DieselDennis

Saturday I was towing an unloaded 7x14 enclosed trailer. Trip was about 100 miles and this was my first time towing anything with my truck. Truck is an '08 Crew 4x4 with 6.5' bed, 5.4 engine, and 3.73 rear end.

I was getting an intermittent vibration or shudder while towing. Speed was ranging from 50 - 65 MPH and I had OD off the entire time. Vibration didn't seem speed dependent. And it wasn't a harsh vibration, more like a low pitched hum, but I could definitely sense it in the cab.

I'm planning on doing a 250 mile tow with this same trailer loaded on Wednesday. I'd like to check a few things it might be in the next couple of days. I've read where it could be the rear end/friction modifier fluid. I've read about axle wrap and wheel hop. But I really don't think it's either of these. I don't think it's anything to do with the trailer, as I never heard any clunking from the receiver hitch. What else can I check?

DieselDennis

BTT for the afternoon crowd.....

SIC_HDPP

Do you have a limited slip in the rear end and how many miles does your truck have?

leopold

If you dont have it without the trailer I would check the trailer itself. Wheel bearings, brakes ect.

DieselDennis

Truck has 61,### miles and does have the limited slip rear end.

I don't believe I have ever noticed this issue prior. I initially did point to the trailer, but it's not a constant vibration. And don't you think I would hear a clunk in the receiver hitch if the trailer was bouncing? It wasn't doing it at a consistent speed. I never did figure out anything I could do to either make it vibrate or make it stop vibrating. Wasn't doing it consistently up the hills, down the hills or in the flat.

I guess I'll have to just play with it some more on Wednesday. The trailer will be loaded down pretty good so it may behave differently. Just don't want to make anything worse than it may be and definitely don't want to be stranded with a load.

diamonbird

I think it might be your spark plugs.....I changed mine out with only 58,000 miles and they were bad/burned up so the speak.
Have you replaced your plug yet?,don't wait to long to do them!
Waiting 100,000 miles on these plugs is a really bad idea! just saying!

SIC_HDPP

When you make turns with your truck (towing or not towing) and it shudders it's your limited slip going. It's a pretty common issue. I can be driving straight and I get a slight vibration. Hope this helps.

RTK

Hi I'm new to this forum, but I have a small business and currently own six F-150s from 07 to 12. I just had a truck into the shop last week for this same problem and changing the spark plugs took care of it. That particular truck has 165,000 miles on it and had just had the plugs changed 50,000 miles ago. We are changing all of our trucks plugs at 50,000 now after much frustration and $$$ dealing with plug issues. All of our problems always end up at bad plugs. Replacing the FPDM fuel pump drive modual seems to help, but won't totally take care of the problem.

If I were you I would go have the plugs changed and don't let the shop waste any time or money trying to diagnose the problem.

DieselDennis

Update:

I want to first off state that this issue was a vibration or a shudder, it was not a STUDDER or a hesitation.

I pulled the trailer loaded 250 miles on Thursday. Trucked pulled fine. Hurt a little to get 10 MPG (OD off all the way).

I'm going to be pulling the trailer unloaded back up the 250 mile stretch on Tuesday. Maybe it will be the first time pulling the trailer that the wind isn't blowing at least 20 MPH. I'll report back if I still notice a vibration.

How much friction modifier should I think about adding for a little shudder?

SIC_HDPP

If you have never replaced the diff fluid I would replace the diff fluid and add in 2 bottles of friction modifier instead on the normal 1. This has worked for a few members here on the form.