PBR Streetgang

This has happened on one other occasion, but nowhere near the level of what happened yesterday.

I have no issues whatsoever while in 4WD high, btw. But while driving in low at about 25mph, not only did I experience a huge "thud," but the truck hesitated in such a violent manner that the ash try on the dash was flung open. It definitely was the type of sound of something "engaging," though the 4WD Low light was already on.

After checking underneath the truck, I found no damage or leaks, and the truck is driving normally (though I don't dare use 4WD low again until this is resolved). I always engage 4WD from neutral as well.

Any help on this is greatly appreciated - I've seen similar postings on this though none yet being in 4WD low.

2007 F150 FX4 SuperCrew, 105k miles, 5.4L

greasyknuckles

25mph seems fast for 4low. what kind of surface were you driving on?
if the tires had too much traction as in you were on a gravel or paved
road with no slippage, you experienced driveline windup. something had
to give so the transfer case clutches slipped. make sure all your tires are
the same size, they need to be within 1/2" diameter of each other. measure
them all with a string. I have seen new tires same size way different there
will be a number on them like 108T or something to that effect, they should
all have that same number

marshallr

Just a guess. 25 mph is really fast for 4 lo, normally only used in 1st gear and for creeping along. I'm guessing your transmission up-shifted pretty hard to 2nd gear at that speed.

Boulevard

I have heard of something like this from the local Ford dealer and they say it is usually from a lack of use/maintenance. According to them if the 4wd section of the truck is not used or exercised than the components can seize so when the truck is called to 4wd the parts do not move than all of a sudden the parts move into place and you get something like what you describe. Basically the parts go in hard and out of alignment and the truck gets a heck of a good shake.

One more thing. I believe in exercising the truck and I have run it up to full speed in 4-low (about 60 mph). Its pretty loud with all the gear whine and if you take it easy the gear shifts are very hard and the truck lurches, hard. Its a very violent shift. Again, its very close to what you are describing and what you have to do is slam your foot down....full throttle, no mercy and keep it there....let the truck shift at full rpm. The shift will still be hard and it will throw your head back but its a good kind of hard, like it was meant to be that way.

All Hat No Cattle

Just out of curiosity, what would you consider full speed, in 4 HI, since you consider 60 mph in 4 LO "reduced speed". That is, if you have read the owner's manual.

mark waller

You drove too fast in 4L

gone postal

60 MPH in 4L????

Drivetrain just isn't made for that at all. read your manual, if you don't have it, download it.

Can does not equal should.

All Hat No Cattle

I'm pretty sure we would never hear about it if they detached.

I can picture that post now, LOL.

Yikes!!

tudunka

I think that is too high for 4x4 L. I only use 4L from 0-5MPH and only if I'm pulling a heavy load up a ramp. If I use 4x4, its mostly 4H.

I will agree that you do need to use to keep gears working. I had my 4x4 lockup on me and I had to get under the truck and bang on the transfer switch to get it to de-engage the 4x4.

Magnetic157

OP said he drove 4H at 60mph, and drove 4L at 25mph.

I agree, 25mph is really fast for 4L and not surprising it clunked, especially if there was friction on the tires.