Syncro 4&4 Discussion and Q&A last answered over 2 years ago.
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New to all this so if you come across any mistakes just remember I'm popping my cherry posting this topic!
Had no speedo or odometer readings and have traced the fault down to the drive gear coming out of the front diff. It doesn't spin when the wheels are turned and I can not turn it even with a huge pair of waterpump pliers hanging off of it! Been to the local VW dealer (only one cos I live in Jersey) and after looking blankly at his PC screen for half hour decided he couldn't help me get one because the parts were discontinued at the end of last year.
He did tell me there are 3 possible part numbers for the drive gear assembly. This depends on the number of teeth which can be either 19,20 or 21. As I have been unable to remove the assembly I can't find this out. Is it possible to tell the correct number of teeth by the diff coding (its an ACU diff originally running 14" wheels) and does anyone know where I can get one from?
Also looking for a new accelerator pump from the carbourettor if any one knows where I can source one. Sorry I dont have much more info on this but I couldn't be arsed to stand at the VW counter for another half hour!
Hi,
if you are trying to remove the speedo drive assembly from the front diff I assume that you have unscrewed the end of the speedo drive cable?
Have you also realised that there is a roll pin just above the unit which holds it in? There is a groove across the drive housing and a drilling in the diff casing which line up. A good roll pin will prevent the speedo drive from rotating as well as hold it. I have seen several where the alloy casing around the roll pin has rotted/split - it sounds like yours must still be good.
You have checked the speedo cable itself, I take it?
You can tell what speedo drive the box is ment to have by the codes on it so Aidan was telling me. The main 3 letter code is only half the story though as the same code can have different gears off the main pinion. SOme of the other numbers next to the main code hold the answer aparently it but I can't remember how - make a note of them all. Aparently gears are colourcoded too but again not sure what means what. For a given number of teeth there are 2 versions depending on what how many teath are fitted in the diff so its important to get the right one to work reliably and accurately (mines got the wrong one, I'm bitter!)
Thanks for your response Garyd. I have indeed noted the roll pin and removed the speedo cable from the assembly which is in working order.
I was wondering if it would be easiest to remove the roll pin by using a drill. As long as I was careful not to damage the diff casing of course.
Thank you Syncro G for your input also. I was kind of hoping someone would say that the coding would be able to help verify the correct drive gear assembly.
The full coding for the front diff is ACU 20624 and there is also another C poisitoned underneath the C in ACU.
You mentioned Aidan. Is he a club 80 90 member?
Thanks again chaps for your warm welcome and comments!
I once took one of the roll-pins out for the speedo drive using an ever so slighlty tapered punch. This was a mistake as it broke off a bit of the casting . Still when I refitted it there was just enough casting left to hold the pin.The moral is use something parallel sided to knock the pin out !
SyncroMonVie wrote: I was wondering if it would be easiest to remove the roll pin by using a drill. As long as I was careful not to damage the diff casing of course.
You will struggle to drill that pin as it is a very hard bit of metal with a slot in it which will grab and break your drill bit! I have removed many of these and some/most are a bitch! Just use a goog quality dimpled roll punch
or pretty well all... some ar easy peasy, some are a bitch as atested to above!
As Andy at Syncro-Nutz says, you won't be drilling it out easy (roll-pins are spring-steel). Maybe with a cobalt drill at a push, then the hole will end up a mess... start now cleaning the whole area and soaking in Plus Gas, while you're arranging a suitable punch. Also, the higher up you can get the van the better.. unless you have a lift or a pit.
It's often better to get the old gear assembly out and match it up, by colour and teeth. Red is common...
Read the Wiki to get a feel for what might become a one chance saloon... mess it up and you may live to regret it.
Happy to send my 4.9mm punch down if you are stuck... (the one depicted)
Harry I have taken a look at the wiki page that you attached and that is a great help. I'm lucky enough to have the equipment to machine a punch to do the job (really appreciate your offer of sending the bespoke removal tool) and a lift to raise the bus high enough to make the job a little easier.
So looks like my weekend will be taken up wrestling with this roll pin.
I was wondering if it would be easiest to remove the roll pin by using a drill. As long as I was careful not to damage the diff casing of course. 
. Still when I refitted it there was just enough casting left to hold the pin.The moral is use something parallel sided to knock the pin out !
