1938 85 1.5 ton gearing

S

Supertuner700

Member
I have a 1938 1.5 ton and need higher gearing for better top speed. Right now runs about 38mph but way to much rpm for my liking. What are my options?

Taller tires currently 6.5x 20 which I believe are roughly 34" tall, so maybe 8.25x20 which are 38" tall?

Higher ring and pinion gearing if anyone makes one or has one, my rear axle does not have a tag on it?

Overdrive unit gear vendors has one but its costly 3300 for parts plus machining work and my time to install (free)?

Different transmissions or secondary trans, not sure if this is an option?

Any ideas or help is greatly appreciated.
 
there were 2 ratios pretty much, 5:14, and 6:66, there were some 2 speed rears, but could be underdrive for heavy loads, or overdrive for grain trucks, had a 46 that had the 2 speed and it would go over 65 --it got sold to a guy that drove it to california in 4 days
 
I had a '40 1 1/2 ton flatbed with a 3 speed Watson auxiliary trans. It was under, direct, and over. But it had an open drive line so the install of the divorced unit was a much easier install than one would be in a closed drive line. 2 speed rear axles for the earlier 1 1/2 tons were available but even if you could find one most (if not all) were low and lower.
 
Probably the simplest means of increasing road speed is the use of the 8.25-20” tires. BUT, be alert to whether they can be safely mounted on your stock wheels. If you now have 6.50-20” tires it is likely that you now have the 3.75” rims (5” by old standard), or 4.33” (6” by old standard). The 8.25-20” was listed in the Green Bible as usable on the 5” (7” old system) or 6” (8” old system). The 5 lug x 8” bolt pattern was used into the 1970s, so yards still have inventory of these newer trucks. The other option would be to find the newer tubeless 22.5” wheels that could be fitted with 9R22.5” tires that are the size equal of the 8.25-20” tube type. Stu
 
Doing the math:
34” tall tire has 107” circumference.
38” tall tire has 119” circumference, an 11% increase.

With the taller tire your 38 MPH top speed would increase 11%, to 42 MPH.
 
Agree, that’s not gonna light up the road. The 38 mph limit is no doubt a feature of probably having the 6.67/1 final drive ratio. Mentioned above is the 4.11/1 custom ring and pinion set that Chuck Mantiglia has available. Unfortunately that set is for the Timken 51524 axle used in tonner and 3/4 ton models. Last I recall Chuck telling me, though, he has NOS 5.14/1 sets on hand. Whether they will work in this early axle he’d have to say. Link below.

Another option discussed for the Bonus Built and later trucks is the substitution of a Dana 70HD axle from a 1970s era motor home, either Ford or Dodge. Same 5 x 8” pattern. These generally have a 4.56/1 final drive ratios. I know of a couple later trucks that were so modified, but again on this early truck the spring perch spacing and spring widths would have to be studied. Stu

http://www.chuckstrucksllc.com/startframe.htm
 
truckdog62563 said:
Agree, that’s not gonna light up the road. The 38 mph limit is no doubt a feature of probably having the 6.67/1 final drive ratio. Mentioned above is the 4.11/1 custom ring and pinion set that Chuck Mantiglia has available. Unfortunately that set is for the Timken 51524 axle used in tonner and 3/4 ton models. Last I recall Chuck telling me, though, he has NOS 5.14/1 sets on hand. Whether they will work in this early axle he’d have to say. Link below.

Another option discussed for the Bonus Built and later trucks is the substitution of a Dana 70HD axle from a 1970s era motor home, either Ford or Dodge. Same 5 x 8” pattern. These generally have a 4.56/1 final drive ratios. I know of a couple later trucks that were so modified, but again on this early truck the spring perch spacing and spring widths would have to be studied. Stu

http://www.chuckstrucksllc.com/startframe.htm
Click to expand...


When I had my '40 1 1/2 ton I bought a rear end assembly from a Dodge motor home complete with springs, perches, and 19.5 wheels and tires. It was a 4.56. The frame width was the same so the swap would have been pretty straight forward. Sold the truck before making the swap. But correct me if I'm wrong but isn't the '38 1 1/2 ton a closed drive line set up? That would make the rear end swap a tad bit more difficult. And the total width of the motor home rear end assembly with the duels was wider that the '40. A couple of inches if IIRC.
 
Thank you guys.

Does anyone know the speed increase if I went to 5:14? What trucks had the 5.14 anyway to tell? Besides counting the revolutions, when you cannot see the driveshaft? Is 3rd gear 1:1?


Chuck is not sure if he has any left, hope he does.


Yes its a closed driveline torque tube

thank you for the calculations 11% is not going to cut it and would cause me more issues with rim width that you mentioned and a higher ride height. I'm making a ramp truck.

I'll keep the motor home idea in mind
 
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This chart is for AA's but the axle ratios in the right column's are the same.
The AA's had 6.00x20 tires.
 

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Let's face it; your truck will always be at the limit just trying to keep up to traffic. Sometimes, you just can't win the war, no matter what you do. If you want to do a lot of long distance cruising, get a more suitable vehicle.
 
Sounds like you have a nice truck! Yes 38 sounds slow. I m going to have a similar thing if I ever get mine on the road too! So I am thinking of all the back road adventures I can take to still move around and enjoy it also. Still faster than my tractors go which are 12 mph.
Regards,
Chris
 
The green Ford parts book has all the numbers. What parts are you looking for?
 

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