M38A1 F-Head Overdrive installed !!!

LeeG · Post by **LeeG** » Tue Sep 18, 2012 8:07 am

I just want to say WOW. What a difference that makes. I bought a new one from Herm as a complete kit with shifter and linkage. I did have to heat the shifter and bend it slightly away from the dash after install. The engine and trans sound so much better. Not only was the engine loud but the trans/transfer was really loud at 55 previously. So far, for road driving, I can just leave it in OD and at 55mph the engine doesn't sound like it's going to explode anymore. Even at 60mph it's not too bad but I don't care to drive it at this speed. At 50 it almost purrrs. I love it and can't believe I tortured my newly rebuilt engine for the past 5yrs.

wilfreeman · Post by **wilfreeman** » Tue Sep 18, 2012 1:34 pm

At 55 - he11, it IS about to explode! At 60? Man you got balls! Seriously though, mine MIGHT do 55 downhill. She is screaming at 52 (fastest I've had her). Not saying mine is like new or anything either.

After that "Death Wobble" episode last month, I don't think I'll push her too much - 35 to 40 is fine with me. I've got another car for a daily driver.

LeeG · Post by **LeeG** » Tue Sep 18, 2012 2:35 pm

I've had my jeep down to nuts, bolts and frame. With that being said, I'm pretty confident in my jeep and it is pretty smooth rolling. This is by no means my daily driver but I do need to drive 55 to get anywhere because the highway is the next road out of my neighborhood. Previous to restore, I did experience the death wobble and it was horrible.

wilfreeman · Post by **wilfreeman** » Tue Sep 18, 2012 3:17 pm

Yeah, I don't think there is a bolt I haven't removed, cleaned and re installed (or replaced) either. I've been through the whole drive train to check and reseal everything (except the axles). Rebuilt the whole steering system. I've got some ideas about the cause of the wobble which I am going to address after the rally next month (springs mainly - I know the driver side are worn out and sagging).

Sounds like you do need a little more speed - I live right off the interstate, but can go anywhere I need without getting on it. I'm glad yours can do the higher speeds with the OD and everything is running smooth and at low rpm's - that in itself will help your engine outlive you!

Deadguy · Post by **Deadguy** » Sat Sep 22, 2012 12:36 am

After going back and forth and having endless problems with an overdrive I got from another company, I returned it and bought a rebuilt one from Herm. Works great. The only problem I have, is that the vehicle really struggles going uphill at more than 45. The gears can handle it, but even though the motor is rebuilt with less than 400 miles on it, the power is not there. Maybe I should shift at a little higher speed. What do you shift at?

Bretto · Post by **Bretto** » Sun Sep 23, 2012 8:10 pm

You're only at about 70hp what do you expect.

LeeG · Post by **LeeG** » Sun Sep 23, 2012 8:32 pm

For the death wobble, my problem ended when I rebuilt my bell crank and drag assembly.
For when I shift: I'm not really sure but the last few drives, I left it in OD the entire time. I do feel that I let it rev a little high before shifting but not with my foot through the floor. Also, I live in southern Louisiana and its pretty flat here. A hill usually consists of a few feet in rise. Lol. Most of the time anyway. Now there are some pretty tall bridges but I haven't crossed any of them, mostly because they are on the interstate. They 2 largest ones in my city rise about 110ft. The few overpasses that I've crossed are just standard ones that cross over 3-4 lanes of traffic. But I've had no problems crossing them at 55. Next time I'm out I'll try to take better note of the speeds I shift at. Not that I feel it matters much but I do have a set of headers and a Webber carb. I don't have a stock replica to race next to me but I honestly don't think these mods made a big difference. Along with some other things I did during my rebuild, they are getting replaced with stock items, slowly.
It's fun to drive and the kids love riding around the neighborhood. Especially a few weeks ago when I laid the windshield down for the first time.

Deadguy · Post by **Deadguy** » Mon Sep 24, 2012 11:29 am

I still love it. I didn't know anything about military jeeps when I first bought it it (I had rebuilt a 1973 CJ5 and a 1979 CJ7 previously) but thanks to input from these forums, and G503, I kept it stock (other than a few items that are easily removable like 11" brakes and an overdrive). I just want to know what some of the limitations are. I'm taking out on some local road trips (not more than 3 1/2 hours away at most), and any tips would help. With the overdrive I essentially have a 6 speed, and I don't have a tachometer, so it would help to know when is best to push it into the next gear. I find that in overdrive, and 3rd gear, it really struggles to make it up an incline.

Post by **wesk** » Mon Sep 24, 2012 9:22 pm

The old vehicle standard shift driver's had the ear for knowing when the engine had reached it's useful peak and it was time to upshift. Try finding one of us old farts near you and you'll learn quickly when to upshift.

If you had a tach you would then need to know the magic numbers at which to upshift. Again the experienced old timer can help you determine those numbers.

Overdrives are there for the old underpowered, low geared vehicles to help them handle modern open highway driving. They are most useful on the long flats and downhills and virtually useless on the long uphills. This will never change as long as you keep the stock 60 and 72 HP engines. Helping those early low power engines to breath with dual exhausts, dual intakes, larger carbs and etc can help on the long uphills. But if you stay bone stock then you must drop the overdrive and put here in the original 3rd gear for those long uphills and accept the resultin reduction in road speed.

Deadguy · Post by **Deadguy** » Mon Sep 24, 2012 9:59 pm

I really don't want to alter it any more than I already have. I even nixed the idea of a dual master cylinder and just bought a replacement from John (the dual involves quite a bit of fabrication, including cutting into the frame). I have no problem sticking to the right lane and shifting out of overdrive on those uphill runs if that's what you'd advise. Maybe do 45 max in direct (not overdrive) 3rd gear up those inclines? I wonder if the PTO winch I have on there is weighing it down? It is pretty heavy.