LSD Help

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wattsmonkey
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LSD Help

Post by wattsmonkey »

Hey chaps,

Having had a good old shakedown I found one of the driveshafts was crap (there may be an American term for this - not the propshaft, but the shafts that connect the diff to the driven wheels - what do you call them?)

Boot had split, much clunking going on.

So, offending driveshaft removed, but then needed to move the car urgently. Car does not move. Disconnected side of diff spins round happily, but no forward motion.

I imagine this points to a worn out diff, but am in error thinking that I should have had some (say 25%, maybe) of the drive being transferred to the other wheel?

If it is a worn out diff, has anyone got any suggestions? Is a Quaife ATB going to ruin the smooth driving experience?

It is the original diff, btw and both output flanges did turn in the same direction when the diff was off the car.

Any thoughts most welcome.

Rob
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baders
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Re: LSD Help

Post by baders »

Sounds like your LSD has become an open diff ! To move the car, try light braking to stop the spinning side and engage the other side. Don't know much about refurbing LSDs but make sure you replace all bearings when you do.
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Re: LSD Help

Post by dwcains »

I've got Quaife diffs in one of my Alfa's and in my 350Z. Couldn't be more pleased. They're smooth, silent, and require no maintenance. The only downside is that if one wheel is ever off the ground, you'll get no drive to the wheel that is on the ground. There is a very similar diff, made by WaveTrac, which doesn't have that issue, and if I eve upgrade the LSD my 635, that's the one I'll buy.
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wattsmonkey
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Re: LSD Help

Post by wattsmonkey »

Hadn't heard of WaveTrac,

Thank you for that,

Rob
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Re: LSD Help

Post by Dan101smith »

Rob, I'd just get the diff refurbished back to factory spec if I were you. Good opportunity to get seals and bearings replaced while you're there, and to check for any significant wear to the CW+P.
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Re: LSD Help

Post by wattsmonkey »

Thanks Dan,

It appears the clutch plates are nla, hence considering other options.

Am enjoying my very limited limited slipping for the time being!

Rob
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Re: LSD Help

Post by Dan101smith »

I wouldn't worry about them being NLA, any decent diff builder should be able to source you some replacements. If memory serves, there was a Volvo diff from the same era that used the same parts.
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Re: LSD Help

Post by bpoliakoff »

Dan101smith wrote:I wouldn't worry about them being NLA, any decent diff builder should be able to source you some replacements. If memory serves, there was a Volvo diff from the same era that used the same parts.
+1 I had my diff rebuilt at a a large tractor(Freight truck) shop. I supplied bearings and seals, he supplied anything else needed.gears were good. His cost to me was $250. he even had shims I needed for fitting the output shaft on my trans and gave them to me as a gift
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Re: LSD Help

Post by duracel79 »

I've bought plates from here before:

http://driveandtraction.blogspot.co.uk/

Regards

Ben
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Re: LSD Help

Post by wattsmonkey »

Nice one Ben,

£120 odd delivered for "two coated drive plates and two steel 4-lug plates".

Thank you very much!

Rob
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ericono
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Re: LSD Help

Post by ericono »

Bringing this one back from the dead.

I need some help understanding LSDs. How does the stock diff in the M635 differ from a Quaife diff, as well as an OS Giken or Drexler diff (or the Wavetec mentioned above)? Any feedback on how any of the diffs perform would be appreciated too.

Thanks,

Eric
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Da_Hose
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Re: LSD Help

Post by Da_Hose »

Ahhhhhh...... you need details. A quaife is a torque biasing differential, not a limited slip. Here is what I understand of the whole shebang.

I imagine you know how an open diff has no balancing, it just free spins in opposite directions. When going through a turn, that allows your wheels to spin at different speeds, but torque is sent to both wheels totally un-balanced. While that provides even acceleration with full traction at both wheels, if a wheel just breaks loose, then all torque (which is unregulated) goes to the slipping wheel.

The Quaife differential has a gear setup that can balance torque based on traction. So if one wheel has less traction, the other wheel gets more torque. However, the quaife relies on the torque differential to determine the amount of bias (balance). Because it needs a reference value, if one wheel is completely off the ground, the differential starts counter rotating like an open diff.

The limited slip differential has a set of locking plates that will bind at pre-set values. Many times a number of 25% is tossed around as a base line, but with proper springs, that rate is (basically) infinitely adjustable. So lets say you pre-determine that one wheel can "slip" at a rate of up to 25% less than the other. Then, when you stomp on the throttle coming out of a turn, the outside wheel hooks up on tarmac, but the inside wheel is on gravel. The inside wheel will start to spin faster than the outside at an increasing rate until it is spinning up to 25% faster than the outside wheel. The moment it exceeds that pre-determined value, the differential will lock up, and equal power is sent to both wheels. That allows you the traction benefits of an open differential through a turn, but prevents total loss of traction due to only one wheel breaking free.

Make sense?

Jose
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Ralph in Socal
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Re: LSD Help

Post by Ralph in Socal »

BMW started installing a factory torsen unit about 2003. Usually found in the Z3 and Z4 cars and easily adaptable to e24/28 as the cars used an e30 rear subframe. I've seen ratios from 3.15 to 4.27.

