The Stovebolt Site Forums The Shop Area Driveline SM420 doesnt always want to go into gear

Question for ya all!
Every now and then, I cannot get trans into a gear without really forcing it. ( SM420 ) Happens very rarely but its usually when I'm at a light with cars behind, and leaves me struggling. She would be shifting perfectly fine, up and down. I can even float gears both ways, no grinding whatso ever! Then It happens, with no warning. Clutch is depressed, and I cant engage any gear. No grinding, nothing. I usually try all 4 forward and reverse. Sometimes it will slip in and others, well, I know it's not nice, But I force her, Into gear that is:) . Clutch is well adjusted and newer, sort of a loss here. Also will happen on a downshift. I did skim through 46 Sparkys post, his has a similar problem, but mine does operate normally 99.9% of the time.

I would appreciate any ideas on what is going on in there.
Thanks
Jim

If the clutch were not adjusted and this problem existed you'd get grinding while trying to find first or reverse, they have no synchronizes. Without grinding then tells you the clutch is fully disengaged, and likely adjusted properly.

If you can't get it in gear from a stand still with clutch depressed could be because nothing is turning and the gears are meeting tooth to tooth, won't go in gear. but if your issue is still there when rolling or immediately after pushing the clutch in this isn't the issue.

Have you eliminated the above?

Do you have oil in the trans? Usually plain old not fancy 80W90 gear oil is OK.

Hopefully it has 90 wt gear oil in her. If so, then remove the 8 bolts off the top loader and take it off for inspection. Should be able to move (actuate) the shift gates on the 1-2. and 3-4. Then if that checks out take a look see into the gear box for any carnage.
I recently saw a guy that had a trans that would act up like this when it got warm and it was really low on 90 wt. and the shift sliders turned blue because of heat.

Just saw Grigg's post too, so he mentioned fluid level too, a bad seal in the torque tube can drain a transmissions 90 weight into the rear axle housing starving the transmission for fluid at the same time over filling the differential.

Thanks guys!
It started happening last year. No oil leaks, fluid level is good. I used the spec’d oil from the info I found in the forums. I did move the clutch adjustment high and low with same results. Put it back to where it should be for proper travel. Not a huge deal, but was reading 46sparky’s post and it reminded me of mine. Next time we’re together, maybe someone can duplicate the issue and come up with a solution.
Take care!
Jim

Jim,

Do you put the truck in neutral while stopped at a light?

Mike B

Mike, almost always. Left leg doesn’t always work too good.

Follow up question!
Problem is getting worse! Took it (her) to a friends farm for them to use in an old fashioned farm wedding. Enough with the back story. Trans was really giving me a hard time. Not wanting to go into gear, had to really slam it in, from neutral position. Once moving it will shift, no grinding, slides right in. Also when starting the truck will jump as if it’s in gear. A friend tried it, he’s a mechanic that restores old junk, I mean Gems, he said it’s probally the shaft bushing that is probably scored, and pinching the shaft, not allowing free play. Any thoughts on this? He said to use a roller bushing instead of the brass!
What do you all think?
Thanks
Jim

Its possible you are getting oil or trans. grease on the linings causing them to stick to the flywheel or pressure plate. I'm not sure what your friend mechanic was referring to. Maybe the pilot brg. They come in bushing or roller brg. A badly worn pilot bushing or brg. could cause this problem. Check engine mounts also. If the engine is shifting around it effects the linkage. The rear mounts on that model are pretty flimsy.

Yes he was referring to the pilot bearing. There’s no oil nor grease on the linings. Everything is 4 years old, from trans up. Guess it’s time to pull the trans and have a look at the bushing
Thanks,
Jim

When you pull the transmission be sure to drop the pressure plate and clutch disc. Inspect the pressure plate for burnt spots. If you find any get the plate resurfaced by someone who knows what they are doing or replace it. 🛠