Transmission won't shift to third?

[ez8]

After taking my transmission out to put on a PTO for a winch, the transmission will not shift to third.

Here are some relevant data points:

1. Gear lash on third gear was measured at 0.003". Specs per the manual I read (Canadian version) read this should be set at 0.003 to 0.008.
2. On the stand, out of the truck, the transmission was able to shift through all gears and spin, no issue.
3. I removed the top of the transmission during install with a rag over it to prevent foreign matters from falling in. This may or may not have been effective.
4. In the truck, using the starter only and not hooked up to the transfer case, the engine will spin in neutral and the PTO will work forward and reverse, but if shifted into any gear (1, 2, 4, and R - remember it won't go into 3) the engine will not turn with the starter.

What is going on here? It's almost like something is binding, but the transmission looks clear based on simple visual inspection. Is my gear lash too tight?

[Elwood]

Sounds like two of the gear ratios are engaged at the same time, locking up the main shaft and countershaft. If so, it likely happened when reinstalling the top cover. If the fingers are not in the right place - especially the reverse - you'll have problems.

[ez8]

If that's the case, it should be a simple matter of removing the cover and pushing things around to make sure the cover is mated back up correctly, yes?

[Elwood]

Yes.

But re-reading your first post, I noticed that you were able to spin the transmission, which suggests that maybe two gear ratios are not permanently engaged. I think that perhaps one of the gear shift forks is not engaged in the matching sliding collar, i.e. one of the gear ratios is always engaged (perhaps 3rd?), and only when you engage one of the other ones is the transmission locked up.

Either way, I'm still thinking that you'll need to remove the top cover, ensure that all of the gears in the transmission are not engaged, and re-install the top cover, being careful to engage the forks and not shift anything in the trans.

I don't recall if you mentioned in a previous topic: is your transmission the early style NP88950 or the later NP420?

[ez8]

I'm not sure which transmission it is. The truck is a 63 and the stamp on the transmission is from October of 1962 if that tells you anything.

[Elwood]

Most likely a later NP420, which is the better transmission. The early 88950 model had an odd reverse gear fork arrangement, among other issues.

When you pull the top cover back off (moving the shift lever to neutral first), check to see if one of the gear sets is engaged. If so, that one will probably be the culprit.

[ez8]

I apologize, but how do I tell if one is engaged?

I'm not sure what I'm looking for.

[Elwood]

Here's a photo of my NP420 with the top cover removed. Reverse gear is at the upper left, the smallish gears sort of hiding in the bottom of the case. First and second gear is engaged by sliding the large spur (straight cut) gear on the left (to the left for 1st, to the right for 2nd), and 3rd and fourth are engaged by pushing the center disc of the synchronizer to the left (3rd) or right (4th, which is actually just direct drive).

NP420 trans.jpg (238.96 KiB) Viewed 1132 times

That large straight cut spur gear is why these transmissions make so much noise in reverse and in first gear. And the synchro on 3rd and 4th only is why engaging 2nd gear can be a bit tricky sometimes.

I believe that all of the gears as shown in the photo are in neutral. The reverse gear must be pushed to the back of the reverse gear shaft (all the way to the left in the photo). The large spur gear is definitely not in second (if it were, the small pointed dogs between the 1st spur gear and 2nd gear would not be visible). I think it's not engaged in first gear, but I can't see the countershaft to be certain. Anyway, it's very close to neutral. The 3rd/4th gear synchro is in the middle, so neither 3rd nor 4th is engaged.

To verify that all of the gears are disengaged, i.e. all are in neutral, leave the clutch released (this connects the input shaft of the transmission to the engine, and prevents the input shaft from turning). Then try to rotate the output shaft flange (you mentioned that your transfer case is not connected to the trans, right?) If the flange can be turned by hand, everything is in neutral. If not, one or more of the gear sets (each speed is a pair of permanently meshed gears, one on the mainshaft, the other on the countershaft) is engaged. Try centering the synchro disc and the large spur gear, and verify that the reverse gear cluster is all the way to the back, until the output shaft flange can be turned by hand.

[ez8]

That did it! Thank you for the visual aid. It's been fixed and now I'm ready to add oil and reconnect everything.

Thank you for all the help.

[ashyers]

Elwood,
Beautiful job!

Andy