Finding a good condition 3rd/4th gear synchromesh assembly for all-sychro transmission

[Dennismo]

I will take my series transmission out for rebuild as my first gear synchro wore out as the clutch was not disengaging completely

But I wish to fix another problem which is that when I am in third gear and apply power, the gearshift lever moves forward. When I take off power, it moves back. I have determined that the sliding synchro hub is actually moving to the rear of the car (under power) which causes the shift lever to move forward.

I think this is a sign of a very worn synchromesh hub. Can anyone tell confirm this?

And can anyone tell me a source in the UK (or in the world!) where I can buy a good condition third/fourth gear used synchro hub assembly?

I can be emailed at dennismaxmolnar@gmail.com

Many Thanks

Dennis

[Hugo]

You have some end-float on the mainshaft by the sound of things. I'm not sure what locates the mainshaft in these boxes (I'm not familiar with them at all) - probably the bearing at the back (output end). The mainshaft gears themselves are free to spin on the mainshaft, but the fixed centre of the synchro hub is not - the whole assembly should be bolted up rigid. What is happening with yours is that the end thrust from the helical gears is pushing the sliding synchro sleeve backwards & forwards as you apply & release thrust.
What is distinctly puzzling, however, is that you say it is pushing the lever FORWARD under load. That means the sliding hub is being pushed BACKWARDS. But it is already being pushed back onto the third mainshaft gear when you engage third gear. I can understand if the sliding sleeve was FALLING backwards (i.e. lever falling forwards) when you apply power, as it would just be following the 3rd mainshaft gear in that direction, but there is nothing I can think of that would push the sliding sleeve backwards (other than the selector fork of course). Certainly when you release the throttle it would push the sliding sleeve forwards & thereby push the lever backwards. This implies either some end-float on the 3rd mainshaft gear which is allowing the sliding sleeve to follow it backwards & be pushed forwards, or the entire mainshaft is moving back & forth.
Having said all that, I'm afraid I don't like the sound of this. I reckon it's probably heading towards a re-build job. Depends if it's sudden onset or gradual. Maybe just a bearing collapsing, or maybe something has come loose in there. I do tend to be a pessimist when it comes to mechanical matters though - that way you're never disappointed!

[Norton]

Hi Dennis.
Just came across your post which I realize is a few years old. I have exacly the same symtoms in my car, -73 S3. Aquired this car seven month ago and did not notice this when testdriving. Did you ever find the cause? And find out what to do / what did you do? Also have a rumbling noise in the gearbox. Pretty sure it is in the box itself, at standstill when idling it silences when pressing in clutch.
Thanks, rgds Harald.

[abowie]

Try Steve Barratt. Curmugeonly but a really good guy.

He's on EBay stirlingmess.

[abowie]

Hi Dennis.
Just came across your post which I realize is a few years old.

Doh. Oops.

[Norton]

Thanks. Harald

[Norton]

Hi again.
-73 series 3.
The OD gearbox from a 420G saloon have been working fine. And original box have rested in peace in pieces all summer. But I have now taken most of it apart. Earlier in this thread I got a lot of good advice.
This gearbox had noises which have been discussed.

And gear stick moved forward when accellerating and rearward when decellerating. Have some sugestion that it might be worn synchro hubs. The syncro hubs, synchro rings & operating sleeves are dismanteled, but how can I determine wether they are good / worn / worn out? What to look for?
The box was shifting just fine, no crunches / teeth counting.
The hubs looks good to me, same with sleeves. There are some wear on synchro rings «teeth». But enough to cause any symptoms? I think ring for first is showing most wear.
Also some wear on selector forks.

See pictures, hopefully good enough.

Rgds Harald.