LSD rebuild and ratio change

[mybmw6]

If you have an open diff in the right ratio (in this case 3.46:1) and you want it to be limited slip is it as much work? Or is it simply a matter of changing the centre with that of the LS variant? I'm using it on my m30 conversion and money's a bit tight. Overhere in Australia it will cost $1100 for a 3.46:1 LSD diff or $550 to take my diff and make it LSD. Just wondering how much work it will be?
Cheers Matt

[stuartgallafant]

Have a peek at this link http://www.metricmechanic.com/pdfs/Differentials.pdf

Gives a good idea of the internals of our LSD's, however our standard E30 LSD's have only 2 sets of plates rather than the 3 illustrated.

A good tip if you're rebuilding one, when fitting the end cover make sure you use strong (green) loctite on the 8 bolts. I've got an LSD here that had unwound 7 of the 8 bolts and snapped the head off the 8th. All the bolts have been chewed up by the crown wheel and pinion damaging the gears and chewing up the bearings with the swarf and metal chippings

The bolts are difficult to get hold of, metric fine M8x1.00x16mm reduced height socket heads in high tensile 10.9 steel

Fortunately I've rescued the clutch unit so I can fit it to another good diff.

Cheers,

Iain T

iain, do you have any pictures, coz i cant quite garsp the part of the diff that you are talking about! it sounds bad though!!

[Templ8e30]

Here's a pic

I couldn't get the correct bolts in M8 fine so had to settle for hex heads

You can just about make out the teeth marks on the old bolts

Cheers,

Iain T

[Templ8e30]

If you have an open diff in the right ratio (in this case 3.46:1) and you want it to be limited slip is it as much work? Or is it simply a matter of changing the centre with that of the LS variant? I'm using it on my m30 conversion and money's a bit tight. Overhere in Australia it will cost $1100 for a 3.46:1 LSD diff or $550 to take my diff and make it LSD. Just wondering how much work it will be?
Cheers Matt

The open diff would have to have the differential gear unit removed, crown wheel and bearings removed without damaging them, then fitting them onto an LSD clutch unit, then the lot put back into the casing and the wear patterns checked to see if it needs re-shimming.

Not easy

Cheers,

Iain T

[gareth]

cor, i've missed a lot! thanks guys! looks like i've started off a diff rebuilding craze!

i knew someone would have the answers.

so, regarding the capri rebuild kit. am i right in thinking that one kit can do either:
1x custom 4 plate E30 diff or
2x standard E30 diff rebuilds?

the machining looks relatively straightforward...

looks like the best bet would be to get an open diff of the right ratio, a spare to throw in the car while i'm doing the work and then get stuck in!

[gareth]

it's funny what you find with a bit of googling...
http://e36coupe.com/forum/viewtopic.php ... 9c9ac9babb
more useful info from mr M3compact! do you have a forum or thread somewhere with any rebuild guides etc? might save me asking repetative answers that you've no doubt been asked before!

[M3Compact]

I couldn't get the correct bolts in M8 fine so had to settle for hex heads

Are the hex heads only 8.8?

I can give you a contact for the socket capscrews in 12.9. We drill/lockwire them, they're famous for coming undone.

Some of the crownwheels use larger bolts for the LSD unit, if you need a collar for the bolt, use an S14 head/block dowel. Number 4.

Agreed shimming isn't a cake-walk, but it's DIYable with patience.

You don't need pinion bearings/crusher etc Stuart, leave the pinion alone, setting it up is the full nightmare.

[stuartgallafant]

You don't need pinion bearings/crusher etc Stuart, leave the pinion alone, setting it up is the full nightmare

i was just gonna change all the bearings for the sake of it!!

what i might do is rebuild the slipper unit myself, then send it away and get the ebarings changed

iain, those broken bolts, are they the ones that hold the unit to the crown wheel?

[DanThe]

So whats best, rebuild an open diff of the correct ratio with LS clutches, or transfer the c/p of the correct ratio to a LSD.
My M3 diff locks up fine but I want a lower ratio, im planning on using a 3.07:1 c/p with my diff

yes no

[M3Compact]

So whats best, rebuild an open diff of the correct ratio with LS clutches, or transfer the c/p of the correct ratio to a LSD.
My M3 diff locks up fine but I want a lower ratio, im planning on using a 3.07:1 c/p with my diff

yes no

Take your LSD unit out and fit it in an appropriate ratio housing, changing the ratio/setting the pinion up within a housing is tricky/awkward.

[Templ8e30]

iain, those broken bolts, are they the ones that hold the unit to the crown wheel?

No stu the broken bolts used to be where the hex heads are now, holding the end plate onto the slipper case.

