Stuck in a mystery gear

[Dillon]

Hey guys, I just swapped a manual trans into my e30. I connected the linkage and it rowed through the gears just fine the first couple of times. I rowed through them two or three weeks ago and the transmission got stuck in gear. I called a couple mechanics and they told me that because the transmission had not had oil in a while, it needed to be lubed up. I rebuilt the motor and so the trans and the engine had not been running at that point. Anyways, I finally fired up the motor today and got it running. But the transmission still will not come out of whatever gear that its in. (I have the driveshaft disconnected so I don't know what gear its in) I'm worried I was a little aggressive and broke something inside the trans when I was trying to put it in reverse several weeks ago. Is that possible? Any ideas? It's fill with 75-80 redline by the way, so its a good oil..

[AndrewBird]

Might have bent/broke a selector fork. Is it just stuck, or can you move the lever and it just does nothing?

[Dillon]

Might have bent/broke a selector fork. Is it just stuck, or can you move the lever and it just does nothing?

It's just stuck. The shifter is in the neutral position, but the car is in gear. Pushing in clutch will put the car in neutral as it should, so thankfully I did that right. But as soon as you let the clutch out its put back in gear. I've been looking at the linkage to see if it was binding on anything but it looks to be completely fine. Would a selector fork be difficult to replace?

[jeffnhiscars]

I had a similar problem from a fractured shifter rod

[Dillon]

I had a similar problem from a fractured shifter rod

I've checked the linkage and all seems to be in good shape. I'm thinking its internal. So I'm going to take the trans out and see if its a selector fork. Is it possible for them to slip out or do you guys think it would have just broken?

[Wanganstyle]

Stuck in a mystery gear

I've checked the linkage and all seems to be in good shape. I'm thinking its internal. So I'm going to take the trans out and see if its a selector fork. Is it possible for them to slip out or do you guys think it would have just broken?

if you look at the internal diagram of the G260 transmission you will see that the forks for the transmission are pinned onto steel rods that take input from the shifter. the pins are stronger than the forks and chance of it coming out is very slim; they are not easy to remove.

the steel rods very likely are just fine; what is damaged is the fork - it moves the syncronizer guide tube between gears - if its jammed stuck not moving its quite possible that its just broken.

The forks are brass; not nearly as strong as everything else which is steel

Pictured below is a g265+ teardown +
grp A dtm gearset install; the g260 will look very similar inside; they share Syncronizers and some other parts like bearings

Extraction of main/layshaft and the steel shift rods.

brass forks+ pins are visible



Grp A OS GIKEN DTM gear set + layshaft installed then detents/forks being set into place




As labeled you can see that 1/2 & 3/4 gears share a Syncronizer guide tube and fork; the fork pushes the guide tube towards either 1 or 2 and engages the synchronizer on that side to equalize speeds so the tube can slide over and engage the splines of the gear selected.



Synchronizer guide tube and fork detail. These 3 springs + the detent springs provide the spring force between gear shifts




New syncronizers / bearings installed both sides of the guide tube to go with new grpA gears. You can see the teeth that must engage in line for the guide tube to mesh and engage the selected gear.

If the syncronizer is worn out and the fork is shifted hard into a gear the stress will fall on the fork; especially when speeds are not brought together between gears between shifts. Worn bearings or lack of lubricant will also make the gearbox extremely angry



Detail of a new syncronizer (guide tube side). The tube has 3 square slots for the syncronizer to be held in place by; the other side is conical and a friction surface

[Dillon]

Wow!! I have looked and looked and I've not been able to find very much detail on the inside of these transmissions. This helps a ton!! Thank you! :)

[e30davie]

damn thats some cool photos.

I have a gearbox in the garage with a suspected stuffed 3/4 fork (very dificult to get into 3/4 gear and it pops out reaaally easy).

With some inventive tools is replacing such a thing doable for a home gamer?

Alot of gearbox shops i spoke to refused to work on it, something about the casing being hard to get appart. I must admit i havent even tried, i just grabbed another box and threw it in.

[Wanganstyle]

Stuck in a mystery gear

damn thats some cool photos.

