Driveline Clunk

[SZR48207]

2002 Ford F-150 with almost 100K miles.

I have recently started to notice a "clunk" or engagement type noise when driving at 50MPH+ on the interstate. If I let off the gas for a few seconds and then let back on, I will hear this engagement noise, which sounds like something on the driveline engaging. Never noticed this before. I don't notice this clunk at lower speeds.

I have replaced the u-joints with Federal Mogul Precision ones around 10K miles ago, so I don't think the problem would be bad u-joints. I've heard that this is a common problem on Chevy/GMC trucks, but less reports with Fords. All other components in the driveline are factory OEM (transmission, rear diff). When I had the driveshaft off to service the u-joints, everything looked OK.

Should I just chalk this up to wear on the yoke splines? Any reason I should try to fix this or just attribute it to high mileage?

 

[tom slick]

I've seen the bushing in the tail housing worn out on a 2002 F150 causing a clunk.

 

[Gene K]

Is it a 8.8? A lot of 8.8 Fords exhibit lash.

Get it up on stands and turn the drive shaft and check for lash.

 

[SZR48207]

Tom - Hope that isn't the case for me. I will check for play, but I hear it is more common on the 4R70W that the extension housing bolts loosen over time.

Gene - Yes it is an 8.8, but the sound of the clunk seems to come more from the middle of the truck, not the rear (although it is pretty difficult to tell). When I did the u-joints a few months ago, the only play I noticed in the driveline was an acceptable amount of around 1/8" to 1/4" in either direction. I think this is within tolerances.

On a side note, I think I found a TSB that may be related to my issue. A tube of this Motorcraft PTFE is supposed to run
http://www.ford-trucks.com/tsb/fulltext/show_article.php?tsb=05-26-10

 

[punisher]

Beat me to it. I fought a driveline clunk in a customer's F150 for almost 4 hours until another tech wandered over (took pity on me) and suggested teflon grease on the splines. Never give a perf tech noises to fix.

 

[SZR48207]

OK so I got around to applying the Motorcraft PTFE lubricant to the slip yoke today. First test drive SEEMED slightly better, but I can still reproduce the noise. I would describe it as a "click" and it seems to only occur between 50MPH-65MPH or so?

Anyway, pics:

Slip yoke. Looks alright to me. No signs of unbalanced wear or damage. The dark ring is present all the way around. I think that is the normal resting area for the slip yoke during "flat" driving.

Splines look good. I never noticed the large notch at 3:00. I wonder if this is something I need to index?

Extension housing on the 4R70W. I did my best to crawl around to look at the copper/brass bushing and it doesn't seem worn. I guess this is a good reference picture for the downstream O2 sensors.

PTFE lubricant applied mostly to inner splines, but I put a little on the outside for safe measure. It's not exactly easy to drop a driveshaft.

Tube of Motorcraft XG8 PTFE lube. Cost around $8 at the stealership. (actually not a bad price because I've never seen this type of lube at any auto store)

I'll see how this works for a week. If I can nail the problem down to the rear differential, I might use the opportunity to rebuild it with some slightly higher gears (3.73) and put in a LSD.

I read on some other forums that the noise could be indicative of a broken engine or transmission mount?