8N Transmission Q

[Southernspeed]

What is the relationship between the input shaft and the mainshaft that it backs on to? Is the bearing between the two constantly turning or only when in neutral? Maybe at differing speeds depending on what gear you're in?

The reason I ask is, I'm just rebuilding the trans because it's a bit noisy (bearing growl type noise). I have bought all the bearings but the 'race' on the back of the input shaft gear is a bit pitted. Not terribly but it may be contributing to the noise. The bearing on the rear end of the mainshaft isn't too good either, so that could have been the noise. I'm reluctant to buy a new input shaft too (around $300) just to stop a slight noise. It's quite a small bearing so I'm assuming it's not doing a heavy job like the other 4 in there.

 

[John0829]

Short answer is yeah, it is constantly turning. When the clutch is engaged the input shaft spins at the same speed as the engine and since it is geared directly to the countershaft, the countershaft is constantly spinning as well. The speed at which the bearing your referring to is spinning is determined by what sliding gear on the main shaft is selected to mesh with the spinning countershaft. Bottom line is the speed at which it turns depends on what gear you are using.

This image should help you understand what I am talking about. It is of a 3 speed transmission but the function is still the same in the 4 speed.

 

[Southernspeed]

Short answer is yeah, it is constantly turning. When the clutch is engaged the input shaft spins at the same speed as the engine and since it is geared directly to the countershaft, the countershaft is constantly spinning as well. The speed at which the bearing your referring to is spinning is determined by what sliding gear on the main shaft is selected to mesh with the spinning countershaft. Bottom line is the speed at which it turns depends on what gear you are using.

This image should help you understand what I am talking about. It is of a 3 speed transmission but the function is still the same in the 4 speed.

That’s great, thank you. It’s pretty much what I figured but wasn’t certain.
I’m surprised the bearing is so much smaller than the others when it’s actually doing the same workload.
Thanks for the reply.

 

[John0829]

Believe it or not I have seen smaller needle bearings used in that same location in some Clark and Spicer 5 speeds used in trucks.