DIY Clutch Delay Valve (CDV) Removal

[pk8]

I went for a long drive today and I can 100% say that the rev matching is complicit in my 1-2 shift problem. With rev matching off for the majority of the drive, I had zero dodgy shifts. As soon as I turned rev matching back on, the hesitation and poor shifts returned at random as per usual. My CDV has been deleted but my gut feeling is that it has no real bearing on the issue, at least in my car.

My issues have resolved since the CDV delete and 100% happy with my shifting right now. I don’t know what to say…

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[BMWAF]

My issues have resolved since the CDV delete and 100% happy with my shifting right now. I don’t know what to say…

Yeah, I don't know. We're probably talking about two different issues which present similarly. I don't know either. ?‍

 

[Funkjaw]

Big bonus of this mod; shocking the drivetrain with a clutch kick is so much easier now.

 

[sinbad]

BMW part# 21526785964

this part number didn't work on my car - 2023 MT supra.

there was no clutch engagement, no pedal feel. ended up putting the stock one back in and removed the CDV

 

[zackarybyrd]

I had been on the fence about doing CDV delete because I never really felt like I “needed” to do it. I was able to shift it fine the way it was on the street and at the track. My car’s use case is primarily a track car but I drive it to work every now and then when I want to remind my boss that everyone agrees my Supra is way cooler than his Rolls Royce. I don’t drag race, I’m too “mature” to get conned into street racing, and I really don’t do many hard launches. There was one time when I launched it in second gear for funsies and the clutch slipped for a second and I got the unmistakeable smell of my clutch pleading for its life.

I did the CDV delete today because I was curious and needed something to do with my hands. I drove it around lunchtime and called it a “baseline” so people couldn’t give me as much shit, parked it on the lift, and did exactly what it says to do in the first post on this thread. It was super easy, as in ANYBODY could do it. I bled it with a manual vacuum bleeder from the bottom, topped off the brake fluid again at the end (and a couple times during bleeding just to be sure I didn’t run dry but I don’t think I’d have had to do that in retrospect), put it back together and took it for a spin and called it the “experiment.” The baseline drive was at 1:00 PM, and I got back from the experiment drive at 3:30PM and I moved slow and took a break to make a reel on Instagram in the middle because it was hot as hell out today.

I gotta say I like it better without the CDV. It’s not like a whole different car or anything like some people say, but it IS different. It does grab better, it does spin the wheels and not the flywheel in a second gear launch, you can chirp the tires easier if you drop it between gears, and it doesn’t feel like there is a middle man inserting his opinion between me and what my left foot is asking of the car anymore, especially in 1st and the 1-2 shift. It’s less ambiguous. I keep the rev match turned off always anyway so that part’s not too much different for me.

Coming from 25 years of three pedals, it feels more like I would’ve expected in the first place, and I agree with the folks who say I wish I’d have done it sooner. I can also see how it could be possible that some of the people who have stock clutch and stock tune and complain about slippage problems may actually be dealing with their CDV instead of a clutch problem.

I am joining camp CDV delete and I say take that shit out.

 

[RyanA90]

I had been on the fence about doing CDV delete because I never really felt like I “needed” to do it. I was able to shift it fine the way it was on the street and at the track. My car’s use case is primarily a track car but I drive it to work every now and then when I want to remind my boss that everyone agrees my Supra is way cooler than his Rolls Royce. I don’t drag race, I’m too “mature” to get conned into street racing, and I really don’t do many hard launches. There was one time when I launched it in second gear for funsies and the clutch slipped for a second and I got the unmistakeable smell of my clutch pleading for its life.

I did the CDV delete today because I was curious and needed something to do with my hands. I drove it around lunchtime and called it a “baseline” so people couldn’t give me as much shit, parked it on the lift, and did exactly what it says to do in the first post on this thread. It was super easy, as in ANYBODY could do it. I bled it with a manual vacuum bleeder from the bottom, topped off the brake fluid again at the end (and a couple times during bleeding just to be sure I didn’t run dry but I don’t think I’d have had to do that in retrospect), put it back together and took it for a spin and called it the “experiment.” The baseline drive was at 1:00 PM, and I got back from the experiment drive at 3:30PM and I moved slow and took a break to make a reel on Instagram in the middle because it was hot as hell out today.

I gotta say I like it better without the CDV. It’s not like a whole different car or anything like some people say, but it IS different. It does grab better, it does spin the wheels and not the flywheel in a second gear launch, you can chirp the tires easier if you drop it between gears, and it doesn’t feel like there is a middle man inserting his opinion between me and what my left foot is asking of the car anymore, especially in 1st and the 1-2 shift. It’s less ambiguous. I keep the rev match turned off always anyway so that part’s not too much different for me.

