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Discussion Starter #1
I tried searching but didn't find anything too obvious or clear to me, maybe i am being a bit blind.

Can you fit the Variable M Diff to an E39?

I have read elsewhere that the E46 variable diff can be fitted to an E36, so going by that it will fit and work fine, have i missed anything before i try to find one ;)
 

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iirc, the E60 M5 diff has been retrofitted into a E39. Perhaps same/similar unit?

the real question is: is it worth the hassle? will you gain anything from putting a variable diff in that has been developed for a car with different vehicle dynamics?
 

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Discussion Starter #3
Yes there is a gain to be had, it can lock to 100%. Admittedly not essential but getting the power down better and also shortening the ratio at the same time should make a big difference to the cars feel.

Plus if I was getting the diff rebuilt anyway its buying the variable lsd thats the additional cost, then sell my old one.

Its more of a thought than going to happen next week, trying to get the car sorted so it lasts a while and if I can upgrade at the same time I would like to look into it well before its due to happen.
 

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The later E60 M5 and E63 M6 has the M Variable differential which is far superior to the E39 M5 version.

Here is a nice video for it


+ http://www.youtube.com/watch?v=CIH0V8pg8jk" title="View this video at YouTube in a new window or tab" target="_blank">YouTube Video
http://www.youtube.com/watch?v=CIH0V8pg8jk"> http://www.youtube.com/watch?v=CIH0V8pg8jk" /> ERROR: If you can see this, then YouTube is down or you don't have Flash installed.




Regardz,


J Irwan
 

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According to BMW, the cars utilizing the Variable M differential lock are listed here: BMW Technology Guide : Variable M differential lock

I also looked up the diff ratios for each model. Not sure how these ratios would work with the E39 M5. I think the best option is a custom 2 or 3 LSD clutch built by diffsonline. Upon further research it looks like they may not offer that for the E39, but definitely worth asking them.

3.85
M3 Sedan
M3 Coupe
M3 Convertible

3.91
M5 Sedan
M5 Touring

3.62
M6 Coupe
M6 Convertible
 
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Those are all too short IMO. I used to have an E34 M5 with the 6 speed upgrade and the stock diff. First gear is pretty much useless. Hell, I've heard people say the same with the Dinan diff for the E39. Unless you're tracking/drag racing your car, those are way too short.
 

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Why not just adjust the lockup of the stock diff and change the ratio?
 

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It's still not a variable LSD. I wonder if that mechanism can be transplanted into the E39 M5 diff housing
I would bet diffsonline are the appropriate and best people to ask
 

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I bought my ring and pinion from diffs online and found them to be extremely helpful. I had my lockup rate increased when the new gears were put in and I couldn't be happier with the setup.
 

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It's still not a variable LSD. I wonder if that mechanism can be transplanted into the E39 M5 diff housing

it's only money and/or long-term access to some CNC equipment!


if the ring gear is replaceable, and is the same diameter as some other BMW diffs, it is probable that it uses the same bolt spacing, too. Let us hope the pinion is the same diameter and spaced the same......
 

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Can someone in this thread please educate a simpleton such as I as to what "lockup percentage" or "rate" is and how it affects the performance of an LSD? For example, I know Jerry (a/k/a Gsfent) has a differential with 2.65 gearing (!) and something like 40% lockup. Someone school me. Available online explanations suck. Thanks.

--Peter
 

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Can someone in this thread please educate a simpleton such as I as to what "lockup percentage" or "rate" is and how it affects the performance of an LSD? For example, I know Jerry (a/k/a Gsfent) has a differential with 2.65 gearing (!) and something like 40% lockup. Someone school me. Available online explanations suck. Thanks.

--Peter
Watch the video (it is in German) and see what the new M6 can do on a hill with one rear wheel on rollers compared to an older M6 and an e39 M5. If the diff can lock up, then power can be routed from the wheel that slips to the wheel that grips!
 

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Peter - the numbers are simple:

Ratio - 3.45:1 means that the rear wheels turn 3.45 times for each rotation of the driveshaft. A "short" number (higher) means that the wheels turn more for each rotation of the driveshaft. In general this translates to more "torque", but also results in a quicker gear change. A 3.15 standard gear is about 9.5% taller than a 3.45 Dinan gear. This means that it can achieve a 10% higher speed in the same gear, but it loses about 10% in torque to the Dinan. The main issue is that if you put to high a ratio in the rear diff, it can cause 1st gear to be useless. There is a balance in the total set of ratios from motor RPM, motor torque, gearbox and diff that is engineered from the factory. You do not want to stray too far from that without compromising drivability.

Lockup % is the amount of power than can be transferred from the spinning wheel to the non-spinning wheel. 100% means that it can act as a solid axle. Lesser percentages reflect a linear amount of power transfer from the wheel with traction to the wheel without traction. Traditionally diffs use a clutch mechanism to implement LSD. In a locking diff, this may include a mechanical system to augment the clutch. LSD clutches do wear.
 

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Peter - the numbers are simple:

Ratio - 3.45:1 means that the rear wheels turn 3.45 times for each rotation of the driveshaft. A "short" number (higher) means that the wheels turn more for each rotation of the driveshaft. In general this translates to more "torque", but also results in a quicker gear change. A 3.15 standard gear is about 9.5% taller than a 3.45 Dinan gear. This means that it can achieve a 10% higher speed in the same gear, but it loses about 10% in torque to the Dinan. The main issue is that if you put to high a ratio in the rear diff, it can cause 1st gear to be useless. There is a balance in the total set of ratios from motor RPM, motor torque, gearbox and diff that is engineered from the factory. You do not want to stray too far from that without compromising drivability.

Lockup % is the amount of power than can be transferred from the spinning wheel to the non-spinning wheel. 100% means that it can act as a solid axle. Lesser percentages reflect a linear amount of power transfer from the wheel with traction to the wheel without traction. Traditionally diffs use a clutch mechanism to implement LSD. In a locking diff, this may include a mechanical system to augment the clutch. LSD clutches do wear.
Thanks, Mike. I understand gear ratios. I ran 4.10:1 in my old Firebird as a teenager; talk about short! I run the 3.45:1 Dinan diff in the Beast and love it, given that I spend more time between 0-60 than I do 60-130. I was just a bit perplexed by the various descriptions of lockup rate/percentage on the web. Do you know what the factory E39 M5 lock rate is? Anyone know if the Dinan diff has a different lockup rate? What lockup rate are people with custom diffs running? Anyone running a Quaife (torque-based lockup)?

--Peter
 

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I was just a bit perplexed by the various descriptions of lockup rate/percentage on the web. Do you know what the factory E39 M5 lock rate is? Anyone know if the Dinan diff has a different lockup rate? What lockup rate are people with custom diffs running? Anyone running a Quaife (torque-based lockup)?

--Peter
OEM BMW M5 Diff 25% ?
Not Sure
Anything you want for the most part,I believe
Plenty of people are on the track
 
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