Author Topic: Manual transmission, Lost 3rd and 4th Gears  (Read 850 times)

Offline Brian

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Manual transmission, Lost 3rd and 4th Gears
« on: February 10, 2018, 06:22:20 PM »
Hi guys, It's been a while since I've browsed RPA.

I just lost 3rd and 4th gears in my N50 xterra. 1/2, 5/6, and reverse all work fine. The gearbox has not displayed any problems up until this point. Clutch works normally.

The gear select simply won't push up or down into 3rd or 4th, as if the gates disappeared. It happened suddenly with no warning, no grinding, clunking, or rattling that I noticed. Went to slide it into 3rd while accelerating from a stop and there was no gate. I've applied some moderate force on the lever and it doesn't budge. It doesn't seem wise to force it with all my might. Same symptoms when moving, stopped, ect.

I'm thinking that the 3/4 fork or rail is bound up or stuck for some reason. I'm inclined to think some "E"clip or spring pin wiggled itself loose  ::). It's clear the transmission will have to be removed. It doesn't really seem to be a Nissan problem, just a manual gearbox in general problem.

Any insight?
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Offline 93Rubie

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #1 on: February 11, 2018, 07:05:15 PM »
When I first started reading this I was thinking automatic transmission. I've never seen a manual box fail in a Xterra or a Frontier (same driveline). How many miles?

FYI, Nissan dealer technician for about 5+ years total.

With no noises, I would be inclined to think a shift fork, pin, or other mechanism has failed. Gear failure or syncro failure is unlikely. I'll honest I don't even know if individual parts are available for these boxes. We don't see many and most are trouble free. I've done a couple clutches in them but that was all.

I can find out about individual parts in the AM.
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Offline Masher Manufacturing

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #2 on: February 11, 2018, 07:27:20 PM »
Congratulations, you have now found the GM patented skip shift feature. 

Before taking the trans out, see if you can remove the shift cover or even the shifter and have a look inside.  I don't know these trans specifically but I'd guess a roll pin on the fork or other end at the shifter worked out and bound the rail. 

For a used trans , have a look a look at car-part.com , they are in the $ 500 range around the PGH area.  Don't bother e mailing the salvage yards as most never reply so calling is best.





Offline 93Rubie

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #3 on: February 12, 2018, 06:35:19 PM »
Individual parts are available from Nissan
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Offline Brian

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #4 on: February 14, 2018, 08:42:23 PM »
More or less echoing my thoughts.

It's getting old driving through 80 traffic signals a day on 20 miles of rt-30 misery, heh heh.

I'm back on the road for about a month next week so the truck will just sit. By the time I return the weather should break and I can drive the M3. Then I'll pull it in the garage and see if I can fix it. If that doesn't work out then yes, the gearbox is readily available as salvage in the $400-$600 range.

It has 150k on it, and it would have needed the transmission removed to put a clutch in sooner or later regardless (Although it's holding strong). If memory serves I have some access to the shift rails from the top. I vaguely recall pouring gear oil in through the console instead of using a pump when I changed it several years back.

I've never actually disassembled a manual gearbox before so I'm kinda looking forward to that, but the counterpoint is that it's gotten awfully rusty under there so it might be an unpleasant time removing it from the block. It does have a lot more access room than the e36 I last yanked a transmission out of a few times.

Definitely an unusual problem. Modern manual boxes are usually all but bulletproof in unmodified cars. Something about fluky transmission problems. My last one was the flywheel/pressure plate dowel pin that dislodged itself in the M3.
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Offline Masher Manufacturing

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #5 on: February 15, 2018, 08:46:21 PM »
If our guy 93 could post a exploded view ( or link to ) of the trans it would be helpful.


Offline Brian

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #6 on: March 10, 2018, 06:15:28 PM »
I'm back from Phila and NYC. Got to work through two nor'easters :) Only one in an outdoor installation.

Pulled the shift lever assembly apart, pics on google drive. Nothing accessible from there. Looks like a single common rail with tabs inside the gearbox that engage the appropriate fork. All pretty standard I imagine. Since the rail is moving it must be the 3/4 fork itself that is jammed.

