how do i tell what rear end is under my 68 it is a 427 390 hp
4 speed(matching numbers) everyone ask , and i feel pretty dumb not knowing.
4 speed(matching numbers) everyone ask , and i feel pretty dumb not knowing.
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Re: rear end 68
If you have access to a pit or drive on lift/trailer, it is real easy. Get under the car and mark the rear tire and the driveshaft. Roll the car until the tire mark makes on revolution. Count the number of driveshaft revolutions. Slightly over 3 - 3.08, just over 3-1/4 - 3.36, about 3-1/2 - 3.55, about 3-3/4 - 3.70, just over 4 - 4.11, 4-1/2 (whoa!) - 4.56
Just make sure you don't roll off the end of the lift or trailer. -
Re: rear end 68
Hi James
I'm not sure when they stopped using them, but GM had a tag attached to one of the bolts on the differential. Some are round with holes in them..If you can jack up your car and look. See the shape, and if there are holes or notches in the tag.Then you can look in a book to get the gear ratio. As an example, I have a 62 vette. My tag is round with only one hole in it for the bolt to mount it to. My gears are 3:36...If you have a parts catalog, they should be in there , like corvette central.. But like I said, I don't know when they stopped using the tags. Other than that, you can try what the other guy said.
JohnComment
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Re: rear end 68
James,
Your rear housing should have a stamped code indicating what ratio it is. ( I believe your judging guide will give exact location and info your looking for. ) The method that Mike has suggested will tell you what really is in there. You could also raise the rear of the car on jack stands, mark the drive shaft and turn a wheel by hand counting the number of revolutions per one full turn of the wheel.
WayneComment
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Re: rear end 68
You'll find the ratio code and assembly date for the diff stamped on the bottom flange of the diff housing, between the spring retaining plate and the camber strut bracket; may take some cleaning to see it. That will tell you what was in it originally, assuming it hasn't been replaced in the meantime.
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Re: rear end 68
John,
May be I'm mistaken but are the bolts that attach the strut bracket to the rear supposed to be grade 8?Comment
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Re: rear end 68
James:
Most likely 3:36 ratio, 3:08 ratio if car has A/C.Comment
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Re: rear end 68
no fac, ac. installed as after market from previopus owner, what do you think it would be then?Comment
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Re: rear end 68
Yes, they are - that's an old photo of the car as I received it.Comment
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Re: rear end 68
Just a note to advise that lifting the car on jack stands, then counting revs as described may or may not identify the correct ratio. I cannot speak for '68 but can assure you this method did not work on my '59 posi. Using jack stands gave me 2 revs of the drive shaft for 1 1/8th turn of the tire. A ration of less than 2:1. Pushing the car wheels down gave a ration of 3.70:1. Took me a while to realize why. I'm slow.
RichardComment
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