It also could be the "trailing arms" They are known to break on some Monaco's.
Go here for a great thread about those trailing arms. Here is a snip from that thread -
Thank goodness for this FMCA forum and the posts about this problem. In September we were on the freeway near Atlanta when our 2006 Holiday Rambler Neptune started rocking from side to side and made sounds like something underneath up front was loose. We slowed down and made it to our campground and when I looked underneath I could find nothing loose up front. I went online and did a Google search and found this post. I went underneath again and found the left rear trailing arm was completely broken with a 1 inch gap between the U-bolts, and the left wheel was no longer centered in the wheelwell.
The FMCA post not only alerted me to the problem but gave me the source for stronger replacement arms. I called Scott Zimmer at Source Manufacturing and validated the information, so when I got to the repair shop I knew what needed to be done.
We had the trailing arms replaced at Apalachee RV Center in Auburn, GA, just outside Atlanta. I cannot say enough about how well we were treated there from the moment we arrived to the final delivery of the repaired coach. They are strictly an RV repair facility and they know what they're doing. This was the first time Apalachee had seen this particular problem on the Monaco RR4R chassis. I provided them with the information I had found and they contacted Scott Zimmer and found that the fastest way to get a pair of replacement arms was through Scott's POC in Melbourne, FL. Dan Kinard, the service manager, did all the coordination with Easy Care under our extended warranty. When the arms arrived their technician did a meticulous job of making the installation correct, and explained to me exactly what steps he was taking. I was very pleased with the whole experience at Apalachee RV Center. Dan Kinard even called me several days later to be sure I wasn't having any problems with the repair. That's first class service.
The coach is now handling better than it did when it was new as it rides over bumps much smoother.
Thanks again to FMCA for providing such a valuable service on their forums.
My advice is worth exactly what you paid for it.
