My truck is a 2000 Lariat 4x4 with Mickey Thompson Baja Belted HP (an AT tire) 33x12.5-17LT, on American Racing Atlas 17x10 rims. My problem is a violent front end shudder that occurs when I hit a bump or dip at speeds of 40mph or faster.

I started to notice about 3 or 4 months ago a front-end shudder when i'd go over a bump or pothole, but it would happen infrequently and would dissipate quickly even if i didn't slow down. 2 weeks ago the shudder got worse and would happen more frequently at bumps/dips at speeds of 45mph or faster. The Ford dealer replaced both lower ball joints (my truck only has 13k in it, though the ball joints did look loose). During this repair i noticed a strip of lead weight (about 100 gm or 1/4 lb) had been dislodged from my rim. The truck was also due for tire rotation so I had a service station swap the rear tires with front. Afterwards the front tires were balanced. About 500g (1 lb) went on 1 rim and about 50-100g on the other. After these, the problem actually got worse!

The truck was now getting much worse front-end wobbles after a bump or dip (even small ones), occuring at speeds at 40mph and up. The front tires seem to wobble hugely; the whole truck would then vibrate and I'd have to slow down to 15mph for the shakes to dissipate. The Ford dealer replaced the idler arm and told me to have the tires aligned. At another service station (the dealer doen't do alignment or balancing) they said my tires were still aligned but i had them do them anyway.

The wobble came back as bad as ever. When the dealer checked the new idler arm it was damaged again and i'm now waiting for the part to be delivered and installed (under warranty). Ball joints and tie rods were checked again and are still tight according to the dealer.

The tires seem to be wearing evenly and still have thick treads. On smooth roads the truck runs fine even at high speeds. Any suggestions on how to fix my problem? Thanks in advance!

 

There are many things that could be causing your problem. My first guess would be that those aftermarket rims are warped. I had a set of American Racing wheels on my last truck, and I remember the shop that sold them to me returned 2 of the 4 because they weren't spinning straight when they tested them on their high-speed machine. Has that ever been investigated?

If it is the type of feeling that sort of comes up through the steering wheel when you hit a bump (like hitting a baseball off the handle of the bat), my guess would be either the pitman or idler arm. I hope this helps you out some, good luck with it.

 

Thanks for the reply. To isolate the problem, the Ford dealer put on original Ford rims/tires temporarily and the shudder went away. So I'll be looking for a tire/wheel shop to check if my rims are out of true. My tire/rim setup did run well for 1 1/2 years though, so the rims started out fine. The tread looks evenly worn.

If the rims are still good and it's just a matter of the suspension not being able to handle the increased mass of the bigger tires, would a steering stabilizer work (don't want to change my rim/tire setup; need wide tires for sand and they still have thick tread)? Or would that just be masking the problem even if it does work?

 

bubut,

What tire pressure are you running? These tires are not radials so they require a little bit more air than a radial. If they are too soft when you unload them and then load them going over bumps they will
not rebound like a radial does. If you need a pound of weight on the wheel to balance it you have some serious issues. But if the wheel was untrue you would have the problem all the time and it would increase with speed. One last thing; are the wheelsyou purchased hubcentric (centered on hub OEM from factory) or lugcentric (centered on the lugs)?

Regards

Jean Marc Chartier

 

Thanks for the reply Jean Marc. I run my all my wheels at 35psi (cold). The wheels are balanced from the hub so i guess they're hubcentric. It has -25.4mm offset and 4.45 inch/113mm backside setting.

I just had the front tires checked and they were still balanced fine. The wheels were also deemed to be true, though it seemed to have been done just by sight as it spun on the balancing machine. The service guy did notice that the tire on the wheel that had a pound of lead weight had some unevenness (a bit wavy on the surface), and I asked if it should go to the back. He agreed, and said I didn't need to replace the tire since the unevenness wasn't that bad. It used to be at the back before I rotated. Even then the truck shuddered. When I rotated (and had the lower ball joints replaced at the same time) the shudder got worse, so it's going back to the rear.

I had the whole front end suspension checked again at an independent repair shop and they also couldn't find anything wrong with the components. I'm guessing that after only about 13k miles (roads here in Manila and environs get lots of potholes during heavy rains), the front-end supension has become loose enough that it can't support the added mass of the bigger tires and wheels when it hits even slight dips and humps?

I'm adding a steering stabilizer tomorrow. The only brand I could find here is Monroe (steep at about US$70, though installation is only about $8 with the cheap labor here). I know it might just be masking something wrong but I'm running out of options at this point.