[aerobod]

Originally Posted by Sleeper

You’re right of course.

But, in my opinion, the fuckery required to trash this gearbox, or something in the drivetrain, with or without the CDV present, would come back to user error. In other words, if you do something so aggressive that parts are breaking, I don’t think the CDV will do much but maybe soften the blow (ie. wearing a helmet jumping off a cliff without a parachute).

The massive improvements in driveability, shifting and clutch feel far surpass the risk (for me).

I typically remove the CDVs from my BMWs, too. I wouldn’t underestimate the effect of the CDV on driveline shock, though. With it installed the clutch will slip briefly and not allow any instant hook-up of the tyres if the pedal is side-stepped.

With the BMW 168K differential and 150lbft of engine torque in a Caterham, driveshafts can be snapped or splines stripped when using R-comp tyres and no CDV equivalent, i know of a few people who have done this at track events in the UK.

[Mr. Hankey]

Originally Posted by Geighty7

Yes dramatically after doing the CDV delete.

Originally Posted by aerobod

I typically remove the CDVs from my BMWs, too. I wouldn’t underestimate the effect of the CDV on driveline shock, though. With it installed the clutch will slip briefly and not allow any instant hook-up of the tyres if the pedal is side-stepped.

This is my 3rd manual BMW and I've never considered the CDV delete until now. Not that I thought there was a problem with the manual other than a very high clutch grab point in all 3 cars (BMS clutch stop deals with that nicely) but help me understand.

I was driving my car yesterday and never realized I do this, but when I do a 2-3 or 3-4 shift for example as I clutch out I tend to hang my foot for a split second at the grab point, then release the clutch and get on it...this makes smoother shifts. If I don't then the shift is just a little jittery...putting this in context of this thread, is the reason I'm lagging my foot a bit to allow the clutch fluid and therefore the position of the clutch plate itself to "catch up" to the clutch position then grab? I don't really notice this with 4-5 or 5-6 gears but they are taller and you're going faster so wouldn't notice the jitteriness as much. I suspect with time I've just adapted how to drive these manuals smoothly and I always struck that behavior up to "power" of the engine.

Does the CDV delete remove this lag? I'm afraid this is one of those things I can't "unsee" now and might just have to do it. I can't think of any downside risks other than getting some air in the system and making it spongy...

[aerobod]

Originally Posted by Mr. Hankey

This is my 3rd manual BMW and I've never considered the CDV delete until now. Not that I thought there was a problem with the manual other than a very high clutch grab point in all 3 cars (BMS clutch stop deals with that nicely) but help me understand.

I was driving my car yesterday and never realized I do this, but when I do a 2-3 or 3-4 shift for example as I clutch out I tend to hang my foot for a split second at the grab point, then release the clutch and get on it...this makes smoother shifts. If I don't then the shift is just a little jittery...putting this in context of this thread, is the reason I'm lagging my foot a bit to allow the clutch fluid and therefore the position of the clutch plate itself to "catch up" to the clutch position then grab? I don't really notice this with 4-5 or 5-6 gears but they are taller and you're going faster so wouldn't notice the jitteriness as much. I suspect with time I've just adapted how to drive these manuals smoothly and I always struck that behavior up to "power" of the engine.

Does the CDV delete remove this lag? I'm afraid this is one of those things I can't "unsee" now and might just have to do it. I can't think of any downside risks other than getting some air in the system and making it spongy...

Removing the CDV will change the lag. It is only a very small amount of time though, a couple of tenths of a second. With the G87 with the CDV in place if you clutch in and out as fast as possible, the clutch pedal will lag behind your foot by a fraction of a second, then come up and hit your foot if it is held at the top of the stroke. The CDV causes a fluid flow restriction that keeps the slave cylinder piston sucked in until enough fluid flows through the orifice to let it fully return.

[Mr. Hankey]

Originally Posted by aerobod

Removing the CDV will change the lag. It is only a very small amount of time though, a couple of tenths of a second. With the G87 with the CDV in place if you clutch in and out as fast as possible, the clutch pedal will lag behind your foot by a fraction of a second, then come up and hit your foot if it is held at the top of the stroke. The CDV causes a fluid flow restriction that keeps the slave cylinder piston sucked in until enough fluid flows through the orifice to let it fully return.

Thanks guys. Just ordered the parts to do this...

This is a good video outlining the process: CDV Valve removal

[Geighty7]

Originally Posted by Mr. Hankey

This is my 3rd manual BMW and I've never considered the CDV delete until now. Not that I thought there was a problem with the manual other than a very high clutch grab point in all 3 cars (BMS clutch stop deals with that nicely) but help me understand.

