I just traded some work for a 1991 Cat 613c scraper. It's a really good running machine. The only issue is that it will shift into first and second gear and pull fine. When I shift it into third fourth or fifth the transmission doesn't engage. It shifts into sixth gear just fine and has plenty of power. It also goes into reverse with no issues. I checked the Trans oil and I don't see any metal. Any ideas of where to start would be appreciated.
Certainly for 3rd & 4th not working it would appear that #5 clutch might be bad. That's the common one for those two speeds. 5th gear is the one that puts the kybosh on it, because it uses a combination of the same clutches that are used for 1st and 6th. The complete table is below Reverse - #1 & #6 Neutral - #4 First - #2 & #6 Second - #3 & #6 Third - #2 & #5 Fourth - #3 & #5 Fifth - #2 & #4 Sixth - #3 & #4 I think a hydraulic test box on the transmission should be your next move.