Front diff questions

[KJH]

Hi all,

I have a replacement front diff unit to fit in place of the original that doesn't have a diff lock. I have two questions please!

1. Speedo drive - I have read the Wiki article, and I can see whats involved. The final drive ratio of the old and new unit is obviously identical, so can I just swap all the nylon speedo drive from old to new? Will the drive pinion on the unit be the same as the final drive is the same or will I have to swap the pinion as well as the nylon gear? Is swapping the pinion gear easy?

2. Diff lock - again read the Wiki. How easily should I be able to push in the diff lock by hand? It is quite stiff? Any thoughts on freeing it up? Should it spring back automatically? I can get it to engage ok.

Thanks.

[Aidan]

Speedo drive swap straightforward if the drive gears are the same, eg both 8 and you are just swapping say a 19/8 set for a 21/8, but I'd say that swapping the drive gear isn't straightforward as the lockring above it is what sets the preload on the pinion bearing, so whilst you might be able to get it off and swap the drive gears and fit a new obsolete lock washer and get the lockring sort of tight with a chisel you can't be sure it's properly tight and loose bearing will whine, wear and fail quick; really should be done pinion out on the bench with the correct tools, though I've seen at least one that's been done without the tools
That's why there are different code front diffs with different drive gears for the different tyre sizes cos it isn't a simple workshop job even for a fully equipped vw workshop
should be able to push diff lock pin in with your pinkie and spring should push it back out when you release, if front dissasemble and sort it on the bench if late rear (ie long pin about 25mm showing) can be done in situ, basically with 2.5mm allen key or suitable rod through the roll pin hole and gear oil in the switch hole and with the bracket still on and the circlip still on the sleeve give it a w..k until nice and free. May require a bit of persuasion at first Lots of clean gear oil in through teltel hole will wash out the crud that is blocking the spring.
If you have removed the circlip or the bracket etc.. then be aware that the sleeve can move in the case rather than the pin so isn't actually working properly and won't work when reassembled

[KJH]

Thanks Aidan,

Yes, the diff lock I am trying to fix is the front one, so I think I'll take the front cover off and seeing what's up. What I noticed last night is that the diff lock pin is easily moved with a push as long as the indicator light switch is removed! The switch works fine and is free, but locks the whole lot up as soon as I screw it in - I can see the hole in the pin that the switch pin drops into ok. No spring back though....

"be aware that the sleeve can move in the case rather than the pin" - yes this might be what's happening. The pin is about 15mm diamter, but something around 30mm moves in and out of the case and has an o ring on the outward end. Is this the sleeve? Maybe this movement is causing the switch pin to lock up?

Anyway, thanks for your help - I'll attack it again and get some pictures. Hopefully I haven't bought a dud as was assured it was good.....

Cheers.

[Aidan]

yes the sleeve is moving not the pin, you'll find that the pin is seized, it doesn't work when the switch is in because the switch is stopping the sleev moving; the plate and external circlip all secure the sleeve so it can't move, the switch is not a lateral stop really.
easiest to do it on the bench,cover off, punch out the internal roll pin of the fork and recover pin with magnet and withdraw the sleeve and pin complete, be aware it's very soft and brittle alloy so don't clamp it up heavy in a vice, tap out the pin, recover the spring, clean out the bore of the sleeve lightly then lots of gear oil, reintroduce the pin into the sleeve and gently but firmly ream them together untill reasonably free, add spring and continue, add oil through switch hole and see it flush out smaller hole till really free and easy and spring returning. O ring may need replacing they often get deformed on fitting.£1 it's a weird non standard size of course thanks vw ; lipped seal on shaft may be deformed by some solvents,but is good for gear oil obviously, will break up if you try to remove it 8/10 times so if it's intact leave it alone it's nearly £15 for a new one.

[KJH]

Aidan,

Thanks very much. I'll give this a go. I suspect that I have further issues as the alloy sleeve is falling to bits on the end so I wonder if these are available as a replacement or I'll need to get one made up on the lathe.....

Cheers.

