have a 772a that will not go in reverse in any gear but will drive forward just fine in all gears. Had a "mechanic" look at it and he said it is something in the gearbox. anyone have knowledge of this and or a particular failure mode?
Of all the various clutch packs and planetary brakes in the transmission, planetary brake “B3” is the one component only used in reverse. Service manual # TM1361 will have the transmission pressure test port locations. Best case scenario ,there is an issue with oil supply tube #13 shown in parts screenshot below.
thank you. do you have access to any repair manuals?
I do , but I don’t have that 77xA series grader manual.
I would check the linkages/cable for adjustment first. If it is like the 670A and I assume it is, there is a modulation system there so when you go from forward to reverse it takes a brief period to go into reverse. But I think pressure tests are the thing to do. Would be an engine out to get to the top of the transmission for repairs, but they are surprisingly modular to work on.