Author Topic: Fitting a "Gripper" LSD to a polo 085 gearbox  (Read 18884 times)

Offline hayesey

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Fitting a "Gripper" LSD to a polo 085 gearbox
« on: June 05, 2008, 12:28:34 pm »
This guide is a rough how-to on fitting a DR Engineering Gripper diff (usually sold in the UK by our very own Yoof of Polo-Performance-Parts).  Fitting other diffs will be pretty similar but there are some key differences.  The only other LSD I have experience of is the old phase one Gemini as was fitted to G40 Cup Cars so I will mention this a little bit.

If you are getting your gearbox rebuilt professionally then I'd recommend just getting them to do this for you at the same time.  I believe JP Race charge £60 on top of a normal rebuild fee as to be honest, it's not a lot of extra work for them.  However, being both a cheapskate and someone who likes the smell of gearbox oil of a saturday afternoon, I did it myself (plus I wasnt getting the box rebuilt right now).

Firstly, you need to make sure you have the right type of gearbox to fit a diff to.  It boils down to whether the crown wheel on the existing diff is bolted on or pressed on.  If you have a proper G40 gearbox (code ATV or something like CEH for later ones - don't quote me on the later code though!) or a GT gearbox (not sure of codes off the top of my head) then you will be OK as these all have bolted on crown wheels.  I think most 085 gearboxes from mk4 (6n) polos have bolted on ones too but you will have to check.  Also, very late mk3 CL 5-speed gearboxes with the code CEG have bolted on crown wheels too, however earlier CEG gearboxes do not, the only real way to find out is to remove the gearbox oil filler hole and poke your finger inside to see if you can feel the bolts or not.  Here is a picture showing the two types of diff next to each other:



The diff on the left has a pressed on wheel, the one of the right is bolted on - you can clearly see the bolts.  The retaining nuts are removed in this picture but you get the idea!

Note: you cannot swap and change crown wheels between different gearboxes.  The size of the teeth matches the teeth on the end of the layshaft in the gearbox - these two form the final drive.  You could swap over the layshaft along with it's corresponding diff crown wheel but this is a major operation requiring a complete gearbox strip down and swapping all the gears from layshaft to layshaft!  You can however swap a crown wheel from boxes of the same code, so if you have a G40 ATV box, then you are fine putting the crown wheel from another G40 ATV box in if you wanted for some reason. 

Parts Required

Right so assuming you have the right gearbox, you will also need these parts:

- 6x high tensile bolts 10mm diameter with a 1mm pitch thread, these are a pretty unusual size but are easily available on the internet.  I got mine from http://www.namrick.co.uk .  This doesn't apply to the Gemini phase one diffs, you will need to get the factory style bolts pressed into the diff casing if it doesn't already come with them. 

- a set of diff bearings and their oil seals, these are about £50 from VW:



Personally, I wouldn't bother getting the bearings from GSF or similar because of varying quality and the fact that swapping failed bearings is such a major operation! 

- "fitted washer" to set the bearing pre-load.  Please read my dif bearing replacement guide to see what this is, it's important that you measure and order the correct size washer when fitting a new diff as the size will not exactly match the original diff. Thinking "it'll be reet" and using the old washer will probably result in the bearings not lasting very long or damage to the diff and gearbox themselves.

http://www.polog40.co.uk/forum/index.php?topic=248

- 3.1 litres of LSD gearbox oil.  I use Silkolene BOA 90 LS in mine (and used it with my old Gemini diff too).  You shouldn't use normal gear oil with an LSD fitted as it can damage the LSD, you need special LSD oil with friction modifiers in (or you can buy an additive to add to normal oil if you wanted).



- small tube of gasket sealer.  This is to seal the two gearbox casing halves when you put them back together.  I've heard of people simply using ordinary silicon sealant for this but personally I prefer something properly designed to withstand engine oils and temperatures so I use blue Hymolar type stuff. 

- possibly a new plastic speedo drive wheel if you decide to replace it, alternatively remove the old one from the old diff and use that.  In my experience they don't tend to wear out.

Tools Required

Other than the usual selection of spanners and a socket set the only special thing you'll need is a dial gauge and stand for it in order to measure for the fitting washer to set preload.  You will also need a bearing separator to remove one of the bearings from the old diff, although you can get around this by buying a new plastic speedo drive wheel.