I have a gearbox in the garage with a suspected stuffed 3/4 fork (very dificult to get into 3/4 gear and it pops out reaaally easy).

With some inventive tools is replacing such a thing doable for a home gamer?

Alot of gearbox shops i spoke to refused to work on it, something about the casing being hard to get appart. I must admit i havent even tried, i just grabbed another box and threw it in.

Complex question:

The 4th and 3rd gears of the g265 took about 12-15 tons of force to pull off. Used some world war 1 tractor tools to do it; not for the faint of heart.

The g260 is less difficult to pull apart but it’s not any easier really. After you extract the pressed on gears then you need a hydrolic press/table to extract the gear tree set from the aluminum housing. Then grow an extra hand to assemble /extract it without damage

It’s fun to learn new things ; if you have nothing to loose try tearing it apart.

Heat will warp; only other option is cutting but that doesn’t really work if you plan on reusing parts.

The front Bearing is a split race and requires some special pre Berlin Wall era tools to extract. Bmw specific crazy s&m looking race pullers.

Then you have the issue of sourcing a new front main Bearing ; some models are nla. Some still avail.....and then the cost

G260/265 Syncronizers are avail new from bmw. Same for most of the bearings ; you just need to wait.

Not sure forks are avail new if you break one. Would be case by case depending on era of make of box and which fork

If it still goes into 3/4 just angry then it will be a combination of Syncro/gear/guide tube and possibly fork also that is causing anger.

Detents are steel balls/springs and keep gears in place and provide the feeling of engage / disengage.

Basically a steel ball pops into place into the shift shaft via spring power.

[e30davie]

Very interesting. Thankyou for taking the time. Yer it was that front bearing that seemed to cause the issue to alot of gearbox shops.

Only reason i thought it was the clutch fork as it felt like you needed to push the gear stick alot further to get it remotely into the gear and you sort of had to hold it there while it was grinding away. I was just imagining half of the brass fork been worn away over the years.

I will get my large hammer and when i get a spare Saturday I will attack it. Worst case i get some cool desk ornaments and more room in my shed.

[Dillon]

Complex question:

The 4th and 3rd gears of the g265 took about 12-15 tons of force to pull off. Used some world war 1 tractor tools to do it; not for the faint of heart.

The g260 is less difficult to pull apart but it’s not any easier really. After you extract the pressed on gears then you need a hydrolic press/table to extract the gear tree set from the aluminum housing. Then grow an extra hand to assemble /extract it without damage

It’s fun to learn new things ; if you have nothing to loose try tearing it apart.

Heat will warp; only other option is cutting but that doesn’t really work if you plan on reusing parts.

The front Bearing is a split race and requires some special pre Berlin Wall era tools to extract. Bmw specific crazy s&m looking race pullers.

Then you have the issue of sourcing a new front main Bearing ; some models are nla. Some still avail.....and then the cost

G260/265 Syncronizers are avail new from bmw. Same for most of the bearings ; you just need to wait.

Not sure forks are avail new if you break one. Would be case by case depending on era of make of box and which fork

If it still goes into 3/4 just angry then it will be a combination of Syncro/gear/guide tube and possibly fork also that is causing anger.

Detents are steel balls/springs and keep gears in place and provide the feeling of engage / disengage.

Basically a steel ball pops into place into the shift shaft via spring power.

Hmm... Well I started pulling my transmission tonight. Hopefully I'll get it out thursday night. (College kid, not much time ) I'll see if I can get it pulled apart by the weekend or at most next week. I'll keep ya updated on what I find. If its a broken fork that would keep it from going into any gears right? I'm assuming it would jam? This is pretty interesting stuff. Thanks for the help!

[Frobill]

Complex question:

The 4th and 3rd gears of the g265 took about 12-15 tons of force to pull off. Used some world war 1 tractor tools to do it; not for the faint of heart.

The g260 is less difficult to pull apart but it’s not any easier really. After you extract the pressed on gears then you need a hydrolic press/table to extract the gear tree set from the aluminum housing. Then grow an extra hand to assemble /extract it without damage

It’s fun to learn new things ; if you have nothing to loose try tearing it apart.

