67 rear end ratio

[Walt W.]

I'd like to confirm the rear end ratio of my 67 without taking the rear
end apart, if possible. Does anyone know if I can calculate it by
turning the rear wheels manually and counting the revs of the drive shaft.

Walt Weems

[Gary S.]

Re: 67 rear end ratio

An crude measurement can be made with the car jacked up. I put a piece of masking tape at the 12 o'clock position on one tire, a corresponding piece on the wheel well opposite the one on the tire. I then put a piece of tape on the driveshaft. Turn the tire one full revolution and have a helper count the number of rotations of the driveshaft. 3 1/3 turns equals 3.36, 3 1/2 equals 3.55, etc. Works well, is idiot proof (well, Gary proof ) and is quick and simple.

You never know what is in the differential housing after all these years.

Gary

[Robert C.]

Re: 67 rear end ratio

Isn't there a ratio "code" and date stamped on the bottom flange of the rear end housing?

[Harry S.]

Re: 67 rear end ratio

Robert, yes there is a stamp with the code and date. But I believe that Walt is looking to verify that what is stamped is really what gear set is installed. It's possible that over the last 41 years bubba may have changed the ring and pinion to something else.

[Donald L.]

Re: 67 rear end ratio

You could use the following calculator . (Youll need your tires diameter)

http://www.angelfire.com/fl/procrastination/rear.html

[Walt W.]

Re: 67 rear end ratio

Harry, you said it all. My car has 3:70 rear, but I think the rpm may be
high.

Walt Weems

[Duke W.]

Re: 67 rear end ratio

Assuming your speedometer gearing is correct for the installed axle ratio:

ratio = (revs @ 60)/60

This calculation is independent of tire diameter.

Significantly different tire diameter will result in significant speedometer error, but has no effect on the indicated rev-speed relationship.

Duke

[Joel T.]

Re: 67 rear end ratio

Guys;

Well, Bubba got me too on this one. My 1963 has the original rear housing for the differential which is stamped 2/28/63 "CD" which would lead one to believe that it is a 3.70 ratio.... The front half, which was replaced as some point in time has a "CC" stamped into it which could also mean 3.55..

Reading this post and thinking about how much clutch slip I need go through to get her moving in first gear, after installing a close ratio tranny during rebuild, I decided to actually see what is in there...

Well, Bubba slipped in a 3.36 someplace along the line!! At least it is a posi unit.

I guess the moral of the story is "don't trust stampings... check".. Wish I did this as I had the unit rebuilt in 2007 and never thought to check the ratio.

Joel