1940 Coupe diff ratios

[Henry Hopper]

Can anyone tell me what rear end ratios the 40 Standard Coupe came with from the factory, or how it's possible to tell what I have without resorting to stripping the unit and counting teeth.

Thanks.

[Kurt in NJ]

put a chalk mark on crankshaft pulley,roll car so tire valve stem is up---or down , put in 3rd(or if other type of trans whatever gear is direct), push car untill valve stem is in same position while counting revolutions of crankshaft ---3-1/2 rev is about 3:54, a little more than 4 is 4:11 ---most likely it is 3:78, about 3-3?4 turn.

Sometimes it is stamped into the web near where the torque tube attaches --but that only works if it hasn't been changed.

[Henry Hopper]

Thanks Kurt.

[Mart]

Hi Nige. My 40 had 3.78 fwiw.

Mart.

[19Fordy]

Originally Posted by Henry Hopper

Can anyone tell me what rear end ratios the 40 Standard Coupe came with from the factory, or how it's possible to tell what I have without resorting to stripping the unit and counting teeth.

Thanks.

85 horsepower Rear gears came in 3.54; 3.78 and 4.11
60 horsepower had 4.55.
Info. is from book shown.

[Henry Hopper]

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Thanks lads....we had a tea drinking ,standing around the garage ,session yesterday mulling over the question.....my coupe has 375x70x16 tyres..it runs about 3800/4000 rpm at traffic speed in the slow lane on the motorway ( @70 mph).... We were just discussing swapping in a set of3.54s but opinion was divided on what I had already....btw, the car drives really nice, but the fuel bill tends to hurt a bit ..lol

[Mart]

You sure on that tyre size? They seem very wide to me. If you could supply an accurate engine rev figure and an accurate speed (via sat nav) I could back calculate the diff ratio.

Mart.

[Henry Hopper]

Oops...275. not 375 ha ha....I'll try and get an accurate speedo reading and a tachometer reading....it's an excuse to take the coupe out..

[joel]

I made an assumption that 375 70 was a typo and 275 70 was intended and I used 3900 rpm, with 29.5 in tall tire. With 4.11 gear he would be at 83.3 mph. A 4.88 gear would give 70 mph; I'm thinking maybe 4.44 ( 60 hp gear ) and the wrong speedo turtle. Just a guess

[Mart]

I just used this calculator

http://www.tremec.com/calculadora.php

and got similar numbers to Joel.

Like I said, an exact engine rev number and vehicle speed will do the trick.

Mart.

[joel]

I would recheck tire diameter, engine RPM at a steady speed (mph) before I tore anything apart.
Tire dia(in.)x3.14159 x eng RPM/ rear ratio x 1056 = mph

[jimTN]

40's with the 60 engine had 4:44 gears