98 nv3500

[79kcrew]

98 nv3500
I'm in the process of swapping the sm465 out of my 79 to an nv3500. I picked one up out of a 98 k1500 that allegedly worked fine, but when i spin the input shaft by hand the output shaft doesn't spin unless it's in 4th. It feels like it goes into the gears smooth and there's no nasty noises. Someone told me that it might need more centrifugal force to engage the gears. Is that true or do I need to tear into it and do a rebuild?

 

[b454rat]

If the gears don't turn then there is something wrong with it.

 

[RichLo]

Yep, manual transmissions are simple inside. Turn one side, the other will turn at whatever ratio is selected.

Are you shifting it with a full length shifter or just the little nub coming out of the top? You might not be getting it fully in gear. Or the top cover could be loose not letting it go fully into gear.

It would be very odd that somebody would hollow out the internals except 4th then sell it

Edit, you may have to spin it as your shifting to let the syncros slide into gear.

And if that SM465 is in good shape, you can probably sell that for more than you paid for the NV3500. I have a sm465 in the plow truck in my avatar and that trans takes a beating every winter and never gives me any problems (I've blown both front and rear differentials and I keep spare driveshafts ready because I blow u-joints that regularly)

 

[Erik the Awful]

Your input shaft and counter shaft are at the front of the transmission. They transmit power in every gear except 4th. In 4th gear, the input and output shaft are locked together for direct drive. If turning the input shaft fails to turn the output shaft in every gear except 4th, one of those two front gears is wiped clean. Whomever told you more centrifugal force is needed has never been inside a manual transmission. It might be rebuildable, or it might just be a parts donor.

Note that if you replace either the input shaft or counter shaft with parts from another used transmission, it will probably howl for your first few thousand miles, but it should eventually quiet down.

 

[79kcrew]

Your input shaft and counter shaft are at the front of the transmission. They transmit power in every gear except 4th. In 4th gear, the input and output shaft are locked together for direct drive. If turning the input shaft fails to turn the output shaft in every gear except 4th, one of those two front gears is wiped clean. Whomever told you more centrifugal force is needed has never been inside a manual transmission. It might be rebuildable, or it might just be a parts donor.

Note that if you replace either the input shaft or counter shaft with parts from another used transmission, it will probably howl for your first few thousand miles, but it should eventually quiet down.

Would gummed up syncros or it being completely empty on fluid perhaps be a cause?

 

[Erik the Awful]

There are no synchros on the input end of the counter shaft. If the input shaft is turning, it's supposed to turn as well. Low fluid would burn up a bearing, not shear teeth. Either something came loose and locked up the countershaft, or they had a habit of clutch dumping it and wiped it clean. You're going to have to take it apart to see.