Anyone Lost 4th Synchro By Over-Torquing Output Flange?

[andyleonard]

I just re-sealed a new-to-me 81 125K miles 245 gearbox, installed it and have no synchro from 5 to 4.

Can I have caused this by over-torquing the output flange?

Can I fix it by releasing and resetting the flange?

[epmedia]

Here's a related discussion, but having mostly to do with loosing 5th gear after working on the transmission. Maybe this can help to narrow things down? https://www.bimmerforums.com/forum/s...P!-No-5th-gear

[andyleonard]

Here's a related discussion, but having mostly to do with loosing 5th gear after working on the transmission. Maybe this can help to narrow things down? https://www.bimmerforums.com/forum/s...P!-No-5th-gear

That's where I got the idea about the flange being over-torqued and boogering up 4th gear - which makes no sense to me based on what I know is in there - so I removed the flange today and re-torqued it. Nothing changed. FYI.

[epmedia]

That's where I got the idea about the flange being over-torqued and boogering up 4th gear - which makes no sense to me based on what I know is in there - so I removed the flange today and re-torqued it. Nothing changed. FYI.

Did you read the entire thread for more possible solutions? On post #41, it was figured out that too long of a bolt was used, which prevented 5th gear from engaging.

[andyleonard]

Did you read the entire thread for more possible solutions? On post #41, it was figured out that too long of a bolt was used, which prevented 5th gear from engaging.

Yes, thanks, I read that and am aware of the bolt issue. I have no issues with engaging gears, just synchro problems.

[Tom D]

maybe you could explain exactly what your problem is and how it behaves.

[andyleonard]

maybe you could explain exactly what your problem is and how it behaves.

Well, the box behaves normally in 1-2-3 up and down, No bearing noise, nothing weird. All clutch parts are new and fine.There's a little skritch from 3 going into 4 if you hurry and 4 into 5 is normal. But there's NO SYNCHRO coming down from 5-4. Nada. Have to double clutch or skip to 3rd. Not really driveable like that.

I pulled the flange to retorque it and noticed there's in and out play in the bare output shaft of maybe .020. Isn't it supposed to be shimmed to zero inside the output bearing? Maybe someone was in there. Could that be it? I think 4th is up front in the case.

[epmedia]

Do you have the 245 transmission? Realoem.com does show a shim(still avail?) behind that seal cover(backup ring).

This link is for the 245 trans.
http://www.realoem.com/bmw/enUS/show...diagId=23_0688

I would think it's shimmed to zero, I also think that Tom may be able to give a definitive answer on this.

And/or maybe the gear oil is too thick?

[andyleonard]

Yep, it's 245 as stated in OP. The Real OEM link is interesting as the pictures from the old book I've been using show the shim INSIDE the rear bearing and the RealOEM pic is clearly outside. I would assume shim to zero also, but shim comes in only one size?

[epmedia]

Yep, it's 245 as stated in OP. The Real OEM link is interesting as the pictures from the old book I've been using show the shim INSIDE the rear bearing and the RealOEM pic is clearly outside. I would assume shim to zero also, but shim comes in only one size?

If you referring to the #9 shim in that link, it says there's 3 shim sizes avail.

[andyleonard]

Right you are. I missed that.That's encouraging. The manuals seem to indicate "shim to zero" on both ends and I found at least .020 endplay on the output when I removed the flange, just grabbing it with my fingers and pushing in and out. If someone got in there (young guys had the car) and somehow lost the shim, I wonder if it would cause what I have going on? I think I see 4th gear up in front, being pushed forward to get from 5 to 4.
I can't see how bad position or float of the OUTPUT shaft would affect the shifter rail's ability to reach the 4th gear slider, UNLESS they left the shims out of the INPUT bearing too. But the box is perfect in 1-2-3. I must be missing something or maybe the 4th synchro is just split.

https://parts.bmwofsouthatlanta.com/...ssembly=423100

[andyleonard]

I pulled it apart to see.
The new 100 mile MTF oil looked like the California Gold Rush. Unfortunately I never saw the original oil as my son dumped it under orders and didn't comment. Pulled the front cover and found the shims present and appropriate sizes front and rear, no janky bearings, everything looked stock and unopened at 125K miles and NO TEETH WHATSOEVER left on 4th gear synchro. Synchro pushed smack up against the gear doing nothing, slider looks OK, not perfect but not damaged, so it wasn't my imagination; it was like driving a non-syncho box for that shift.

I wonder what did it?