84 chevy 4x4 jerks

[joeyd208]

hey i have a 84 chevy scottsdale 1/2 ton 4x4 anyways when its in two wheel it drives nice but once i lock the hubs and use 4 wheel it jerks real hard like the front and the back arent workin with each other i dont know if the front or the rear diff's have ever been changed or not?? if someone has a way to tell if they have or not please let me know or if you think you know whats wrong please let me know ok

[mehoff400]

are you putting it in 4 L and are you doing this on pavment

[Pete95Sierra]

if its on pavement it will do it, also are your tires different sizes by chance?

[CarpenterGuy]

jack the truck up and put all four corners on jack stands (using 4 stands of course) and have a buddy watch the front and back tires as you turn the truck on and let the tires spin a little (not fast) and mark the tires with something on the same side (liek tape on the bottom of both tires) and after a while if they arent in the same position, then there's different diffs. I had to do that on a buddy's truck.

[joeyd208]

well its in 4 hi and yeah its on the pavment if i do it on dirt it does the same **** it jerks back and forth real bad i never noticed it till i used the 4 wheel durin winter and it went from ice to pavement then it started to do that? so what you mean mark the same side tires?

[Crawdaddy]

NEVER USE 4 WHEEL DRIVE ON DRY PAVEMENT. That's one quick way to kill drivetrain components. Also, like Pete said, are you running the same size tires on the front and rear. Just because the tire says it's a 31 doesn't mean that the final height is 31". It can vary by manufacturer. Also, if one set of tires is worn more than the other, that can cause binding because the rolling diameter is different.