technical GS6-45BZ Gearbox | 2nd Gear Weirdness

[andrewza]

Hey peeps,

The second gear in my manual box (GS6-45BZ I think?) in my E82 135i is missbehaving but I can't seem to pin it down exactly. But they only started happening after a recent clutch-swap (OEM clutch kit, thrust bearing, new pivot pin+spring.

Symptoms:

• Sometimes, if shifting down from 3rd to 2nd with heel-toe, say third at 3,000 RPM, after shifting into 2nd the gear "pops-out" with some relatively light grinding sound, as if you tried to shift without depressing the clutch pedal.
• Occasionally, even though 2nd engages and at low speed, the gear does a similar pop-out, and grinds in a similar way.
• The two symptoms above seem to be related to heat, if it's colder it apparently happens less, but not always, the 3rd to 2nd downshift pop-out has happened while warm after a decent trip of ~20-30 kms.

Synchros?
Something else? 🙏

 

[NBN]

Sounds like a synchro to me as its mostly 2nd to 3rd and when downshifting from 3rd to 2nd...

Also check to see if you can adjust the clutch stop, it really makes a difference to the way the clutch pedal engages

 

[andrewza]

Thanks!
And thinking removing the clutch delay valve might help with clutch modulation?

 

[NBN]

Thanks!
And thinking removing the clutch delay valve might help with clutch modulation?

i did the burger tuning clutch stop and their cdv but i am not sure if anyone sells those parts locally anymore....

was a worthwhile "upgrade" for me, for not alot of money

 

[Mytfine]

Have you checked mountings and gbox fluid level ? You can try a little thicker oil, will give you a little more life out of the syncros.

 

[Teezoh]

If this did not happen before the clutch swap, I would not jump straight to the syncros as the culprit.

It sounds more like the gear not fully locking onto the hub and the load kicking it out.

I would start by the clutch, anything from air in the hydraulic system, the slave cylinder not fully extending or even the release bearing not being installed correctly. From there maybe the shift link or selector alignment.

 

[andrewza]

If this did not happen before the clutch swap, I would not jump straight to the syncros as the culprit.

It sounds more like the gear not fully locking onto the hub and the load kicking it out.

I would start by the clutch, anything from air in the hydraulic system, the slave cylinder not fully extending or even the release bearing not being installed correctly. From there maybe the shift link or selector alignment.

Thanks for the reply.
I don't recall this happening previously. Occasionally with 1st but that was more user error/getting used to the gearbox.
The hydraulics weren't disconnected for the clutch swap, so don't think any additional air etc got into the system that way.
I'll start with a bleed perhaps and see if it makes a difference.
The issue seems to be getting worse day by day, which is a bit concerning...

 

[andrewza]

Have you checked mountings and gbox fluid level ? You can try a little thicker oil, will give you a little more life out of the syncros.

Haven't checked gearbox fluid or mountings to be fair, but when I was underneath the car all the mountings seemed okay. Think it's time to just get under there and see if there's an obvious issue.

 

[andrewza]

So I've tested "loading" the synchro by not rev-matching/heel-toeing and I think you guys are right, the synchro seems to spin the gear up appropriately without grinding. Grinding seems to mostly happen on shifting where the engine speed is relatively high.
Confusing. Will be checking the suggested items this weekend.