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#1 |
Junior Member
Join Date: Jan 2012
Location: Wyoming
Posts: 6
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I'm going to build up a 59A flathead with factory relieved valveports for my 1936 1.5 ton dually. I want a custom grind on the cam, but I know I won't be successful putting a typical modified cam into a truck engine. The cam specialists I'm talking to need to have an idea what my rear differential gear ratio is. Since my drivetrain is completely enclosed with a torque tube, it is not easy to measure. I have heard that the gear ratio is stamped on the speedometer gear but this is the problem...the rear end was changed in the forties or the fifties and I don't know if the speedometer gear matches the differential. I know that my speedometer doesn't read my actual speed, but that could be in the speedometer (I haven't had it restored yet). Anyhow, I think there were three ratios offered for the big trucks in 1936. Whatever is the lowest ratio is likely mine because the truck has no problem cruising at highway speeds. So, if anyone can help,
1. What were the rear differential gear ratios offered in 1936 for big trucks? 2. What were the rear differential gear ratios offered in 1932 for big trucks (for my dad's 1932 Ford one ton)? 3. Has anyone had experience modifying cams for big trucks, and has any advice? |
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#2 | |
Member
Join Date: Aug 2010
Location: Tauranga , New Zealand
Posts: 37
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Jack up the rear, Put it in top gear, ( 1:1) take the spark plugs out and turn both rear wheels one turn, while counting the number of turns of the crank pulley.....there's your ratio..... You will need two assistants ![]() |
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#3 |
Senior Member
Join Date: May 2010
Location: Hansville, WA
Posts: 776
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What are you planning to do with the truck? If you intend to restore it using the 4 speed transmission and the original rear end, a stock cam that produces good low to mid range torque will do the job. If your 59A block was factory relieved there's a high probability it was a truck engine to start with so why not use the cam profile that's in it? If you're going to change the drivetrain to taller gears in the back with a 5 speed transmission, then changing the cam profile to allow for more torque at higher RPM might be worthwhile, but you should think about the associated steering and braking issues that the higher speed presents. Trucks are not as nimble as the passenger cars or even the 1/2 ton pickups. From personal experience operating a one ton truck at 65 MPH I can attest to the fact that driving at those speeds will require your full attention.
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#4 |
Junior Member
Join Date: Jan 2012
Location: Wyoming
Posts: 6
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I should have done a little more research into my owner's and shop manuals. There were only two rear axles offered for the trucks from 1932 to 1936: 5.14:1 and 6.6:1. It should be pretty easy to figure it out now. Thanks!
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#5 | |
Junior Member
Join Date: Jan 2012
Location: Wyoming
Posts: 6
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#6 |
Senior Member
Join Date: Nov 2012
Location: Tauranga, New Zealand
Posts: 726
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#7 |
Senior Member
Join Date: May 2010
Location: Hansville, WA
Posts: 776
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I can't speak to any year but 1940, but I know that the original cam in my 221CI engine was a stock Ford cam. The heads were different using a larger combustion chamber resulting in a slightly lower compression ratio. Whoever rebuilt the engine may have used higher C/R heads and discovered that under a load the C/R was too high thus the need for 2 head gaskets. When I rebuilt my engine I bored it to 239CI, installed a Potvin 3/4 cam, and kept the original heads. I also redid the driveline changing the differential gears to 4.11:1 and installing a 49 Merc O/D transmission. This improved freeway driveability but with that improvement came the need for more aggressive driving technique. A good starting point with your engine would be to see if you can identify the cam profile and go from there.
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