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willysmjeeps.com :: View topic - Jeep M38 Rebuild
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Jeep M38 Rebuild

 
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labmonkey
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Joined: Oct 03, 2017
Posts: 3

PostPosted: Tue Oct 03, 2017 3:31 pm    Post subject: Jeep M38 Rebuild Reply with quote

Hey all,

I'm looking to rebuild my '52 M38 over the next few years. My goal is to make it a daily driver for when I graduate college. It's currently almost running. The rear axle is just cracked, but other than that it runs okay. I want to rebuild or replace pretty much everything on it.

I do have one question though. What will need to be done in order to let it go 60-65 mph comfortably. I want to be able to drive it on the freeway, but currently the engine is screaming at anything over 50. I've looked into transmission replacements, but couldn't find anything with a smaller gear ratio than a direct drive that would fit. It currently has a warn overdrive. I saw that if I change the ratio in the differential, then it will go faster at a lower rpm, but by how much? If I change that ratio will I be able to reach 60 mph?

Thanks for all your help,

Cooper
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4x4M38
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Joined: May 30, 2014
Posts: 2538
Location: Texas Hill Country

PostPosted: Tue Oct 03, 2017 4:21 pm    Post subject: Reply with quote

Hello Cooper,
Good for you restoring an M38!

There are many things to consider when thinking
about driving an M38 at highway speeds.

Use the search function above. This has been discussed
many times here.

The one thing I would ask is do you really
want to drive a vehicle with an 80" wheelbase
at freeway speeds?

Anyway, welcome, and use the search function. You'll
find a lot of information in the archives.

Take care,
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Brian
1950 M38
MC11481
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labmonkey
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Joined: Oct 03, 2017
Posts: 3

PostPosted: Tue Oct 03, 2017 4:30 pm    Post subject: Reply with quote

Hey, I'm not really sure how the search works. I searched for 'highway speed', but when I looked through the first few topics that popped up, I didn't find 'highway speed' anywhere in the thread. Am I missing something?
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labmonkey
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Joined: Oct 03, 2017
Posts: 3

PostPosted: Tue Oct 03, 2017 4:33 pm    Post subject: Reply with quote

Regardless though, I did find a few topics about raising the gear ratio. Thanks.
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4x4M38
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Joined: May 30, 2014
Posts: 2538
Location: Texas Hill Country

PostPosted: Tue Oct 03, 2017 4:59 pm    Post subject: Reply with quote

Use the search button above, not the one to the left.

Also, use Search For All Terms.

Also try daily driver and other out of the box terms.

This is a good thread and starting point:
http://www.willysmjeeps.com/v2/modules.php?name=Forums&file=viewtopic&t=2521&highlight=highway+speeds

Take care,
_________________
Brian
1950 M38
MC11481
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Bretto
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Joined: Nov 24, 2010
Posts: 1364
Location: Orem, UT

PostPosted: Wed Oct 04, 2017 5:34 am    Post subject: Reply with quote

Plain and simple, these little guy's aren't equipped to go that fast and the surrounding traffic isn't going to wait up or lookout for ya either.

You can't just go raise the diff ratio and expect the 134 to keep up. It's a balance game and it's probably dialed in best right where it's at. You may find a MB/GPW may run higher gearing but they also run smaller tires.

In order to achieve your goal for those sustained speeds, I feel you would have to run a whole different drive train. With that, then you'd need to turn the page and look at the other equip......steering, brakes, tires, suspension.........etc.

Just sayin.
Brett
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Brett
'51 M38
PHOTO DIARY OF MY BUILD
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wesk
Site Administrator
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Joined: Apr 04, 2005
Posts: 13031
Location: Wisconsin

PostPosted: Wed Oct 04, 2017 9:41 am    Post subject: Reply with quote

Very important that you do a complete upgrade on the jeep. If you want to make it go faster then the steering and brakes must be upgraded for the greater speed. This means converting the ancient Ross steering gearbox with the later Saginaw from a 72 or newer jeep and the upgrade to 11" drum brakes or Front discs and 11" rear drums. And as mentioned above the 60HP L134 was never meant to wind up that high!

The only jeeps that left the factory designed for sustained freeway driving speeds were the AMC 1972 & later units.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

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m3a1
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Joined: Aug 13, 2017
Posts: 53

PostPosted: Wed Oct 04, 2017 7:29 pm    Post subject: Reply with quote

I would also like to add that you should give some very serious thought to the question of "what is the advantage of doing this?"

You might consider is there is a better vehicle option out there for achieving higher speeds and in the long run, it would be far less expensive than transforming your M38 into something it was never meant to be.

If you want to stay 'Jeep' then as Wes said, "The only jeeps that left the factory designed for sustained freeway driving speeds were the AMC 1972 & later units." You can trust him on that. He knows his stuff.

You've said that your most immediate problem is with that axle. I believe I can see your thought process which probably is going something like this - (replace the bad axle with something with better gears and you're nearly half way there because all that is left is having to replace one more axle and problem solved, right?) Well,....not so much.

Well, think of your truck as having a homogenous design; consistent throughout with each thing complimenting the other. Every system of the M38 is designed to work hand-in-glove with every other system in terms of ability and it is that consistency and balance in its design is the great strength of the M38.

Swap axles and you'll immediately find there isn't enough power. Sort that out and you'll find there isn't enough brakes and that the steering is substandard...and so on and so on. You'll quickly find that you would have been ahead to swap the body onto a more modern Jeep and ultimately the value of your M38 will be lost. It will have become...well....something other than an M38, whose first home was always meant to be off-road, right?

As has already been stated, freeway speeds in an 80" wheelbase vehicle is dangerous and that is simply something you cannot change, or improve upon. That is the first big problem and there is absolutely no solution for it and there is no way to make it SAFE. I was in law enforcement for many years and handled more than one wreck that began and ended with a home-brewed vehicle that was its creator's bad design, and/or poorly executed.

But if you really like the look of the M38 and you want to keep it, there IS a solution. Keep and fix the M38 properly and enjoy it within the limitations of its design, and select a second vehicle to go faster in...preferably one that is capable of towing your prized M38 so that you can take it places and do fun things in it. That's a HUGE bonus!

I think you'll find the money you'd have to spend transforming the M38 will be nearly the same as what you'd spend on a second truck that just might be one that is just as cool as your M38.

Cheers!
TJ


Last edited by m3a1 on Thu Oct 05, 2017 6:20 pm; edited 2 times in total
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RonD2
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Joined: Oct 02, 2014
Posts: 237
Location: South Carolina, Dorchester County

PostPosted: Wed Oct 04, 2017 9:39 pm    Post subject: Reply with quote

Hey labmonkey,
It's kind of like trying to get a stock 1963 VW Beetle to do highway speed today (or 45 years ago when I first learned to drive with one). It was might be a maybe on a good day, but only with a stiff wind at your back, a full throttle going downhill both ways, and about a mile head start..... Shocked

Like my hero Dirty Harry once said: "A man has got to know his limitations." I think that included his horse. Smile

Naturally, one of the great things about being an American is that nothing stops you from trying.......gotta love it. There's nothing like a real education.

J.E.E.P. >>> Just Empty Every Pocket Laughing

Gotta love that handle too!
_________________
Ron D.
1952 M38,
1951 M100, Dunbar Kapple 01169903, dod 5-51
1954 M100, Dunbar Kapple M750759, dod 1-54

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