What to do

(I'll assume you already have the gearbox removed from the car at this point!).  Put the gearbox on a bench with the open clutch housing end upwards, make sure you support it with something so it's not going to fall over when you open it up.  Drain all the oil out first. Then remove the two allen head bolts inside the driveshaft flange-cups and pull the flanges out.  Remove the bolts holding the two halves together and tap upwards on the top half with a mallet to split the casing open.  you will be left with this:



Take the diff out, don't throw it away as you need several parts off it.  The first thing is to remove the crown wheel, carefully support the diff body in a vice with the nuts facing upwards.  The nuts are pretty tight so it's easiest if you've got a breaker bar.  Now remove the three linking washer things:



you don't need the nuts or these washers on the Gripper diff as the diff body itself is threaded for the new bolts you'll be using. 

Now tap the crown wheel with a mallet to slide it off the diff, it's a snug fit but not tight.  At this point, if you are fitting a Gripper diff, you WILL need to get the six bolt holes in the crown wheel machined out to 10mm, they are 9mm from the factory and bolts to suit the Gripper diff wont fit through.  This is a machine shop job as the crown wheel is made of very hardened steel.  It only cost me a tenner but it was done by a friend (who commented something like "f**k me that was made of hard stuff").  If you have a Gemini then you don't need to get this done as the factory 9mm pressed in bolts are used.

Other parts you need from the old diff are the driveshaft flange-cup retaining nuts.  These are circled in this pic from ETKA:



To remove them, hold the diff in your hand and rotate the internal assembly of pinions and planet gears.  Remove one of the planet gears and take the nut out of it, you should then be able to get to the back of the other planet gear to take the nut out of that. 

Lastly, you need the speedo drive wheel from the diff (unless you decide to buy a new one, they aren't particularly expensive if I remember correctly).  Use a bearing separator to remove the old bearing inner race and rollers from the old diff:



Now you can lift off the speedo drive wheel:



Now to fit the nuts into your new diff.  To open the diff up, there are three allen head bolts holding the two casing halves together.  Note: this doesn't apply to Gemini phase one diffs (prob not later phase two and Ricardo diffs either) as they have totally different driveshaft flanges which are thicker and have a spring clip on them to keep them from coming out.  If you have a phase one gemini without these different flanges, it's useless.  At least, my phase one gemini was like this anyway, maybe not always the case.

I found these bolts to be made of very soft metal and they will round off easily so be careful (this is shown with the bearing fitted which you probably wont have done by this point, I'll get to that later on):



When you have the diff opened up, be very careful not to get any dirt inside it.  Lift out the centre cog:



Now you can put one of the nuts into this cog:

 

It basically just drops in and will fall out when you turn the cog upside down to fit it back into the diff so refitting can be a little fiddly as you have to hold the nut in. 

Now carefully lift out the clutch pack from the diff:



This is a bottom piece with a lot of thin discs and spacers stacked on top of it, keep the whole lot together so it stays in the right order.  Also try not to rotate any of the discs as they will need lining up to fit the centre cog back into which is fiddly.

Now carefully lift out the pinion and planet gear assembly, try to keep this all in one piece too:

 

Now if you look into what's left inside the diff casing you'll be able to see the top of the other centre cog, drop the other nut into it:



Now put all the parts back into the diff and put the casing halves together.  It can be a bit fiddly to get all the different parts lined up right to get it all to fit back together.  just keep at it.  Then put those three soft bolts back in, they don't need to be mega-tight they only hold the casing together before the crown wheel is bolted on - then those much stronger bolts do the work of holding it together.

Now to put the speedo drive wheel onto the limited slip diff.  If you have a gemini phase one then it simply fits right on.  If you have one of the newer Gripper diffs then the casing doesn't have the slots for the tabs on the wheel to fit into.  Someone I spoke to said they got the casing machined to fit these tabs into.  I've not done that though as I found the wheel fits satisfactorily (depending on how fussy you are!) with a little bit of modification to the plastic wheel.  Also I didn't want to risk weakening the diff casing by taking metal out of it.  The whole reason I had to replace my Gemini with a Gripper is because the weak casing on the Gemini broke during an over-enthusiastic botched gearchange!  To make the wheel fit, I simply cut off a small part of each tab as per this pic:



compare this with your wheel and you should see what I mean.  I then found that this would allow the tabs to locate into two recesses in the diff casing that are intended to be there in order to get a bearing seperator under a bearing to remove it at a later date.  What I've done will probably mean I'll have to break the speedo wheel if I ever need to replace the diff bearings but I'm not going to lose any sleep over that.  The wheel will seem a bit loose but you'll find that when you knock the new bearing on it'll hold it tight.  I'm yet to see if this solution will last but it seems OK so far and as I said, seems preferential to maching metal out of the diff casing - it's up to you to make your own mind up. 

