Was towing my 8x20 enclosed trailer (~5-6k) on a long road trip this weekend using tow/haul mode. I noticed that at times, usually when it's a somewhat quick slowdown, the transmission would produce a pretty significant "clunk" or "bang" when it downshifted from 3rd to 2nd or 2nd to 1st (not sure).

I'll probably be taking it to the dealer soon for a service, but I'm sure they'll want to reproduce the issue which could be difficult without the trailer.

Any ideas?

Thx.

 

Yeah, I know exactly what you felt. I have 124,000 miles on my 250, I tow constantly, and have tried til blue in the face to explain this clunk to 2 dealers service depts. and also have published it here on FTE. Nobody really has anything to say about this.

As the trailer weight gets heavier, the clunk can get really violent. ABS will kick in, anything on the center console will go flying, and people riding with you will look at you like you just landed from Mars.

Only way I know to prevent this is to do as you know which is slow down slowly, taking as much distance as you can to reduce speed. Obviously this is not possible most of the time.

 

Mine has done it before while towing our RV (14K). The clunk is so bad that you are hoping it doesn't throw the driveshaft. It does it badly in stop & go traffic. I just took it out of tow haul while stopping in traffic and would put it back in when I was back on the road. I have also tried explaining it to the service guys and they looked at me with the deer in the headlights look and said sometimes strange things happen with these trucks.

 

Not suprised to hear both of you say that. i'll mention it to them the next time i have it in for service and let you know what they say.

Glad I'm not the only one. Thanks for the feedback.

 

Are your driveshafts one or two piece shafts? If its a two piece shaft it could be the drive shaft slip yolk / spline. If that's the case it probably is binding / clunking from friction because of a lack of grease.

 

Yeah, also if your truck squats it could be binding the u-joints. I use air bags to bring the truck to level when carying a heavy load and have never experienced the clunk you all are experiencing...just a thought.

 

It doesn't squat when I hook to the camper, thats what the airbags are for. Besides that it only does it when I am in tow/haul mode. The truck still has plenty of power to pull but I like the tow haul for slowing down on steep grades and what not. I don't think it would be the drive shaft spline as it only has 24k on it now, and if it is then there is a problem with the engineering. My 99 F-350 had 278k on it and I only lubed the splines once the in 200k I owned it. I think it is in the programming myself but try convincing Ford of that.

 

Mine too!!!! Very, very severe downshift at about 25 mph. I have a 2010 6.4 auto. with just under 5,000 miles on it.

We just completed a 1400 mile trip with a 10,000 pound fifth wheel.

Evertthing was fine until we pulled off the interstate after about a steady 150 mile pull. Went about two miles running 45 mph looking for the campground then slowed to 30 when we saw the sign and coasted close to the turn in to the campground. I touched the brake pedal before the turn...and WHAM!!!! I mean a major serious, sudden (downshift?) wham. It was like the tranny went to first gear without any cause under very light braking. (All I did was just barely touch the brake pedal.)

Interesting that a true downshift did not actually occur. It was like the tranny found the wrong gear or something. After the "slam" everything went immediately back to normal driving.

This was huge "slam" and am suprised the drive train was not damaged! Enough of a jolt to snap my head forward!!

We ignored this instance and finished out trip, but we did experience the same type of behavior three more times during our trip, but never as severe as the first.

This is going on my complaint list and I will surely get a copy for my records.

 

ME TOO...ME TOO.
My 2008 "job 1" with 80K miles on it did this exact same thing.

I just bought a bigger boat (27' Excalibur speed boat) and decided to use the "tow/haul" setting when towing it home. Well I experienced this exact "clunk" you are describing when slowing down.

If I tow withOUT putting it in "tow/haul" mode...NO CLUNK.

 

I have spent a lot of time behind the wheel lately with a 8-10K trailer. (6K miles since 2/17). Been messing with the trailer brake settings.

My theory so far, the big clunk that makes you check your mirror for transmission parts laying in the road can me minimized by having a near perfect balance of truck and trailer brake bias.

Not enough gain, truck works hard to stop and is pushed creating a negative load on the tranny that makes the downshift hard.

Too much gain, strong positive load on the tranny making it work hard to downshift.

I think we should behave as if we were driving a manual tranny. You know the little lag between positive and negative load on the transmission? Makes things get a little funny. Good even load under braking seems to smooth it out quite a bit.

 

i have noticed that with just a slight touch of the brake when in tow/haul mode the computer tells the tranny to downshift a gear as a safty measure to help control a heavy load on a down hill grade. when using this mode if youre running as fast as you would not using this mode, the truck does this down shift at a lot higher of a rpm than it would in normal mode. these engines are powerful and the back pressure when at a high rpm will slow them in a hurry. the clunk is annoying product from the shock on the drive line when the down shift happens. using the t/h mode with a lighter trailer the downshift will be more severe than with a heavy load, plus the slower you go the lower the gear, the more violent the head snap as the truck drops to even a lower gear. all the nascar fans that pull a lot should invest in a Hans Device.

 

I had this issue and kept taking it in. they flashed it with the latest flash over the summer and ever since, things have been much better. not really happy that I went with an auto this time.

 

I have an inquiry to my Ford service dealer about this and they owe me a call back abiout this on my 2010 F250.

I specifically asked about a flash of new software????. Maybe a bad sensor????

Like others say above, mine downshift clunk was so severe that it's a wonder that drive train parts were not strewn on the road.

Maybe others havning heavy loads in tow haul can add?

Going to keep this hot if I can.

 

My 08 has done the same thing except I wasn't towing and it wasn't in t/h mode. Truck was empty except for 1 passenger and I made a sudden stop and turn to get out of on coming traffic. Like others have said I looked for parts on the road but everything has been fine since.

 

Sorry to bring back an old thread, but I am having this same problem on my 06' F350 PSD with a 6.0.

It only occurs while in tow/haul. An example would be:

Getting of the interstate. Coasting down the ramp, and the trucks gets to about 30 mph. Wife and I are suddenly jolted by a bang and jarring of the truck. If I had to describe the sound and feel, the best I could say is that it is sort of like reaching the end of the chain.

As I said, it only happens in tow/haul mode. Have any of you figured out what was going on, because so far, I am not having much luck. I did see a report stating that it may need reprogrammed, but nothing that substantiates that.

Thanks in advance.