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Re: LSD Help

Post by Da_Hose »

That's great info. Ralph.

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Ralph in Socal
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Re: LSD Help

Post by Ralph in Socal »

This one is ready to install in my euro 635. Case, Rear Cover and Flanges are exactly the same as E30 so adapting to E24 requires only the Flanges and Rear Cover.

Internal pic to show what it looks like inside. There are multiple planetary gears inside the center section to effect the distribution of torque to the proper output/wheel

Ralph
Z3 Torsen.JPG
Z3 Torsen.JPG (412.26 KiB) Viewed 9266 times
3.15 Torsen Guts.JPG
3.15 Torsen Guts.JPG (176.17 KiB) Viewed 9266 times
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ericono
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Re: LSD Help

Post by ericono »

Jose,

Thank you very much for the detailed explanation. That is helpful in explaining the difference between an LSD versus the Quaife torque biasing. What I am not clear on is the following:

1) What is in the stock diff of an M635?
2) Are the OS Gikan and Drexler LSDs that you can vary the % of lockup by varying the clutch plates?
3) Is the Quaife the only torque biasing diff?
4) Where does the Wavetech fit in?
5) What sort of diff is the Z3 dif shown in Ralph's post and how is it better than other options?

Sorry for all the hand holding, but I really appreciate the help.

Eric
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Re: LSD Help

Post by tschultz »

1. 3.73 'big case'
http://www.Drive4Corners.com
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ericono
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Re: LSD Help

Post by ericono »

Thanks for the reply, but I see my question wasn't very clear. I meant what sort of lsd is in the stock M635?

I'm just confused by the different types, how they compare and what makes one type better than the other.

Again, sorry for the hand holding.

Eric
'85 M635, '00 528iT, '98 Z3
wattsmonkey
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Re: LSD Help

Post by wattsmonkey »

Clutch type in the m635 diff. Almost certainly worn clutch type! Torsen doesn't t wear out as no friction discs, just cool gears.clutch plates not expensive.
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Brucey
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Re: LSD Help

Post by Brucey »

ericono wrote: Sat May 26, 2018 1:13 pm I need some help understanding LSDs. How does the stock diff in the M635 differ from a Quaife diff, as well as an OS Giken or Drexler diff (or the Wavetec mentioned above)? Any feedback on how any of the diffs perform would be appreciated too.
Operation of all LSDs is not obvious. The standard BMW diff is a plate-type one and the factory standard is 25%. AIUI this does not impose any control whatsoever on the relative speeds of the two halfshafts. It confers a maximum torque value which can be applied to the slower moving/less grippy wheel. The diff is either locked (which means that the halfshafts are turning at the same speed) or the LSD is slipping in which case the halfshafts are turning at different speeds and the torque applied to the (usually inside) wheel with the least grip is 25% of that applied to the outside (grippy) wheel.

Note that when the grip on the inside wheel is not enough to withstand 25% of the torque, the diff is locked and the inside wheel skids. In a tight turn there could be quite a lot of skidding and tyre wear this way. If you are heavy footed, you may start to spin up the grippy wheel too and then the back end is stepping out. Note that under some conditions this can cause the rear end to break away more easily than normal.

If the grip on the inside wheel is enough to withstand 25% of the torque, the diff slips and still allows different speeds on each rear wheel (which you need going round corners).

Obviously if the locking action of the diff is too aggressive (say 75%) then the tyres tend to wear badly in nearly every corner, because the inside wheel must be slipping on the road surface whenever the grip is less than perfect. It almost isn't worth having a diff at all.

The locking action is generated by two things; spring preload on the plates and an automatic loading via a torque-generated thrust. If there isn't enough spring preload (eg because the plates are worn) then when the inside wheel has no grip, there is no torque being transferred and therefore no locking action in the diff too.

Other diffs work differently to this and they all have their peculiarities.

cheers
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Re: LSD Help

Post by GazM3 »

Also with the clutch type lsd oem bmw have pressure rings that have a bearing on how easily they lsd unit locks up. Often people just add more clutch packs for more lockup % but a less well known method is to change the ramp angle on the acceration side of the pressure rings of the diff (for memory I went from 45deg to 33deg). so it more easily locks up under acceleration but unlocks under deceleration. I have this in my m3(well when it was working) and it seemed to work really well. Chattered a tiny bit in concrete car parks but was very streetable

The only other diff I had experience with is a trutrac (non bmw) which locks positive the diff under acceleration and unlocks under deceleration. It is streetable enough for daily driving and doesn’t wear like an lsd. As it wis in my Holden work Ute rapid fire short changing at low revs briskly with about 3/4 throttle dosent work like it does on my bmws as it feels like the diff mounts are going to rip out so it’s old school hot rod slow and steady gear changing only. How it works I don’t know. Magic?

Lots of people have high praise for the Quaife (even the obx copy of the Quaife) which can be purchased for the medium case diff for reasonable $$, not the drug money asked for the original anyway.
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