I'm having a problem with my Transmission. I have a 77 F250 4X4 with a New Process 435 four speed transmission. Two days ago I drove into town and when I would take off in 2nd and try to shift to 3rd I got the old grinding noise that makes you cringe and it wouldn't go into either 3rd or 4th. With every attempt I made to shift from second into 3rd or 4th it would not go into either gear. However, after several attempts I tried shifting from 2nd into 3rd at higher RPMs (approximately 3000 RPM) and it worked.

While the grind when shifting into 3rd or 4th was the worse it's ever been two days ago I've had it happen intermittently for the last few months, but it only happened on the first and sometimes second shift from 2nd to 3rd as I was leaving home then everything was fine.

First thing I thought of was the clutch, but the clutch is definitely disengaging. I say that because the clutch pedal has to be raised off the floor two thirds of the way before it starts to engage and if the truck is standing still the transmission shifts into any gear easily when the clutch is pushed in.

During the problem two days ago I even tried double clutching and that didn't work and that usually always works when there's a gear shifting problem.

The only other thing I can think of that might make a difference is that I'm not sure what year truck this transmission came out of. I'm pretty sure it came out of a 77, 78 or 79 F150 or F250 and the only reason I mention this is in case there were changes made to the NP 435 transmissions in different years.

Also, whereas I don't know a lot of history about this truck or its transmission, but I'm pretty sure the it has way over 100,000 miles on it.

In thinking about it, another thought I have is that the transmission is not fully disengaging 2nd when I try to shift into 3rd or 4th.

Has anyone ever had an experience with this kind of thing before or does anyone have any ideas about what could be causing the problem?

Thanks.

 

Sounds like the synchros are going out. But I would do a fluid flush before getting too deep into it and see if that takes care of it

 

Second the motion for bad synchros.....shouldn't take much effort if any any at all, to engage 3rd and 4th gears. I sometimes grind 3rd and 4th, but that's due to me trying to shift too fast. Can't speed shift these old toploaders...at least I can't. YRMV hehe (your results may vary)

 

Dang, replacing the Synchros sucks because it means transfer case and transmission removal. I was hoping it would have something to do with the Shifting Forks like excess wear or bent forks. In other words I was hoping it could be fixed enought by removing the Gearshift Housing.

The reason I say "fixed enough' is because I've had the truck about 10 years and have only put about 1,000 miles on it.

I think I'll try the flush thing first with fingers crossed. What's the best way to fluid flush and what type of fluid is best for the flush? I've never done one before.

Thanks for the replies.

 

I know whatchya mean......removing trans is a pain. Im pretty much in the same situation, but mine is still driveable. Got 255K on it and 2nd and 3rd are getting pretty noisy. As for flushing, not sure what to recommend outside of draining as much as you can and refilling with 80-90W. Shifting forks could be an answer. I recall hearing about the teflon pads on the ends of the forks. As they get wore down I guess they can cause problems.

 

From late 78 and newer NP 435s had a change in the shifter stick - they went from a solid nubbie (where it rides in the slot) to one with inner "O" rings held to the stick with a shear pin. Why?? Who knows!!! Pull yer stick by turning the stick locking hub thingie with some channel locks ccw. You'll have to push down and turn at the same time.
Could be that shear pin went south and it's flopping around when you shift from 2nd....

 

1958/81: The NP435 shift lever retainer cap (B8T-7220-D) has two notches, is retained by two pins that protrude from the shift tower.

The cap has to be pressed down by hand and held down while turning it to remove it.

People that are unaware, use pliers/channel locks to remove it, which TEARS OUT one or both of the notches. Not pleasant!

 

Thanks a bunch for the tips about removing the shifter and Bill, thanks for the part number as well.

After reading these posts about the shift lever that will be the first thing I'll screw with, but I still am interested in doing the flush. If anyone has more to add to this thread or if anyone knows the best method of flushing the trans (how to do and what type of flushing fluid to use) it will be greatly appreciated.

Thanks.