I am having a hard time figuring this one out. I have a 1991 f-250 2wd 4.9L m5odr2, and it keeps blowing passenger side motor mounts. The front right corner is an inch or two lower than the left and I have new springs and shocks in it. Air bags in the rear. I bought the truck used. I don't know if the front corner was always low or if I did it. I do not beat on this truck. I haul wood and some rock and use it for a daily driver.

I had a load of black locust on last summer and got on it to pass my brother and the front of the truck twisted 3-4 inches and then returned. It will do this if I am loaded and get on it, but I try not to. I don't know if the motor is stock, but it has gobs of torque down low.

I think the tranny mount is ok, but I will check it again to make sure. I don't think it is a bad shock, but I could check those. It rolls to the right in turns but is pretty solid to the left. Any ideas?

 

Can you clarify this? Are you saying the right side temporarily drops down 3-4 inches? If so, I'd say you've got something broken on the right side - either a spring perch or the spring itself.

That would also explain why you're destroying motor mounts. Heck, I know my passenger side mount has been in 2 pieces for at least the past thousand miles but I just drive it accordingly and it's been fine. I'll replace it in warmer weather.

 

sounds like something broken to me too

 

I don't see anything broken. The frame twists when under heavy torque.
I have seen a lot of other fords around with the front right corner lower than the left and suspect it has something to do with the design.

The right I-beam is shorter and seems to put more leverage on the spring. The engine also pushes the right side down when under power so both of these can't be good for the frame. I don't understand why the right I-beam would be shorter. That does not balance the suspension.

If I lift up on the right corner, it levels out.

 

The unequal beams are, of course, purposeful. They provide for a central roll-point of the vehicle - lots of geometry behind that which someone smarter than me can explain.

By what you've explained, something is worn/broken with your truck. What you are describing is not "normal". As you've sorta suggested, I also don't believe the broken motor mount is the cause - it's a symptom of another problem.

 

Check the Harmonic Balancer, I bet that if it's worn out the vibration will harm engine mounts.