Hard Shifts? Normal or not?

[drivem3]

I’ve been doing an overhaul on my M3 over the last year, but after getting it back this week I’m feeling like some 1-2, 2-3, 3-4 shifts are aggressive and I can feel it. I’m not sure if this is normal for the M3 and part of the “M clunk” or something I should look into?

I have the following done and refreshed:

• Autosolutions SSK
• Diff (OEM) + trans mount (rouge)
• Diff fluid flush + trans flush
• Guibo + CSB

Doesnt happen on every shift but occasionally will feel the clunk from the bottom of the car.

[sapote]

“week I’m feeling like some 1-2, 2-3, 3-4 shifts are aggressive and I can feel it”
Why aggressive is a symptom of a problem?

[drivem3]

“week I’m feeling like some 1-2, 2-3, 3-4 shifts are aggressive and I can feel it”
Why aggressive is a symptom of a problem?

Mostly because it’s not a consistent feeling and also a sanity check to see if it’s normal. I’m not sure if the worn parts previously hid the clunk feeling and I’m just feeling it now, or if fixing those items has highlighted another problem to address.

[sapote]

Almost no part in the transmission can cause the clunk during a shift, so I would check for plays on the driveshaft from the guibo end to the diff input end.

[Slideways]

When you put the shift lever in gear too quickly, mainly from a standstill into 1st or a quick shift from 1st to 2nd, there will be certain times where you will hear a thud coming from the rear end. I believe others refer to this as the M-clunk. It will not always happen, but if you catch the gear engagement at the right moment, you will hear quite the thud coming from the driveline. It is made more evident with a short shifter as now you are engaging 1st or 2nd even faster. If one gives the gear engagement a split second longer even with a short shifter, you can avoid it mostly. My guess is that the normal lash/play in the differential is causing this sound. They all do it, but it is less apparent with everything stock.

[sapote]

When you put the shift lever in gear too quickly, mainly from a standstill into 1st or a quick shift from 1st to 2nd, there will be certain times where you will hear a thud coming from the rear end. I believe others refer to this as the M-clunk. It will not always happen, but if you catch the gear engagement at the right moment, you will hear quite the thud coming from the driveline. It is made more evident with a short shifter as now you are engaging 1st or 2nd even faster. If one gives the gear engagement a split second longer even with a short shifter, you can avoid it mostly. My guess is that the normal lash/play in the differential is causing this sound. They all do it, but it is less apparent with everything stock.

Making the diff to clunk (the M-clunk is the result of the internal clutch pack slip) needs a good torque from the driveshaft. But during gear shifting, the clutch is disengaged before the gears are meshed, so I don't know how the engine torque can transmit to the diff. OP didn't say the cluck happened when releasing the clutch, just during shifting gears.

[Slideways]

Making the diff to clunk (the M-clunk is the result of the internal clutch pack slip) needs a good torque from the driveshaft. But during gear shifting, the clutch is disengaged before the gears are meshed, so I don't know how the engine torque can transmit to the diff. OP didn't say the cluck happened when releasing the clutch, just during shifting gears.

It has nothing to do with the clutch. When you select 1st or 2nd with the clutch pushed in and not yet released, occasionally there will be a thud coming from the back.

[sapote]

It has nothing to do with the clutch. When you select 1st or 2nd with the clutch pushed in and not yet released, occasionally there will be a thud coming from the back.

I believe this happened and I try to understand the physics of it. With the clutch disenaged, when the gears engaged, either the spinning input gear energy drives the driveshaft, or the spinning driveshaft drives the input gear, but consider the input and output gears are speed matched by the synchro, not much delta energy drives the driff or removed from the diff, so don't know why the diff clutch slips to make the clunk.

[heinzboehmer]

I believe this happened and I try to understand the physics of it. With the clutch disenaged, when the gears engaged, either the spinning input gear energy drives the driveshaft, or the spinning driveshaft drives the input gear, but consider the input and output gears are speed matched by the synchro, not much delta energy drives the driff or removed from the diff, so don't know why the diff clutch slips to make the clunk.

It's just play in the spider gears. Synchros can definitely spin the driveshaft enough to hit the spider gears against each other.

I can reproduce the noise in my car if I engage the first gear synchro with the clutch disengaged. No need to fully select the gear.

[sapote]

I can reproduce the noise in my car if I engage the first gear synchro with the clutch disengaged. No need to fully select the gear.

understand on the plays in the spider/side gears, but it should not be a loud M clunk (old clutch pack slip at start rolling). soft clunk as in this case is normal.

[drivem3]

When you put the shift lever in gear too quickly, mainly from a standstill into 1st or a quick shift from 1st to 2nd, there will be certain times where you will hear a thud coming from the rear end. I believe others refer to this as the M-clunk. It will not always happen, but if you catch the gear engagement at the right moment, you will hear quite the thud coming from the driveline. It is made more evident with a short shifter as now you are engaging 1st or 2nd even faster. If one gives the gear engagement a split second longer even with a short shifter, you can avoid it mostly. My guess is that the normal lash/play in the differential is causing this sound. They all do it, but it is less apparent with everything stock.

Thank you! I think after driving it around more this is what I'm finding. If I shift too quickly I have the thud from the driveline.

[oceansize]

My philosophy is to drive it like I stole it. I shift with a light touch, but I care not one iota about clunk. Let it clunk. When something breaks I’ll fix it.

[sasha]

When you put the shift lever in gear too quickly, mainly from a standstill into 1st or a quick shift from 1st to 2nd, there will be certain times where you will hear a thud coming from the rear end. I believe others refer to this as the M-clunk. It will not always happen, but if you catch the gear engagement at the right moment, you will hear quite the thud coming from the driveline. It is made more evident with a short shifter as now you are engaging 1st or 2nd even faster. If one gives the gear engagement a split second longer even with a short shifter, you can avoid it mostly. My guess is that the normal lash/play in the differential is causing this sound. They all do it, but it is less apparent with everything stock.

I experience the same and rationalized it the same. On 0-1, I assume it is that the synchros try’s to move the (disengaged) clutch to align gears, but because of the gearing, it has more leverage over the drive shaft so that needs to lock up first. So the drive shift preloads against the spider, then 1 engages. On 1-2, I figure the shaft doesn’t yet have the moment to resiste this and can recoil as well.

I feel it the worst going from 1-2 while turning - making a turn from a stop sign. I also have a short shifter.

a slightly slower shifter movement and shifting from 1 higher at 3-4k, helps.

[L0okitzRaj]

One thing I've noticed with my current e46m and past ones are if you are short shifting, and not revving the car out shifting doesn't feel as smooth. the higher you rev it, the easier and more fluid my shifts are.

[sapote]

On 0-1, I assume it is that the synchros try’s to move the (disengaged) clutch to align gears, but because of the gearing, it has more leverage over the drive shaft so that needs to lock up first. So the drive shift preloads against the spider, then 1 engages.

I can't understand how the clunk happens in this scenario. On 0 to 1, car stands still so driveshaft speed = 0. To engage 1st gears, the synchro has to stop the spinning input shaft by friction, then the slider can engage the first gear dog teeth without making the grinding noise. So with the clutch disk and input shaft stopped when the gears are engaged, so does the diff input, how does the clunk happen? The only way to have the clunk is the long driveshaft must be rotate or try to rotate, this means the clutch disk and input shaft were rotating when the gears engaged, but this should cause gear grinding inside the tranny box.