Topic: 66 Coupe Differential

[koski19]

This morning I pulled the rear suspension and differential from my coupe.
Pulled the data tag which reads:
WCY-R
2.83  6FD 903

Fits 65-70 Mustangs 2.83:1 gearing  7"1/4 ring gear, non locking, non removable carrier.

Looks like alot of different gear ratios can be installed in this housing from 2.83 to 4.00:1, so here's my question:

1. Car to be used as a weekend driver.

2. Rebuilt 200 6 cylinder and C-4 Transmission.

3. What alternative gear ratio would be most beneficial other than the 2.83?
I was thinking of 3.50:1 for alittle more pep. How would this effect the
cruising speed at 55-65?

Jeff

[jwc66k]

This morning I pulled the rear suspension and differential from my coupe.
Pulled the data tag which reads:
WCY-R
2.83  6FD 903
Fits 65-70 Mustangs 2.83:1 gearing  7"1/4 ring gear, non locking, non removable carrier.
Looks like alot of different gear ratios can be installed in this housing from 2.83 to 4.00:1, so here's my question:
1. Car to be used as a weekend driver.
2. Rebuilt 200 6 cylinder and C-4 Transmission.
3. What alternative gear ratio would be most beneficial other than the 2.83?
I was thinking of 3.50:1 for alittle more pep. How would this effect the
cruising speed at 55-65?
Jeff

Gear sets that are readily available for 7 1/4 axle are: 2.83:1; 3.08:1; 3.20:1 and 3:50:1. There may be others that were used in Econoliners.
A 3.50:1 ratio is what my "K" car has. It does not get good mileage but accelerates "very" well. The original owner replaced that ratio with a 3.00:1 in 1973 due to the first (of many) gas price increases. It was a daily driver, used for trips and mileage was the goal. The second owner put the 3.50:1 gears back in. The car was undergoing a restoration.
A six cylinder engine will not do well at a ratio higher than 3:00.1, it's just not built or it. Your mileage will drop, your engine will rev more at higher speeds and your acceleration will not be that much better.
In your case, stay stock - or replace the C with a 3 speed manual transmission and try the 3.20:1 gears.
Jim

[Brian Conway]

     I owned and drove a 66, 6 cyl., automatic, hard top for about 30 yrs. The gear set was, as recall, 2:80 but could have been the 2:83 mentioned.  Great pep off the line, steady & reliable acceleration, about 15 mpg and absolute top end speed 96 mph.  Brian

[JKWilson]

Jeff remember this, everything depends on how you want to use the car. Since you stated you wanted it to be a weekend cruiser you then need to decide on which side you want to compromise on, comfortable cruising speed or acceleration? You have to give somewhere. Keep in mind that using the 2.83 gear and 6.95/14 tires (or metric equivalent), and in top gear (1.00/1), engine rpm at 60mph will be about 2200rpm! If you start lowering the gear ratio, yeah, acceleration will improve, but that little 200 will be screaming at highway speeds. I owned a '65 fastback with a 200 with a 3spd and 2.83 rear. It would scoot right along and was a fun car!  I'd recommend sticking with what you have. You'll also end up with decent mpg!

[koski19]

Thanks for the info. I'll stick with the 2.83 gearing. Have you guys rebuilt one before? Should this be farmed out?

Jeff