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The BMW Range
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Pointers pls on a contemplated 2002 e46 m3 purchase
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<blockquote data-quote="e34_lover" data-source="post: 646126" data-attributes="member: 16259"><p>Yea, I think its that part.</p><p></p><p>Ah, understand where you are coming from now. I am not fortunate enough to have ever driven an R8 or any other single clutch automated transmission so I can't say why the R8 has a similar issue. By driveshaft head, do you mean the giubo? My brother's E46 M3 (Manual) is now clunking again. It went away before which was due to the diff mounts being broken but that has been replaced. After about a month or two, a different type of clunk showed up. Hes probably gonna change the giubo and csb before finally accepting that he has the infamous M clunk. Hopefully it is one of those two parts because a loose diff does cause unnatural movement of the csb and giubo and wears those two parts out faster. No matter how gently the clutch is let out, a clunk is heard. Everytime from 1-2 at low speed like the BMW SIB states. I have jacked the car up from the rear and the play from the diff is amazing. Theres like an inch or more of movement before the other wheel moves. Tried it on my E36 and that didnt happen. This is the drivetrain lash that is causing the noise I believe. Shift aggressively at high rpm and this issue is not there. Floor it in first, change gear anywhere above 4k rpm and change gear as aggressively as you want and it will never clunk.</p><p></p><p> Well, BMW issued the technical bulletin so I don't know what to say. I will see if I can get the SIB off the BMW dealer network.</p><p></p><p>I don't believe that the E46 Variable locking diff was derived from the E36 M3 Evo clutch style diff. The E46 diff locks all the way from 0-100%. The E36 clutch style locks at 25%. The only similarity is the 210mm pinion.</p><p></p><p>Copied and pasted info on what the M Variable locking diff is</p><p></p><p>"An understanding of existing torque-sensing limited slip differentials will help us understand the improvements offered with this new variable differential locking system. In the past, limited slip differentials have used a constant basic locking torque. When one wheel spins, the differential locks and sends torque to the other wheel. The differential lock value for current M class BMW’s is 25%.</p><p></p><p>This system works well, but a problem occurs when one wheel is on very low traction surfaces such as ice or when the car is turned hard in a corner and the inside wheel lifts off the road. Then there is not enough traction provided by the slipping wheel to cause the differential to lock. The traction advantages of this differential lock are limited by the maximum traction torque of the slipping wheel.</p><p></p><p>The Variable M-differential lock can provide traction advantages even when one wheel is on glare ice. The factor that determines torque transfer is the speed differential of the drive wheels. As soon as one wheel starts to spin, torque is transferred to the other wheel. The greater the speed difference, the more torque is transferred.</p><p></p><p>To accomplish this, BMW is using a sheer pump located inside the differential. One drive wheel is connected to one part of the pump and the other wheel is connected to the other part. As wheel speeds differ, the pump provides a variable pressure that applies multi-disc clutches preventing the spinning wheel from turning faster than the other wheel.</p><p></p><p>The pump is a sealed unit that uses high viscosity silicone oil between two sheer discs. As soon as the two sheer discs turn at different rates, the silicone oil is sheered by the grooves in the sheer plates and this generates a pressure dependent on the speed differential of the two plates. Thus, a variable differential lock effect is achieved. As soon as the two wheels are turning the same speed, the pressure of the sheer plates decreases and the differential unlocks.</p><p></p><p>Conventional limited slip differentials use a little constant pressure on their clutches to preload the differential. This works fine for performance applications but it is undesirable on ice. When two wheels are “locked” constantly together even with limited force, they tend to fight each other when the vehicle turns corners and the wheels have to travel different distances. On slippery, icy road surfaces, the action tends to cause both drive wheels to loose traction. This can have a dramatic effect on lateral stability.</p><p></p><p>The Variable M-differential lock system continually varies the “locking” of the two drive wheels. During cornering, the speed differential is low enough the differential remains unlocked so lateral stability is maintained. As soon as one wheel looses traction, the differential holds, and the car continues to move. Combined with the BMW M3′s 50:50 weight distribution and their stability control system, the M3 is a superb handling vehicle on any road conditions."</p><p></p><p>If you read my previous post that I believe is an extract of the SIB, it says it is due a "normal design characteristic of the new M differential lock style rear axle used on E46 M3 models"</p><p></p><p>I have compared my M3 to by brothers E46 M3 and the way the car takes off is so different. The E46 really puts the power to the ground and can fishtail when really gunning it. The E36 on the other hand does not squirrel around so much because the lock is maxed out at 25%. I am really tempted to change my diff over to the Variable M diff. I believe my clutches are probably worn as well.</p><p></p><p>What do you believe causes the clunking if its not the diff? </p><p></p><p>Disclaimer: I don't claim to be anyone with huge technological knowledge. These posts are based on my assessment of what information I have been given. If anyone see's this as an argument, it is not. It is interesting to see another point of view from a fellow owner and I am probing so I can correct my understanding if it is wrong :rock:</p></blockquote><p></p>
