Thanks for all the input. What would be a good starting point on the motor since you think that is where my problem lies?

 

I would shoot for 8-12 degree BTDC initial timing and verify the centrifugal and vacuum advance are functioning.

Josh

 

X2 on the timing. Let us know what you find out on you timing. It could be 180 degrees out. Does it turn over good when you start it, hot and cold.

 

Hello friends, I want to know what differential incorporates my 1975 f100, by the VIN code is a differential with relation of 3.50: 1, and I would like to obtain a relation as much as possible of 2.75: 1 or 3: 1. I would also like to know what model of differential it is, if it is a 9 "ford or it is a Dana or some other, I await your answers, greetings.

 

That pics too small for me to read.Doe,s the rear diff have a cover on it.with bolts.

 

F10 = F100 2WD Pickup

B = 300 1V I-6

E = Mahwah NJ Assembly Plant

V41118 = 1975.

117" Wheelbase.

P = Not listed in paint section of truck parts catalog.

F100 2WD Pickup, 4,650 lbs. GVWR

D 4: D = Black Vinyl // 4 = Styleside Pickup.

C = Ford type 3.03 3 Speed Manual all Syncromesh Transmission.

08 = Ford 9" Rear Axle / 3.50-1 / 3,300 lbs. Axle Capacity.

4,650 lbs. Gross Vehicle Weight Rating.

1975.

91 = Export.

 

I DD a truck with a 302 and C6 that originally had a 3.50 rear gear running 235/75/r15's. I swapped it out for a 2.75 to see what it would do and it lost a lot of power AND lost 4 mpg. But it does 70-80 and doesn't scream like the 3.50, whereas the 3.50 would wind plum out around 70 and it was all I could do to keep up with traffic in the slow lane. My commute to and from work is about all interstate so I decided to leave it 2.75 and I can run the fast lane and shave a few minutes off my commute. So a lot depends on what speed you need it to go regularly.

I've heard the consensus was that 3.25 was the ideal gear to run with this setup for mpg and cruise speed. But I personally have never ran that gear.

 

I have a 1976 F-100 2 wheel drive with a 302, Holley 600 cfm 4 barrel carb., 3.03 3 speed trans., and 3.25 rear gears in a Ford 9 inch, 28 inch diameter tires and my truck is also a dog down low. I'm going to change to a 3.73 posi. center and see what that does for performance . I will not be driving on any freeways, if I were I'd probably go with a 3.50.