Diff ratio checking again. Sorry

[tony.g]

Hi sorry if i am being stupid,
I am trying to check my diff ratio while still in the car.
I have locked up one wheel and,
when i rotate the wheel 10 times the prop rotates 17.75 times.
If i rotate the prop 10 times the wheel rotates 5.66 times approx.

Where am i going wrong and how do i work out the ratio?

Thanks
Tony

[David H]

depends on which of your forward gears is the 1:1 ratio. Its normally 4th on a road car but not always

[tony.g]

Thanks for the reply David but i just want to check the diff ratio.

['The Gaffer']

Heres a vid on the subject. One comment says... With an open differential you need to stop the other tire from turning. Sit the other tire on some blocks or something. Then you need to turn the free tire two times instead of just one time. How much your driveshaft rotates is your ratio. For example if you follow the instructions and rotate the tire twice and the driveshaft rotates about 3-3/4 times then you've got a 3.73 gear ratio.

I guess the above will not apply if you have a LSD diff??

[paintman]

Hi sorry if i am being stupid,
I am trying to check my diff ratio while still in the car.
I have locked up one wheel and,
when i rotate the wheel 10 times the prop rotates 17.75 times.
If i rotate the prop 10 times the wheel rotates 5.66 times approx.

Where am i going wrong and how do i work out the ratio?

Thanks
Tony

   This way I found which worked well on my Hood:

1.   Position the car so it can be pushed on a flatish surface.......ie. your drive.
2.   Stick a piece of white masking tape to hang down from the end of the prop. where it joins the diff. (so you can see it from the side of the car.)
3.   Make 2 Tipp-Ex. "dots" at the top and the bottom of one rear wheel vertically.
4.   Lie down next to the marked wheel and get someone to push the car forward, noting from looking at the white tape how many revolutions of the prop. takes place for 1 of the wheel. (tipp-ex dots)

    You should be able to work out part revolutions in relation to the diff. ie....3.62, 3.98 ect.......

    I worked mine out like this and then found a metal tag on the diff. bolts that confirmed it!!  Typical......

          Tony



 

['The Gaffer']

       I worked mine out like this and then found a metal tag on the diff. bolts that confirmed it!!  Typical......

Been there with similar things

[Quarrycars]

By my calculations you have a 3.55:1 final drive.

['The Gaffer']

JT, out of interest, what were your calculations?

I guess what we need to know is what type of diff you have so we can compare calculations.

Typical ford diffs are as below but you may have another type.

3.38 : 1
3.62 : 1
3.77 : 1
3.92 : 1
4.625 : 1

If you happen to find a vin plate on the diff then the following Ford codes will apply.

Ratio Code
3.14 M
3.36 A
3.38 V
3.62 U
3.64 3
3.92 D

If you really want to be sure, drain the diff oil, take the cover off and the ratio will be stamped on the crown wheel.

[Westiebusa]

By my calculations you have a 3.55:1 final drive.

I believe he's running an English diff? (Front loading diff) which would be inline with your calculations as the English diff equates to 3.54:1 true ratio.
Adrian

[tony.g]

Thanks for the advice guys.
As i said it was me being stupid.

You are spot on Adrian.

I need about a 3.3ish ratio i am told,
has anyone fitted any other axle with this ratio,
would like to try something Japanese like a Toyota etc if possible.

Tony

By my calculations you have a 3.55:1 final drive.

I believe he's running an English diff? (Front loading diff) which would be inline with your calculations as the English diff equates to 3.54:1 true ratio.
Adrian

[Quarrycars]

JT, out of interest, what were your calculations?

Oh Dear I'm in trouble!  Gaffer wants me to show my workings...flashback to school!
If ten revs of the wheel rotates the prop 17.75 times, 2 rev of the wheel will rotate the prop 3.55 times.
Also important is the rolling circumference of the wheels.  You can measure this by pushing the car forward one revolution of the rear wheels and measure how far the car moved.  For example if you pushed the car 2 meters for one wheel rev with a 3.55 final drive and assuming 4th gear is 1:1 then 3550 rpm in 4th gear would be 1000 wheel revs or 2 km.  2 km per min would be 120 kph.

['The Gaffer']

JT, out of interest, what were your calculations?

Oh Dear I'm in trouble!  Gaffer wants me to show my workings...flashback to school!
If ten revs of the wheel rotates the prop 17.75 times, 2 rev of the wheel will rotate the prop 3.55 times.
Also important is the rolling circumference of the wheels.  You can measure this by pushing the car forward one revolution of the rear wheels and measure how far the car moved.  For example if you pushed the car 2 meters for one wheel rev with a 3.55 final drive and assuming 4th gear is 1:1 then 3550 rpm in 4th gear would be 1000 wheel revs or 2 km.  2 km per min would be 120 kph.

Ah Gotcha, makes sense now

['Mendip Wurzel']

This is what I do. I think Phil has said the same above.

How to Check the Differential Ratio
Jack one wheel, other wheel to be locked.
Turn wheel 2 full turns and count flange turns, ie – 3.62 turns = 3.62 ratio.
(Can do this 20 times for more accurate result but not necessary)

[paintman]

This is what I do. I think Phil has said the same above.

How to Check the Differential Ratio
Jack one wheel, other wheel to be locked.
Turn wheel 2 full turns and count flange turns, ie – 3.62 turns = 3.62 ratio.
(Can do this 20 times for more accurate result but not necessary)

I originally tried this method but it did not work somehow for me but by having both wheels moving at the same time it was spot on.......must be me.