Whatever it is, it's REALLY stuck. I wedged a spud wrench down there and put some force on the rail. It doesn't wiggle or budge at all when it hits the jambed up limits. It moves a smidgen freely rearward (3rd) and not at all forward (4th). I think I'm just feeling the lash between the rail tab and the fork. The fork itself isn't budging. Rather incredible because at no point did I shove or force the shifter into a position before it got locked up. I suspect something is broken or cracked. If it was a dislodged roll pin I'd feel some degree of wiggle and play.

I think that makes it very probable that I'll need an entire transmission. I probably got lucky that it didn't end up stuck in one particular gear. I still plan to disassemble it to see if it can be fixed, and for fun.

Nissan did engineer a very robust shift linkage. Beats the heck out of the e36 BMW linkage arm arrangement.

Time to start ordering ancillary parts. The truck has needed some TLC for some time now so it'll be an opportunity to do a lot of maintenance.

https://drive.google.com/file/d/1xbMtAS1bEvly4E1mUTni_Fv8rXPSei8i/view?usp=sharing

https://drive.google.com/file/d/1vVssXayWvpg8Bq0nkU1vCrBM6nicy6g9/view?usp=sharing

https://drive.google.com/file/d/1mnfsJXo9BEbx0spyf5HgwEJeSokchV1U/view?usp=sharing
Neo: Why do my eyes hurt?
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Offline Masher Manufacturing

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #7 on: March 11, 2018, 09:57:25 AM »
Have a look farther up the trans, there may be an access cover. 

If we could find a exploded parts view that would really help things along. 

Offline Brian

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Re: Manual transmission, Lost 3rd and 4th Gears
« Reply #8 on: June 22, 2018, 02:09:38 PM »
Bringing some closure to this thread:

The truck has been repaired and back on the road for several months. I ended up driving it with missing gears to Niagara to pick up a used transmission. There were some closer in Frontier pickups but this one was out of the exact same xterra so I got it to avoid any (unlikely) differences between the transmissions. The new-old one works perfectly. Feels exactly the same as my old one.

While I was in there I put in a new clutch, and was delayed because I didn't realize the truck came with a dual mass flywheel until I had it apart so got stuck waiting several days for the DM flywheel to be shipped. The factory clutch/PP are Excedy and the DM flywheel LUK (Schaffer). Both were in acceptable condition. I bought LUK for all three parts and in the box was a LUK DM flywheel, and Excedy PP and disk. Exactly the same as the OEM parts.  I'd project that the disk would have run up to 225k and the DM flywheel was only mildly out of spec and I expect it would have lasted that long as well.


Special notes:

You definitely need to buy a Torx Plus bit to remove the flywheel/crankshaft bolts. The socket heads are very short. A regular torx would probably do it but it fits loosely and that's not somewhere to be messing with a stripped screw head.

I replaced both upstream O2 sensors and the crankshaft position sensor while I was down there. The new crankshaft position sensor caused a nasty hard miss (spark cut) when tapering off from high to lower throttle at a variety of RPMs. I reinstalled the old sensor and the problem went away. I can only guess that there was some sort of signal disagreement between the new crank and old cam position sensors confusing the computer. Never threw any fault codes.

I think the transmission is designed to come out without dropping the exhaust. There are reliefs in the bell housing that are probably there to clear the catalytic converters. However this required rotating the gearbox about 70deg while it's still engaged with the clutch. I opted to drop the exhaust because bench pressing and pirouetting a transmission alone on my back didn't seem wise.


I haven't gotten around to taking the gearbox apart. It's just taking up space in my garage right now. I'm reasonably confident something failed in the check/interlock plate for the 3/4 intermediate shift fork rod. The factory service manual is very thorough in it's transmission disassembly section.

It's rather complicated in there. the striker rod (the rod sticking out the tail that engages the shift lever) doesn't directly interface with the fork rods. The striker rod mates with intermediate fork rods that contain the check/interlock rods/balls in a plate at the rear of the box. The intermediate rod then pushes on a lever like a see-saw that pushes the actual fork rod.

This allowed Nissan to move the 3/4 synchro assembly down to the transfer shaft instead of the output shaft like a normal transmission. It also reverses the normal direction of gear engagement. 5th gear is the 1:1 instead of 4th in traditional gearboxes. It's all very complicated in there but works wonderfully, present malfunction notwithstanding.
Neo: Why do my eyes hurt?
Morpheus: You've never used them before.