Most of you who have been around the site for a couple of years remember my little episode with the drive shaft on the way to the Washington GTG. That was in the fall of 2009. I lost a u-joint and took out the whole drive shaft and both flanges on the transmission and rear axle. Cost of repairs $1,300.00 plus an eighty mile tow. Luckily the tow was covered by our road service.

Last Saturday all nine of us loaded in the coach for a 25 mile trip to Old MacDonald's Fish Camp for dinner. With Rusty riding shotgun, as soon as we pulled out onto I-20, I felt a vibration. I told Rusty, That feels awful familiar, I think I have a bad u-joint. Now remember, these u-joints are about 18 months old and have about 10,000 miles on them.

This is a picture of the u-joint mounted to the transmission



And the cups that were 180 degrees from each other mounted to the transmission.





Believe me, after a $1,300 repair, these joints have been greased before EVERY major trip., including the trip to Breaux Bridge. So what caused this premature failure. One possibility is a blocked passage in the u-joint not allowing enough grease to get to these trunnions.

After consulting with our resident expert, one other possibility was discussed. My coach is on a Gillig chassis has a Viscous Vibration Dampener mounted on the back of the transmission. The dampener was scarred and gouged when I lost the drive shaft but seem to still be okay to use.



When I inspected the dampener I found a gouge in a welded seam that look like it could have let the liquid be thrown out of the unit. Also I could shake the unit and hear the inner metal disc rattle. I visited the CAT dealer and the Allison dealer. Both had never seen a dampener mounted on the transmission. I called Gillig and was told that they installed them on SOME RV chassis but not all and never on a bus chassis. Also the part is no longer available and that they would have to get the manufacturer to build one at a cost of $805.00 plus tax and shipping. It could not be ready until August. After again talking to "our resident expert", I decided to replace the u-joints and install the drive shaft without the dampener. So far, two test drives of about 25 miles each and I can not feel any vibrations.

Wish me luck.

Nick

Did they say why they put them on some and not others?

I think I would get a few hundred miles on those U joints and then pull them out for a quick look see. We sure don't want anything to happen to you and Donna on the way to the Florida GTG.

quote:

Originally posted by bill h:
Did they say why they put them on some and not others?

Bill, according to Gillig it was an option that could be ordered by the coach manufacturer.

Nick

Additional comments. Might should be a different thread on the importance of price shopping when you need parts.

When I had to replace the u-joints in Washington, they were supplied by the drive shaft shop and were $56 and $63 for a total of $119. This time I went to NAPA and they were $67 and $73 for a total of $140. NAPA didn't have them in stock and they would have to come out of Atlanta. Since I was going to the CAT dealer to check on the dampener I told them I would check for u-joints there before they ordered them. U-joints at the CAT dealer were. $18 and $42 for a total of $60. Want to guess where I bought the u-joints.

Nick

Nick, I think the basic problems is that your drive shaft is so short and you have air suspension. This means that there will be a lot of action through the "U" joints. If the diff angle against the trans angle isn't just right, there will be a lot of stress placed on the short shaft.

I have 160K miles on my Breakaway now and I also grease every time I leave on a trip. This summer I will replace the "U" joint bearings as PM. I drive hard an fast but so far no issue but my drive shaft is probably 12" longer then yours.

Nick: Based on our Cobra engineering and custom driveshaft analysis I cqn tell you a few things about U Joints. In order for a U Joint to function properly the needle bearings must always have a preload. With the U Joint perfectly aligned, either in the vertical or horizontal plane the bearings have no load and will vibrate becasue of the clearances that exist. It takes only a short time for damage to begin. The recommended installation is to have between 3 and 5 degrees deflection when the coach is sitting level. When you are just running down the road the ride height and angles will normally be at rest and it is this time the joint comes under vibration. Failure can usually be traced to motor and transmission mount wear as the chassis was certainly engineered by Gillig to inlude the proper preload. On my coach I had the mounts completely replaced when we changed the joints ( they had not failed, yet) and I would at least have them checked against the Gillig Chassis manual specs.
nction