Synchromesh?

Hi all,

I have a S3 1972 which I believe has a fully synchromeshed gearbox. I barely understand what that means but think it is that when changing down the clutch will speed up to match the new gear to the right revs for the current speed being travelled.

If that's wrong please put me right...

If I'm right though, then my question is how 'should' this operate in practice? I ask because, for example, if I am running in 3rd at 15mph and change down to 2nd without breaking and let the clutch back up the car will jerk a fair bit and a lot of speed is taken off. Also, the engine doesn't noticeably increase its revs as I would expect. My only experience is of a modern gearbox where the engine revs high, there is little or no jerk and the cars speed lessens gradually. Perhaps I should not expect such a smooth change down from this old Series gearbox but want to make sure it is not something else which may need investigation.

Thanks,

Andy!

in older boxes gears or dog clutches were slid into mesh physicaly meaning if you didnt match speeds of the two gears they would grind as you tried to engage them ,in synchro box,gears arent splined to shaft and are free to turn but synchro hub is which has a sliding collar which slides over onto a set of teeth on the gear to enable this without grinding gear has cone machined on it and synchro has a baulk ring which has a cone too ,synchro hub pushes cone onto gear and this acts as brake to align the two speeds,it also has triangular shaped teeth aroun outside to align outer sleeve of hub teeth with gear teeth, baulk rings wear so that either they dont match speeds so grating occurs or they jam or teeth wear so that teeth wont line up a synchro cant slide over as meaning you cant push gear stick far enough you shouldnt try second gear till car is going slow enough to fit in with second gear speed, thats what brakes are for ,obviously series boxes are a bit cruder than modern boxes

That's fine thanks mate. I don't typically use gear changes down to brake so no problem I was just doing it to experiment and see what I should be expecting. Sounds as though nothing is abnormal with mine so I can move on to the other hundreds of things that are

Landy's give plenty of engine braking (just as well...) so don't be afraid to use it. It's an old design of box and even with synchro (which will probably be worn) it's worth trying to match the engine revs when changing gear. It'll be a lot less jerky - especially if you can master double declutching. (google it). Jerkiness in the transmission chain could also be worn propshaft and/or diff, so check these as well.
Get everything right and you can make clutchless gear changes, which may well prove useful one day......

That's very educational Oxides, thanks.

I looked up double declutching for something else recently and realised it's something I've been doing as needed for some time. I also drove from Norfolk to Surrey with no clutch fluid one night and so was pretty expert at clutchless gear changes by the end of that!

I take on board what you say about worn diffs/prop, they are things I still need to overhaul so will bear in mind that until I have they may be having an effect. I understand the Series should rock (back and forth) somewhat when parked as the slack in the drivetrain is taken up. Mine does this a lot (sometimes I'll lean on it to do something like put a shoe on and it feels as though it's about to roll away! ). Perhaps this is normal but now I'm also considering that this could be excessive and symptomatic of the kind of wear that you are suggesting may be present? - What do you think??

Lots of rock with the handbrake on can only come from the prop and diff (unless the gearbox mounts are broken) or badly worn half shaft/drive member splines. Propshafts are reasonably cheap so it might be a good place to start.