I need help diagnosing a problem with a noise and vibration issue.

'99 / F-250 Superduty Crew Cab / 7.3 / Automatic / 4wd w-Auto Lock Hubs / 201,000 miles

Originally noticed a loud vibration and fairly high pitched sound (similar to running on grooved pavement) when I hit a bump in the road at Hwy speed in 2wd. Tried shifting to 4wd HI and noise quit. Did this enough times to confirm that the shift would stop the noise. Then locked the hubs and drove in 2wd. Could not cause the noise and vibration while hubs were locked. Unlocked the hubs and noise and vibration occurred. I could cause the vibration and noise by running over the lane seperation bunps on the Hwy.

I had another thing happen while trying to figure out the the noise. When I shifted to 4wd HI, the AC started blowing out the Defroster vents. This only happend two or three times, not every time.

Pulled the Auto Lock Hubs and found the right side bearing was dry and rusty. Also, the little vacuum diaphragm was hanging loose. Had both hubs replaced with new ones from Ford. Also replaced all three of the main drive shaft u-joints at the same time.

Took off on a road trip and began to notice a very low pitched noise and vibration when hitting a bump in the road. Shifting to 4wd HI stops the noise. Locked the hubs and drove in 2wd and no noise or vibration.

It sounds like one of the Auto Hubs is engaging and spinning the front differential.

If anyone has had this problem and figured it out, please let me know.

I guess it is possible that one of the new Ford Auto Hubs is malfuntioning.


Ford replaced the left side Auto Hub at about 75K miles. Other than that, I have had no problems with the truck.

P.S. How do those Auto Lock Hubs work. I saw the vacuum diaphragm and the little plastic spring housing but cannot figure out how engaging the drive shaft causes the gears to engage and disengage in the hub. If there are vacuum lines going to the wheel, I cannot see them.

Thanks in advance for your knowledgeable input.

Byrd

 

There is a vacuum line and it is atached to the ABS lead. It uses pulse vacuum to engage and pulse vacuum to dis-engage. Really not a very good system. Usually fails at the worst time possible. Many times when buddies that have other than fords are nearby.
There are needle bearings inside and are probably way beyond needing to be replaced. These are not the same as the big unit bearings, these are small needls bearings. I would bet a cold beer that this is your trouble.
Search needle bearings and you will find plenty of guys with the same troubles with this.
I see you are new here, so welcome to the site. You may not be able to search yet, so I looked around for you. Here is probanly where you will find some good info. It also has links attached to get you most of your questions answered.
Good luck, and welcome again

https://www.ford-trucks.com/forums/6...eedle+bearings

 

Thanks for the reply.

I believe you are correct. I went by a 4wd shop yesterday afternoon and the guy showed me an old outer axle where the needle bearing had gone out and wore a groove in the axle. Once it gets this extra slop, a bump in the road can cause the splines to engage and spin the hub and differential up.

He also showed me where the vacuum line goes into the hub. A vacuum leak should be what caused the vents to change on the a/c when I shifted to 4wdHI. The rubber boot/seal on the outer axle is probably leaking.

I am going to let the shop go through the front and rear differentials. I told him we just as well replace all the bearings while it it cracked open. It is probably going to be expensive.

I will check with you guys when it's "name that noise" time again. Should have the truck back in a week. I need to get educated regarding other things that should be replaced before they wear completely out and cause repairs to be more expensive than they should. This truck has had the lowest repair cost of any that I have owned, so I am happy with it.

Thanks again for the response.

 

May consider just having them upgrade to the Dynatrac kit, and these problems will never plague you again.
If you are going to spend all of that money, might as well do it right, and do it once.