rear end ratio

37 Cab

37 Cab

Well-known member
How do I check my ratio with the driveshaft enclosed? I can`t count turns of the driveshaft.. At 60-65 it runs 3000 RPM.. 3.73 be a good guess? I am thinking about a Mitchell overdrive. Would you recommend a 26% or a 36% unit with that gear.
 
There are ways to check it with jacking up one wheel and counting something, but I can never remember it correctly! An easy solution would be to use one of the online calculator, you need rpm (which you know), mph (which you know), and tire diameter (you need to get). Pop in the numbers and you should have it. If you want to go to the work and have help, you could jack up the rear end, crank over the engine by hand and count the number of engine revolutions for one wheel rotation (you need to make sure the wheels turn together!).
 
Ok, with 6.00:16's on the back, with a 3.78 at 3000 rpm you would be doing a true 66.08 mph. With 4.11's, at the same 3000 rpm you would be doing 60.77.

If your car has a starting handle you could check it like this:

Jack up one rear wheel. Turn the crank handle until it is at an easy place to start from. (12 O'Clock for example.)

Mark the raised wheel and the ground so you have a datum.

Now turn the crank (counting the turns) until the raised wheel has turned exactly TWO revolutions.

The number of turns of the crank handle equals the rear end ratio.

As we know the most likely candidates are 3.78 and 4.11, that makes it easier to judge. A bit more than 4 turns but less than 4 and a quarter means it is a 4.11. A bit past 3 and 3 quarters means it is a 3.78.

If you have a reliable rev counter and can get the true speed by a sat nav device, that would be the easiest way to get an indication.

Mart.
 
If it still has the original gears, the tooth counts should be stamped on bottom webb of the center housing. Divide the little number from the big one and you have the ratio.
 
One of the quickest and easiest ways to check the rear gear ratio in a Ford banjo rear is to count the teeth on the ring gear through the filler plug hole. This was posted recently by Lawrie:

"One easier way to determine the ratio with out pulling the gear or turning wheels etc, is to count the teeth on the ring gear, put a paint pen mark on the ring gear through the drain or level plug,
this will tell you the ratio,
34=3.78
37= 4.11
39= 3.54 or 4.33
40=3.63 or 4.44
41=4.55
from the green bible parts book.
Lawrie"

Hint: to do this you must have the rear wheels off the ground and transmission in neutral. I usually use jack stands under the small ends of each axle housing and turn the ring gear through the rear filler hole using a small screw driver.
 
Last edited:
JM 35 Sedan said:
One of the quickest and easiest ways to check the rear gear ratio in a Ford banjo rear is to count the teeth on the ring gear through the filler plug hole. This was posted recently by Lawrie:

One easier way to determine the ratio with out pulling the gear or turning wheels etc, is to count the teeth on the ring gear, put a paint pen mark on the ring gear through the drain or level plug,
this will tell you the ratio,
34=3.78
37= 4.11
39= 3.54 or 4.33
40=3.63 or 4.44
41=4.55
from the green bible parts book.
Lawrie
Click to expand...

I have never tried that, but thought it was a good idea the first time I read it. Sounds even better the second time. I've always rolled them on the ground and counted driveshaft (or engine) revolutions, but it's just an old habit from years of doing it that way. Might need to learn a new trick.
 
I can't edit my post above. I omitted to say "engage top (3rd) gear" before turning the starting handle.

mart.
 
JM 35 Sedan said:
One of the quickest and easiest ways to check the rear gear ratio in a Ford banjo rear is to count the teeth on the ring gear through the filler plug hole. This was posted recently by Lawrie:

"One easier way to determine the ratio with out pulling the gear or turning wheels etc, is to count the teeth on the ring gear, put a paint pen mark on the ring gear through the drain or level plug,
this will tell you the ratio,
34=3.78
37= 4.11
39= 3.54 or 4.33
40=3.63 or 4.44
41=4.55
from the green bible parts book.
Lawrie"

Hint: to do this you must have the rear wheels off the ground and transmission in neutral. I usually use jack stands under the small ends of each axle housing and turn the ring gear through the rear filler hole using a small screw driver.
Click to expand...

That's how I do it, if it is not stamped on the banjo housing. Wipe a tooth off and mark with a little white paint.
 
Can't always trust stamping on housing . Once bought a rear end that said the gears were 3.54 , once in was apart ,it turned out , some one had changed gears.
 
Interested to hear the responses to the second question on available Mitchell OD ratios. The 36% OD is fairly steep, more than any modern car excluding those with 2 OD gears. 2nd gear OD with a 36% ratio is a duplicate of 3rd gear direct so not a good option if gear splitting is part of the plan.
 
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