well well well... rearend question

[TbagginTbird93]

I have a 1978 grand marquis with a 460 eng , c6 tranny and ford 9" rearend, the car is really really really quick on takeoff, but wont run but about 85-90 on topend, I tore the rear end up on it, and was looking to replace just the spider gears, i was wondering if anyone would have any idea on the gear ratio? im sure its stock but the way it does donuts and smokes the tires and the 0-60 time makes me think someone has changed the gear ratio, any help apprechiated

[TbagginTbird93]

noone?

[jimmytroanoke]

Jack up the rear of the car. (If your rear end is at all functional) Mark thedrive shaft and a tire. Put the car in neutral. Rotate the tire exactly one turn while counting revs on the driveshaft. Ie: If the drive shaft turns 3-1/4 turns you have a 3.25 rear gear. Late 70's cars were so strangled by smog stuff, so if your car will really burn them up your rear gear is probably not stock, or your motor is not stock. To find the original rear gear ratio, go to your public library and look for old chiltons books or do a google search. You will probably find something.

[TbagginTbird93]

nah the rearend is locked up

[fredjacksonsan]

You'll end up opening the rear end up; just count the # of teeth on the carrier, and divide by the number on the input shaft and you'll have your ratio. (Of course it might be on a tag or stamped on the axle housing somewhere)

What year is the Chrysler Lebaron in the pic in your sig? Mine was an '81.

[fredjacksonsan]

Oh yeah, and with top speed under 100, you've probably got some 3.90 or higher gears in there.