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Old 06-14-2021, 06:47 PM   #1
Supertuner700
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Default 1938 85 1.5 ton gearing

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.
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Old 06-14-2021, 09:00 PM   #2
Kurt in NJ
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Default Re: 1938 85 1.5 ton gearing

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
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Old 06-14-2021, 09:11 PM   #3
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Default Re: 1938 85 1.5 ton gearing

Check with Chuck Manzione at Chuck’s Trucks. https://www.chuckstrucksllc.com/. I bought a set of 4.10 gears from him when restoring the tonner. He’s very knowledgeable about the early Ford trucks.
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Old 06-14-2021, 09:26 PM   #4
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Default Re: 1938 85 1.5 ton gearing

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.
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Old 06-15-2021, 07:50 AM   #5
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Default Re: 1938 85 1.5 ton gearing

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
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Old 06-15-2021, 09:07 AM   #6
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Default Re: 1938 85 1.5 ton gearing

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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.
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Old 06-15-2021, 09:35 AM   #7
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Default Re: 1938 85 1.5 ton gearing

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
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Old 06-15-2021, 10:49 AM   #8
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Default Re: 1938 85 1.5 ton gearing

Quote:
Originally Posted by truckdog62563 View Post
Agree, thats 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 hed 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

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.
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Old 06-15-2021, 01:49 PM   #9
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Default Re: 1938 85 1.5 ton gearing

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

Last edited by Supertuner700; 06-15-2021 at 02:00 PM. Reason: forgot info
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Old 06-15-2021, 02:07 PM   #10
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Default Re: 1938 85 1.5 ton gearing

The calculator I’ve used bases speed on engine RPM. Guessing 2500 rpm with the 5.14 and 34” tires it gives 49.22 mph. Stu

https://spicerparts.com/calculators/...rpm-calculator

Edit: playing with this it looks like a 7.00-20” tire at 35” tall gets you up to 50.66 mph.

https://spicerparts.com/calculators/...rpm-calculator
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Old 06-15-2021, 02:30 PM   #11
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Default Re: 1938 85 1.5 ton gearing

That's alot better than what I have!
Thank you

Now to find one of those two gears!!


Quote:
Originally Posted by truckdog62563 View Post
The calculator Ive used bases speed on engine RPM. Guessing 2500 rpm with the 5.14 and 34 tires it gives 49.22 mph. Stu

https://spicerparts.com/calculators/...rpm-calculator

Edit: playing with this it looks like a 7.00-20 tire at 35 tall gets you up to 50.66 mph.

https://spicerparts.com/calculators/...rpm-calculator
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Old 06-15-2021, 03:19 PM   #12
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Default Re: 1938 85 1.5 ton gearing

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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Old 06-15-2021, 07:14 PM   #13
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Default Re: 1938 85 1.5 ton gearing

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.
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Old 06-15-2021, 11:27 PM   #14
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Default Re: 1938 85 1.5 ton gearing

Im not even trying to go on the highway, just local roads. So this vehicle should suit me just fine.
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Old 06-16-2021, 11:45 AM   #15
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Default Re: 1938 85 1.5 ton gearing

Quote:
Originally Posted by Bob C View Post
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.
Thank you Bob, Very helpful
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Old 06-18-2021, 08:28 AM   #16
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Default Re: 1938 85 1.5 ton gearing

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.
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Old 06-20-2021, 10:03 PM   #17
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Default Re: 1938 85 1.5 ton gearing

30 is really my cruise speed, it’s nice to enjoy the ride just looking for a little more
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Old 06-21-2021, 01:05 PM   #18
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Default Re: 1938 85 1.5 ton gearing

Anyone have the part numbers or know of a place to get the part numbers
I know that the rear end and gear was made by Timken.
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Old 06-21-2021, 04:20 PM   #19
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Default Re: 1938 85 1.5 ton gearing

The green Ford parts book has all the numbers. What parts are you looking for?
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Old 06-21-2021, 07:42 PM   #20
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Default Re: 1938 85 1.5 ton gearing

Ring and Pinion and any other parts I need to change them
5:14 and 4:11. Where do you buy that green book?
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Old 06-21-2021, 09:51 PM   #21
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Default Re: 1938 85 1.5 ton gearing

My go to place for manuals:
https://www.faxonautoliterature.com/Product/Index/24396
Also available on CD

(951) 786-4177
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Old 06-21-2021, 10:19 PM   #22
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Default Re: 1938 85 1.5 ton gearing

I don't think there is a 4.11 for the big trucks. i would call Chuck's Trucks for gears.
http://chuckstrucksllc.com/
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Old 06-22-2021, 10:49 AM   #23
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Default Re: 1938 85 1.5 ton gearing

Buying the book now, thank you

Bob, I was told Timken made some 4:11 gears, Chuck said no.
Chuck also doesn't think he has any 5:14 left.

Last edited by Supertuner700; 06-25-2021 at 01:56 PM. Reason: mistake
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