Heat will warp; only other option is cutting but that doesn’t really work if you plan on reusing parts.

The front Bearing is a split race and requires some special pre Berlin Wall era tools to extract. Bmw specific crazy s&m looking race pullers.

Then you have the issue of sourcing a new front main Bearing ; some models are nla. Some still avail.....and then the cost

G260/265 Syncronizers are avail new from bmw. Same for most of the bearings ; you just need to wait.

Not sure forks are avail new if you break one. Would be case by case depending on era of make of box and which fork

If it still goes into 3/4 just angry then it will be a combination of Syncro/gear/guide tube and possibly fork also that is causing anger.

Detents are steel balls/springs and keep gears in place and provide the feeling of engage / disengage.

Basically a steel ball pops into place into the shift shaft via spring power.

Damn .......... this guy must have a PHd in Mechanical Engineering. Much to learn from him. Liking this very much.

[Wanganstyle]

Hmm... Well I started pulling my transmission tonight. Hopefully I'll get it out thursday night. (College kid, not much time ) I'll see if I can get it pulled apart by the weekend or at most next week. I'll keep ya updated on what I find. If its a broken fork that would keep it from going into any gears right? I'm assuming it would jam? This is pretty interesting stuff. Thanks for the help!

well the shift rod that your shift selector rod is controlling more than just one fork; if the shift rod is not moving happily (bushings done) or the linkage mechanism that engages the forks is worn /binding /angry then you won't really even get to activate the forks.

a broken fork usually happens (at least in circuit racing) while shifting, often the unit will be stuck in a particular gear and will not come out because the item to shift it out is broken and broken pieces causing havoc of sorts also.

Very interesting. Thankyou for taking the time. Yer it was that front bearing that seemed to cause the issue to alot of gearbox shops.

Only reason i thought it was the clutch fork as it felt like you needed to push the gear stick alot further to get it remotely into the gear and you sort of had to hold it there while it was grinding away. I was just imagining half of the brass fork been worn away over the years.

I will get my large hammer and when i get a spare Saturday I will attack it. Worst case i get some cool desk ornaments and more room in my shed.

the clutch fork contacts the guide tubes only; smooth surface to smooth surface (hopefully lubricated in transmission oil). Grinding will be from dead syncro not equalizing speeds between gear & guide tube; the guide tube has female splines and the gear has male splines.

clutch fork pushes guide tube towards gear, syncro equalizes speeds and then the female splines can accept the male gear splines and mate into gear.

angry grinding noises = did not get the female side syncronized properly for mating.

remember:

1. timing (syncro)
2. lubrication

are both required for happy mating (of gears)

Damn .......... this guy must have a PHd in Mechanical Engineering. Much to learn from him. Liking this very much.

I'm just a normal guy who read a lot of manuals and went over diagrams carefully, then learned through many hours how to do things the factory way.
I've been fortunate enough to be immersed in a lot of motorsports and support some hardcore shops/racers so am always learning about how things fail in competition and can be made stronger.

[Dillon]

Welp I got the transmission pulled last night. So I'll pull it apart and take pictures when I can. It seems to be stuck in reverse while the gear stick is in neutral. I spine the output shaft and the input shaft spins the opposite direction and vice versa. (that is reverse right?)

Thanks again for the information. Knowing more about this makes me less annoyed that I have to do it in the first place. :D

[Wanganstyle]

Stuck in a mystery gear

Welp I got the transmission pulled last night. So I'll pull it apart and take pictures when I can. It seems to be stuck in reverse while the gear stick is in neutral. I spine the output shaft and the input shaft spins the opposite direction and vice versa. (that is reverse right?)

Thanks again for the information. Knowing more about this makes me less annoyed that I have to do it in the first place. [emoji3]

a M20 bmw engine spins clockwise [emoji4]

stuck in reverse seems to be the case

when you get it apart see if the shift selector rod (the thing poking out of box your gearshift connects to) have any visable damage.

or if you can see any mechanism out of place.

the selector rod has to interact with multiple different shift forks to handle the 5f+1r gear; trace the path of connection between them and should find what is broken