The Stovebolt Site Forums The Shop Area Engine Shop SM420 Issues

Today I changed the clutch, pressure plate, TO bearing, and pilot bushing on my '53 3600. I then adjusted the clutch pedal linkage and put the SM420 in.

Mind you, the truck hasn't been on the road in 35 years. I removed the side cover and looked around and didn't find any metal shavings. Just a bit of gunky oil on the bottom. I drained the old oil out of the transmission and put 3 quarts of new 80w-90 gear oil in it.

When I went to drive it after installing the transmission, I ran into a problem. I was able to put it into 2nd and drive it in the driveway. I then put it into reverse and reversed up the driveway. When I went to put into 2nd again, I couldn't get it into gear. The gear lever moves freely around in neutral, but I can't find any gears. I tried readjusting the clutch pedal to no avail. I can watch the throwout working the pressure plate, but I still can't get it into gear.

Is there anything I could have screwed up in the clutch install that could cause this? Or is this a transmission issue?

Thanks

Did you check the free clutch pedal travel/play after the transmission was installed?

Clutch disc backwards? That's about the only thing I can think of. Although I have had a disc stick to the flywheel making it impossible to shift.

If the clutch isn't adjusted properly, then it might not release. It is also possible that damage has been done to the pressure plate by improper adjustment of the clutch.

Did you remove a pivot bolt about halfway down the driver's side of the transmission? It's there to retain the shift linkage that moves the big bull gear for Granny gear. If the linkage falls off that pivot bolt, there will be definite shifting issues. Pull the top cover off the transmission, and make sure all the shifting forks are engaged in the proper slots in the synchronizers. Reposition the bull gear shifter if it's out of place. Unless the gears are grinding as you try to move the shifter with the clutch depressed, you don't have a problem with your new clutch.
Jerry

The clutch disc had "flywheel side" stamped on it so I know I had it the right way.


Hmm, I didn't remove that bolt. I guess I will the top cover and have a look around.


Yea, I checked it before and after the transmission was installed.

I would pull the top cover off and check the forks. I have seen problems with the forks in the past with the sm 420 and the sm 465. Check the operation of the forks real well when you have the cover off. I bet something is locked.

Try shifting it with the engine shut off. If you can shift without the engine running but it won't go into gear with it running then you have a clutch problem.

I can't get it into gear regardless of whether or not the engine is running.

Does anyone have a good picture set of the inside of an SM420? I know the shop manual has some, but I prefer larger color pictures over tiny B/W ones any day.

Pull the gearshift lever out & look down the hole & make sure the slots in the rails are all lined up. If not take a big screw driver & shift the one out of line back into neutral.

Oops, I forgot to mention something. I couldn't get into first gear, even when the transmission would shift. I'm guessing its the same problem thats causing me to be stuck in neutral.

is the shifter original to the transmission? maybe the shifter has disengaged from the shifting forks as Hotrodlincoln suggests.

The shifter is original to the transmission.

It really confuses me how I couldn't get into first gear, than after shifting into reverse twice and second once I suddenly lose all the gears.

when you dropped the transmission, did you pull the shifter? I have on a couple of times been able to set the shifter in wrong, and not be able to go through the gears.

Disconnect the driveshaft. Pull the shifter. Play around with the shifter stuff in the tranny till you can turn the back of the transmission, indicating you are in neutral. Replace the shifter ball and try to go through the gears again. This should take all of 10 minutes to do.

I didn't pull the shifter. I wanted to, but I couldn't get it off. I wish it was something easy like putting the shifter back in wrong

Still sounds like shifter forks are off. Pull the shifter. Push down on the cup and turn clockwise about 90 degrees. The shifter should pop out.

bigbadswingdaddy that should be Counterclockwise and less than a 1/4 turn will do it. If after it turns it doesn't pop up on its own, tap around it like you are trying to get a jar lid off.

I'll try that. What would cause the shift forks to get outa whack? As far as I know the truck was driving 35 years ago when it was parked.

It could be too much force in trying to get it into first gear or not coming completely out of one of the gears you had it in. A transmission that has been laying around unused for 35 years should be inspected thoroughly before use especially in the rusty climate of the northeast. Good transmissions like to be used and will rust up inside if they aren't treated properly.

Yup! I feel sheepish.

A lot of times the trucks are parked because they stopped working. It is possible that the shift fork inside the transmission has also lost an arm. No worries as the sm420 is still relatively easy to come by.

