Nasty shudder decelerating 15-10 mph

[Royk]

Back in December while visiting out of state, my 06 megacab started to shudder on deceleration when coming to a stop or making a slow turn onto a side street. Then all the sudden it stopped happening for a few months, until now again. It starts at 15 mph and stops at 10 mph. It doesn't matter if it is in gear or not or whether my foot is on the brake or not. It never shudders at any speed during acceleration. I did a visual under the truck and the only thing I found was that there seems to be a lot of slop in the carrier bearing, like half an inch. I can't imagine that is normal. Other than this shuddering problem the truck runs great. The truck has 129,000 miles on it. Any ideas?

Roy

 

[Bob V]

Have any of the u joints been replaced? If not I would bet the front axle and the rear driveline joints are bad

 

[Prairie Dog]

I had that exact symptom one time in my 93. It was a badly out of balance front tire.
I couldn't believe a tire could case such an imbalance at so low a speed and while decelerating.

 

[Royk]

Tires are only a few weeks old and freshly balanced. And the truck did it before the new tires.

 

[seafish]

I would also suspect and check the ujoints.

Alot of times, however, you cannot actually feel the excessive play of the bad joint unless the truck is on jack stands and the transmission is in neutral...even then you MAY have to hammer or pry on the a little to see or feel the play. Actually, the easiset way to check for a bad ujoint is to drive the truck for awhile and then use an infrared thermometer to check the temp of each and every joint...the bad one will show up with a substantially elevated temperature...you can even check each cap of each ujoint this way.

If you do not yet have an infrared thermometer, know that they are VERY useful to keep in the truck, particularly if you tow a trailer, to check anything from wheel bearing temps, ujoint temps, transmission temps and diff temps on the truck, as well as wheel bearing/brake rotor temps on a towed trailer.
Regular use of one when you gas up, will give you an idea of normal operating temps, and anything more then 30* outside that range would generally be indicative of a problem developing.

All that being said, the play in your carrier bearing does sound excessive, unless it is only in the rubber bushing, although that can also tear and fail to perform properly.

 

[Bob V]

The 3rd gen u joints tend to seize and not get loose. That is what causes the vibration. After a long drive safely crawl under the truck and feel the u joint caps. If any are wormer than the others that is the bad joint. The front joints will show as as a hop when turning. All mine in my 2005 where bad by 50,000 miles. .