NP435 Fourth Gear Issues
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4wd Low
Joined: Sep 2024
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NP435 Fourth Gear Issues
Hey everyone, just finished up my rebuild of my NP435 out of my 80’ Ranger.
Slight issue,
I was pretty careful and precise in the build but now i’m having issues with fourth gear.
Shifting into isn’t the issue but turning by hand results in a problem.
After some spinning, it gets gradually tougher until it “jams”
Reversing it slightly will then allow movement until the issue happens again. (spinning in opposite direction in 4th makes no issues, but opposite direction in 1,2 and3 not allowed?)
All other gears shift and spin fantastic. Any thoughts????
Slight issue,
I was pretty careful and precise in the build but now i’m having issues with fourth gear.
Shifting into isn’t the issue but turning by hand results in a problem.
After some spinning, it gets gradually tougher until it “jams”
Reversing it slightly will then allow movement until the issue happens again. (spinning in opposite direction in 4th makes no issues, but opposite direction in 1,2 and3 not allowed?)
All other gears shift and spin fantastic. Any thoughts????
Last edited by JadenBullNose; Sep 7, 2024 at 08:30 PM. Reason: Further Info
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From: Virginia
All I know is, 4th is not really a "gear". All it does is lock the input shaft to the output shaft. I am not great with manual transmissions, or automatics for that matter.
Where the input shaft engages the output shaft, isn't that where all those little needle rollers live that fall out all over the place when you take the transmission apart?
Where the input shaft engages the output shaft, isn't that where all those little needle rollers live that fall out all over the place when you take the transmission apart?
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4wd Low
Joined: Sep 2024
Posts: 11
Likes: 2
All I know is, 4th is not really a "gear". All it does is lock the input shaft to the output shaft. I am not great with manual transmissions, or automatics for that matter.
Where the input shaft engages the output shaft, isn't that where all those little needle rollers live that fall out all over the place when you take the transmission apart?
Where the input shaft engages the output shaft, isn't that where all those little needle rollers live that fall out all over the place when you take the transmission apart?
I believe so yeah. I was very precise in doing the build, didn’t rush it at all. Just weird to experience this
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From: Virginia
Thinking about it some more, these modern transmissions have helical gears to make them quiet. But that puts a thrust load on the shafts and pieces in the transmission, so they have all these specs and shims for shaft end play when you are putting it together. Maybe some of that needs to be re-checked. I think I read if the end play is too sloppy, it can cause it to pop out of gear when you goose the engine while in gear. I am thinking maybe having it too tight can cause it to bind up like you are experiencing.
Lead Driver
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If your 4-speed jumps out of 3rd when engine braking (or 2nd gear in a 3-speed), the input and output shaft bearings are probably worn and have too much axial play.
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4wd Low
Joined: Sep 2024
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From my limited experience, the teeth are beveled so as to pull the two shafts together when accelerating. Deceleration pushes them apart. I’m guessing the idea was you don’t want the transmission to jump out of gear when pulling out into traffic.
If your 4-speed jumps out of 3rd when engine braking (or 2nd gear in a 3-speed), the input and output shaft bearings are probably worn and have too much axial play.
If your 4-speed jumps out of 3rd when engine braking (or 2nd gear in a 3-speed), the input and output shaft bearings are probably worn and have too much axial play.
Rebuild kit came with them!
Lead Driver
Joined: Nov 2013
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Laughing right back if you’re convinced a component must be good because it’s new! I do not care to discuss how I learned otherwise. 
However, in your situation, I don’t think axial play in the bearings is an issue. If it popped out of gear decelerating in 3rd? Definitely a strong possibility in that situation.
But for binding in 4th gear when turned by hand? I don’t think the bearings are a likely cause. Have you tried turning the input shaft the other direction? Not sure what an improvement there would indicate. Mostly just thinking out loud, piecing the clues together.
However, in your situation, I don’t think axial play in the bearings is an issue. If it popped out of gear decelerating in 3rd? Definitely a strong possibility in that situation.
But for binding in 4th gear when turned by hand? I don’t think the bearings are a likely cause. Have you tried turning the input shaft the other direction? Not sure what an improvement there would indicate. Mostly just thinking out loud, piecing the clues together.
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4wd Low
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Laughing right back if you’re convinced a component must be good because it’s new! I do not care to discuss how I learned otherwise.
However, in your situation, I don’t think axial play in the bearings is an issue. If it popped out of gear decelerating in 3rd? Definitely a strong possibility in that situation.
But for binding in 4th gear when turned by hand? I don’t think the bearings are a likely cause. Have you tried turning the input shaft the other direction? Not sure what an improvement there would indicate. Mostly just thinking out loud, piecing the clues together.
However, in your situation, I don’t think axial play in the bearings is an issue. If it popped out of gear decelerating in 3rd? Definitely a strong possibility in that situation.
But for binding in 4th gear when turned by hand? I don’t think the bearings are a likely cause. Have you tried turning the input shaft the other direction? Not sure what an improvement there would indicate. Mostly just thinking out loud, piecing the clues together.
I have spun the input shaft in reverse on 4th and that DOESNT cause the same binding. Only in forwards motions which is why i’m confused.
Also in general, haven’t even driven the tranny yet at all. Still on the table being diagnosed and built. This is just the issue after spending time putting it all together
Last edited by JadenBullNose; Sep 10, 2024 at 11:16 PM. Reason: autocorrect
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We got to talking about other potential problems, but not actually the one at hand. Another thought is to remove the top cover and manually move the shift rings. Maybe you could see what’s happening with the shift tower removed.
