According to the vin, my truck came with a 240 straight 6. I'm trying to figure out whether or not the rear end is original to this truck as it has a 302/FMX in it now. It is a 9 inch but I have yet to calculate the gearing or pull an axle. Does anyone know what gearing I should have, what the options possibly were if any, and whether or not trucks used 28 or 31 spline axles. The truck is a 2wd.

 

Odds are it is the original rear end. You can pull the numbers on the tag located on the door providing it is the original tag & that should decode to tell you ratio. You could pull the pig and check ratio just to be sure. The ring gear should be stamped. Count your splines when you pull the axles to drop the pig

 

The tag on the drivers side door correct? When I get home I'll see what it says. I'm gonna give the driveshaft a spin just to get a rough idea. I'm more or less just curious whether it's a 28 or 31 spline, but I can pull an axle to figure that one out.

 

When you open the door you will find a tag with all kinds of numbers including the VIN.

 

The tag has been painted over but on top is the vin, below that reads 131 M F103 7 4 C 09 04500 114 3800 71

What does it all mean?

 

jack her up chaulk your drive shaft and count of times it turns when you turn the tire once. thats your ratio.

 

Ok. Driveshaft turns 1.25 revs per 1 rev of the tire, whether I turn the tire or driveshaft, tried it with one wheel off the ground and both off the ground.....but that ratio doesnt make sense....what am I doing wrong??

 

Does the rear-end still have the metal tag on it? It will be held on by one of the nuts fastening the third member to the axle housing. It will have the ratio stamped on it if it's still there.

 

No, the metal tag is gone. I can tell the pumpkin has been out at one time, theres a decent amount of rtv evident at the splitline. Im still trying to figure out why the driveshaft turns one 1.25 turns when the wheel is turned once. If the other wheel is on the ground that should hold the spider gear engaged with the axle on the other side. The carrier and wheel are then turning at the same speed. Somethings not addong up

 

Your truck should have left the factory with a 28 spline and likely with a 3.75 or 4.10 ratio.

I have never been able to figure the jack up one side out thing out. If you can get on a garage floor or other flat area, mark one of the rear tires where it contacts the ground, mark the drive shaft at the rear. Hand roll the tire one complete revolution while counting the revolution of the ds. This will give you the accurate ratio.



John

 

131 = Wheelbase
M = Wimbledon White
F103 = F100
4500 = GVW
114 = BHP
3800 = Recommended RPM
71 = District (Los Angeles)

09 Designates a 3.70 rear ratio. You are on your own for trim pkg or options. You can check out the link below for more info.

Decoding Your 1970 Ford Truck VIN - FORDification.com

 

Being a six banger, likely just 28 spline. If it had been a 390 or such(or maybe 4wd), it could have been 31 spline.

 

I believe you will find the FEs used the 28 spline also. The 31s came along a little later.

Also I am unaware of any advantage of the 31 over the 28 for daily use. Failure is a topic rarely seen on that issue.




John

 

John, yup, both my FE trucks were 28 spline. They were only 352 and 360 powered. Don't know when they upgraded?

 

Well I had to pull the pinion to replace the O-ring as it was leaking. 47 Tooth ring gear, 19 Tooth pinion = 2.47:1. As I suspected it's not original to the truck. In fact that's not what I calculated based on RPM as around town at 45mph I'm seeing about 1600 rpm... but I take it the convertor is just slipping away... I've yet to take her on the freeway to see how it does but it should cruise along pretty nicely with the 33 inch rear tires but I doubt I'll be doing any towing anytime soon.