Transmission/Clutch Noises?

[CSCameron]

Hey all,

I just swapped an M37 NP420 transmission into my 1955 Civilian Power Wagon. Swapped it for the original crash box tranny. Anyway, I have some noises that I didn't have before the swap. When I push the clutch in and start the truck (in neutral), everything is as it should be,that is, normal and quiet.

However, when I let the clutch out, again in neutral, I get some noise from the clutch and it noticeably drags on the engine idle rpms. Sounds like the clutch disc is spinning and dragging on something? If I push the clutch pedal in, the noise stops and the rpms rise. This is new, it did not make these noises before the swap.

Could it be the synchronizer's spinning creating the drag? Is the normal to the M37?

Oh, I test drove it around the block and it shifts fine, just like it should. Reverse works great too.

Ideas?

Thanks for your help.
Clark

[isaac_alaska]

My wm300 does something very similar, I get what sounds like an engine knock when the clutch is out in neutral, and noise goes away when I push the clutch in.

[Carter]

The pilot shaft bushing may be the source of the noise, to tight or worn and loose.

[RMS]

when I let the clutch out, again in neutral, I get some noise from the clutch and it noticeably drags on the engine idle rpms

that's bad. pull and inspect.

I would not suspect pilot bushing as the input shaft would be spinning at the same rpm as the crank with foot off clutch in neutral.

if the noise was constant I would be suspect of the bellhousing seal to flywheel.

but if your suffering from loss of rpm in neutral I would suspect trans bearings.... unless its below freezing and your running 90/140w or 400w gear oil in the box it should not drag the rpm down.

[MSeriesRebuild]

I think based on your short description of issues; the 420 has internal issues going on. Did you pull the top and check the internals of the 420 before installing it? If you did not; it is almost a certainty that you have installed a 420 that should have been totally rebuilt prior to installation. If my suspicions are in line with what you actually did, the next step is to pull the trans, disassemble completely, clean and inspect every part before you destroy it past the point of no return.

If your clutch was ok before the gearbox swap, it should be good now unless you damaged something during the swap. This can happen if you did not have alignment correct or had to forcefully push the transmission into position. The pilot bushing spins on the input shaft only when the clutch is released, you said all was quiet then, so it appears that is not the issue. If the drag is persistent when engine is idling, gearbox in neutral with clutch engaged; most likely issue is the main shaft and gears rotating on it have a rust buildup or have worn past allowable specs, which lets oil escape before it can do its job. In this case a seizure of components on the main shaft isn't far out. If rust has gotten to the point of causing this, it is most likely on the bearings as well which only multiplies the problem of drag. All speculation as I can not see or hear what you have in play, fact remains though, it is time to do some serious checking.

[CSCameron]

Thanks for all the replies!

Yes, I inspected the inside of the tranny (m37 B1) before install, all gears/shafts were shiney with no signs of rust. I could rotate the shafts by hand and did not feel any roughness. The shift tower is NOS (civilian) and was function tested at VPW before shipping. After installation it shifts fine into and out of all gears. The tranny came from Bob Stahl and he checked it out before shipping it. I was going to have him rebuild it for me but he thought it would be a waste of money. He looked it over and didn't have any concerns.

I did have issues when installing the transmission as it would not fully mate up with the bell housing, stopped hard with about 3/8ths of an inch gap. I never forced it. Eventually figured out that the front bearing cover flange on the M37 transmission was larger than than the bell housing hole by about 1/4". So, I swapped the bearing cover with the one from my crash box, bolted right up and the transmission slid right into place.

I still have slight drag on the clutch when I release it (in neutral), it begins to turn the jack (intermediate) shaft about a 1/16th of a turn and stops. Nothing else happens. It's like it takes out the slop in the gears and stops, the vehicle does NOT attempt to move. I can shift through all the gears fine. I disconnected the main drive shaft yesterday and ran it through all the gears. I have some grumbling/knocking in 3rd and 4th, it is loudest in 4th. No noises in 1st or 2nd or reverse, sounds good. I let the tranny heat up to temp and the drag on the clutch seemed to lessen by the end of the session but it's still there, however it didn't move the jack shaft at all (when in neutral).

The clutch worked fine with zero issues before the swap. I did not have any alignment issues when installing the transmisson.

Thanks again for all the replies. Let me know what you think with this new info. I'll try to shoot a video of what I'm seeing and hearing...

Clark

[MSeriesRebuild]

Not sure a video is worth much. I have respect for Bob Stahl, however simple fact is this. Anyone, myself included can pull the top and say it looks ok, realize though that you can only see so much at that point. If you install and all sounds and functions well, you may be good to go. BUT if you install and see, hear, or feel evidence of concern as obviously you have, there is an equal chance that with that quick initial look inside, something could have been missed. At this point realizing all is not visible from a quick look, I'll err on the side of caution every time. The gears on the main shaft spin directly on the shaft with no bushings or needle bearings. A very small amount of wear in gear bores or on the shaft surface is enough to cause drag which typically worsens as the trans warms up. Too much clearance between gear bore and shaft will be the cause of not enough oil retention to lubricate and cool as needed. You can't see or judge this by just looking into the unit. Trust me, it is better to go in search of whatever this drag is coming from now than it is to realize later after a seizure where it was coming from.

[CSCameron]

Thanks Charles. Yes, I think it needs to be rebuilt for peace of mind and safety's sake. I really didn't want to have to do it but it is the prudent thing to do.

Thanks for your expertise.

Clark

[MSeriesRebuild]

Thanks Charles. Yes, I think it needs to be rebuilt for peace of mind and safety's sake. I really didn't want to have to do it but it is the prudent thing to do.

Thanks for your expertise.

Clark

I'm not saying a rebuild is a must, simply do not know that. Checking it out thoroughly is a must in my opinion, especially since you mentioned noise in 3rd and 4th. A total rebuild is where I would go personally, but you may wish to do something less if the problem could be pin pointed and corrected by a lesser means.

I'll also say this, when you definitely locate what is going on, why, and determine whether it is an issue; I would suggest you get back in touch with Bob Stahl. If it were me you had purchased it from based on my description that I felt it was a good take-out, and it was discovered that problems did exist, I would appreciate the opportunity to take appropriate action to make it right, that is simply my opinion. I certainly can't speak for Bob on such an issue.