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4wd Low
Joined: Sep 2024
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IIRC, the fore/aft movement (due to the bevel gears) is only an issue in 2nd and 3rd. So no, I don’t think a bearing problem is at work here. I blame Dave for leading us down that rabbit trail. We got to talking about other potential problems, but not actually the one at hand.
Do you have the nut (and any spacers) installed on the end of the output shaft? Or is this just a bare transmission? If not fully assembled, I’m wondering if the output shaft is able to walk fore/aft inside the bearing. Still not sure why that only affects 4th gear, but who knows?
Another thought is to remove the top cover and manually move the shift rings. Maybe you could see what’s happening with the shift tower
removed.
We got to talking about other potential problems, but not actually the one at hand.Do you have the nut (and any spacers) installed on the end of the output shaft? Or is this just a bare transmission? If not fully assembled, I’m wondering if the output shaft is able to walk fore/aft inside the bearing. Still not sure why that only affects 4th gear, but who knows?
Another thought is to remove the top cover and manually move the shift rings. Maybe you could see what’s happening with the shift tower
removed.
haha, all good, I do love the questioning, helps get rid of potential problems.
But okay, I have removed the top cover and did shifting by hand. At first, holding back third speed gear would allow for smooth movement in fourth, so that’s where i assumed syncro shimming was the problem (adding more to keep it back)
I cannot see any obvious signs, been holding or pushing on individual components to see what can free up the jamming when in 4th.
Did some inspecting, found small amount of back and forth play with the counter shaft, but no where near enough to move and catch a new gear?
Also, this is a bare transmission on the floor. Only thing hooked up is the tunnel / adapter to my NP208 transfer case (dry gasket on as well). But i like the idea, I could applied in or out pressure on the output to see if it can solve it
Last edited by JadenBullNose; Sep 11, 2024 at 07:47 AM.
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From: Angier, NC
The output is a slip shaft like some drive shafts like on my truck and dont remember any output play adjustment?
Only adjustment that I remember is on the input shaft and that is done with different gaskets between the front bearing and the front bearing retainer.
This would adjust the end play for the output shaft too I believe as it is a straight through shaft.
Dave ----
Only adjustment that I remember is on the input shaft and that is done with different gaskets between the front bearing and the front bearing retainer.
This would adjust the end play for the output shaft too I believe as it is a straight through shaft.
Dave ----
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From: Virginia
haha, all good, I do love the questioning, helps get rid of potential problems.
But okay, I have removed the top cover and did shifting by hand. At first, holding back third speed gear would allow for smooth movement in fourth, so that’s where i assumed syncro shimming was the problem (adding more to keep it back)
I cannot see any obvious signs, been holding or pushing on individual components to see what can free up the jamming when in 4th.
Did some inspecting, found small amount of back and forth play with the counter shaft, but no where near enough to move and catch a new gear?
Also, this is a bare transmission on the floor. Only thing hooked up is the tunnel / adapter to my NP208 transfer case (dry gasket on as well). But i like the idea, I could applied in or out pressure on the output to see if it can solve it
But okay, I have removed the top cover and did shifting by hand. At first, holding back third speed gear would allow for smooth movement in fourth, so that’s where i assumed syncro shimming was the problem (adding more to keep it back)
I cannot see any obvious signs, been holding or pushing on individual components to see what can free up the jamming when in 4th.
Did some inspecting, found small amount of back and forth play with the counter shaft, but no where near enough to move and catch a new gear?
Also, this is a bare transmission on the floor. Only thing hooked up is the tunnel / adapter to my NP208 transfer case (dry gasket on as well). But i like the idea, I could applied in or out pressure on the output to see if it can solve it
Thread Starter
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4wd Low
Joined: Sep 2024
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Do you have a book or rebuild manual for it? All that back and forth movement you are talking about is supposed to be measured and adjusted in various places. And you do have to assemble and then disassemble the transmission several times to get it right. I am assuming if you are a tranny guy and get good at it, you can make a guess and get it in spec without taking it apart too many times.
It’s 100% the 3rd gear / rear syncro ring moving foward. If i apply pressure to keep it back, 4th spins freely without jamming.
Thread Starter
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4wd Low
Joined: Sep 2024
Posts: 11
Likes: 2
IIRC, the fore/aft movement (due to the bevel gears) is only an issue in 2nd and 3rd. So no, I don’t think a bearing problem is at work here. I blame Dave for leading us down that rabbit trail. We got to talking about other potential problems, but not actually the one at hand.
Do you have the nut (and any spacers) installed on the end of the output shaft? Or is this just a bare transmission? If not fully assembled, I’m wondering if the output shaft is able to walk fore/aft inside the bearing. Still not sure why that only affects 4th gear, but who knows?
Another thought is to remove the top cover and manually move the shift rings. Maybe you could see what’s happening with the shift tower removed.
We got to talking about other potential problems, but not actually the one at hand.Do you have the nut (and any spacers) installed on the end of the output shaft? Or is this just a bare transmission? If not fully assembled, I’m wondering if the output shaft is able to walk fore/aft inside the bearing. Still not sure why that only affects 4th gear, but who knows?
Another thought is to remove the top cover and manually move the shift rings. Maybe you could see what’s happening with the shift tower removed.
It’s 100% the rear syncro ring / 3rd gear move forward and put pressure on the syncro rear blocking ring. (In the video i push the gear forward to duplicate what happens when spinning input, hoping it upload)
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Please let the record show I’m being uncharacteristically good and am refraining from making a cheap joke here, even though it would have been really, really funny.