Replacing NAA PTO shaft

[ClarkR]

Trying to replace the PTO shaft in my NAA with one bought on
this site. When I push it on to seat the last 1/4 inch it engages
and you can?t disengage with the side lever. I have removed
and reinstalled several times and removed the side plate.
When comparing the shafts the length is identical but there
are almost 1/2 more splines in length on the the internal part
of the new shaft. Is there an adjustment or something? I?m
stumped. Help. Thanks

 

[ClarkR]

Apparently the additional spline length is the problem. Put the old shaft back in and it engages and disengages fine. Is there an adjustment or so I need to look for another new shaft?

 

[TheOldHokie]

(quoted from post at 15:56:42 10/27/19) Apparently the additional spline length is the problem. Put the old shaft back in and it engages and disengages fine. Is there an adjustment or so I need to look for another new shaft?

I can't see how longer splines would cause that problem. Shorter might but not longer. I suspect something else is amiss.

TOH

 

[ClarkR]

I?m at a loss. Put the old shaft back in and it engages and
disengages like it?s supposed to.

 

[shaun wallace]

NAA shaft is different than 100 series. Bet sent a shaft for 6-800.

 

[ClarkR]

Possible I suppose, but the box was labeled for NAA. The original has about 3 inches of splines on the internal part of the shaft and the replacement has about 3.5 inches. Length is the same, etc.

 

[TheOldHokie]

(quoted from post at 19:00:13 10/27/19) Possible I suppose, but the box was labeled for NAA. The original has about 3 inches of splines on the internal part of the shaft and the replacement has about 3.5 inches. Length is the same, etc.

PTO shifter slides rearward on the splines to disengage. Longer splines will not impede that movement. If you are sure it is the correct application I'd inspect the splines closely for signs of damage/twist/burrs etc.

TOH

 

[ClarkR]

I just examined the splines on the new shaft and they are
straight with no burrs. Makes no sense that it forces the PTO
to engage the last 1/4 inch but the old shaft does not. If you
put the new shaft all the way in you can then make it travel
the 1/4 inch back out the back of the tractor (bolts not in)
when you place the side lever in the disengage position. PTO shifter definitely binding with the splines for that last 1/4 inch.

 

[TheOldHokie]

(quoted from post at 09:23:02 10/28/19) I just examined the splines on the new shaft and they are
straight with no burrs. Makes no sense that it forces the PTO
to engage the last 1/4 inch but the old shaft does not. If you
put the new shaft all the way in you can then make it travel
the 1/4 inch back out the back of the tractor (bolts not in)
when you place the side lever in the disengage position. PTO shifter definitely binding with the splines for that last 1/4 inch.

Depends on what you mean by "makes no sense"". To me that would seem to strongly indicate there is a problem with the fit between the splines on the shifter collar and the shaft. I take it you have put the bolts in and you cannot force the collar to slide back using the shifter lever. Short of splitting thhe tractor and removing the shifter collar so you can test/examine the fit on the bench I don't have much more to offer in the way of help.

TOH

 

[ClarkR]

Yes. The shifter lever will move the internal shifter collar back and forth. It will engage and disengage on the old shaft with no problem. When in disengage you can turn the
external pto shaft. When in engage you cannot (unless you press the clutch). When you insert the new shaft the lever will still move the shifter collar but will only disengage if
the shaft is still out of the tractor about 1/4 inch, not seated against the tractor. When you seat against the tractor that last 1/4 inch if physically forces the shifter lever
into engage and will not go back into disengage (as long as the shaft is all the way in seated against the back of the tractor). If I pull the new shaft, insert the old shaft, the
lever engages and disengages (checked by ability to move or not move external pto shaft). Obviously something is mechanically binding. All I meant when I said that it makes no
sense is that the shafts are the same length and the only difference is the length of the internal splines. Based on what you're saying that shouldn't make any difference.

 

[Jim L WA]

Interesting problem. I'm suspecting the splines on the shift collar. Why are you replacing the shaft in the first place?

 

[ClarkR]

Thanks Jim. Since I haven't had one of these apart, please excuse my ignorance here. If it's the splines on the shift collar why would it engage and disengage fine on the old shaft, but not the new one? The tractor has a ton of hours on it and the original small shaft had some wear where the original owner used an adapter that didn't fit tight and had side to side play. It snapped/twisted off at that point while I was brush hogging over very rough ground (North Florida hog wallers in a field). When it broke, the shaft continued to spin coming out of the tractor until I disengaged using the lever. The old shaft came out without a problem and the new one went in without a problem until that last 1/4 - 3/8 inch. After not being able to get the new shaft to seat and engage/disengage properly yesterday I reinstalled the old shaft and it went right in and engaged and disengaged as it should. There's no obvious wear or other marring on the internal splines of the old shaft and as noted in the post, the only difference in the two appears to be that the new shaft has 1/2 longer splines on the internal part of the shaft.

 

[HFJ]

are u absolutely sure u haven't missed any small imperfection in the splines of the new shaft? if age hasn't fogged my brain too badly, i'm thinking at ~ three quarters of an inch in from the (rearward) end of the splines.

 

[TheOldHokie]

(quoted from post at 15:25:08 10/28/19) Thanks Jim. Since I haven't had one of these apart, please excuse my ignorance here. If it's the splines on the shift collar why would it engage and disengage fine on the old shaft, but not the new one? The tractor has a ton of hours on it and the original small shaft had some wear where the original owner used an adapter that didn't fit tight and had side to side play. It snapped/twisted off at that point while I was brush hogging over very rough ground (North Florida hog wallers in a field). When it broke, the shaft continued to spin coming out of the tractor until I disengaged using the lever. The old shaft came out without a problem and the new one went in without a problem until that last 1/4 - 3/8 inch. After not being able to get the new shaft to seat and engage/disengage properly yesterday I reinstalled the old shaft and it went right in and engaged and disengaged as it should. There's no obvious wear or other marring on the internal splines of the old shaft and as noted in the post, the only difference in the two appears to be that the new shaft has 1/2 longer splines on the internal part of the shaft.

Focusing on the extra spline length is fruitless. Too long is fine. Too short may not be. The collar wont slide far enough on the new splines to disengage so something in the "slide area" seems to be holding it up. Either exchange the part or pull the assembly apart for better inspection of the fit between the splines. I can easily invision splines that are cut too shallow at the end of travel and bind the collar. Repetitive debate is not going to identify the cause.

TOH

 

[ClarkR]

Thanks for your help.

 

[Tall T]

Anything useful here?

If it is anything like the floating axles in my 3/4 ton truck, the inner end of each axle needs to be elevated slightly for the last bit of insertion by tipping the 8-bolt axle flange outward at the top to lift the differential end of the axle.

Could it be that your shaft has to be bolted in before it positions itself correctly at the shifter end?

But never having done a PTO, I don't know if the final bolting in has any bearing on how true the PTO shaft lays.