Posted by Keith in Washington [108.162.245.86] on Thursday, December 01, 2016 at 12:16:04 :
In Reply to: Re: NP420 Advice posted by Hal54M37 [173.245.52.128] on Thursday, December 01, 2016 at 11:25:06 :
I have a NP420 where I am popping out of second from time to time. It is caused by the shift fork not being located on the shift rail correctly so the poppet ball is not engaging. I have a very short throw into second and a very long throw into first.
With the engine running and the truck sitting still depress the clutch and shift from 1st to 2nd and back to first. When you are doing this feel for the resistance of the poppet balls when you go into to and out of each gear. If your shift fork is out of position or the poppet ball or its spring is broken or missing you will not feel any resistance going into or out of a gear. Also do the same for all shifts to get a good feel what is happening. In my case I have no resistance going into or out of 2nd gear as my shift fork has shifted on the shift rod and the poppet ball does not pop into the detent on the shift rod. I have pulled the transmission top and confirmed this. I will occasionally hit first gear while shifting to 3rd like you because there is no resistance out of 2nd and it is easy to go all the way to 1st gear and grind.
You can remove the transmission top without pulling the transmission from the truck. Go to your hardware store and buy two 5" bolts that are the same size as the bolts that attach the transmission to the bell housing. Cut off the heads. Now remove the drive line and PTO drive line from the tranny. Remove the floor pans. Remove top bolts that hold the transmission to the bell housing and replace with the new bolts that you bought. Now remove the lower bolts on the tranny. You should now be able to slide the transmission back a couple of inches so that the transmission cover will clear the lip on the fire wall. DO NOT PUSH THE CLUTCH IN ONCE YOU PULL THE TRANNY BACK!! Pull the transmission top and do any needed repairs. When your are done put the top back on and slide the tanny back into position (you may need to rotate the transmission gears to get the splines on the input shaft into the clutch disk).
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