What's this?

[ChrisR]

Good day all.
I recently was inspired to change the gearbox oil, which I have not done for some time.
I found this small pin in the pan with the old oil. Can anybody tell me what it might be please?
It is 0.426" long and 0.140" in diameter.
The car is a 1968 S3 SE and the gearbox seems to work just fine.
The pin was not in the pan before I drained the oil!
Any ideas?
Thanks, Chris

[oldelanman]

It could be the pin that sits in the cross drilling in the 1/2 shift rail between the two interlock plungers - item 30 on the attached diagram. It may have fallen out unnoticed as the gearbox was assembled in the past and been sitting in the bottom of the box since.

[ChrisR]

Roger,
Thanks for that.
What would be the effect of it not being in place? I have never rebuilt the gearbox (and the car was only five years old when I bought it).
Not having seen the inside I can't get it into my head what it does.

[oldelanman]

The interlock plungers are to prevent engagement of two gears at the same time. They sit in cross drillings in the gearbox between the shift rails and engage with detents in the rails, as one rail moves to engage a gear the plunger is pushed sideways locking the adjacent shift rail and pushing the pin mentioned here which in turn pushes the other plunger and locks the third shift rail also. Difficult to explain but hopefully you get the idea, there are some good explanations and images on the internet if you do a search.

If the pin is missing I think the effect will be that the 3/4 shift rail will not be locked when you engage reverse and similarly the reverse rail will not be locked when you engage 3/4th gears, engaging 1st or 2nd will still lock both rev and 3/4. Sorry for the rather clumsy explanation, hope this helps.

[ChrisR]

Thank you very much for that far from clumsy explanation!
I should have been able to work it out having done an engineering apprenticeship in the distant past...
As I have had no trouble from the box so far, I will let sleeping dogs lie for the time being.
I am wondering if it was dropped inside during the original assembly and someone couldn't be bothered to retrieve it and just fitted a new one.
Many thanks again.

[oldelanman]

No problem.
Yes I would agree it's best to leave well alone. You've had no issues so far and now the pin is no longer floating about in the bottom of the box it can't cause any problems in the future.

[elanner]

When my gearbox was taken apart for inspection the pin was found to be missing. The gearbox had worked fine for years. It's hard to be convinced that the interlock mechanism is even needed because selecting two gears at the same time would seem to be impossible. But presumably it wasn't put there for the fun of it, so perhaps a very unfortunate bump could do it.....

Nick

[ChrisR]

Thanks for that. Good to hear it works without the pin.
Hope it continues this way!

[prezoom]

I have had the two gear lockup happen twice. The first time was during a race coming out of turn 8 at Riverside. The gear lever selected 3rd and 1st gears when shifting from 2nd gear, completely locking up the rear tires, resulting in spin while in a group of cars. This was with a brand new transmission, just purchased from the manufacturer. The shuttle pin was missing during assembly. The second time was in the Elan when shifting from 1st gear to reverse, while making a U turn in a very tight intersection. This time it was not the shuttle pin, but the gear lever being pulled up and grabbing both reverse and 2nd gear. Just enough to lock up the transmission in the middle of the intersection, rendering the car immobile, blocking the intersection. The gear lever was locked in place, unable to rectify the situation. On this occasion, it was the first time, taking the car out on a driving tour, NFIBMT, having just getting the car running after purchasing the Elan. Panics ville on steroids. The growing crowd had no suggestions other than blowing their horns. Wound up removing the gear lever and using a large screwdriver to move the shift rails into their proper position. Very careful shifting was done while completing the 1200 mile tour. The problem was resolved by making a small Delrin spacer that prevented the shift lever from being pulled up too far. No more problems since 2006. So, if not having the shuttle pin installed, shift very carefully, so as not to select two shift rails at the same time.

[mbell]

If the gearbox has never been open it might have just been dropped in during its original build and the assembler simple picked up and fitted a new one, leaving that one in the bottom of the gearbox.

Maybe remove the gearstick and see if you can manually select two gears or not. Then you know if you have to be careful or issue to fix at some point.

[ChrisR]

Very good idea, I'll try that.
Thanks.

[alan.barker]

When the rear of gearbox is removed it lets you remove the selector Rods. But when you remove the middle selector rod backwards the "little pin" falls unknownly into the bottom of Gearbox.
Don't ask me how i know lol.
Alan