Grinding Gears

["David Macedonia" <david.macedonia@verizon.net>]

Hi All!

When I shift from 2nd to 3rd gear at speeds greater that 30mph (I don't know 
what the RPMs are at that point since my tach is still acting flaky), the 
gears tend to grind. Is this a synchro problem? The transmission was 
professionally rebuilt and currently has less than 300 miles on it. Any 
ideas? Operator error perhaps?

Thanks,

Dave

1966 MGB (Mark I, 3 synchro transmission)
Crofton, MD