M38 lacks proper ground speed... is the manuel correct

bucky · Post by **bucky** » Sun Mar 09, 2008 9:31 pm

My M38 at full speed will do 40-45 MPH tops on flat pavement. I reciently put in a new clutch. It just doesnt seem to have the speed it did last year. I have to floor it to get 40 MPH now, and the books claim the M38 could do 60 MPH. I checked fluids and seals they are fine both tranny and transfer make no strange sounds. IS the manuel correct about speed? Also I swapped the tranny and transfer in mine out of a CJ 2A. I was told they were the same. Is this correct information? Thanks Bucky

Post by **wesk** » Sun Mar 09, 2008 11:45 pm

That 60 in the book was for a top condition new unit. You should still be able to get 45 to 50. Before I accept my speedometer reading and start spending a lot of time and money I would first check the speedo's accuracy. The easiest way to do this is to take a small hand held GPS for a ride with you and observe the speed shown on the GPS.

The 2A and M38 tranny & transfer will interchange. The gear ratios differ very slightly. With all other numbers the same the 2A 1st gear is 3.339-1 vs M38 2.798-1 and transfer Lo range was 2A 2.46-1 vs M38 2.43-1. Final gear ratio's for both trannies is 1-1 and both transfers 1-1.

Did you change or repair anything else at the clutch change?

maeserik · Post by **maeserik** » Mon Mar 10, 2008 3:45 am

Mine M38 with right engine, T90 and transfercase max speed is about 50 mph. ( with window up ) The only difference i have is a smaller intakemanifold, foundout a year after the complete restoration, maybe if i changed it with a normal one the speed could higher, but i find 45 mph fast enough for the jeep.

We are now restoring a 1942 GPW and so we found out the intakemanifold on our M38 is smaller. Maybe to limit the max speed ? The M38 came from the Greece Army.

On the motorway in Belgium the min speed is 70 km/h = 44 mph

Erik

bucky · Post by **bucky** » Mon Mar 10, 2008 6:06 am

Wesk, I changed fluids and seals in tranny and transfer, I pulled the rear output yoke on the transfer after I wrote last night. It has more wobble than I think it should and its only got 2 shims. I wonder if the drag I feel is the gears against the case. Ill let you know.. Thanks Bucky

bucky · Post by **bucky** » Mon Mar 10, 2008 7:05 am

OK now for a more a length answer. Clutch,pressureplate and release bearing are new. The tranny and transfer Ive left basically alone except for seals and fluids. I do agree 45-50 MPH is plenty. I notice that the engine labors harder than it used to no matter what gear Im in. I put the dail indicator on the transfer case rear shaft, Ive got 16 thousands clearance instead of 4-8 using only 2 shims. I used the jeep this winter to push round bales of hay to the horses. I bet I ruined what bearings I had left in the transfer with the stress...... Oh well, with your help I think I got a grip on my problem. Thanks guys Bucky

Post by **wesk** » Mon Mar 10, 2008 8:37 am

Glad you're on track. I am very familiar with pushing round bails around in the snow and how it tears up equipment.

TomM · Post by **TomM** » Mon Mar 17, 2008 3:28 pm

Erik
you describe a "small intake manifold". Am I reading this correctly? Is it a generator manifold?

Tom

maeserik · Post by **maeserik** » Tue Mar 18, 2008 2:45 am

This is the manifold on the M38:

on the GPW :

Erik

4x4M38 · Post by **4x4M38** » Mon Aug 15, 2016 8:48 am

This is an old thread but I ran into something the other day that may be
relevant. My Bubba M38 has a WO carb. In the process of pulling things
apart I found the gas pedal and linkage is not original/has been modified.

I was installing a replacement pedal and repairing the bell crank. When I
finished I was checking everything and found the bell crank hitting the block.
I took the rod off at the top of the bell crank and found the carb linkage would travel a good bit more. There was no way the carb would open completely
as modified.

So, Bubba had a self installed rev limiter which I guess out on the ranch he'd
never figure out.

It was a simple adjustment to loosen the nut on the rod and run it back towards the carb to give more travel. Now it moves from closed to full open without hitting the block.

skyjeep50 · Post by **skyjeep50** » Tue Aug 16, 2016 6:39 am

My M38 will do 62 mph - that's as far as I've pressed it, just once, might have had a little more. And that was way too fast! Usual cruise speed is 50 mph. Motor is/was a fresh rebuild and everything else has been gone through. The speedometer is accurate - verified with a GPS unit.

Post by **wesk** » Tue Aug 16, 2016 8:33 am

Skyjeep just mentioned what no has mentioned before in this post. Accuracy of instrumentation verified and that instrumentation was even analysed. A simple 10 minutes under the hood with the "proper test instruments" will confirm the condition of the equipment a lot better than this feels like this and that feels like that! All controls should be checked visually for proper travel limits. Another 20 minutes checking tire pressures and wheel rolling freedom will confirm rolling resistance levels. Then a tape measure and 3 more minutes checking the front end toe adjustment and you will have a handle on why your OLD jeep doesn't do 60 MPH.

"proper test instruments"
1-Dwell /TACH meter
2-Vacuum gauge
3-Timing light
4-Fuel Press Gauge
5-Tape measure

leecarr · Post by **leecarr** » Tue Aug 16, 2016 11:24 am

How about tire size ?

4x4M38 · Post by **4x4M38** » Tue Aug 16, 2016 1:31 pm

And who wants to do 60 in an 80 inch wheelbase with a Ross steering
box among other things?

Just saying.....

Post by **wesk** » Tue Aug 16, 2016 6:12 pm

The M38A1 with the different steering ratio handled 60 quite well. My stock 52 M38A1 I used as a daily driver to and from work in the 1980's, 20 miles each way on I-90 at Rapid City SD. She cruised at 60 MPH perfectly.

Tire size on our resto's should have been 700-16. Bigger is an obvious doggy ride lacking snort and smaller is an obvious slower ride with higher RPM's.