55.2-59 58 4 speed Transmission issue

[oldironpeddler]

I have a 1958 Apache Fleetside with a 4 speed Transmission. I recently swapped out the 6 cylinder for a OM617 Mercedes Diesel. Now that everything is put back together the transmission shaft continues to turn even when it is neutral. I cannot seem to figure out what the problem is. I have the top cover off and have manually shifted thru the gears, yet the only way I can get it to stop is holding in the clutch pedal. Other than that is seems to be in gear no matter what I do. Any Ideas how to solve this? Thanks.

[mongocanfly]

welcome..

are you referring to the trans output?...sounds like you got internal trans issues...are you sure the trans is going into neutral?...

[mr48chev]

The input shaft will turn unless the clutch is disengaged but a too tight pilot bushing could cause to want to turn then. There might be enough internal drag/friction in the trans to cause the tailshaft to spin a bit when running in neutral with no driveshaft.

That shouldn't be a real issue and cause the truck to move in neutral though.

[1project2many]

This could go several different ways so I think more clarification is needed. Is the driveshaft connected? Is the engine trying to drive the truck even if the trans is in neutral? Or is it a different problem?

[dsraven]

like said, just a little more info required.

driveshaft is installed and truck moves like it is in gear even though the trans is in neutral? this only stops happening if the clutch is pushed in.

or

there is no driveshaft installed yet and it is just the trans output shaft or yoke that is turning when in neutral? this can happen due to drag in the transmission bearings between the input and main shafts and the drag between the main shaft gear bearings and the main shaft, also, there can be a certain amount of resistance caused by the gear oil in the trans which can make the output shaft want to turn if there is no driveshaft attached. if you have ever had the opportunity to start a vehicle when it is -30 outside you will know that the vehicle can lurch forward when the clutch is released simply due to the resistance from the thickened gear oil not allowing the bearings to turn freely.


driveshaft installed, if the whole truck moves when in neutral but stops doing this when the clutch is pushed in, it appears that there could be an issue with the trans input shaft possibly dragging in the pocket bearing where it fits into the trans main shaft. this goes away when the clutch is pushed in because the trans input shaft isn't moving anymore. when the clutch is released the input shaft turns with the crankshaft, the bearing drags between the input and main shaft (output shaft) which is like the input shaft and main shaft are one piece. that makes the truck move like it is in gear even though there is no gear selected. when the clutch is pushed in the vehicle stops moving because the input shaft stops moving. another scenario for this could be that the input shaft and the crankshaft are not perfectly lined up with each other so the input shaft is "at an angle" or "off center" with the main shaft and that increases the drag between these two parts. if an adapter plate was used to adapt the Mercedes engine to the GM bell housing/trans then there is likely an alignment "step" in the procedure to ensure the bell housing and trans input shaft is actually running on center with the engine crankshaft. basically, a dial indicator is placed on the engine crankshaft (or flywheel with no clutch installed) and the indicator rod is set up to follow the inside of the circle on the bell housing where the trans bolts up. as the engine is turned slowly the indicator dial is watched and the adapter plate is adjusted as required until the dial indicator run out is at zero, or within the tolerances laid out by the adapter manufacturer or the trans manufacturer.
if the pilot bearing were seizing up or dragging it wouldn't matter if the clutch were pushed in or not, the input shaft would still try to turn with the engine because the pilot bearing would effectively be seized to the input shaft and want to keep the input shaft turning all the time. the tell for a seized pilot bearing is, if the truck is started when in neutral, the trans grinds going into gear, it's like the clutch isn't pushed in. if started in gear the truck would lurch ahead like the clutch isn't pushed in at all. those vehicles are also hard to shift to the next gear, once moving, unless the engine revs are matched to what they would be in the next gear.

in the off chance that you don't know how a manual trans works, there is an input shaft driven by the engine. there is a mainshaft that is attached to the driveshaft to the wheels. these two shafts have a bearing between them so they run true to each other but one does not directly drive the other. there is a countershaft below those which is driven by the input shaft at all times. there are gears which ride on bearings on the main shaft but are not splined to the shaft, so they float on the mainshaft. these gears are meshed with gears on the countershaft which are splined or cast into the countershaft. on the main shaft there are syncros that have their hubs splined to the main shaft but which don't mesh directly with any of the gears as long as the trans is in neutral. so, power comes in through the input shaft and turns the countershaft all the times, which in turn spins the gears on the mainshaft but those gears are not splined to the mainshaft so no power is transmitted to the main shaft (in neutral). when a gear is selected a shift fork pushes one of those syncros over to mesh with the gear normally freewheeling on the mainshaft. since the syncro is splined to the mainshaft this is the connection of power between the input and the main shaft (output shaft). since the synco hub is splined to the mainshaft and is now also meshed with a gear being turned by the countershaft there is a connection between the input shaft and the mainshaft so the main shaft turns at whatever ratio the meshed gears have between themselves.

maybe this will help. check the link and then read the part after that.

http://www.pearltrees.com/jordanmall...6/item97067019

green (input) turns red (countershaft), red turns blue (mainshaft gears), blue is just spinning on the gold shaft (main shaft or output shaft as some call it). purple (syncro) is splined to gold and when a gear is selected purple is pushed into blue to connect those parts. that means blue is now connected to the output and input shafts and turns gold at whatever ratio the gears are set up as.
make sense?
there is a pocket bearing in the green shaft and the gold shaft sits inside the end of the green shaft riding on/in that bearing, this keeps those two shafts nice and lined up. if that bearing is tight, starting to sieze or the two shafts are at different angles or the input shaft is being jammed back into the gold shaft, then the green shaft will try to turn the gold shaft even though no gear is selected. this is what sounds like your problem could be.
when you dig further you find the syncros have what looks like a modified brake drum and shoe set. when the fork pushes the syncro into the gear those shoes start to touch the drums attached or machined into the gears just before the lugs on the syncro start to touch the lugs on the gears. this slows down the gears so they don't grind when the lugs on the syncros start to mesh. if you try to shift too quickly the gears don't have time to slow down and the gears grind.

here is a blurb on bell housing alignment checking procedure

http://www.superchevy.com/how-to/tra...wear-and-tear/
hopefully that all helped, if not, sorry man. you aint getting that time back.

[dsraven]

did that make sense? scare anybody? sound like hooey?
a pic of the actual scenario or a link to the supplier of the adapter (assuming there is one) would be great.
question,
stock old trans that was a known "no problems" trans (shifted great before) or just a stock old trans with no actual history?

[mr48chev]

Thinking on it I have seen the tail shaft of a couple of rigs turn in neutral with the engine running. Usually when firing the engine up in the bare chassis before hooking up the driveshaft. The "we got it in place, lets fire it up" thing.

[1project2many]

Yep, that's what I was thinking also. But without more info, how to know??

[dsraven]

thats why I asked if the driveshaft was in place. if not it's a whole different kettle of fish.
a quick note back from the OP would be great.

[1project2many]

Well, at least three of us are on the same track. Prolly never know the real answer.

FWIW, dsraven, always impressive how much time you put into an answer. Hopefully some of the folks you are helping realize how long it can take to put together a good and accurate reply.

[dsraven]

1project,
thanks for noticing.
some guys appreciate the effort, some guys never get back to you, I guess because they figured it out. some will belittle you for trying to help them. I don't usually go back to that guy's thread. I figure if he's that smart then he can surely figure things out himself. lol.

[1project2many]

I don't usually go back to that guy's thread. I figure if he's that smart then he can surely figure things out himself. lol.