No 5th GEAR, Selctor Gear to Shaft Stripped (w Fix)

[eszut]

Last week the wife's 02 Jetta wagon ( 237K) miles would shift into 5th gear but the car responded like it was in neutral. Removed 5th gear cover to find that the 5th gear Selector gear to transmission shaft was stripped. So 5th gear was engaging, but was not able to transmit the shaft rotation to the the Selector gear and 5th gear set.


I was able to source a replacement selector gear from a Junkyard transmission (marked in yellow) and there was enough of the shaft splines left to engage with the replacemnet selector gear AND as an added measure I drilled (1/8 carbide bit) and pinned the Selector gear to the shaft 180 degrees apart. Cut off excess drill bit with dremel tool. Selector gear bolt and washer should retain the cut off drill bits in the shaft and gear.
5th gear is working again (will report back mileage if/when fails). Replacement 02J gearbox purchased and standing by.
The big Question I have is what or Why would cause the interference fit (needed a gear puller to remove the junk yard selector gear)Shaft splines to Selector Gear splines to wear out. (Please don't say gear oil) As I have replaced gear oil with VW gear oil (G 070726 A2) at each 100K and when I pulled the 5th gear cover gear oil drained out not to mention NO room for gear oil in the splines when pressed together.
I suspect that the spline wear occurs not when 5th gear is engaged and under a load but when the car is being operated in the other gears 1-4 and the 5th gear is along for the ride not under a load and it starts a slight vibration and begins wear the gears more and more over time.
This thought makes me think one might want to remove cover and inspect shaft to selector gear splines for "play" and depending on severity apply "Loctite" retaining compound to eliminate the "Play" in the splines and OR drill and Pin.
THOUGHTS????
Please also note I did a Auto to Manual swap approximately 100K miles ago and do not know the mileage previously on the 02J prior to installation.

 

[BobnOH]

Nice thread! Excellent use of pics.

 

[KrashDH]

Nice work. Out of curiosity when you pinned with the bits were they pressed in and did you use any green (620 locktite)? That stuff is made for bearing fits and would ensure that the pins would never go anywhere or have the chance of wearing the parent material down.

 

[eszut]

Did not use any loctite on the pins had to tap them in with Mallet but it would be worth trying. Would have liked to apply it to the splines and pins.

 

[PakProtector]

I would have to bet on the spline wear caused by fretting. Near no relative motion required, and likely due to low RPM lugging which has the potential to deliver the largest pulse which would deliver just this scenario. Or you may have unknowingly just upset a witch doctor and she put a hoo-doo on your car.
cheers,
Douglas

 

[CaptainJackson]

I just had the same thing happen to my 5th gear. I'm interested in trying this. You made a key and a keyway which would have been nice for this thing to have in the first place! Would have prevented a lot of people's headaches.

Since you drilled the bits in, I'm curious, why did you have to drive them in with a mallet? And drive them into what? The bit is in the hole already as deep as you made it...

I'm going to use the loctite. Thinking about some welding too.

 

[gforce1108]

I am guessing that the pins will not hold up. I've seen them welded and still break. My understanding is overheating from low oil is the primary cause of the failure (5th is impacted first).

 

[94cobra2615]

I just bought a cheap gasser 5 speed and swapped the main shaft into the tdi 5 speed. Shafts are identical and gasser 5 speeds are plentiful/cheap

 

[PakProtector]

I just had the same thing happen to my 5th gear. I'm interested in trying this. You made a key and a keyway which would have been nice for this thing to have in the first place! Would have prevented a lot of people's headaches.

A key will not carry any near as much torque as a press( or shrink) fit spline. A key would have left even a gasser with failures had they had the lack of sense to implement it.
cheers,
Douglas

 

[CaptainJackson]

I just bought a cheap gasser 5 speed and swapped the main shaft into the tdi 5 speed. Shafts are identical and gasser 5 speeds are plentiful/cheap

I found a trans off a diesel near me. A couple of gears have worn syncros, so I'll be swapping with the good ones from mine.

