clubstylus

Going to be fitting this at the weekend - any advice before I take the diff to pieces?
Have bought a complete bearing and seal kit including collapsible collar - although I'd like to just put it all back as I took it apart and therefore not need to set the crown gear back lash thingiemijig.
Any advice gratefuly used !!

norma wrote:Going to be fitting this at the weekend - any advice before I take the diff to pieces?
Have bought a complete bearing and seal kit including collapsible collar - although I'd like to just put it all back as I took it apart and therefore not need to set the crown gear back lash thingiemijig.
Any advice gratefuly used !!

YES Don't touch it ---------- get it fitted by a professional , it's going to cost you so much if you get it wrong . Engines are a doddle --- gearboxes and diff's are tricky

we re-built our standard diff and it took a good part of a day to set the backlash! We havent driven it yet with it re-built, but are a little concerned when we do! we shall see.....

I have the mkII haynes manual (you know - 'fitting is the reverse of the removal process' and everything starts with 'disconnect the battery first')
But to be fair, it goes into quite high detail about setting backlash.
BUT surely if you put the retaining nut back exactly the same amount of turns and use the original crusher spacer - your backlash will stay as Henry intended?
Can't be that hard - all your doing is setting the pinion gear in the correct place on the crown wheel surely? (famous last words!)

norma wrote:BUT surely if you put the retaining nut back exactly the same amount of turns and use the original crusher spacer - your backlash will stay as Henry intended?

I might be wrong but the retaining nut only gives the pinion preload which is the easy part to do.

so what's the hard part then?

norma wrote:so what's the hard part then?

Getting the back lash which is moving the crown wheel and shimming the pinion to get the mess right involves engineer blue and hours of setting up. Did it years ago when serving time but this was on a tractor with a old journey man who was sh*te hot. As said earlier try to find a gearbox reconditioner who could take it on or do it yourself but make sure you understand the instructions because it will wear out quickly and whine badly and cost a fortune in parts as the pinion and crown wheel will be US.
Cheers George

hearbear wrote:

norma wrote:so what's the hard part then?

Getting the back lash which is moving the crown wheel and shimming the pinion to get the mess right involves engineer blue and hours of setting up. Did it years ago when serving time but this was on a tractor with a old journey man who was sh*te hot. As said earlier try to find a gearbox reconditioner who could take it on or do it yourself but make sure you understand the instructions because it will wear out quickly and whine badly and cost a fortune in parts as the pinion and crown wheel will be US.
Cheers George

Thanks George - advice heeded!

I agree with you all, that it can be difficult job... but..

Just my two peneth.

I fitted an ATB diff in place of the original one.
I too was a bit bothered, but in the end its just a mechanical engineering job, so was worth an attempt !
After all if you cock it up, that's when you give it to a specialist.

Where I cheated, was that I retained the same 3.89 ratio between the old & new diffs.
I bought & still have in the garage a new 4.7 CWP set, but having thought about the ratio itself & how to do it, decided to keep it simple.
Having little time before my first ever sprint, I changed the diff over on a saturday afterrnoon, for a sprint on the sunday.

In 2-3 hours.. this is what I did...

Pulled the shafts split the prop, then removed the diff from the car.
Take the open diff assy out, leaving the pinion/crush tube/nut & diff flange flange alone.
Then simply changed the crown wheel from the open diff onto the ATB.
Rebuilt the diff assy (with the ATB) using new bearings.
When this was dropped back in the diff case the backlash and gear meshing was the same as original (& within the picture tolerance shown in the haynes book).
Reassemble & drive round the block !

Has been OK for the sprint, over a year on the road , the Llandow trackday, etc...
No nasty noises (so far !) & I still have the 4.7 on the shelf if I really want to go there.
Would recommend a 4.44 like Rob's really, 4.7 will make the gearing a bit tooooo short.

Matt

That's exactly what I intend to do - take the crownwheel out and put it back in again with the ATB attached.
I like your idea of "have a go and if you fail - give it to an expert".
I'm going to take it out tomorrow and make my mind up then - if you don't even have to remove the crusher spacer, then it sounds pretty straightforward (I though the whole lot needed removing )
If I can rebuild an engine from the basic components then surely a diff ain't too hard?

norma wrote:That's exactly what I intend to do - take the crownwheel out and put it back in again with the ATB attached.
I like your idea of "have a go and if you fail - give it to an expert".
I'm going to take it out tomorrow and make my mind up then - if you don't even have to remove the crusher spacer, then it sounds pretty straightforward (I though the whole lot needed removing )
If I can rebuild an engine from the basic components then surely a diff ain't too hard?

