Clunk when downshifting pulling trailer

One source of cluncks can be the transmission mount, if there was any trans fluid leaked it has made the mount mush and you get metal to metal, most probable a U joint.

To check the U joints, park the vehicle in a level place, chuck one rear tire and one front tire really chucked, parking brake off, transmission in neutral, engine off.

Crawl under and move the U joint up and down, rotate 90 degrees and check the other U joint, there should be very little side to side movement, anything else the U joint is toast and needs replacing.

navegator

DougE wrote:
For a driveline clunk, the first thing to do is crawl under the rig and check for looseness in the u-joints!

I service all my vehicles, was up to 6 and 2 OHV's. All my services include me on my creeper inspecting from nose to tail all underside components. The coach gets special attention as there are wire looms and plumbing to check. The doghouse comes off also and the engine
gets a look at. You would be surprised at some of the squeaks and loose and missing hardware I have found. The coach has 31K on the odometer, had 19K when I purchased it.

punomatic, you wont believe it, but I had taken it in 6 times, and each time they lubed the spline. each time I told them it was a clunk sound. this last time I went in and said same thing. They called me and said the test drive did not make a clunk sound. they shoed me a tech order that said if I complain of a clunk sound when shifting that is normal. I made them go for a test drive. when I stopped there is the clunk sound and a little bump. was told the tech order for a bump is to lube the spline, if this occurs again then need to replace spline and special grease. they did this. why did it take 7 times????
clunk and bump are 2 different issues according to dealer

klutchdust wrote:
Seemed like the tranny hesitated, went into neutral then shifted

into gear.

This is the part of the OP's original post that would be of the most concern to me. This is more than merely a clunk in the driveline. Something in the tranny does not seem right ... and this is definitely similar to some of the symptoms I experienced during my 5R110 transmission's complete failure last August.

For a thorough analysis, a mechanic sat in the RV's passenger seat with an analyzer plugged into the Ford E450's electronic access port while another mechanic drove my Class C. The analyzer then showed what parts in the transmission were not functioning properly .... clutches, valves, etc..

It is important to pay attention to where the clunk noise is located as you sit in the drivers seat, is it right next go you from around the dog house or further back where the differential is, or all the way back where the trailer is hooked.

There are certain areas that that give you a clue, a clunk when you step on the brake and sounds up front are the brake pads climbing up and banging on the calipers.

A clunk next to you when applying the brakes can be the U joint going bad my first choice or the transmission.

A clunk where the differential is located can be the rear U joint or the crown and pinion that are not properly set up.

A clunk at the rear of the RV is the trailer moving forward as the RV begins to decelerate and is taking up the little bit of slack on the ball and the arm that connects to the RV, this is normal and should be eliminated by adjusting the response time of the electric brakes.

Last but not least there can be clunking noises coming from the front end in the suspension and/or the sway bar as the RV starts to slow down and the suspension dips down, worn bushings tend to clunk at the oddest times.

I hope this helps a little bit.

navegator

analyze it closely, I thought i had a transmission issue...it would make a thud sound poradically only when towing.

an honest transmission shop, told me thats an "ignition problem". one of my coils was bad, never got a check engine light. had to replace all 8 coils.

ebay cost under 100 bucks ... issue solved

For a driveline clunk, the first thing to do is crawl under the rig and check for looseness in the u-joints!

punomatic wrote:

bbaker2001 wrote:
my spline needed to be lubed

X2 My mechanic told me he needed to put some kind of teflon preparation that is only available from Ford in my driveline spline. I was skeptical, except that I really trust this guy, and he got his start as a Ford mechanic and only drives Fords. I said, "OK." To my amazement it completely fixed the clunk, which happened just as I was starting up and just as I was stopping.

Don't know if this is your problem, but if it is, the problem is fixable and relatively inexpensive (under $100).

I think this would be the best place to start. As long as the driveline is I could see how lube would help. As i previously stated my PU needed the spline lubed and it cured the clunk.

bbaker2001 wrote:
my spline needed to be lubed

X2 My mechanic told me he needed to put some kind of teflon preparation that is only available from Ford in my driveline spline. I was skeptical, except that I really trust this guy, and he got his start as a Ford mechanic and only drives Fords. I said, "OK." To my amazement it completely fixed the clunk, which happened just as I was starting up and just as I was stopping.

Don't know if this is your problem, but if it is, the problem is fixable and relatively inexpensive (under $100).

Our home lies in the mountains at the end of a moderate-grade long uphill pull and then a steep-grade short uphill pull. After arriving home with the RV I merely shut the engine off. Perhaps the transmission is hot after pulling these grades to our house and I should be idling the engine for a few minutes after arriving home to cool the transmissions down?

I don't know if it is related to the damage, but I had a similar thing happen to me last summer. Pulled into a scenic overlook after a long uphill grade. Stopped, looked at scenery-a textbook hot soak. When I pulled out the clutch fan hung on and on.. and held on to higher RPM for a very long time. The drivetrain had accumulated a lot of heat... I thought at the time in the future I'll idle it like a turbo engine after a pull like that.