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willysmjeeps.com :: View topic - Cruising speed M38A1 Cdn 3
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Cruising speed M38A1 Cdn 3
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Bearbait
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Joined: Aug 24, 2013
Posts: 19
Location: Saskatchewan, Canada

PostPosted: Fri Apr 04, 2014 5:31 pm    Post subject: Cruising speed M38A1 Cdn 3 Reply with quote

So I finally got the jeep out on the hwy for a 20 mile drive. I got up to 60mph engine was screeming, dropped back to 50mph sounded much better.
My question is am I going to hurt my jeep travelling an hour down the road at 50-55mph? Some back ground I have no overdrive, it does have locking front hubs, the engine was rebuilt 10,000 miles ago(22,500 miles on the odometer).
Another question, besides some unforeseen disaster how many miles should these engines go between rebuilds? I ask because it was just over10,000 miles when the military rebuilt it the first time.

Thanks
Brad
(Bearbait)
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BullRun
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Joined: Mar 10, 2009
Posts: 459

PostPosted: Fri Apr 04, 2014 8:46 pm    Post subject: Reply with quote

I know a guy who actually snapped his crankshaft on his M38A1. He was traveling on I-81 in Virginia headed south when a tractor trailer started tailgating him. Trying to get out of the way and a potential accident he sped up to 70 mph while going up hill. He got about half way up the hill and blew the engine. So 70 or so up hill is about tops for speed!

I would guess that 40,000 to 60,000 is about it for engine life span since most unrestored M38A1's with worn out engines seem to have mileage in that range from my experience assuming the mileage is accurate.

As a collector car I would guess it might be greater due to less severe use.

These days I'm the dude in the slow lane doing 45 mph! With 5.38 gear ratio's I always get the feeling I am driving a tractor down the road.

Around here the deer population has exploded so greatly it is not really safe to drive over 45 mph at night with a short wheelbase vehicle anyway.


Last edited by BullRun on Sat Apr 05, 2014 6:22 am; edited 1 time in total
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wilfreeman
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Joined: Mar 13, 2006
Posts: 1079
Location: Richburg, SC

PostPosted: Sat Apr 05, 2014 1:30 am    Post subject: Reply with quote

I want to see under the hood of that 'a1! These Jeeps weren't designed to run those speeds. The engines have long strokes and the axles have low gears - designed for high torque and fairly low speeds. Keep it at 45 and she will live a long life. Run it at 55 (or more if you have an overdrive and it will do it) for any length of time and you will ruin the engine.
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Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
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jaycee
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Joined: Feb 23, 2014
Posts: 19

PostPosted: Sat Apr 05, 2014 2:41 am    Post subject: Reply with quote

yep those engines are tractor engines with really long rods and only three main bearings. high rpms wil kill them every time. id install an overdrive if i were you. unless you just want it for a local vehicle. but even with an overdrive it still takes horsepower to overcome drag (it has the aero dynamics of a shoe box) and well hills are another story. i guess thats why they changed so much over the years as every one wanted a four wheel drive sports car. try to keep in mind that its still about the same truck as a MB with minor upgrades and no revolutionary drive train mods with marginal brakes
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wesk
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Joined: Apr 04, 2005
Posts: 15813
Location: Wisconsin

PostPosted: Sat Apr 05, 2014 8:05 am    Post subject: Reply with quote

These comments are based on factory stock MB's and M38A1's.

12 HP and 5:38 gears were really a serious improvement over the MB as was the stronger T-90 and D18's and steering gears introduced.

I take stated speeds in access of 65 MPH with a grain of salt. Unless of course they are quoting modern GPS ground speeds the speedo system is not that accurate. All analog speedos and tachs were tuned for best accuracy in their normal cruise ranges. The normal cruise speed range for the M38A1 was 45-50 MPH hence accuracy is increasingly off in either direction above or below that figure.

