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rotorwrench · 05-31-2017, 01:01 PM

I agree that the transmission should not normally back out of gear during normal deceleration.

Deceleration causes the working faces of gears and synchro teeth to reverse pressure from the drive side of the tooth to the back side. Using the engine as a brake when going on a long down hill run will increase the scenario even more. This might require a new 2nd gear plus the blocker and synchronizer hub have to be in very good condition with near perfect mesh to hold up to that. Some play might still exist but it sounds like Mac minimized end play pretty well. Mac mentioned about linkage checks and that is important here. The teeth of the second gear locking fully into that synchro hub sleeve has to be as far as it can go to stay locked in. As I mentioned previously, gear teeth reverse their thrust on helical type gears during deceleration so something has to counter the thrust load change between second gear and the counter shaft cluster gear in that position. If the gear faces are worn a lot, this creates a bit more room for movement during this scenario. This added backlash can cause a bit more of bounce between the gears when a person decelerates.

I don't know of any checks that can be done for gear wear since there are no set dimensions that I am aware of (maybe someone else knows?). They would have to be measured over specific sized pins, just like splines are. I just look at condition of the gear teeth and use ones that are still in good condition with no chipped edges, spalling, scoring, or pitting if possible. It may be that they have a lot of wear but are still visibly in good condition I don't know.

I hope that the situation can be rectified.

05-31-2017, 01:01 PM	#58
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,457	Re: VanPelt 47 Tranny Rebuild I agree that the transmission should not normally back out of gear during normal deceleration. Deceleration causes the working faces of gears and synchro teeth to reverse pressure from the drive side of the tooth to the back side. Using the engine as a brake when going on a long down hill run will increase the scenario even more. This might require a new 2nd gear plus the blocker and synchronizer hub have to be in very good condition with near perfect mesh to hold up to that. Some play might still exist but it sounds like Mac minimized end play pretty well. Mac mentioned about linkage checks and that is important here. The teeth of the second gear locking fully into that synchro hub sleeve has to be as far as it can go to stay locked in. As I mentioned previously, gear teeth reverse their thrust on helical type gears during deceleration so something has to counter the thrust load change between second gear and the counter shaft cluster gear in that position. If the gear faces are worn a lot, this creates a bit more room for movement during this scenario. This added backlash can cause a bit more of bounce between the gears when a person decelerates. I don't know of any checks that can be done for gear wear since there are no set dimensions that I am aware of (maybe someone else knows?). They would have to be measured over specific sized pins, just like splines are. I just look at condition of the gear teeth and use ones that are still in good condition with no chipped edges, spalling, scoring, or pitting if possible. It may be that they have a lot of wear but are still visibly in good condition I don't know. I hope that the situation can be rectified.