I have the infamous "Thunk/Clunk" noise somewhere in my drivetrain. You know, the noise that is heard just as you start to accl. after begin stopped. Anyhow I have now taken it to two different dealerships and amazingly I was told the same thing from both. This is "Noraml Operation". Can anyone give me some advise on what to do? I have contacted 1-800 # for Ford Customer Service and they were very nice but did't give me any real help. The service tech I spoke with said that they had contacted the "HOTLINE" and that there was nothing wrong with the truck. Anyone with any info as to how to solve this would be greatly appreciated!!!

 

That infamous clunk you are hearing is probably due to drive line slack. The drive shaft has splines in it that connects it to the output shaft of the transmission. These splines are supposed to have grease between them. The grease helps to take of the free play between the splines and the shaft. If you were to crawl under your truck and attempt to turn your driveshaft by hand and are successful, then free play is the problem. Keep in mind even if you can’t turn the drive shaft by hand the mass of the truck can still produce the clunk if there is to much free play between the splines. Anyway, I hope my rambling helps.

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99 4X4 XLT S/C with ORP
5.4L 3.73LS
Flow Master Dual Exhaust
K&N Filter w/ Intake Mod
Flex-a-Lite Black Magic 150 Electric Cooling Fan
Jason "Hugger" Truck Lid

 

I still have the clunk in the rear end! I have heard that there is a TSB out for this problem but that it was only for the 97-98 F150s. Does anyone know if there is one for the 99's. This problem seems to be getting a little worse. I have noticed though that with a full tank of gas that I rarely hear the clunk noise, I'm wondering that with that additional weight over the rear axle that it doesn't allow the rear springs to wrap as much therefore the slip yoke doesn't move in and out as much?!? Does this sound possible? Any suggestions on how to solve this will be great, seeing that the Ford Guys are zero help regarding this problem.

 

The thunk could be axle wrap. If the truck got lifted the axle could have more leverage to the frame and could "wrap" producing a thunk when you accelerrate rapidly. For that you need to get lateral stabalizers or don't go WOT.

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1999 4.2l 2wd super cab F-150. Mods: 3in body lift, 285/75 R16 BFG AT, 3.55 gears, snuglid tonuea cover (white) 10 disk changer K&N Air Filter Tow package 6000 Lbs GVWR

 

have you checked your u-joints?

 

Get the dealer to try to put some grease on the slip yoke if nothing else. That would be the best starting place in my opinion