I was driving my car yesterday and never realized I do this, but when I do a 2-3 or 3-4 shift for example as I clutch out I tend to hang my foot for a split second at the grab point, then release the clutch and get on it...this makes smoother shifts. If I don't then the shift is just a little jittery...putting this in context of this thread, is the reason I'm lagging my foot a bit to allow the clutch fluid and therefore the position of the clutch plate itself to "catch up" to the clutch position then grab? I don't really notice this with 4-5 or 5-6 gears but they are taller and you're going faster so wouldn't notice the jitteriness as much. I suspect with time I've just adapted how to drive these manuals smoothly and I always struck that behavior up to "power" of the engine.

Does the CDV delete remove this lag? I'm afraid this is one of those things I can't "unsee" now and might just have to do it. I can't think of any downside risks other than getting some air in the system and making it spongy...

So actually what you’re describing is proper manual driving. You won’t want to dump your clutch due to shock to the drivetrain. The CDV will allow 0 lag when disengaging the clutch, but under normal circumstances you will still want to hold that foot until you feel the clutch properly sync.

In lower gears, your engine and transmission are spinning faster than higher gears at lower speeds due to the RPM ratio. What you’re describing is actually the right technique in letting the clutch connect the transmission to the engine properly at lower gears but higher RPM. If you were to simple take your foot off, regardless of the CDV, you’ll feel a shock. What the CDV does is allow a driver room for error when they don’t do what you’re describing, which is easier on the driveshaft etc. this is put in place for users who don’t understand the mechanics on how to disengage and engage clutch properly in accordance to their rev range in certain gears.

Taking it out will allow you to “row gears” at higher speed and achieve smoother shifting along the way without a lag in clutch engagement.

At higher gears the reason you’re able to engage the clutch faster than at lower gears is your engine is already up to speed and the rev range ratio on higher gears is lower. The engine and transmission does not need much finesse in fitting accordingly with the clutch at freeway speeds going into larger gears with longer gear ratio.

So think of being able to drop a puzzle piece into a larger space vs having to really get it right to fit it in (at lower gears and lower rev range hence the hold of the clutch with foot).

Hope this helps!

[Mr. Hankey]

Originally Posted by Geighty7

...you will still want to hold that foot until you feel the clutch properly sync.

Love that feeling, yes thats exactly how I drive it....been driving manual for 33 years, but that delay in this car and the F80s is certainly longer than others and wondering if the CDV delete shortens that lag slightly. I imagine it will and I imagine I won't notice too much of a difference given my driving style. I am more slow deliberate shifts over quick shifts, so I've never noticed this clutch pedal lagging behind my foot position, but that valve must certainly be creating some lag at the throwout bearing that isn't 1:1 with pedal position.

[Geighty7]

Originally Posted by Mr. Hankey

Love that feeling, yes thats exactly how I drive it....been driving manual for 33 years, but that delay in this car and the F80s is certainly longer than others and wondering if the CDV delete shortens that lag slightly. I imagine it will and I imagine I won't notice too much of a difference given my driving style. I am more slow deliberate shifts over quick shifts, so I've never noticed this clutch pedal lagging behind my foot position, but that valve must certainly be creating some lag at the throwout bearing that isn't 1:1 with pedal position.

You’ll for sure notice it smooth out when you slightly slip the clutch for smooth 1-2 and 2-3 shifting.

[MrJDS]

Finally did the CDV delete.

Just wanted to be one more voice on here recommending it to anyone on the fence. It's not night and day different in feel but the slight change does make it a more enjoyable - the whole process is smoother and more predictable. starting off in 1st is a lot better and 1st to 2nd shift is a bit better.

Also the clutch pedal feel feels a bit heavier to my leg (not much maybe 5-10%) but that could be my mind playing tricks on me.

[Mr. Hankey]

Originally Posted by MrJDS

Finally did the CDV delete.

Just wanted to be one more voice on here recommending it to anyone on the fence. It's not night and day different in feel but the slight change does make it a more enjoyable - the whole process is smoother and more predictable. starting off in 1st is a lot better and 1st to 2nd shift is a bit better.

Also the clutch pedal feel feels a bit heavier to my leg (not much maybe 5-10%) but that could be my mind playing tricks on me.

Got to this as well today. The clutch now feels more like my NA miata, more linear for sure. When just normal tooting around driving doesn't feel much different. But definitely improved with faster shifts. Agree with everyone here, it's a better feel to me, definitely an improvement but not a drastic change, but I like it.

Interestingly my clutch feels just a tad lighter to me...must be all the air I let in!

[BIGW0RM]

Does this mod move the clutch engagement point at all? I’d like the clutch to engauge sooner. I dislike how bmw clutches are so late in the pedal throw.

[RobM2]

Originally Posted by BIGW0RM

Does this mod move the clutch engagement point at all? I’d like the clutch to engauge sooner. I dislike how bmw clutches are so late in the pedal throw.

No, if you want the clutch to engage sooner you'll want a clutch stop, which raises the fully depressed point to eliminate free travel.

This mod removes a moderating effect to the clutch engagement. The clutch will engage at the same point but it will feel more consistent and controllable.

I suspect most people want both mods, and taken together they get the clutch feel, travel, and engagement they want.