Trailer hitching during braking

[Philsauto]

Friends,

This is a non-Duramax truck, but since I belong to this forum, I thought I would try here first. The vehicle is a 2001 Dodge 2500 with a 5.9 Cummins. It is a short bed and has a very high quality sliding hitch. The vehicle tows a 29 foot, all season 5th wheel that weighs about 12k. It has a Prodigy electric brake controller very similar to the one in my own truck that works very well. The problem is a violent jerking during slow speed braking, below 30 mph. The problem is not evident at higher speeds. Disabling the trailer brake completely, and disabling the ABS on the truck has no effect on the problem; likewise turning the Prodigy up to maximum trailer brakes does not change the issue; it continues as before with serious jerking as you slow down. Very light braking avoids the problem. Without the trailer installed, there are no signs of any problems with the truck brakes. Braking with trailer brake only does not cause the jerk.

I am at a loss as to where to go to solve the jerk. I'm wondering if anyone has run into this problem before. The stopping is good and it doesn't pull, but the jerk is so severe as to be frightening.

Thanks!

[DmaxMaverick]

Auto or stick? Could be important, if it's engine surge causing this. The manual tranny won't have the engine speed cushion to allow a little variable load input. Also, some power adders or a failing fuel pump will cause engine surge at certain RPM's and load. Sounds like the trailer is "pushing" the engine, and it isn't settling on a fuel/load balance.

If auto, try putting it into N as soon as the jerking starts. If a manual, depress the clutch. If it's engine load/compression related, it should stop the jerking. If it's chassis related (like frame beaming or U-joint angle related), unloading the drivetrain won't change it.

Does it have an engine brake (exhaust brake)? Could also be a cause.

[DickWells]

My son had the same problem with his Dodge a few years back. A manual 5 speed. Had tweaked IP and big exhaust and cold air, etc. Too late to call him back home tonight, so will wait till morning. DMax is probably right on with his assumptions. I just can't remember what my son did to smooth things up. Maybe something to do with the throttle return spring or something? I know that it was a simple solution in the end. Will check.
Good luck.
Dick Wells:)

[DickWells]

Sorry, forgot to call him in the morning! Regardless, seems like I can't be of help. Back then (96), Dodge put out a bulletin on a brake surge problem. My son can't remember all that was involved, but it did have something to do with throttle cable/linkage. The thing is, yours' seems to eminate from the truck brakes, as we understand your post. The kid does remember that there were issues with bad grounds in the brakeing systems that Dodge had put out data on. Even had cases whereby the turn signals would pulse the brakes for you!
Hope you've resolved your problem, and sorry I don't have anything for you.
Dick Wells:)

[DennisG01]

I can't comment on sliding hitches. But I can give a 1 1/2 cent worth opinion on a bumper or hitch ball. Working at a marina, I have the opportunity to tow many, many truck/trailer combinations, but always a ball mount. I have run into the same scenario you describe quite often. I don't know if the underlying cause in my case transfers to yours or not, but thought I'd offer. Bear with me a bit, I'll get to the point eventually...

In boats with surge brakes, it is sometimes the coupler (surge mechanism) itself. Some brands have more "play" in them then others. When you apply the brakes, this will appear as a "jolt" - and it is definitely more apparent at lower speeds. The other cause is sometimes a loose fitting ball mount. The same symptom appears if the ball mount doesn't fit into the receiver well.

OK, my point is that maybe there's something slightly loose? It only takes 1/4" of play/looseness to make a big jolt. In retrospect, the above comments sound better than mine, but I've already taken the time to write this so I don't want to delete it now! :):p Anyways, just a thought.