98 F150 XLT 4x4. when accelerating from a stop, I hear and feel a thunk. I can't really tell if it's front back engine trans diff...Just hunting for suggestions. U-joints were replaced yesterday and symptoms still persist. New to F150's, I would have thought it was the u-joint for sure.

Steve
Huntsville, Ontario

 

Did you grease the slip yoke when you changed the u-joints. This seems to cure many of these problems, at least temporarily.

 

I didn't do them, so I can't answer that. Is this a severe thing?

 

I have the same sound on my 1999 F-150. It's only when I take off hard. That leads me to believe that maybe something is hitting my dual exhaust or something. I don't know if you have dual exhause or not, but you could look to see if maybe that's what causing your thump. Hope this helps and let me know what you find out.

 

I also have the same problem with my 93 F150. But now it also does it on corner turns and hard bumps in the road. Not sure if it's something different or the same problem just getting worse.

Hope you find a solution.

 

I was able to leave a few stopped situations yesterday WITHOUT hearing anything, so I'm thining that might rule out u-joints, I lso noted that first thing in the morning or after sitting in a while, it doesn't do it at all, but will do it probably next time I stop and start. I don't have duals, just factory piping for exhaust. I don't think anything is rubbing, but I'll look over the weekend. I MAY hear/feel something as a decellerate and come to a stop, but I'm not sure about that yet. Thanks for suggestions so far...keep them coming.

(could this be the T/C locking up??) - just a quick thought before posting


Steve

 

Do a search on slip yoke in the full forum. You should be able to get some more information about it.

 

This is a really common F150 problem. I did grease mine with the recommended ford PTFE (Teflon) grease when I changed my u-Joints about 4 or 5 months a go. The fix lasted about 2 weeks for me. When I got nothing to do, I'll try greasing it again.

The problem is the Slip Yoke moving in and out of the spline. The slip yoke is not slipping in and out freely like it should because it is too dry.

Like Kingfish said, Do a search for things like: "Slip Yoke", "Clunk" "Thump". You'll get a few hours worth of reading.

I read somewhere to use the Ford Specified Teflon Grease so that it will not contaminate Transmition Fluid if there were any contamination. But I also read that some were using regular Bearing Grease. I personnaly think the Bearing grease would be a longer lasting solution but I wonder about the contamination thing, is it even possible to contaminate the transmition fluid from the slip yoke/spline assembly ?