Cheers,

Iain T

[DanThe]

So whats best, rebuild an open diff of the correct ratio with LS clutches, or transfer the c/p of the correct ratio to a LSD.
My M3 diff locks up fine but I want a lower ratio, im planning on using a 3.07:1 c/p with my diff

yes no

Take your LSD unit out and fit it in an appropriate ratio housing, changing the ratio/setting the pinion up within a housing is tricky/awkward.

Thats going to be a problem as I dont think any E30's came with 3.07

I know some E36's did and their crown wheel is the same size

[mybmw6]

If you have an open diff in the right ratio (in this case 3.46:1) and you want it to be limited slip is it as much work? Or is it simply a matter of changing the centre with that of the LS variant? I'm using it on my m30 conversion and money's a bit tight. Overhere in Australia it will cost $1100 for a 3.46:1 LSD diff or $550 to take my diff and make it LSD. Just wondering how much work it will be?
Cheers Matt

The open diff would have to have the differential gear unit removed, crown wheel and bearings removed without damaging them, then fitting them onto an LSD clutch unit, then the lot put back into the casing and the wear patterns checked to see if it needs re-shimming.

Not easy

Cheers,

Iain T

Are there any guides on checking the wear patterns? I haven't had much experience with Diffs?

I think for A$550 it'll be worth getting the shop to do it. But it'd be nice to know what is involved so I can be sure they are doing it properly. Sorry to sound uninformed but what is involved in "reshimming". Which part of the diff gets reshimmed?

That was a good page by the way (metric mechanic). I read up on exhaust section ages ago. Didn't realise they had other information.

Sorry I didn't read the whole post again

Liam, if you swap the clutch unit from an LSD to another diff you need to swap ring gears and still need to shim up the output bearings. Ideally you should remove the inner bearing races from the LSD and fit the inner races from the open diff, the bearings are made as a matched set and mixing inner/outer races from different bearings is not a good idea.

I think I need to examine the parts of the e30 diff a bit closer before I ask anymore questions.

[oze30]

shimming.. usually between pinion and crush bearing or anything that is not sposed to have too much lateral float I think.

The main part of a diff that gets shimmed.. I think is the pinion/crownwheel mesh, and not sure what else ( that;'s what was involved with my jeep's lsd.. though how similar they are to bmw.. NFI mate!!!

[stuartgallafant]

So whats best, rebuild an open diff of the correct ratio with LS clutches, or transfer the c/p of the correct ratio to a LSD.
My M3 diff locks up fine but I want a lower ratio, im planning on using a 3.07:1 c/p with my diff

yes no

Take your LSD unit out and fit it in an appropriate ratio housing, changing the ratio/setting the pinion up within a housing is tricky/awkward.

Thats going to be a problem as I dont think any E30's came with 3.07

I know some E36's did and their crown wheel is the same size

dan, how about a diff from a Z3???

they had some pretty low ratio's on them, esp the 2.8 models... just a thought

[stuartgallafant]

so, regarding the capri rebuild kit. am i right in thinking that one kit can do either:
1x custom 4 plate E30 diff or
2x standard E30 diff rebuilds?

Can anyone confirm this? i think i'd like the custom 4 plate diff type!!! :winkeye:

the machining looks relatively straightforward...

what is onvolved in the machining, i dont quite understand!!

[gareth]

it looks like a case of getting the E30 thrust plates modified for the extra length of the extra clutch plates and machining new 'V' grooves (90° round from the original ones) at a shallower angle, like 30° not 45°. plus some other farting around and grinding shims up etc

[stuartgallafant]

i understood about machining the new grooves into the thrust plates. but do you have to make them shallower? (not as thick?!)

also, Simon mentioned something about machining something, 50 thou??? i assume he means 50 thou of an inch, but what part is he talking about?

[gareth]

not sure as yet! i suspect the carrier cover or thrust plate.

i'm quite looking forward to having a play now!

i first need to find a donor diff for the ratios and a scrap rear beam / diff to roll the car about on while i rebuild the whole subframe.

[stuartgallafant]

yeah, im looking forward to it as well, should be one more thing for the learning curve!!

fortunately i got mine off the road at the moment, so i can play about for as long as i need to!

simon, can you confirm what exactly has to be done?

[M3Compact]

You need to machine 50 thou to allow for the taller cluster and leave the washer out from the other end, it'll all become clearer when you've got the cluster apart.

Good thread here.

[stuartgallafant]

You need to machine 50 thou

from where though simon?

checking that thread now...

[stuartgallafant]

there is a good bit of info in that guys write up

[stuartgallafant]

Atlas LSD Plate Repair Kit. Consists of 4 steel external drive plates and 4 coated internal drive plates


Atlas Gp4 Plate Repair Kit. Consists of 2 steel external drive plates, 4 coated internal drive plates and 2 external lug wavy plates for added preload.