Can you reach in and spin the T.O. bearing by hand? (obviously with the engine off.) Floor shifter lever comes off by pushing down and twisting the cap. Pull the cover plate. There should be a lever inside on the right that fits into a corresponding slot in the cover. Also the forks should be on the corresponding grooves on the two gears. You migh try moving those around by hand, then replace the cover. If you have it lined up correctly, the bolt holes will be lined up. Install a couple of bolts and try going thru the gears without start up with the clutch depressed. You shoud be able to go thru all forward gears and reverse.

Alright, I was able to get the shift lever off. I looked down inside and didn't see anything broken. I guess I will have to pull the top and look into it more closely. Is there anything that will fall out when I pull the top? Or is it as simple as pulling the bolts and lifting it up?

For the curious, here's a couple pictures with the shifter removed:

http://i47.tinypic.com/333g2nl.jpg
http://i45.tinypic.com/98vree.jpg

before pulling the top cover, see if you can move those sliders around and get the transmission into neutral.

I see rust. I would pull it off and do some housework.

As far as I'm aware, the transmission is stuck in neutral. Revving the engine doesn't move the truck, and pushing the truck with the engine off doesn't spin the engine.

Ferndale53; I agree the transmission is likely stuck in neutral however something prevents the shifter from putting it into a gear. This is most likely caused because one of the shift forks not aligned in the neutral position. The rust I see in your pictures could easily have caused this problem. When the shifter is in does it move door to door direction smoothly or do you feel resistance?

I'm going to try to slide the sliders around and see what happens, but most likely I'll pull the top. What exactly is connected to the top? Am I going to have bits falling off, or what should I expect? The shop manual is a bit vague there.

it's just a cover

I took the cover off, there was a bit of rust, but nothing bad. I put the cover back on, and I still can't get into gear.

You mentioned sliding the sliders, I could only find one piece that slid in the cover. Are there more than 1?

PROGRESS! I've got gears R, 3, 4.

good! Now keep working those 1 and 2 and maybe you will get them back. I think you should pull the side cover and drain plug and flush it out with something, I would use gas and install all new and clean 90w gear oil.

I already drained the gear oil and flushed it with new gear oil. Could there be an adjustment or something keeping me from getting into 1/2 or should I just keep trying. The other gears all go in nice and smooth .

Hard to say from 2000 miles away, just keep studying it and working it. good luck.

How much should the smaller of the two forks move on the rod? Mines only moves about a half inch in either direction, which seems a bit short.

I think it's time to remove the top transmission cover again. On the underside of the cover you will see 3 "sliders" (known as shifter shafts). I think the first and second gear shifter shaft is siezed (it's the middle one). Holding the cover, try to move the shift lever (assuming it's still attached) in 3rd and fourth gears positions watching the movement of the 3rd and 4th speed shifter shaft. That's how the first and second gear shifter shaft should move. Try tunking (tapping with a hammer) on the middle shifter shaft to see if it will move. If it doesn't move it's siezed and your task will be soaking it with PB blaster or the like until such time it starts to move after a few taps back and forth. BE SURE your fingers are not in the path of these shifting shafts when you are trying to move them. Yeah! I'm real sure of that.

Good luck.

The middle shaft moves, but is stiff. It takes a good pull to get it to move. Your right about watching your fingers! How easy should it be to move?

Do you have access to another SM-420? Maybe a parts trans? If so swap the top cover, making sure the forks are the same. Sounds like the problem is in the top cover on one of the shift rails. I work part time with my wifes uncle at his garage. He works mainly on older medium duty grain trucks and I have seen this issue before. Usually he will swap the cover out and repair the old cover at a later date. I have seen both the Sm-420 and SM-465 get stuck like this. The trucks usually show up on a hook. I am not sure how he fixes them but I think that there is a spring and ball type detent that gets stuck on the shaft that supports the forks. Sometimes the fork will get bent and the shaft gets damaged from forcing the truck in or out of gear. Good luck. Patience endureth all things.

darn, that doesn't sound good. I'm going to keep looking at it tomorrow, but I'm not going to give up that easily.

In this part of the country these trucks / transmissions went to the junkyard years ago after rotting out, not many extra transmissions around here .

They used them in late sixties and early seventies grain trucks too, still fairly plentiful in midwest. You can probably fix your old top assembly. Try a penetrant named AeroKroil on the shift fork shafts. Its the best I have ever used. I will talk to my wifes uncle this weekend as I got some work to do for him. I would pester him tonight but he just got home from the hospital from getting two stents put in and being 81 years old I image it set him back a bit.

Well, I don't think its the top cover. I put the cover on the bench and could get into each gear easily. It seems the gears for 1/2 aren't moving on the shaft in the transmission. With the cover on, I can fee where the gate is for the gears, but I can't get it to go in.