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I have a 77 F350 dually, it seems like the rear of my truck is "loose" when going around turns. Not like the rear axel is gonna fall out but just feels like its gonna fishtale out on me. and it feels like i am steering on air while empty and its even worse with a load on the back. I have those 16" split rims with bias ply tires in the rear (all 4). Are the tires causing this problem or is it something else? Could the springs be a cause of it, they have 10 main leafs and 3 overload springs. With the mason dump empty the overload springs do not touch the perches on the frame. I like this truck a lot and i need it to work for me but its not to fun to control or safe like this. Any ideas would be a big help.
Just an idea, but have you checked your rubber leaf spring bushings? I had them wear out on an older truck then yours, and I could feel the rear of the truck shift a little. Another thought is that one or both of your leaf spring center bolts could be broken. That's all I could think of.
The rear springs in this truck i took out of a 76 F350 dually and put in this 77. I put new rubber bushing in them and the center bolts didn't seem to be broken cause the whole pack of leafs stayed together, both of them that is.
Other then tire pressure being low, the idea of a locked rearend sounds right to me. I have an 84Vette with a pretty healty 377 (destroked 400) sbc. When I make turns I have to idle it threw them. With just a touch of the gas the diff locks up and the rear will try to meet or beat the front around the corner.
There is a way you can test to see if the diff is locked. Take it to a large gravel or sand lot and make sharp left and right turns at idle. You only want to go fast enough to move your truck. Have someone watch the rear tires while you're doing this. If the inside tire is kicking up a good chunk of sand or gravel then it sounds like the diff is locked. You can try this on a paved lot too by listening for the tires to "chirp" or see if they are leaving scuff marks behind as you are making the turns.
All,
The symptoms described are not as severe as the possibilties being suggested. If the rear end was actually moving with respect to the springs we would see an instant deformation of the u-joints and or a bending of the drive shaft. The originator has stated the problem is amplified during hauling and that it occours during turning. My guess is that, turning is exciting but, turning left/right/left is terrifying. Your vehicle is under damped. How old are your shocks? Check them and make sure that both ends are still fastened. Inspect the shock for dents and for oil leaking. A bent shock can give symptoms that are completely unexplainable and definietly unpredictable. Check the swaybars while your down there. They are not likely to give you such drastic symptoms. Play in the steering system can contribute to this panic. Lift the frontend off the ground and shake the passenger side tire left/right repeatedly and listen for the play. It's pretty easy to find it when the front end is off the ground. Check your flexible steering column connector.
My Way is the Highway,
KingFisher
I put a set of Kelly tires on my 99 and had the same feeling. The way I was telling everyone its like my rear tires are covered in greas or oil and they are sliding back and fouth. When I took it back to discount tires they changed the tires out to Perlies and the problem went away. I would bet money if you single out your rear wheels and drive it you will find the problem will be gone or atleast not as bad.
I know the rear end is an open diff. It doesn't have any sway bars. The shocks could be the problem or part of it, i'm not sure of their condition. They are the ones with the coil spring overs. I have some feeling its mostly the rear bias ply tires and the manual steering that the truck has thats causing the problems. I will be doing a power sterring conversion in the next 2 or 3 weeks. I have all the parts, just need to find the time now. Thanks for the input, it was a help.