Today I was driving my truck up some gravel and happened to look back and something just hit me kinda strange. A while back I give out all the codes I have found on my rear axle and it came back from all posts that it was 355 and open. Good enough for me, but maybe I am not certain of what open differential means as I thought I was. Here is what happened, upon looking in my mirror and noticing the gravel I decided to back it up until I was half way into the main paved road ( I don't recommend this) I slightly reved the 300 and let off the clutch I got the usual wheel hop that the ford rear gives but when I looked back there were two 3 foot marks??????????? I found that odd so I backed up again and did it again this time I heard a pop when I let off the clutch and had only one mark, again???????? So for reasearch reasons I figured I should probably do it again. On the third time I reved it up and let of the clutch partially to kinda lock the non existant traction then I engaged the clutch reved hard and let off and low and behold I have two marks. I have the widest tires on those stock rims I could fit and the 10.5" of tread laid on the road I am sure there are two marks. Someone please explain posi and open to me cause I must not be as smart as I thought I was cause this looks like limited slip to me???????????????????? The codes say otherwise again????????????? Any thoughts, thanks

 

Hmmmm. My theory of doing a hole shot to see what kind of rear end you have may be all wet. Any rear end experts out there? Engineers? Please tell us what is going on. Perhaps under certian conditions there is a balance achieved that causes both wheels of an open to spin?

 

I'm not a rear end expert, but I have seen open differentials spin both wheels for a short time in the right conditions where everything is level. My son's little Nissan 200SX race car does this and I know his has an open rear.

'82 F150 2WD w/351W (orig 300 I6)
Slik

 

My 95 f-150 does this as well, as does my 93 crown vic. I have only owned the vic for a month and a half, and for the first few days, I was convinced that I had a limited slip, even though they never came that way. Still can't even get it to chirp on dry pavement, which is dissapointing

 

I'm no expert, either, but I don't think you're crazy. The open diff fails to spin both when there is a difference in the traction for each wheel. Your test probably provided equal traction to both wheels.

Try putting one wheel in the gravel, and one wheel on dry pavement, then pop the clutch. An open diff should spin the wheel in the gravel and do nothing on the good traction side. That's how people end up getting stuck. A limited slip should spin both, though the one on the pavement will get more of the torque, so you may just find you pull smoothly away, depending on how much power you apply.

Let us know what happens.

Of course, if you break an axle doing all this testing, don't blame me.

 

Jack up the back end of the truck(block the front wheels so it won't roll away) and with the engine off and in neutral, release the parking brake and then manually turn one wheel. If the opposite whell goe the opposite way it is a standard diff, if the opposite wheel turns the same way it is a locker/posi diff. Please correct me if I am wrong on this.