I recently was experiencing the famous "clunk" during initial acceleration. If I feather the throttle, it is not there. If I accelerate (normally) going up a hill (from a stop, u hill) the clunk is there. If I mash on the throttle from a dead stop, the clunk is there.

I do not feel anything out of the norm during braking (like many people posted when i did the "search function"). It does it going straight as well.

I keep reading about re-packing the slip yoke with grease. How would this help ? The slip yoke is bathed in the Transfer Case ATF, correct ? Once fluid reaches normal operating temp, wont is just wash the grease away, mixing it into the fluid ?

I am thinking this maybe more of a transmission cluth problem, no ?

Any input is really appreciated.

(2004 Ford F150 xlt 4.6 L 4x4. Running the 4R70W trans. 3.73 LS rear end sitting at about 50,500 miles)

 

No, the slip yoke is not bathed in ATF. There's a seal that has the job of keeping the ATF in the trans. That means the slip yoke doesn't see much ATF, so it needs to be packed with grease.

It's EXTREMELY unlikely to be a transmission clutch issue.

 

At what RPM's, MPH, gear does this happen in?

 

It happens when I take off from a dead stop. It especially happens when I am under load (stopped at the bottom of a hill, got get going up it) or if I really jump on the gas from a stop. If I am rolling at all, it generally wont do it.

Does not clunk if I feather it, or on flat ground, take off normally (I tend to NOT gun it from stops). Originally, it would do it everytime under acceleration, I got under the truck and noticed my driver side front shackle (rear leaf) was loose. Tightened that up and it seemed to fix the problem. On the drive home, I noticed there was still a clunk under those heavy loads. It also is not very consitant. I can jump on the gas, and have no noise, but once in awhile I get the clunk. When I am home today, I will try to catch "at what RPM" it does it in. As for MPH, its from a dead stop, and on the initial take off.

As for a seal on the transfer case... ??? There is a seal that prevents the ATF from getting into the slip yoke, yet when you remove the slip yoke, ATF leaks out. Does that mean there is a O-ring type seal on the slip yoke ? Preventing fluid once its on ??

 

Well the clunk sounds like a rear end problem. With your foot on the brake, move the trans from R to D and back and forth, allowing it to engaged each time, see if it clunks then. If not, park on a hill or put it on jack stands(under the rear only and chock the front, this should not let it leak) and remove the d-shaft and grease the yoke. The yoke presses against the seal to keep it from leaking while in place, other than when removing, it shouldn't contact the ATF.

 

Alright, I'll have to try this. Thank you. It is much appreciated.

And thanks for clearing that up. Should I plan to make "re-greasing" the slip yoke part of regular maintenance ? About how often ? Or should I just wait for it to start to "clunk" again ?

 

Grease the yoke and while you have the shaft out check the nut on the axle yoke. They loosen up. Get new nut torque to spec then check how much torque is needed to turn the yoke. When with in spec stake the nut.

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