The tag on the differential of my 78 F-150 351 reads as follows:
D-M-BJ 8FD
2 75 9 3.78B

I am going to be towing a 27ft 5th Wheel RV GVW-5999#. Can anyone tell me what this code means and how good it is for towing?

Bill K

 

Bill, it's a Ford 9" with 2.75 gears aren't much good for towing(good for gas mileage and top speed though) Switching to a lower (numerically higher) gear ratio would be a good idea for towing. Something like 3.50 or 3.73 would work fine.

 

hey there, any chance u could give me a hand figuring mine out?
i have 2

1st wfeac6mc l259395b thats in a 77 supercab, im pretty sure its a 9" ford rear


2nd wdmcg8gd 759360a thats a 79 f150, again pretty sure its a 9"ford

i dont know if either is oem

i am building a 351m to almost stock to go in the f150 and want the better gears in it also

thanks for any time im wasting!!!

 

 

OK- Thanks for the help. My 78 F-150 350 towed a 2000# trailer alright, but it acts like it does not have enough power to pull the 6000# 5th wheel up steep grades, which we have plenty of here in the mountain west. I wonder how bad it will affect my MPG if I change gear ratios? Also,I am running on a single glas-pac muffler. Maybe installing 2 mufflers will help the milage and power a little.

Bill