Raceline put mine in together with it's changed crown/pinion 4.4 . However , I was surprised to learn afterwards that even they considered it to be a specialist job and they send all diff's away to a guy who just does diff's.(Pete Mckewan at Raceline is ex - F1 engineer too) If you get it wrong it'll be too late to pass it to a specialist --- any damage will be done .
Perhaps as you're not changing ratio's you'll be fine

norma wrote:That's exactly what I intend to do - take the crownwheel out and put it back in again with the ATB attached.
I like your idea of "have a go and if you fail - give it to an expert".
I'm going to take it out tomorrow and make my mind up then - if you don't even have to remove the crusher spacer, then it sounds pretty straightforward (I though the whole lot needed removing )
If I can rebuild an engine from the basic components then surely a diff ain't too hard?

Yep, if you can build up an engine, then a diff seems OK

Just a follow up thought...
Leave the pinion alone as I said (meaning the front/rear mesh axis is fixed), then when you refit the ATB diff assy with new bearings, use the pre-load on each bearing cup to set the left/right mesh axis.
ie count the number of turns to undo the old bearings before you take the open diff apart, & fit the new ones to the same depth on each side (+/- a bit for wear on the old ones !).
You'll then be able to fit the locking "claws ?" back into the same holes on the lock rings.
That's how you get the same CWP mesh, its not just drop it straight in.
(It'll make sense when you do it !!!!)
Mr Haynes tells you all this too, so do think it through.


I don't think changing the ratio would be beyond most of us either, its just a trial & error job with engineers blue.
The main component is Time... where the specialists win is that they've got all the right tools & are well practised, meaning they save time. It could take you all weekend buggering about in the shed to get it right at home !
If you want someone else to do it, Hardy Engineering in Leatherhead is the place (that's where Raceline send theirs!)

Matt

Matt - I wish I'd read your post before dismantling it
The bit where you say "count the number of turns to undo the old bearings before you take the open diff apart, & fit the new ones to the same depth on each side (+/- a bit for wear on the old ones !).You'll then be able to fit the locking "claws ?" back into the same holes on the lock rings. "
That was the bit i din't do
So what I've done (with new bearings) is tighten the lock rings up quite tight, then back them off 1 hole which has given me a very slight amount of backlash. I now realize it is possible to shift the whole cronwwheel/diff assembly side to side by adjusting those lock rings - I know its better to have a small amount of backlash rather than none - but how much should I have? When the diff gets warm, everything will tighten up (much like a wheel bearing) so have I left enough slack???
The gears look like they are meshing perfectly, and gut instinct tells me I've left enough play - but gut instinct isn't always right is it?!!
Anyone care to comment on backlash values?
Cheers
Alex
p.s. might post this on the chat list too -

Hi Alex

Sounds ike you're having fun ! & you're a long way from me for a visit !
(although I'm in Stockport on Tuesday night, if you haven't solved it)

If I had got myself in your position I'd have done exactly what you have.
Use one bearing to position the crownwheel side-side into the pinion, giving an approximate mesh as per the "correct" haynes picture. (I assume you've got them ?? If not I'll post them).
Then tighten up the other side & recheck the mesh. I used grease on the teeth to show the contact pattern.
From you're post I'd guess you've done this already ??

From this point I'd go up quite tight on the lock rings (to no backlash), which should be too deep on the gear mesh pics.
Then back them off to the point where the mesh is too loose (loads of backlash/the third pic) counting how many holes/turns that is. Then refit at a mid point setting & recheck.
I'd err on too much backlash rather than too little, for the same reasons you're thinking.

Get it to the point where it looks wrong at either end of the scale & go back to half-way ?!
For me, gut instincts are usually right, just explore the boundaries ?!

What that equates to in a measurable backlash value I couldn't guess !

Cheers

Matt

Thanks Matt - that's more or less what I've done.
Spent ages last night looking for info on the net and found instructions on setting up a landrover diff - they looked near identical and used the same system exactly.
see: http://www.kamdiffs.com/land_rover/fitt ... ctions.pdf
They said to tighten the one side so you just had no backlash, and then tighten the other so that it pushed against the first side and ended up giving you a littel backlash. So their method basically involves removing all play from bearings and keeping minimal backlash.
I have follwed their instructions but then just eased off one hole as I felt it would be too tight.
So I'd say I'v got a little play, but according to them, one hole too much and for my gut feeling one hole too little! (seemed like a good compromise).
At the end of the day, its not going to damage the diff and I only do about 3k miles a year, so even if it is slightly too tight/loose, and I accelerate the wear on the bearings, its probably going to take 5 years before it starts to whine, and I'll probably have changed ratios again by the anyway!
Anyway - the pdf makes interesting reading.
Thanks for all your help peeps
Alex