Front locking diff upgrade - CVs and codes

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Front locking diff upgrade - CVs and codes

Postby KJH » 12 Jan 2009, 17:47

Hi all,

I have been offered a locking front diff and am toying with fitting it to my syncro. However, I have noticed that outer front CV joints are listed differently in some parts books for use with and without a front locker.

So, what are the driveshaft / cv differences for syncros with / without front diff locks. What will I need to do to get it in my van? I do already have the wiring and vaccum pipes in place for a locker, so don't need to worry about that. I'd rather not source new drive shafts!

Also, my rear gearbox is code AHF. The offered front diff is AHU, so I think this is ok? The original diff is 6N (E) - which will be for sale if all goes well!

Van is a 1991 1.6TD if that matters.

Thanks all!

KJH.
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Re: Front locking diff upgrade - CVs and codes

Postby syncropaddy » 12 Jan 2009, 18:36

PM Aidan. he will be able to answer all of your questions
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Re: Front locking diff upgrade - CVs and codes

Postby Aidan » 12 Jan 2009, 18:46

is it a 16" ?
VW felt it necessary to fit upgraded driveshafts to the front if diff lock fitted to 16" van, otherwise they ran the same shafts/cvs as 14" van of all types.
I guess that the service life of 14" cv's used in conjunction with 16" hubs/wheels/tyres/suspension was not optimal, so you may feel it necessary to upgrade, CJ will be able to help :ok
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Re: Front locking diff upgrade - CVs and codes

Postby Syncro G » 12 Jan 2009, 18:58

Both are 5.43 diffs so ratio will match unless its been rebuilt and not marked up.

16" locking diffs have bigger CV's than non locking 16" and all 14" diffs. Bigger tyres put more stress on driveshafts (ground can aply more torque on it) so maybe VW found them vonrable to damage when locker used with big tyres - probubly not an issue if you don't give it a real hammeringand slam it onto the ground when its going a different speed but they buit them to take it whaever. Personly I'd have thought the non lockers more vonrable as you can't control reduice wheel spin with locker - maybe they thought people would spec locker if they were going to nail it (and its not always possable to drive with locked front)

ADM is standard CV size 5.43 locking diff (as used on british spec TD) so as AHU is same ratio I suspect must have big joints if its a locker, otherwise it'd just be an ADM?
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Re: Front locking diff upgrade - CVs and codes

Postby Aidan » 12 Jan 2009, 22:23

no real difference between front diffs of same ratio same flanges just different speedo drives for different tyre sized vehicles
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Re: Front locking diff upgrade - CVs and codes

Postby Syncro G » 12 Jan 2009, 22:34

Aidan wrote:no real difference between front diffs of same ratio same flanges just different speedo drives for different tyre sized vehicles


But can't you get ADMs with 2 different speedo worms in them? You said it was another letter after the main code that signifys which worms fitted.
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Re: Front locking diff upgrade - CVs and codes

Postby KJH » 13 Jan 2009, 09:17

All,

Thanks for the answers. The van is a 14" for clarification. So, it looks like this upgrade will work. Not really fussed about the speedo, as it's wrong since changing the wheels / tyres and has never read right!

I also need to rebuild my front drive shafts, so I presume while the gearbox is out, the whole shaft can be extracted when the hub nut is undone - save unbolting the upper ball joint and sway bar when removing axle with gearbox in situ?

Thanks again.
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Re: Front locking diff upgrade - CVs and codes

Postby Aidan » 13 Jan 2009, 11:04

ok I took another look at the parts programme and I think it's a mistake in Etka showing the speedo drive for 16" versions against the ADM, as the ADM and 6N are 14" diffs and have a 8 tooth speedo drive, whereas AHU and AHT are 16" diffs and have a 9 tooth speedo drive, it's clear that the 16" speedos are 9/20, 9/21 and 9/22 for the 38/7 depending on which tyres fitted new; the actual driven part of the speedo drive must pair with the inner so don't try swapping the speedo drives over as the tooth pitch will be different and will quickly eat the nylon cog.
The extra letter stamped on the case below the code shows the correct speedo output shaft, but I haven't worked out the complete sequence yet as I haven't had them all through my hands. MG and I have been trying to compile a list, but we are some way from completing it - the nylon parts are colour coded and correspond with the letter stamp, but it's not as simple as suffix F is F, suffix F speedo is G on the case AHU 21/9 grey 16" on 205s, thanks VW :ok
If anyone ever removes the speedo drive I'd ask they note the colour of the cog and number of teeth on it (confusingly the same colour may have two or more different teeth counts, so you can't say black is 19) and the gearbox code and the extra letter and let me have it to help in verifying the list.
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Re: Front locking diff upgrade - CVs and codes

Postby KJH » 13 Jan 2009, 11:25

This forum is great...! Thanks all.

As I'm now running 16" wheels with 205x16 AT tyres leaving the original 16" speedo drive might improve the accuracy of the speedo! Although it's been wrong for so long that I use the GPS and it's in km/h....

Sounds like a straight forward swap into my 14" - although I'd appreciate anyone's thoughts on my driveshaft removal question in my last post.

Thanks again.
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