I have an F150XLT with Extended cab.I have a shudder or vibration that only occurs when I make a left or right turn from a dead stop. It doesn't happen when I move straight forward from a dead stop. The Drive shaft and U joints have been checked. The idler arm has been replaced as well as ball joints and control arms. Has anybody else experienced this?

PS: This problem didn't always exist. It's getting worse with time.

 

If it's a limted-slip differential, you may need to add friction modifier.

 

I don't know if it's a limited slip differential.How do I find out and
what is friction modifier? My truck is a 4.2L V6 Ext cab.

 

On the drivers side door is your Vehicle Certification.

F-150, rear axle ratio codes:

18 - 3.08
19 - 3.55
26 - 3.73
27 - 3.31
H9 - 3.55 Limited Slip
B6 - 3.73 Limited Slip

If it's a limited-slip differential, it has clutches. Without the friction modifier, it will do just what you're describing. It's in the owners manual. If it is a LS, it needs: Ford part number F1TZ-19580-B 4 oz of Additive/Friction Modifier.

If this is not the issue, there is a TSB that involves installing a revised clutch pack on early '97 F-150's that the dealer tech should be aware of.

If you can feel it in your seat, it sounds like the differential. If you can only feel this in the steering wheel, then it's in the front suspension.

 

I've added the friction modifier and it still vibrates/chatters. Does
it take time for the oil to have an effect? What does friction modifier do?

 

I've added the friction modifier and it still vibrates/chatters. Does
it take time for the oil to have an effect? What does friction modifier do?

 

start whining above 40MPH? if the answer is yes you'd better take it in

 

No. While in motion, there is no problem. It only occurs when I turn left or right from a complete stop. As I begin to move I get a shudder/vibration and it lasts only 1 to 2 seconds, then it stops.
If I go straight, there is no vibration. I've added the friction modifier ( 2 weeks ago ) but the vibration is still there, but not
so intense. Not sure if the friction modifier is the cure because the problem was always less noticable on cold days.

 

Mikeg,

Did You use OEM, Ford or Dana part# 43161 modifier? If not, I would advise you to do so. Many generic friction modifiers on the market that are absolute garbage! Owners manual should recomend 4oz. bottle. I would use (2) bottles of the good stuff and see if it cures your problem.

Friction modifier allows the clutches to grip when torgue bias is needed at rear wheel that has lost traction (on OEM trac-loc) yet allows clutches not to grab when diff. is differentiating (going around corners).