Now fit the inner bearing races and rollers, see my bearing replacement guide for details:

http://www.polog40.co.uk/forum/index.php?topic=248

Now fit your crown wheel to the new diff.  On my Gripper this was a very tight fit.  I tapped it on using a mallet until it was far enough to start tightening the bolts into the threads in the diff casing, this then pulled the crown wheel fully on.  These bolts need to be fecking tight so get out the breaker bar.  Note: if you need to remove the crown wheel again for some reason you will need a press to do it!

The diff with the crown wheel, new bolts and bearing fitted:



That's about it, everything else you need to do concerns the fitting of the new bearings and can be taken straight from my bearing fitting guide (which as you can see from the pictures, I wrote when I was actually fitting my LSD):

http://www.polog40.co.uk/forum/index.php?topic=248

Here's the finished article placed back in the box ready for the final re-assembly:



Now enjoy muchly improved cornering with no inside wheel spinning and better traction off the line.  Just watch out for lift-off understeer which catches you out the first few times it happens!

cheers,
Paul.
« Last Edit: May 09, 2009, 05:59:05 pm by hayesey »

Offline giorgio

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Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #1 on: June 05, 2008, 08:59:27 pm »
A truly great How to.

Offline Nick_S

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Re: Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #2 on: June 07, 2008, 12:45:45 pm »
Excellent guide Paul.

How much a bottle did you pay for that Fooks oil?
« Last Edit: June 07, 2008, 12:46:23 pm by Nick_S »

Offline hayesey

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Re: Re: Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #3 on: June 09, 2008, 09:38:20 am »
I think I paid about £8 per litre bottle last time.  I got the last lot from Opie Oils but have also bought it from RSM Motorsport in Morecambe before.

Offline hayesey

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Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #4 on: September 28, 2008, 06:47:58 pm »
Update:

after speaking to John at Gripper Diffs I've found out that the oil he recommends (and also sells) is Morris XFS 80W/140.  Link here:

http://www.morrislubricantsonline.co.uk/scripts/prodView.asp?idproduct=68

Miller also do a very similar oil which he also said was good. 

John said the Silkolene oil I had been using was fine but he finds it makes the diff "chatter" more during low speed maneuvers.  Certainly doesn't do any harm.

I had an issue with my diff where it lost too much preload during run-in, I've not fixed this and will do a separate thread soon!

Offline hayesey

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Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #5 on: May 09, 2009, 06:03:49 pm »
a bit of an update:

I fixed the preload issue some months ago now.  John at Gripper was very helpful and said it just happens sometimes during initial run-in.  He sent me a selection of clutch plates for free and I reset the static preload to about 80lb/ft by trial and error fitting different plates.

I would also highly recommend using the Morris Loxedol 80/140 LSD oil as oppose to the Silkolene stuff shown in the original post.  While my old gemini diff used to get on fine with the silkolene the Grippers don't seem to like it much.  Both myself and yoof find the grippers less snatchy and less noisey at low speeds using the Morris oil.  Not that the Silkolene isn't good oil but differnt plate-LSDs suit different oils better.

Offline nannytenerife

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Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #6 on: July 13, 2009, 04:50:20 pm »
Thanks for such an amazingly informative post. Could you describe how the diff reacts on really bad days when B roads are slippery and a bit muddy?

Cheers

Offline hayesey

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Re: Fitting a "Gripper" LSD to a polo 085 gearbox
« Reply #7 on: July 13, 2009, 05:38:32 pm »
I wouldn't want one in a daily driver.  you get lift off understeer round corners if you lift off.  Makes the steering heavy for low speed maneuvers too.  For fast driving and on track they are awesome.  For more day to day use it might be worth looking at the ATB diffs that Quaife now do for 085 gearboxes, they ain't cheap but they should be better to live with day to day (although I'm yet to drive a g40 with one fitted).  I think Alex on here is about the only person I've had feedback on them from and he likes it.