[Van-Driver]

Hi Aidan,

What can be done to stop KJH's problem happening again ?
I understand that there should be some sort of rubber cover over the pin/actuator between the servo and gearbox, neither lock on my van has aything.
Is there a standard work around for this ?
I am concerned that if not done properly a cover could trap water and be worse than nothing at all.

Cheers,

[Aidan]

pins seize because of external corrosion and or internal corrosion, the lube is poorly gathered splash drip small hole and can gunk up and go solid from inside as well as steel pin and alloy sleeve corroding the way dissimilar metals do plus the steel pin just rusting which is where the rubber boot comes in, it's just suitable thick wall water hose (the heater supply and return hose is great) cut the length between the body of the vac unit and the bracket against the circlip, add some grease when fitting.Front is solid piece, most rears had a two piece affair with a wonderful obsolete never listed platic joiner which peeps cut off or just loose. Platicparts are us don't have a widget this form and I can't think of an application that would have used them....suggestions please

[KJH]

Aidan,

So I took it apart last night as per your instructions and managed to free it up. Unfortunately, the external part of the sleeve fell to bits with nowhere to put the circlip back on! Options? or do you or anyone have one I can purchase?



Also, is there anyway of checking the final drive ratio by counting ring teeth?

Cheers all,

[Ye Olde Syncrospares]

you have a syncro and and you need some spares,mm i wonder were i can get spares for my syncro,its like spares for my syncro,mmm syncrospares,

[KJH]

Hi CJ,

Yes - have had parts from you recently - I did email you a month or so ago wanting a few spares for this diff unit but no reply so presumed you didn't have what I needed.

I'll email you again with a list of what I need..

Cheers.

[KJH]

Aidan,

CJs offered me the parts I need for the speedo drive (and diff lock!) but says you're the man to identify the correct colour code for the speedo drive I need? The diff unit is AHU code, which is hopefully a match to my rear being a AHF 5.43 / 38:7 unit. I am running 205R16 tyres, which are 36cm radius. I'm not overly fussed if the speedo is out, as I use GPS to be honest and it's in Km/h - I just need it to mesh with my pinion correctly and work to keep PC Plod happy.

Can you help at all? Any assistance much appreciated!

[Aidan]

according to my notes AHU, speedo 21/9 205R16 is GREY 21 (that will be the one CJ tried to sell to Glen then) code G on the box 094 409 181 F fom VW, but I may be wrong I've only had one through my hands

I'm fairly confident on the 14" speedo drive Z=8 series which covers the uk spec vans
21/8 is RED
20/8 is BLACK
19/8 is WHITE and
18/8 is GREY

Mike Ghia has also been figuring them out. I have some of the codes for the cases figured I think, like the G example above, but not many and I'm not confident of them have to cross check some more.
CJ you should have figured them out over the years you'll have seen the most variants

[KJH]

Many thanks Aidan,

Forgive me - if I understand this correctly you are saying AHU has a X / 9 pinion and the original 14" box code 6N(E) will have a X /8 pinion and therefore it won't mesh so I cannot just use the original speedo drive?

If the wrongly meshing speedo drive was installed, would it be obvious, like clearly not meshing or not fitting or something?

Is there any way of being 100% sure on diff ratios by counting teeth or something - just like to be sure before I fit it! There were some hand scribed numbers on the diff body but cannot remember what they were, I'd have to have another look....

Thanks again.

[Aidan]

yes the different number of grooves means the pitch of the drive worm gears is different and so the nylon cogs on the speedo drives are different pitches. I've never tried to mate the incorrect ones but I've seen one that was wrong and it just ate the nylon cog end of speedo drive. They are designed to do that and cause no debris that could damage the pinion bearing or pinion if they seize and fail in normal use.
On the crown wheel you will find a very small stamped mark of the ratio eg K738 and the hand etched numbers are the pinion set match number and the pinion height for optimum quiet running
The only way to be sure is to count the number of grooves in the worm gear, mark one and count the number of starts on the edge of the face below the lockring

[KJH]

Thanks again for the help. I owe you a beer or three if we ever meet.