M38A1 maxes out at 35mph

[vforge]

I was going through some TM’s noticed the top speed of an M38A1 is 60mph. I can only get up to 35mph cruising in mine. It seems slow compared to what I’ve read online. 1st gear shifts usually at 10mph and 2nd at 20mph. 3rd comfortably cruises around 35mph before pushing it. What would cause this? Did someone change the rear differential gearing?

 

[NDT]

Sounds like you are way short on engine power. Mine goes 60+ with ease. The axles have 5:38 ratio, there is no ratio that would make it slower only faster.

 

[vforge]

Sounds like you are way short on engine power. Mine goes 60+ with ease. The axles have 5:38 ratio, there is no ratio that would make it slower only faster.

I don’t quite understand how that works. If your engine is running at X rpm and going at X speed. If it’s not struggling, how would engine power affect speed?

It drives considerably slower than my ‘63 CJ5.

 

[NDT]

Are you in transfer low range? Dumb question but have to ask.

 

[msgjd]

Are you in Low range ? .My A1 maxes out at 29mph in 3rd Low

 

[vforge]

Are you in transfer low range? Dumb question but have to ask.

Nope. I drove it in low to make sure it wasn’t stuck in low or something.

 

[264charlie]

Is the speedo reading incorrect?

 

[vforge]

Is the speedo reading incorrect?

Somewhat but still slow.

 

[DeetFreek]

Another dumb sounding question, but needs asked as well. Correct tire size?

What's the story on the engine? Been rebuilt or overhauled in the recent past? A weak engine can give you shoddy performance. Other than that, there's not much else to give any reasons for such low speeds.

 

[G744]

Maybe check your mixture ratio at the tailpipe.

 

[vforge]

After some research, in 1962 Willys changed the axle ratios and the 1st and 2nd gear ratios. Also, my speedometer is off by quite a bit. I can hit 45 without pushing it too hard.

 

[CMPPhil]

Are you sure that the throttle plate in the carb is opening all the way?

 

[NDT]

All M38s and M38A1 were 5.38-1 axle ratio regardless of build year. The T90 transmission ratios didn’t change either.