I have a 1966 Fastback I am working on and wondered what the rear end ratio was. It was suggested that we jack up the car and since no engine/trans we could turn the yoke on the diff and count the number of times the wheel turns. First of all when the car is jacked up if you turn one wheel forwards the other wheel turns the same way POSI? It does not turn the opposite as I would have expected. Second the yoke turns about 2 turns to one turn of the wheel. I can't believe it is a 2.0 rear end ratio. What am I doing wrong

Kery

 

try with one wheel off
How original is the car? what does the door plate say it is?

 

I have tried it with no wheels and 1 wheel...How original who knows Data Plate it is missing

thanks
Kerry

 

Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading. Most likely to have a 280.

 

I actually turned the yoke10 times and the rear wheel turned less that5 times actually about 1.75. so no it isn't anywhere near 2.8. I am just baffled. I get the same results if I hold one wheel and turn the yoke or let both wheels turn while the yoke is being turned

thanks
Kerry

 

Well, 2.8 is the tallest pinion Mustang used back then. Are you sure you have a Mustang (Ford) 8" rear?

 

no it looks more likea 9" rear end does that make it even more confusing?

Kerry

 

Is there a metal tag bolted onto the housing? Most of the fords of this era that I have seenhavehad a tag that has the ratio imprinted into it.

 

That was the first thing I looked for and of course there isn't one.

kerry

 

Ford does have a 2.79:1 ratio.