<VV> FC Axle/Transmision Ratios - (was: 61 Loadside questions and updates)

[Dale Dewald]

At 21:02 11/24/2008 -0500, Bob Hall wrote:

>I have a '64 95HP Greenbrier 4spd.  Does your comment about the  factory
>combinations mean that the diff ratio determined what ratio first 
>gear  had?  I
>have a rebuilt posi 3.55 in the 'Brier now, but the original diff  was a
>3.27--

Hello Bob,

A bit of history is in order:

In 1961 when the FC line was introduced, the 80hp was the only available 
engine.  The standard 3-speed transmission and optional PG came with a 
3.89:1 axle.  The optional 4-speed had a 4.26:1 first gear and came with 
the 3.27:1 axle.  I believe at that time [but have no proof] if you 
specified a 3.89:1 axle and 4-speed, it came with a 3.65:1 first gear unit 
shared with the car.  After several months of production the special 
4.26:1/3.27:1 combination was dropped and all FC's thereon from mid-61 
through 1963 came with a 3.89:1 rear axle.  The 4-speed transmission was 
identical to the car, with a 3.65:1 first gear.

With the introduction of the 164ci 95hp and 110hp engines, the standard 
axle ratio for FC's moved up to 3.55:1, with the 3.89:1 ratio kept as a 
factory option. While the '64-65 car transmission was revised with a 3.20:1 
ratio first gear, the FC 4-speed kept the earlier 3.65:1 first gear ratio 
[making these special to accept a 14 spline input shaft].  Therefore, any 
3.27:1 axle in a '62-65 FC has to have been rebuilt as such or swapped in 
from another vehicle.

>it required "stirring" in the mountains, but gave great cruising  speeds with
>less thrashing.  At some time I want to go back to the original  diff, 
>when it
>is rebuilt, so I'm archiving your chart for future  reference.

I have had the same experience with our previous '64 Greenbrier and current 
'65; both are 110hp/4-speed (3.65:1)/3.27:1 [rebuilt diff] combos.  One 
nice thing is that both can maintain 55-60 MPH up the steepest highway 
grades in 3rd gear. It was not as easy to do this with a 3.55:1 axle--some 
grades require downshfting no matter what--then you are limited to about 50 
MPH.

With the 3.27:1 one has to watch; on moderate grades with a strong head 
wind the engine will continue to pull you along but temperatures can get 
out of control and it will be necessary to back off the speed somewhat.

Dale Dewald
Hancock, MI