[QUOTE="e34_lover, post: 646126, member: 16259"] Yea, I think its that part. Ah, understand where you are coming from now. I am not fortunate enough to have ever driven an R8 or any other single clutch automated transmission so I can't say why the R8 has a similar issue. By driveshaft head, do you mean the giubo? My brother's E46 M3 (Manual) is now clunking again. It went away before which was due to the diff mounts being broken but that has been replaced. After about a month or two, a different type of clunk showed up. Hes probably gonna change the giubo and csb before finally accepting that he has the infamous M clunk. Hopefully it is one of those two parts because a loose diff does cause unnatural movement of the csb and giubo and wears those two parts out faster. No matter how gently the clutch is let out, a clunk is heard. Everytime from 1-2 at low speed like the BMW SIB states. I have jacked the car up from the rear and the play from the diff is amazing. Theres like an inch or more of movement before the other wheel moves. Tried it on my E36 and that didnt happen. This is the drivetrain lash that is causing the noise I believe. Shift aggressively at high rpm and this issue is not there. Floor it in first, change gear anywhere above 4k rpm and change gear as aggressively as you want and it will never clunk. Well, BMW issued the technical bulletin so I don't know what to say. I will see if I can get the SIB off the BMW dealer network. I don't believe that the E46 Variable locking diff was derived from the E36 M3 Evo clutch style diff. The E46 diff locks all the way from 0-100%. The E36 clutch style locks at 25%. The only similarity is the 210mm pinion. Copied and pasted info on what the M Variable locking diff is "An understanding of existing torque-sensing limited slip differentials will help us understand the improvements offered with this new variable differential locking system. In the past, limited slip differentials have used a constant basic locking torque. When one wheel spins, the differential locks and sends torque to the other wheel. The differential lock value for current M class BMW’s is 25%. This system works well, but a problem occurs when one wheel is on very low traction surfaces such as ice or when the car is turned hard in a corner and the inside wheel lifts off the road. Then there is not enough traction provided by the slipping wheel to cause the differential to lock. The traction advantages of this differential lock are limited by the maximum traction torque of the slipping wheel. The Variable M-differential lock can provide traction advantages even when one wheel is on glare ice. The factor that determines torque transfer is the speed differential of the drive wheels. As soon as one wheel starts to spin, torque is transferred to the other wheel. The greater the speed difference, the more torque is transferred. To accomplish this, BMW is using a sheer pump located inside the differential. One drive wheel is connected to one part of the pump and the other wheel is connected to the other part. As wheel speeds differ, the pump provides a variable pressure that applies multi-disc clutches preventing the spinning wheel from turning faster than the other wheel. The pump is a sealed unit that uses high viscosity silicone oil between two sheer discs. As soon as the two sheer discs turn at different rates, the silicone oil is sheered by the grooves in the sheer plates and this generates a pressure dependent on the speed differential of the two plates. Thus, a variable differential lock effect is achieved. As soon as the two wheels are turning the same speed, the pressure of the sheer plates decreases and the differential unlocks. Conventional limited slip differentials use a little constant pressure on their clutches to preload the differential. This works fine for performance applications but it is undesirable on ice. When two wheels are “locked” constantly together even with limited force, they tend to fight each other when the vehicle turns corners and the wheels have to travel different distances. On slippery, icy road surfaces, the action tends to cause both drive wheels to loose traction. This can have a dramatic effect on lateral stability. The Variable M-differential lock system continually varies the “locking” of the two drive wheels. During cornering, the speed differential is low enough the differential remains unlocked so lateral stability is maintained. As soon as one wheel looses traction, the differential holds, and the car continues to move. Combined with the BMW M3′s 50:50 weight distribution and their stability control system, the M3 is a superb handling vehicle on any road conditions." If you read my previous post that I believe is an extract of the SIB, it says it is due a "normal design characteristic of the new M differential lock style rear axle used on E46 M3 models" I have compared my M3 to by brothers E46 M3 and the way the car takes off is so different. The E46 really puts the power to the ground and can fishtail when really gunning it. The E36 on the other hand does not squirrel around so much because the lock is maxed out at 25%. I am really tempted to change my diff over to the Variable M diff. I believe my clutches are probably worn as well. What do you believe causes the clunking if its not the diff? Disclaimer: I don't claim to be anyone with huge technological knowledge. These posts are based on my assessment of what information I have been given. If anyone see's this as an argument, it is not. It is interesting to see another point of view from a fellow owner and I am probing so I can correct my understanding if it is wrong :rock: [/QUOTE]
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