Hi all. I need some information on my 06 mastif. I have owned it since near new only 500 miles. I bought it in 2007 from Idaho and shipped it to New Zealand. I have had problems with 4th gear slipping most of the time I have owned it so it has only done just on 11000 miles. Seen as 4th is the main gear I tend to just ride my my v rod instead. So what causes the 4th to slip. The gear box is mint I have had it out and apart and back in and it was good for a couple of rides then slipped again. I just want to ride a hassle free bike. Please help
Because you have had this problem virtually from the start, your issue is most likely a clutch failure. If your problem was in the transmission it would be missing shifts , popping out of gear, audible grinding etc. You state that your slipping is in 4th but I'm fairly certain 5th and 6th would be even worse.
A maladjusted clutch will slip under load. Another possibility ( less likely) is that the original plates were installed incorrectly. Because you have 11,000 miles on a clutch that has been slipping, it should be replaced.
You could try adjusting it first . These files will help you.
www.dropbox.com