Atlas LSD Gp4 Wavy Plates. Manufactured from profiled carbon steel, formed, and heat treated.

Simon, sorry to be a pain in the 4rse, but can you tell me which of the above kit i should purchase, as im not sure!

also, is it the thrust plate that must be machined 50 thou? the same part that you cut the new grooves into?

thanks again

[Aragorn]

looking at his image of the groove angles in his first post the 50thou comes off the same face as your cutting the new angles into

[Templ8e30]

I think you'll find that you need to machine 50 thou off the end plate that bolts on to the carrier, the inside of which exerts pre-load pressure onto the clutch plates.

You need to make space for the extra clutch plates, one side needs the thick washer removing and the other side needs 50 thou taking off the inside of the cover (number 4).



Cheers,

Iain T

[M3Compact]

looking at his image of the groove angles in his first post the 50thou comes off the same face as your cutting the new angles into

No, the pressure rings/ramp angles are only machined to change the locking characteristics, this is optional and not req'd to fit the 4-clutch upgrade.

The 4-clutch upgrade improves the durability, the cluster stack height affects the pre-load which can also be used to influence the locking characteristics - but it doesn't have to.

It's the casing/end that needs machining to accept an extended cluster stack height, it all becomes clear when you get it apart and see how it works. The thread I linked to earlier has some great pics.

This is what you need Stu....

Atlas LSD Plate Repair Kit. Consists of 4 steel external drive plates and 4 coated internal drive plates

Wavey plates increase the pre-load via compression without altering the cluster's fixed stack height, again it all becomes clear when you get inside it.

In simple terms, the LSD unit is a self-contained 'loaded' unit that can allow open drive from either end, the more loaded/poised it is when open, the more readily it will lock. Wavey plates are like spring loaded Pringle/crisp shaped washers that increase the pre-loaded poise.

Altering the ramp angles on the pressure rings makes it easier for the unit to lock, without increasing the pre-load/poise.

Extra Pre-load/poise = lots of locking action. (Gravel.)

Altered ramps = normal action - but more readily locked when stretched. (Tarmac.)

Combined extra pre-load/poise and lowered ramps = Riot.

[stuartgallafant]

simon, you are the MAN!!!!

my god, i cant wait to try this!! the diff is coming off friday afternoon now!! im on the search for a 4.27 open diff, medium case now!!!!

[stuartgallafant]

there is some really useful stuff on the metric mechanic website that we can use when doing this rebuild

[odbod]

Looking at the metric mechanic website it shows there are small medium and large case diffs, which is well known. But it also states that the different diffs use different size friction plates. The atlas re-build kit is £80 from driveandtraction but what size diff do the atlas plates fit? It seems the 4 cyl engines had the small case diffs (168mm ring gear) and 6 cyl used medium case diffs (188mm ring gear), if so re-building and 318is diff may not work with the Atlas re-build kit. Or alternatively re-building a medium case diff may not work with a 4.10 ratio. I'm very interested in doing this as well so if anyone knows teh answers to the above comments it would be very helpful...

[stuartgallafant]

ah, thats why i swapped my small case 4.10 open diff for a medium case 3.91 LSD!!

[M3Compact]

Looking at the metric mechanic website it shows there are small medium and large case diffs, which is well known. But it also states that the different diffs use different size friction plates. The atlas re-build kit is £80 from driveandtraction but what size diff do the atlas plates fit? It seems the 4 cyl engines had the small case diffs (168mm ring gear) and 6 cyl used medium case diffs (188mm ring gear), if so re-building and 318is diff may not work with the Atlas re-build kit. Or alternatively re-building a medium case diff may not work with a 4.10 ratio. I'm very interested in doing this as well so if anyone knows teh answers to the above comments it would be very helpful...

You're correct in your assumptions. The Atlas kits will only work in medium case (188mm CWP) diffs and the small case CWPs can't be used with medium case LSD clusters.

4.1:1 188mm is available with medium case tho, I've just sold one herethat was bought from Jimbob.

[stuartgallafant]

there is a medium case 4.27 open and LSD and a medium case 4.10 open floating around

mainly used on things like 320i SE or 320 tourings and stuff

[odbod]

Hmm best keep looking for a diff then, There are a few floating around on ebay @ 3.73 and 3.91, they all look the same externally. The metric Mechanic site seems to show them as medium case diffs. Question is...

Can you tell externally whether they are medium or small? If so anyone got a picture to confirm?

If not how can you tell?

[M3Compact]

Medium case has 8 bolts on the back plate.