With that said I averaged highway speeds of 55-60 MPH for several years in South Dakota using my M38A1 as my daily driver 40 miles each way on the interstate and for hunting in the Black Hills. Anything above 60 was too much RPM and noise. The key is a quality level of maintenance and correct repairs.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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Bearbait
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Joined: Aug 24, 2013
Posts: 19
Location: Saskatchewan, Canada

PostPosted: Sat Apr 05, 2014 11:43 am    Post subject: Reply with quote

Thanks for all the replies, I am planning on getting an overdrive and installing next winter but I wanted to be sure I wasn't hurting my jeep in the mean time running back and forth to cruise nights and car shows this summer.
Wes it was nice to hear hitting 60 isn't likely to hurt anything, there are times you need to get moving until an area where I can pull over to let others pass.
50-55 will be my normal cruising speed with or without the overdrive.

Thanks
Brad
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BullRun
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Joined: Mar 10, 2009
Posts: 459

PostPosted: Sat Apr 05, 2014 4:51 pm    Post subject: Reply with quote

Hard to believe but that is what he told me. I saw the engine. Definitely something catastrophic had happened. That area is all rolling hills and valleys. For his attempts at avoiding an accident he almost created one.

Something to keep in mind too is not all tailgaters are actually in a hurry. I have had people chase me down the road to find out what I am driving as many people have never seen an M38A1 jeep.
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cabinfever
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Joined: May 14, 2013
Posts: 201
Location: Between Crosslake and Emily, Minnesota

PostPosted: Sun Apr 06, 2014 9:17 am    Post subject: Reply with quote

Geez, I never drive faster than 40mph and that is very rare occassion and for very short distances. My normal cruising is around 30 to 35 mph. The reason I drive relatively slow is that the suspension on my A1 is so stiff that if I hit so much as a seam in the blacktop, I can feel shockwaves all the way up my back and into my neck. Its like trying to break a bucking bronco when I take the Willys out for a drive, especially if I'm driving over 30 mph.
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skyjeep50
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Joined: Feb 20, 2007
Posts: 606
Location: Illinois

PostPosted: Sun Apr 06, 2014 10:40 am    Post subject: Reply with quote

The top speed on my F150's speedo is 120 - how many times do you think I've run it at 120? The top speed on my M38's and M38A1's speedo is 60 and, yes, I've been there a few times, very few. Cruise is 50 mph for me. Besides, my jeeps have no roll-over protection, no shoulder harnesses, no doors, stiff suspensions, non-collapsable steering columns and run on NDT's. Any non-planned sudden stop... Shocked These vehicles were designed to be cross-country tactical vehicles for the military, not "cars" per se. Heck, even my old CJ7 wasn't much of a car! The engines can survive being run at top rpm but how long do you expect, or want, a 60 year old engine to survive that stress? That being said, the light aircraft I fly have a max rpm of 2,700 rpm and absolutely every take-off is MAX RPM because the engines were designed to take it. Roll the dice.
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Deadguy
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Posts: 776
Location: Bellmore, NY

PostPosted: Sun Apr 06, 2014 11:04 am    Post subject: Reply with quote

I have an overdrive, and rebuilt drive train. I usually go about 40. 50-55 on my brief trips on the highway. The vehicle won't even reach 60 unless I am going downhill. It's running healthy, it just doesn't have the power. Even at 60 it is pretty scary-what with the manual steering, drum brakes, stiff suspension, and NDTs.
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1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
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Bearbait
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Joined: Aug 24, 2013
Posts: 19
Location: Saskatchewan, Canada

PostPosted: Sun Apr 06, 2014 12:05 pm    Post subject: Reply with quote

The only concerns I have about the cruising speed were of the drive train. My jeep is a 1971 M38A1 Cdn3. This means it came out with 11 inch brakes not the 9 inch you are all used to. I don't think the suspension and steering is any different, but in this case the jeep only has 25,000 miles and is only 40 yrs old instead of the 60 yr old jeeps most people associate with the m38a1. Yes there is no rollbar, and the seat belts would only hold you in the vehicle so the police would have less mess to clean off the pavement but people travel far faster on motorcycles and snowmobiles with no protection either. I'm not trying to sound like I don't appreciate the responses, I'm just stating the facts. Honestly if Wes K says he travelled at 55-60 mph in his jeep and it had no ill effects I am willing to believe it as he seems to be very knowledgable on all aspects on these jeeps(I have read many posts that he has responded to he knows his stuff).

