Annoying vibration at 40-50 mph - 2003 F350 PSD, 7.3, Crew Cab, Short Box

Jan 04, 2005 4 Replies
N
2003 F350 PSD, 7.3 liter, Crew Cab, Short Box Auto Tranny with 43,000 miles. All stock except the 5er hitch and the windshield wipers.

I recently developed a vibration at 40-50 MPH. It is worse when I am braking to slow down and will continue to vibrate until I hit 15 MPH while braking. Otherwise, the only time I feel it is between 40-50.



I recently put new tires on and had it rebalanced twice. The first time was because highway speed vibrations indicative of wheel balance problems. The second time was due to this new vibration and it did not help. And the tire tech said they were all in balance...but he pulled all the weights and re-did it anyhow.



If the tires were out of round I would think the vibration would be there at various speeds, but that is the kind of vibration I am feeling.



I have not looked at the truck to diagnose this issue yet. I plan to crawl under her this weekend. Any tips on what I should look for?



Nate


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C

Just to rule out wheel balance problems or tire problems I'd throw the front wheels on the back and vice versa. Chad

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N

Been there, done that. The tire tech did that last time I had them spun. Forgot to mention that.

Nate

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S

These can be a bear to find. U-joints failing is one area. the bearings can go bad and not give any visible play. you don't know until you disassemble the joint. With the low mileage on yours I wouldn't suspect this. Another area I've heard about but have never verified is the flex plate (what the torque converter bolts to) getting warped or out of balance. A friend of mine had his replaced for a vibration issue. I also read about it in a ASE study guide on transmissions. I suspect my dad's 90 F-250 of having this problem, but he won't let me take it apart to see. His vibrates about

35 mph, and his transmission was removed a few years ago. I would like to do this to learn but.... I don't know what could cause this to become a problem, except for improper disassembly and reassembly Just my 2 cents
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N

U-Joints...maybe. I'll check that out. But the flex plate would cause a vibration at an idle, not even moving. It would increase in intensity as the rpms go up, not speed related. A flex plate can get out of shape by a pin head mechanic trying to force it in backwards. Two of the three bolts will line up when it is out of key. So you tighten those two down and then go back to try the third one. Guess what just happened. Warped flex plate. And yes...I fired the mechanic.

Nate

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