 

[tdidieselbobny]

Someone pointed me to this thread. Lost 5th in my '03, but it was the smaller gear closest to firewall that shaft spins without turning gears. I talked the owner of welding shop nearby and his main concern was if there was any bearings on that splined shaft inside the main housing....

 

[gforce1108]

Someone pointed me to this thread. Lost 5th in my '03, but it was the smaller gear closest to firewall that shaft spins without turning gears. I talked the owner of welding shop nearby and his main concern was if there was any bearings on that splined shaft inside the main housing....

Here's what it looks like inside - FYI this is the welded one I mentioned earlier. Didn't last very long...

 

[CaptainJackson]

Someone pointed me to this thread. Lost 5th in my '03, but it was the smaller gear closest to firewall that shaft spins without turning gears. I talked the owner of welding shop nearby and his main concern was if there was any bearings on that splined shaft inside the main housing....

I believe you're talking about the counter shaft. It's sole purpose is for 5th gear. That shaft will spin loosely until the shift fork pushes the 5th gear syncro hub engagement teeth onto the larger 5th gear engagement teeth. Then the main shaft is married to the countershaft.

There are needle bearings the large gear rides on. There are a number of sources that say to use heat from a torch to free the 5th syncro from the shaft and that was the only way the transmission shop could pull the hub off of my main shaft.

For sure if you used an acetylene torch to heat the hub and the shaft to weld it, the heat could transfer back as far as the needle bearings. But if you arc welded it, the duration heat is applied is so much shorter, I dont think it would get hot enough to damage the needles.

Maybe but new needle bearing on first since you're probably never intentionally going to get that hub off again. I cant remember if the whole main shaft disassembles from that end.

I also tried to pin the hub, but could never get any progress with drilling. If I had known gassers trans had the same everything except gear ratios before I found a donor diesel trans, I would have gone that route because they are so easy to find with low miles and cheap.

Good luck!

Sent from my SM-G955U using Tapatalk

 

[PakProtector]

Area for transferring the load: PI*D*length of splined engagement.

Area for the weld to try same: PI*D*length/7 or 8

cheers,
Douglas

 

[tdidieselbobny]

I believe you're talking about the counter shaft. It's sole purpose is for 5th gear. That shaft will spin loosely until the shift fork pushes the 5th gear syncro hub engagement teeth onto the larger 5th gear engagement teeth. Then the main shaft is married to the countershaft.

There are needle bearings the large gear rides on. There are a number of sources that say to use heat from a torch to free the 5th syncro from the shaft and that was the only way the transmission shop could pull the hub off of my main shaft.

For sure if you used an acetylene torch to heat the hub and the shaft to weld it, the heat could transfer back as far as the needle bearings. But if you arc welded it, the duration heat is applied is so much shorter, I dont think it would get hot enough to damage the needles.

Maybe but new needle bearing on first since you're probably never intentionally going to get that hub off again. I cant remember if the whole main shaft disassembles from that end.

I also tried to pin the hub, but could never get any progress with drilling. If I had known gassers trans had the same everything except gear ratios before I found a donor diesel trans, I would have gone that route because they are so easy to find with low miles and cheap.

Good luck!

Sent from my SM-G955U using Tapatalk

Nope, put the transmission in 5th and when I turned wheel the rear sprocket didn't move while the bolt into the shaft just turned. I removed the t-60 bolt and the sprocket was wobbly on shaft and I could pull it out some with my fingers till it hit the big front sprocket. The sprockets need to be pulled off with puller and possibly heat under normal circumstances, so I'm guessing the teeth in sprocket and the splines on shaft are worn.Car has 452k on it, really don't want to put another tranny in it, as it probably would have to go to shop for it, looks out of my skill set, along with probably needing another transmission mount and bracket if it did come out.I may try the drill and pin method with loctite, or I may just leave it be and drive in 4th. I filled up today and it got 44 mpg with no 5th.....

 

[goose737700]

EZUT, Any update as to how the repair is holding up? I just spun my 5th as well and its in a eurovan gearbox, and it's cheaper to buy a rebuild from Germany than find a local shop that can source parts. I want to give it a try.