August 2, 2010 11:23 AM   Subscribe

AutomotiveFilter: Please help me diagnose this squeak in my 99 Ford F150.

This is a 1999 Ford F150 XLT 4WD with automatic transmission and the 4.2L V6 gas engine and short cab. It has only 53k miles on it. Also, I believe this vehicle was in a flood before I bought it. There's a lot of corrosion up to a certain level on the underside, and then none above that line.

About a year ago it began developing a squeak that seemed to come from right behind the cab, like it was coming up in the crack between the cab and the bed. The squeak is fairly high pitched, about 1kHz, and is definitely connected with the drivetrain:

Engine on, in park, revving engine = no squeak.

Engine off, in neutral, manually moving rear wheels = slow squeak.

Engine on, in drive, moving at a slow speed = squeak that varies with travel speed, but is too fast to be 1:1 with wheel rotation.

Okay, so I'm thinking U-joints, especially with the flood history. I try to listen to each u-joint individually with a cardboard tube as a helper rotates the rear wheels and driveshaft, but I can't pinpoint a problem joint. So I bite the bullet and remove the rear driveshaft between the transfer case and differential, and the u-joints feel fine. Silky even. Reinstalled driveshaft. Checked ATF, transfer case and differential fluid levels. All fine. So I pulled the rear axleshafts out of the differential. They're fine, riding in an oil bath from the differential like they should. Parking brakes aren't rubbing either.

Flash forward to now. The squeak is far more persistent and clearly is tied to the movement of the driveshaft. Also, it's making that clunk when you go from drive to reverse that, to me at least, screams U-Joint.

So...should I just replace the U-joints? I'll take it to a shop if I have to, but you probably can tell by now that I really like to DIY, and a set of U-Joint bearings are cheap, so I thought I'd query the hive mind.

P.S. No the current U-joints don't have a grease zerk.
posted by werkzeuger to Travel & Transportation (5 answers total)
It might be worth jacking up the rear end and having a buddy put it in drive while you listen under the truck. This may seem dangerous but it's perfectly safe if you are careful (verifying it's in 2wd doing a practice run without you under the truck...)

FWIW- I would just replace the U-joints anyway. It's about $60 for both of them...
posted by WhiteWhale at 11:38 AM on August 2, 2010

Are you sure it's not the brake wear sensor? If the rear pads and rotors on that truck are old, there's a chance that you're getting a frequency that's greater than 1:1 because the rotor has more than one high-spot that's contacting the sensor. They're not worn to the point that the sensor is squealing constantly, but if the rotors have a lot of lateral run-out, they might be clipping the sensor more than once per revolution. Do you ever feel a faint pulsation or pushback in the brake pedal?

Sounds like you're being systematic in your assessment of the noise, but if the squeak isn't coming from the joints, then it has to be coming from elsewhere.
I also recommend jacking up the rear and having a responsible friend put the car in Drive while you listen.
posted by Jon-o at 1:00 PM on August 2, 2010

Maybe the slip spline in the drive shaft? I'm betting u joints. make sure the new ones have grease fittings.
posted by patnok at 1:39 PM on August 2, 2010

I'm guessing it is going to be some kind of thrust washer/bearing or input/output bushing/bearing in the transmission to transfer case area.

Other things to try: put the transfer case into low gear and see if that changes anything. If the squeak is on (or before) the input side of the transfer case, it will change. If it's on (or after) the output side, it won't.

Is it a manual transfer case? Does it have a neutral sort of thing? I forget if they do or not. That might help.

Is there a driveshaft between the transfer case and the transmission? Maybe pop that out and see what's what...?

Good luck!
posted by gjc at 6:14 PM on August 2, 2010

Final update from the OP:
About six months after asking this question I figured it out, mostly by a close reading of truck enthusiast forums. This truck has a short wheelbase, the result of a short bed combined with a non-extended cab. The short wheelbase means the driveshaft angle between transfer case and differential is too extreme for standard U-joints. Instead, a combination of U-joints and a constant-velocity joint is used. The CV joint was the squeak culprit here. It's basically a metal ball that rotates on-axis on needle bearings similar to a U-joint. The job was a DIY pain-in-the-ass but doable. Parts were available online from driveshaft specialty vendors. Hope this helps someone!
posted by restless_nomad at 5:42 PM on June 9, 2013

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