C2 Rear Differential Change

[John H.]

Re: PS-Joe-I'm Confused

Terry -

If you look closely at the Power Team charts in the Spec Guide, there are lots of optional ratios between 3.08 and 4.56, but if you look at the applications by engine (300hp specifically), you'll see that the only ratios that were ever available with the 300hp engine were 3.08 and 3.36; all the other ratios were only available with the optional SHP engines.

[Duke W.]

Re:C2 Differentials

If your car still has the proper speedometer gearing for the installed axle ratio, you can determine it by observing top gear revs at 60 MPH.

Axle ratio = (revs @ 60)/775

775 is the revs per mile for the OE 7.75-15 tires. This relationship holds regardless of installed tire revs per mile as long as the speedometer gearing has not changed from OE.

Different installed revs/mile tires will just increase speedometer error by the percent differce in revs/mile. The speedo/tach relationship is established by the speedometer gearing and holds for any installed axle or tire.

The most likely ratio is 3.36. The only available optional ratio for the 300 HP engine was 3.08 and this was ONLY available with the optional wide ratio four speed.

As John pointed out this is CLEARLY indicated in the NCRS Spec Guide powertrain charts that show available transmissions and axles with EACH engine.

Duke

[Brian Monticello]

Re:C2 Differentials

from my '65 brochure:

[William V.]

Re: C2 Rear Differential Change

Ralph

When I bought my 66 300 hp in 1972, it came with the optional 308 rear. I could not stand driving it with all the hills in my town so I changed the ring and pinion to 370.

I advise changing to the 308 only if you live in a flat area.

Your car came standard with the 336 or optional 308 so you must check to be sure someone changed your car to a 370 rear.

In the late 60s a good friend of mine had a 64 300 hp vette and he claimed it had a 370 rear. I know now it was a 336 with the m20 4 speed. The final drive line ratios in 1st 2nd & 3rd for cars equipped with the 336 rear and m20 are almost the same as having 370 rear and m21/22.

If in fact you have a 336 rear and m20, I also suggest you leave well enough alone.

Good luck

[Larry S.]

Re: C2 Rear Differential Change

WOW some great information here.

What Duke has posted is what I have been looking for the last couple of days.(I hate to admit it but I have been collecting this type of information since I have been on the boards here but can never find it when I need it)

The best place to start is what is definatly installed in the car.