
Image
I put about 500 miles on the GPW that trip, most of it on the freeway, the rest on desert dirt roads and trails got about 14-15 mpg overall. More pics of the trip on my Photobucket album:
http://s551.photobucket.com/albums/ii47 ... th%202010/" onclick="window.open(this.href);return false;

Frankenjeep, My old '61 CJ-5 had a built 283, with a T98, 4.27s and Warn overdrive, I really liked the OD in that rig. I had it over 100 mph, no problem with modern radials. My current CJ is a CJ-8, I swapped in a Mopar 5.2l Magnum and a NV3500 5 speed. It actually gets better mileage than the old straight six when loaded, with almost twice the HP as the 258. The speed limiter in the Dodge Dakota PCM limits me to 115 mph. The power comes in handy at times while towing my 1/4t trailer, merging onto the freeway, climbing the Banning Pass, etc. However, I usually drive both of them like a grandpa in the slow lane and around town, a man has to know their jeeps' limitations!

I have some older pics of the CJ-8 on my Photobucket Scrambler album:
http://s551.photobucket.com/albums/ii47 ... er%20pics/" onclick="window.open(this.href);return false;
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
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Cuz
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Re: M38 Speed with Overdrive

Post by Cuz » Tue Oct 11, 2011 9:17 pm

Frankenjeep, My old '61 CJ-5 had a built 283, with a T98, 4.27s and Warn overdrive, I really liked the OD in that rig. I had it over 100 mph, no problem with modern radials.
Was this jeep still running the stock Ross steering and model 25 frt 44 rear axles with stock springs and 8 or 9" brakes?
Cuz (AKA Wes K)
45 MB, 51 M38, 54 M37, 6? M101A1, 60 CJ5, 76 DJ5D & 47 T3-C

Marty, SoCal
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Re: M38 Speed with Overdrive

Post by Marty, SoCal » Wed Oct 12, 2011 5:18 am

Stock Dana 25 in front, 44 in rear with a Detroit locker and a full floater conversion. 2-1/2" lift with 31x10.50 BFG AT's on late CJ stock 7" chrome wheels. 11" drums all around, stock brake master. GM power steering conversion. It did have a full roll cage. It had dual fuel tanks, the stock one under the seat, with a 15 gallon extra tank in the rear, and a Ramsy RE8000 winch (which is now on my Scrambler). At 100 MPH, it still had 1/2 throttle left. The built 283 pulled hard to 6500 rpm! I sold it and bought the Scrambler back in 1996, the CJ-5 was to small with a new kid, you could only carry a small cooler, no gear without having the trailer hooked up.
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
MVPA #8266
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license

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Re: M38 Speed with Overdrive

Post by FrankenJeep » Wed Oct 12, 2011 7:28 am

:lol: Well, you don't have to worry about me holding up traffic on the freeway: I won't be out there! Ole "Willy" and me........we stick to the country roads with a speed limit of Max 50----usual cruising speed= 30-35. If I get 2 cars following me for any distance at all, I let 'em get a good look then pull off the road!
That way, MOST enjoy the sight of the old military Jeep, and don't get mad at me for holding them up. Same as it was with my former Model A Ford. I have no need for high speed in an antique Jeep, and most trips are for pleasure anyway! They weren't designed for high speed or cornering, so I generally adhere to the old USAF/CAP Manual 77-1 pertaining to transportation safety and driving these old warriors! Willy grumbles anyway if you push him! :wink: I'll leave the high speed driving to others! :D

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Re: M38 Speed with Overdrive

Post by Joe Gopan » Wed Oct 12, 2011 7:40 am

And I putt along effortlessly at 55+ in my M-38A1 on the interstate. A nice relaxing M-38A1 Jeep ride is good for what ails you. :wink:
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jpet
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Re: M38 Speed with Overdrive

Post by jpet » Wed Oct 12, 2011 11:06 am

Last edited by jpet on Wed Oct 12, 2011 11:45 am, edited 1 time in total.
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Marty, SoCal
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Re: M38 Speed with Overdrive

Post by Marty, SoCal » Wed Oct 12, 2011 11:23 am

The link doesn't work :?
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
MVPA #8266
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license

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jpet
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Re: M38 Speed with Overdrive

Post by jpet » Wed Oct 12, 2011 11:46 am

Marty, SoCal wrote:The link doesn't work :?
:oops: sorry. Try them now
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raymond
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Re: M38 Speed with Overdrive

Post by raymond » Wed Oct 12, 2011 4:59 pm

A set of all terrain light truck radials makes a BIG difference in jeep handling.

Raymond
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Marty, SoCal
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Re: M38 Speed with Overdrive

Post by Marty, SoCal » Wed Oct 12, 2011 6:16 pm

jpet, Nice videos! However, you forgot to include the link for your video of the BEST reason to add an overdrive:

http://www.youtube.com/watch?v=DmXfn3iq ... re=related" onclick="window.open(this.href);return false;

Have you since readjusted your throttle linkages? Have you tried the unlocking front hubs? Should make a difference! Also for best accelleration try regular first, then second then second OD, then third OD. I've found that at higher speeds, driving with the windshield glass opened up about 2" results in alot less buffeting of the windshield frame,and less turbulence inside the jeep. I also won't run with the summer top up, I'm afraid it will come off on the freeway! My jeep runs out of RPMS at 65 in direct drive. I'ts probably able to pull to 72+ in OD because of the 8-1 compression head I have on it. (It added 6 HP and 20 lbs/ft torque to the rear wheels on a dyno.!)
43 Ford GPW 92098
53 Dunbar Kapple M100
Sold: 61 CJ-5, 41 T207 WC-1 Dodge closed cab pickup
MVPA #8266
USMC Tanker (1811, 1812), 85-93
ASE Automotive Master tech, former Chrysler-Jeep Level 4 Mastertech, CA state EA smog license

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jpet
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Re: M38 Speed with Overdrive

Post by jpet » Fri Oct 14, 2011 5:14 am

Marty, SoCal wrote:.......Have you tried the unlocking front hubs? Should make a difference!......
Hi Marty,

I did try the same experiment with the hubs disengaged and I did not notice any increase in speed or power.

Pedal linkage is adjusted correctly now.
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