Thanks again for all the responses and experiences.

Brad
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wilfreeman
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Joined: Mar 13, 2006
Posts: 1079
Location: Richburg, SC

PostPosted: Sun Apr 06, 2014 2:16 pm    Post subject: Reply with quote

skyjeep50 wrote:
Roll the dice.


It's yours
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Matt
1953 M38a1
1964 USMC M38a1
'51 USMC M100 trailer, '54 M100 trailer, '90 M101a1 trailer
Http://wilfreeman.wordpress.com (M38a1 build blog)
http://m38a1usmc.wordpress.com (USMC M38a1 rebuild blog)
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Deadguy
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Joined: Jun 09, 2011
Posts: 776
Location: Bellmore, NY

PostPosted: Sun Apr 06, 2014 3:04 pm    Post subject: Reply with quote

Yes, Wes knows his stuff. I couldn't have rebuilt my jeep without his help. That said, I bet Wes has years of experience on everybody in driving these jeeps. I did a complete rebuild. As in frame up. Everything is new or rebuilt. The engine has 1,000 miles on it. The transfer case and transmission were rebuilt better than spec by Novak. The overdrive was rebuilt by Herm the overdrive guy. All the suspension and steering is new, and I even have a steering stabilizer shock. I installed 11" drum brakes as well. so this is my experience with a jeep that runs like new.
_________________
1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
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wesk
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Posts: 15813
Location: Wisconsin

PostPosted: Sun Apr 06, 2014 9:34 pm    Post subject: Reply with quote

You don't need thousand of hours in a jeep to understand how to drive it wisely. I started driving when I was 14 in a 52 Studabaker, and progressed through a 53 Ford Flathead V8 3 speed OD, 50 Pontiac six stick 3 spd., 52 Chevy six stick 3 spd, 58 Chevy V8 stick 3 spd, 62 Impala Conv V8 auto. That's just 1961 through 1968. Got over 100 MPH in the last two very often. Some things they all had in common: manual steering, manual brakes, stiff suspension and I hotrodded and raced them all both off and on the track. After a year in Southeast Asia I bought my first new car, a 69 Camaro V8, manual steering but power disc brakes and raced it as well. In 70 I got my first jeep, a 42 GPW and it would handle 50 MPH on the highway in Bossier City LA. Every jeep I have owned since will cruise 50 MPH safely on the highway because I make sure they are in safe operating condition and I maintain them that way. I didn't run NDT's or NDCC's on any of them because those tires are not safe on hard surface roads, wet or dry over 50 MPH. Those tires were meant for off road use, 45 MPH military convoys on hard roads and parades.

If your jeep scares the crap out of you over 35/40 MPH then I believe it needs some serious improvements in it's quality of maintenance and condition.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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Deadguy
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Joined: Jun 09, 2011
Posts: 776
Location: Bellmore, NY

PostPosted: Sun Apr 06, 2014 10:37 pm    Post subject: Reply with quote

I would rather have NDTs and just drive it around locally, that put on new tires and drive a higher speeds. Long trips and in the winter, I use a different vehicle. Straight away, on level asphalt, I haven't had a problem even with NDTs. The roads in Philly, especially after the winter, are pretty rough.
_________________
1952 M38A1
Marine core reinforced rear bumper, military transistorized turn signal upgrade, arctic heater, 11" drum brakes, 200L PTO winch, Huffy overdrive, deep water fording kit, RT 68 vehicle mounted radio, Trac Locs front and rear.
www.danhenk.com
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