Strange transmission noise - now solved :)

[folkswagon]

 So, after 12 years off the road my 1968 SemiAuto is running again, but I'm still trying to understand where this noise is coming from. Any help greatly appreciated -

https://youtu.be/winneQGvym0

[volkenstein]

Folkswagon,
                  Sounds like bearing rumble to me. Process of elimination now....

1. I hope the GB has correct level of oil in it? lol...and there is oil in there anyway?
1a. You could drain it and check for shavings/material in your GB oil/drain plate.
1b. While you are there you can check that big lock ring on the mainshaft nose for looseness.
2. It only happens when a gear is actually engaged but not in Neutral of when the solenoid activates?
  2a. That tells me it is not clutch or mainshaft related.
3. After checking 1., drop the car off those stands. Do the same shifting. I think your CV's are OK because your wheels are spinning anyway.
4. That leaves the layshaft being engaged (ie a gear) with the mainshaft is where your noises start.
5. That'll be ugly as it means you will have to check those bearings. You can drop the engine/GB out after oil draining, then get the nosecone off...you can visually check the rearmost
    mainshaft & layshaft bearings + shim & circlips (and wobble test etc).
5a. Any else requires fairly major disassembly.

Most bearings are available - except for the mainshaft bearing that is closest to the pinion. Looking around may get you one....but you may be visiting
places where you can pick up a S/H trans.


HTH
Volkenstein

[folkswagon]

Thanks Volkenstein

So I've covered a few of your suggestions -

1a - I've drained the oil but as it's a 68 semi auto it's got a drain plug so I didn't take the plate off. Oil looked clear with no shavings. Video was made after new hypoid oil was inserted so there's definitely enough oil in the GB. I've purchased some molyslip gearbox oil additive but not tried it yet, think it would need significant driving to bed that in and as the car is off the road thats not possible at the moment.
1b - As I said I didn't take the plate off so couldn't see any of the gears.
2 - Correct
3 - I know the outer CV's are ok as I've re-packed them whilst replacing the rear wheel bearings but don't know the state of the inners. Will try another test today and put the brakes on to stop the rear wheels.
4&5 - There is some good news as I have a complete spare transmission from another 68 semi that I'm cleaning up and getting to know. Only issue found with this box so far is a cracked torque converter housing at the main bolt by the vacuum servo, but with this type of bolt this may be a common problem (see separate picture link). Can the housings be swapped between GBs? If not can it be welded, not sure if it's mostly aluminium or if there's any magnesium in it?

Although she's running again I'm going to have to remove the engine as oil is leaking all over the place (mostly push rod tubes) so I want to be able to give it a good check over and replace all that is needed.

Anyway here's a pic of the now clean spare box and many thanks again for your support

Picture of my spare transaxle
Pictures of cracked torque converter housing

[volkenstein]

folkswagon,
                That crack isn't hideous, and non life-threatening. The bellhousings are interchangable between similar years (just about one or two temp sensors). I would suggest you do the old drum kit trick and drill a small hole where the cracking has stopped for now.
A GB swap is certainly a more practical option than mucking around with the gears - you already have one - so off to the races:).

You can autopsy later...

HTH
Volkenstein

[folkswagon]

Finally tracked down the likely culprit

Volkenstein was spot on in guess #4/5, with the main shaft bearing being pitted. Very obvious once the nose cap was removed so I'm currently building up a new transmission from the best bits of the two.

Upper right pic and lower right pic show the pitted and perfect versions of the bearing on each box -



I'm assuming this may be a bearing quality issue as the replacement box is same BO type, and slightly earlier S/N, so the bearing has either been previously replaced or was a different make from new (assuming similar servicing/oil changes). Knackered bearing is manufactured by FAG with PN 515828 visible. Good bearing has no markings but could be reversible hence markings on the other side maybe?

Is this a common bearing to fail in other normal dub transmissions? Anyone seen similar?

[folkswagon]

Search engine always has the answer! Turns out this is a common dub problem on the swing axle transmission too. VW part no is 113 311 123A curtesy of VWJim.

As the bearing is flanged it can't be reversed hence I assume my spare box has been rebuilt at some stage

Quote from cip1.com -

'This is the main culprit of a noisy transmission. A way you to check yours- is to push the clutch in while you are driving. If the noise goes away then its the main shaft bearing. By pushing the clutch in the throw out bearing supports the main shaft quieting the main shaft bearing'

[drinksuxmetoo]

Hello folkswagon,
did you find your answer?
I have excatly the same noise...
Thank you