Synchromesh:noun:A system of gear changing, especially in motor vehicles, in which the driving and driven gearwheels are made to revolve at the same speed during engagement by means of a set of friction clutches, thereby easing the change.
With the bell housing off and the temperatures a little bearable in the garage, I removed the synchromesh and and replaced the detent springs.
But first…. by way of introduction… a multimedia experience !
First of all the selector shafts need to be removed. There are 3 of these and have to be removed in order.
Selector shaft cover needs to be removed
Detent (word of the day) springs and caps are removed from the cover. If you ever do this with the gearbox in the vehicle, make sure you extract the ball bearing from the large hole in the middle of the cover. If you don’t, and remove the cover, the ball bearing will drop into the bottom of the gearbox! A magnetic screwdriver should be enough to draw it out. Or turn the gearbox upside down and shake it 😉
Selector shafts exposed. On the left, reverse selector. Middle, 1st and 2nd selector. Right, 3rd and 4th selector… that’s the one we’re interested in.
3rd and 4th selector shaft engages on the centre of the synchromesh. This is the component that actually performs the gear change. The steel centre of synchromesh engages with the gears and all drive passes through the piece. The bronze parts “grip” the gear being selected and spins it up to speed, thus facilitating a smooth gear change.
With the selector shaft removed, the synchromesh can be withdrawn from the main shaft
…and there it is… the offending broken spring causing the unit to jam (I’m using a centre such to point at the broken spring which the steel rod you see)
Not a good look… Lets pull the broken one out and fit the new one.
One and a half springs…. Where the other half of the set have gone is anyones guess. They’re not in the gearbox!
3 new springs (lower) ready to fit.
They simple push into place and are held fast by the corresponding relief in the stainless steel pin between the bronze rings, or synchro cones to give them their correct name.
Springs all fitted. It took maybe 1 minute to do all three. The synchromesh now engages in the middle with a satisfying click. The third spring is obviously out of site.
Refitted on the main shaft. These devices are actually handed and it’s important to install them the right way round… which i did. 🙂
Whilst I was at it, I cleaned all the old gasket and sealant off the face of the main case and gave it a good rub back with wet and dry . I’ll do the same with the bell housing at a later date.
Replacement gaskets and a few other bits and bobs have been order from the UK. I might be lucky and they arrive in time for next weekend.
There’s no guarantee it won’t happen again but failures like these are quite rare. When I rebuilt the gearbox during the restoration, the original springs and synchromesh were still looking OK… with 250,000 km of use. I think I was just unlucky with the aftermarket supplier I used.
I’ve heard of people field stripping a gear box but I wouldn’t want to do it. The Santana trophy (for which I still need a co driver) is a supported event so I wouldn’t by that worried.
Hi, I am just rebuilding my series 2a, very helpful post 😊, thank you. One question, on the syncromesh, where you have the inner splined section, one side has a counter bore with no splines for about 3mm. Is this facing towards the spring clip and the back of the vehicle, or towards the front of the vehicle and the bell housing?
Hi Julian, thanks for leaving a message. The recessed area on the inner of the synchromesh needs to face towards 3rd speed gear… i.e… towards the rear of the vehicle. The recess allows the spring clip to sit inside the synchro. (Operation C1-20 in the workshop manual).
Hope this helps.
Andy.
Little Green Landy 
This looks very complicated! How would you make sure this doesn’t happen during the Santana Trophy race? Or would you be able to fix it in the field?
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There’s no guarantee it won’t happen again but failures like these are quite rare. When I rebuilt the gearbox during the restoration, the original springs and synchromesh were still looking OK… with 250,000 km of use. I think I was just unlucky with the aftermarket supplier I used.
I’ve heard of people field stripping a gear box but I wouldn’t want to do it. The Santana trophy (for which I still need a co driver) is a supported event so I wouldn’t by that worried.
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Hi, I am just rebuilding my series 2a, very helpful post 😊, thank you. One question, on the syncromesh, where you have the inner splined section, one side has a counter bore with no splines for about 3mm. Is this facing towards the spring clip and the back of the vehicle, or towards the front of the vehicle and the bell housing?
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Hi Julian, thanks for leaving a message. The recessed area on the inner of the synchromesh needs to face towards 3rd speed gear… i.e… towards the rear of the vehicle. The recess allows the spring clip to sit inside the synchro. (Operation C1-20 in the workshop manual).
Hope this helps.
Andy.
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Perfect, thank you. This is what I assumed. Julian
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