Bed hopping - Diesel Forum

JB4LCM · 08-02-2007, 07:16 PM

If this is the wrong forum, sorry - I thought I'd start here as this seems to be the best place for this question.

In my 2001 F350 PSD, at 43-46 MPH, I get a bad shake/bounce going on, like a tire - or tires are out of balance. I just had the tires replaced - all balanced - and the same thing happens with the new tires. Originally, I had BFG 35" on it, then went down to an E rated 285 (32") tire for better towing. And the bounce/shake happens at the exact same speed - so it can't be the tires out of whack.

The tire place talked about BED HOPPING that could be the culprit. They suggested reducing the tire pressure from 60 to 40 psi and see how it goes. (When towing they are inflated to 80 psi).

Anyone have any experience with this? Do you have a speed range where your truck has a bouncing going on?

Thanks!

JB

suv7734 · 08-02-2007, 09:10 PM

JB,

By the title of the tread I though this was going to be more interesting [img]/ubbthreads/images/graemlins/biggrin.gif[/img]
Did you have the speedo recallibrated for the smaller diameter tires? Is the vibration happening at the same speed or is it at a different speed now? The reason I ask is your driveline is now turning more revolutions, in relation to when you had the old tires on, per mile. I find it strange that the tire shop told you to pressure down since this will usually 'magnify' an imbalance issue with regard to a tire/wheel combination. Can you tell if this is coming more from the front or rear of the truck? Is there lift on the truck?

Bruce

Foxx · 08-02-2007, 09:19 PM

My truck does the same thing. From what I gather it's pretty common. You need to check your driveshaft universal joints and your carrier bearing. If the carrier bearing fails, it lets the entire driveshaft move kind of like a jump rope when the truck is in motion, which can cause it. A universal joint not properly turning can throw the driveshaft just enough out of whack while in motion, too.

Just noticed you have a lift- did you lower the carrier bearing when you installed the lift? If not, that can also cause it.

nascarj · 08-02-2007, 11:31 PM

JB,

I'm with Foxx, most times I've work on shudders at a certian speed it is in the drive shaft. Either worn u-joints/carrier bearings or impropper drive shaft angles off the trans or into the rear dif.

With the age of your truck and the lift, it could be either. If it just started and the truck has been lifted for a while, I'd look into the u-joints/carrier bearing.

j

JB4LCM · 08-03-2007, 04:11 PM

I had a 3" "LEVEL" done on the truck when new - (front end only). So the rear is still the same.

I never had the speedometer changed in the first place when I had the 35s put on. The speed difference is approx 9% up from stock - the wobble/bounce happens in the similar speed range - mid 40s. So the speedo is now back to the correct tire size. Even so, at 9% difference at 40-50 mph is only a 3.6-4.5 mph variance. Still in the speed range the problem happens to fall in.

Two years ago is when I first noticed it. But that's when I first moved (full time) to Havasu where the top speed in town just happens to be 45. A coincidence? Interesting - first I had Nitto grapplers put on, thinking the problem was the tires. They couldn't do anything about the wobble so they changed the tires to BFGs. Seemed to be a LITTLE better, but not great. Still wobbled in that speed range. I just lived with it.

Just before I changed the tires out this past week, the wobble seemed to be getting WORSE. Like 41-50 mph. I thought the tire change would fix it. But that I think about it, it seems NOT to wobble as much when I'm accelerating thru that speed range.

Hmmmmmm . . . I think I need to test drive that situation and see if it wobbles during acceration, or just when cruising and decelerating . . .

JB