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I remember a thread where the pressure solenoid tip had broken. I've been thinking whether this is your issue, I'll try to find it see what other details were posted...
 

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I remember a thread where the pressure solenoid tip had broken. I've been thinking whether this is your issue, I'll try to find it see what other details were posted...
Yep. I'd bank on a broken tip on one of the two PWVs. I've seen it about 6 times in the last year, just shipped a set of PWVs to a place in CA for the same reason.

When executing a gear change, one PWV lines up to control the outgoing gear while the other incoming. Outgoing gear gets large pressure and ramps down to zero via PID as hall sensor position approaches that shift rod's "neutral" setting.

Incoming gear PWV starts at zero and ramps on once outgoing "neutral" reached and incoming PWV moves of zero to apply more pressure. Once the incoming gear position is reached on a normal shift commanded by the SMG, the PWV goes back to zero.

In that video, when manually selecting a gear, the PWV holds pressure on that shift piston, thus the continual fluid flow noise.

When manually switching from one gear to the next, it sounds like the outgoing PWV can't find neutral so you're hearing the shift rod slamming back and forth uncontrollably. The PWV spool spring retention disc usually shears one or both of the die-pressed retention lands on the tip allowing the disc to extend and relieve spring pressure thus throwing off the null current the PWV should have to zero pressure.

I'd drop the trans, pull the two PWVs on the back of the shift block and look at the tips.
 

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Discussion Starter #23
Two quick questions...

What does PWV stand for?

Are the tips on these plastic? The reason why I ask is because the screen on the transmission had some plastic pieces on when we serviced the fluid. I didn't think much of it because the car does have 88k miles and there wasn't a whole lot of it but now maybe?
 

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It's the same noise and issue no matter the gear that you choose. It does the same noise and sequence when you try to shift multiple times in any or the same gear.
What does PWV stand for?

Are the tips on these plastic? The reason why I ask is because the screen on the transmission had some plastic pieces on when we serviced the fluid. I didn't think much of it because the car does have 88k miles and there wasn't a whole lot of it but now maybe?
Couple things: you must depressurize the system before doing level check (hence why it spilled over). When bleeding there's 2 separate routines that must be run in order: hydraulic block first and then actuation block. No idea if your scanner list those separately or what. The solenoids are all metal. Which screen are you referring to? The only screen I know of is in the gear oil circuit, which is separate from the hydraulic circuit.

If you look at the smg hydraulic diagram (just google it) there's 2 pressure control valves that control pressure to the shift solenoids and ultimately pistons. My guess is they are pulse-width modulated, and Jim refers to them as pulse-width (modulated) valves or PWVs.

One could test this theory. The idea is simple: one PWV controls the 2,4,6,7 gears and the other one controls R,1,3,5. So if you only actuate the gears controlled by the good PWV the system should work fine. Engage 1, then switch to R,3,5 (or neutral). Do the same with the other set of gears (2,4,6,7). Assuming only one of them broke and they are independent from each other then this could tell you which one is bad.

I quoted where you say the noise also happens if you try 'multiple times in any or the same gear' so maybe they are not independent or both broke.

Either way seems you have to drop the trans. If you're interested here's my list of stuff to do when dropping the trans: https://www.m5board.com/vbulletin/e63-bmw-m6-forum-bmw-m6-convertible-m6board-com/578106-smg-problems-need-help.html#post7556106
 

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I wish there was a follow up on this thread. I’m pretty sure this is what’s going on with my car after I’ve replaced PLCD and SMG pump.. my guy is pulling my trans soon. And PWVs an easy fix?
 

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The gearbox doesn't seem to fail often. As for the SMG unit it's not easy to diagnose so most people just end up replacing the whole thing.
 
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