2002 Excursion 4x4 7.3..I posted this in the SuperDuty forum but meant to post it here first. This will probably be an easy one for y'all...I've read about this issue on here before but I've forgotten what the problem is. When the wheels are turned and the vehicle is going forward at some speed, there is a knocking sound, like a ba-doomp ba-doomp ba-doomp. Does it going left and right, sounds like its in the front hub area. Looking for any and all info on this issue. Thanks

 

I have Auto hubs, and have also been having the vacuum leak issue, air coming out of defroster vents only. Could my front hubs be stuck in 4wd?

 

Son of a....I just jacked up the front end, spun both the front wheels, and it turns the front driveshaft. That means my hubs are locked correct? What would be the proper course of action now?

 

Turn the **** on the hubs to the left, that puts them in Auto. Turning them to the right locks them full time.


It sounds like you have been wearing your front end pretty hard.

 

Yeah I keep them in auto but they hadn't disengaged from the last I put it in 4wd I guess. So I took the hubs off, twisted the **** back and forth a few times, put them back on, spun the wheels, and they are obviously unlocked now because the driveshaft doesn't turn when I spin the wheels. Test drove, no knocking! So! Air still coming out of defrost vents, I guess I have a vacuum leak or bad vacuum pump and need to figure out how where the vacuum leak is. Any suggestions on where to start?

 

I use a Mity Vac with a gauge to test all vacuum lines. If the vacuum in the truck isn't running, you'll notice right away - it's not silent. The most common culprit is the tubing near each wheel - you'll likely find cracks. I shortened my hoses there about 1 1/2", and that took care of that leak.

 

I dont understand what you mean by that. The vacuum pump runs pretty constantly when the key is on. The lines I have checked looked pretty good, no cracking. But, I haven't checked them all, and haven't pulled the wheel off to check the very end of the line going to the hub. Could I be losing all the vacuum at the outer O-ring on the esof hub itself? It looked pretty hard and somewhat deformed when I pulled them off.

 

Yes, the o-rings in the hubs are common failure points from what I read when I was dealing with it. When my passenger hub/bearing went south, new o-rings, Timkin bearing, and stub axle went in. The disintegrated needle bearings did a number on the stub axle. Been smooth sailing (and 4wd shifting) ever since.

 

Thanks for the input guys, just ordered new o-rings....

 

Stud. Take a few plugs or vise grips etc... Pull your vac lines from your hub. Close them off. Koeo, see if your compressor runs for a minute to build and then shuts down. If it does, you have a hub leak. If not, go up to your compressor and disconnect the output line. Put your thumb over it. Compressor should shut right down.


If not your leak is in the Hvac system in the truck. Check the bulb over your passenger side foot rest and make sure it's plugged in. If it is. Plug it and see if your compressor shuts down. If it does, look at the dash control **** and see if you plug that if your compressor shuts down.


Pretty much, just saying (and it is hard to find) plug one unit at a time and leave the plugs in place, until your compressor shuts down and when it does, you have isolated your problem area.


Do left hub (drivers side line first, do koeo test) then the right, then the compressor itself, then the valve above the pass feet, If they all fail to kill the compressor, Pull the blend door switch at the dash and plug up the input.


Not mister wizard at this but just trying to help. It has worked for me. (I call it baby steps on my truck) happens a lot.


If you do find your hubs leaking I would offer you to move to a manual locking hub like warn or milemarker premiums and eliminate the vacuum threat down there.


Hope it helps out. I'm sure others will reply. (Vacuum really does suck!!!!)


Denny

 

Excellent advice from Denny.

 

When my hubs went out, I replaced them with OEM on Amazon. I figured they worked for 300K miles, that's good enough for me for the next round.

 

thanks Denny, I haven't pulled the lines to the hubs, but I did pull the output line and put my thumb over it and it stopped. So that would suggest its between there and the hubs, correct? Im gonna replace the orings and see what happens. I know, I know, throwing parts at a problem, not diagnosing correctly....but orings and clips are only $15 shipped so WTH.

As fas as replacing the hubs, I love the look and reliability of Warn hubs, but also love the auto hubs, so would probably just rebuild replace the OEM.

Another question, could I have done a lot of damage by driving around with those front hubs engaged for a few thousand miles? It only knocked when turning sharp so I made sure to make the widest turns possible at all times. I seriously thought the knocking noise was a maintenance issue with the "non-servicable" hubs or ball joints or something that I needed to have fixed, and had just been putting it off because of time/money.

 

This is where I'm a bit confused about the source of the noise. Even with hubs locked, you're just spinning the front axle, diff gears, and front driveshaft. There should be zero binding going on. You're just spinning a little extra weight. I think you'll find your noise to still be present with hubs functioning properly and unlocked. Just my two cents though. Definitely follow up after your hubs are back to working order.

 

with those front hubs locked, on dry pavement, when turning sharp, I get a "ba-doomp ba-doomp ba-doomp" noise. When I unlocked them and made turns, no noise.