Ford Sierra aficionados and super-geeks on diff ratios

[Larkingabout]

so we THINK it is 3.36 but tonight my daughter is going to count 100 turns of the rear wheel whilst I count how many turns of the propshaft that equates to. Then we have the real answer for sure. Nothing better than the hard way!

That is true family dedication. Hope you buy her a good Easter egg as recompense.

[kent zero]

Hi if you have the full chassis number i can look on Ford Etis should be able
to find out what it is.

John.

[AshleyO]

ok before we splash out on Easter pressies
panic stations
just done the 100 turns test
100 wheel turns (checked by watching where the air filler is)
= 167.33 propshaft turns (measured by a piece of tape on the UJ)
I was expecting 336, 362 or 392
Help, how does that happen?
I did a half way check on the right-hand wheel (83.5) and then changed to the other wheel
Am I doing this right??
Many thanks in advance, oh clever ones!

[AshleyO]

Hi if you have the full chassis number i can look on Ford Etis should be able
to find out what it is.

John.

Now that WOULD make you a true hero! Full chassis No is SFAFXXBABFKR65302
ENgine No KR65302
Ford Sierra Sapphire GL 4-door Saloon Petrol Reg'd Aug '89

And you get the Easter Egg then!!!

Thanks

Ashley

[DJ.]

Thinking about this, I suspect the lack of LSD has caught you out. By rotating one wheel only I think you have got the wrong figure, and suspect if you had rotated both wheels at the same time as would happen on the road, you would turn the prop twice as much. Twice 167.33 is 334, so it does sound closer to a 3.36 if I'm not talking utter rubbish

[greenwoo]

no, i think you should just jack one wheel up - and in effect you need to look at how many turns of the prop = whatever turn of the wheel, not the other way round ( which is what i think you've done)...
so unless i'm being thick ( always a chance)...jack 1 wheel up, turn the wheel until the prop has made 10/20/30 complete revolutions and then all should become clear. ie/ the more complete revolutions the prop does, the more accurate/easier it shd be to divide the final wheel revolution BY that figure.
its the output you're measuring, not the input!

[AshleyO]

no, i think you should just jack one wheel up - and in effect you need to look at how many turns of the prop = whatever turn of the wheel, not the other way round ( which is what i think you've done)...
so unless i'm being thick ( always a chance)...jack 1 wheel up, turn the wheel until the prop has made 10/20/30 complete revolutions and then all should become clear. ie/ the more complete revolutions the prop does, the more accurate/easier it shd be to divide the final wheel revolution BY that figure.
its the output you're measuring, not the input!

Not sure of this one. 2 x 3 = 6. 6 / 3 = 2
wheel spins vs prop spins are surely always the same ratio, times or divide
1 wheel up or both wheels up, I cant see why there would be a difference

[David T]

Did you stop the 'other' wheel spinning in the opposite direction and messing up the count?

[AshleyO]

Did you stop the 'other' wheel spinning in the opposite direction and messing up the count?

The other wheel didn't move - forwards or backwards. Just stayed there

[Richard]

If it is on the road, drive along at a constant rpm with satnav / phone showing speed and back calculate diff ratio. I have the spreadsheet if you want a copy - PM me with e-mail address.... or use one of the many calculators out there.