Coming from 25 years of three pedals, it feels more like I would’ve expected in the first place, and I agree with the folks who say I wish I’d have done it sooner. I can also see how it could be possible that some of the people who have stock clutch and stock tune and complain about slippage problems may actually be dealing with their CDV instead of a clutch problem.

I am joining camp CDV delete and I say take that shit out.

Amen!

 

[Spart]

I am doing this same mod in an Integra Type S, and this time I got some before and after data to quiet down the likes of phil and others who poo-poo on this type of mod without having actually experienced the difference first-hand. Now they can argue from inexperience and willful ignorance simultaneously!

I used 1000fps high-speed video to measure the speed of clutch engagement before and after.

Not only does the clutch engage about 42% faster (94ms deleted vs 162ms stock) but the clutch *starts* to engage about twice as fast (32ms deleted vs 63ms stock.)

And before anyone goes off about "you can't notice a 32ms difference" - ask a PC gamer friend if they can notice 32ms of lag in their game. It's REALLY noticeable.

I don't know how closely similar data from the MkV would align with the ITS, but I will say that the difference in the MkV seemed even more pronounced than the difference in the ITS. That could be down to the amount of torque being put down amplifying the effect. Anyway, here's the data in a chart:

The diamond at the bottom indicates the initiation of travel and the dot at the top represents full travel. There's a bit of a bounce at the end. The lag in getting started even with a full delete is likely down to friction, pressures equalizing, and a rubber hose if I had to guess.

 

[swrdply400mrelay]

I am doing this same mod in an Integra Type S, and this time I got some before and after data to quiet down the likes of phil and others who poo-poo on this type of mod without having actually experienced the difference first-hand. Now they can argue from inexperience and willful ignorance simultaneously!

I used 1000fps high-speed video to measure the speed of clutch engagement before and after.

Not only does the clutch engage about 42% faster (94ms deleted vs 162ms stock) but the clutch *starts* to engage about twice as fast (32ms deleted vs 63ms stock.)

And before anyone goes off about "you can't notice a 32ms difference" - ask a PC gamer friend if they can notice 32ms of lag in their game. It's REALLY noticeable.

I don't know how closely similar data from the MkV would align with the ITS, but I will say that the difference in the MkV seemed even more pronounced than the difference in the ITS. That could be down to the amount of torque being put down amplifying the effect. Anyway, here's the data in a chart:

The diamond at the bottom indicates the initiation of travel and the dot at the top represents full travel. There's a bit of a bounce at the end. The lag in getting started even with a full delete is likely down to friction, pressures equalizing, and a rubber hose if I had to guess.

ITS has a CDV???

 

[Spart]

ITS has a CDV???

Seems like most Hondas from the past 15-20 years all have the same CDV design. Both gens of the new CTR (FK8 and FL5) have both a CDV and a damper. I can't speak to the damper design in the FK8, in the FL5/DE5 it's a diaphragm with the fluid on one side and some sort of spring on the other. I need to take it apart to see exactly how it works.

 

[zackarybyrd]

I am doing this same mod in an Integra Type S, and this time I got some before and after data to quiet down the likes of phil and others who poo-poo on this type of mod without having actually experienced the difference first-hand. Now they can argue from inexperience and willful ignorance simultaneously!

I used 1000fps high-speed video to measure the speed of clutch engagement before and after.

Not only does the clutch engage about 42% faster (94ms deleted vs 162ms stock) but the clutch *starts* to engage about twice as fast (32ms deleted vs 63ms stock.)

And before anyone goes off about "you can't notice a 32ms difference" - ask a PC gamer friend if they can notice 32ms of lag in their game. It's REALLY noticeable.

I don't know how closely similar data from the MkV would align with the ITS, but I will say that the difference in the MkV seemed even more pronounced than the difference in the ITS. That could be down to the amount of torque being put down amplifying the effect. Anyway, here's the data in a chart:

The diamond at the bottom indicates the initiation of travel and the dot at the top represents full travel. There's a bit of a bounce at the end. The lag in getting started even with a full delete is likely down to friction, pressures equalizing, and a rubber hose if I had to guess.

This is dope. Cool science project man!

 

[lucky phil]

I am doing this same mod in an Integra Type S, and this time I got some before and after data to quiet down the likes of phil and others who poo-poo on this type of mod without having actually experienced the difference first-hand. Now they can argue from inexperience and willful ignorance simultaneously!

I used 1000fps high-speed video to measure the speed of clutch engagement before and after.

Not only does the clutch engage about 42% faster (94ms deleted vs 162ms stock) but the clutch *starts* to engage about twice as fast (32ms deleted vs 63ms stock.)

And before anyone goes off about "you can't notice a 32ms difference" - ask a PC gamer friend if they can notice 32ms of lag in their game. It's REALLY noticeable.

I don't know how closely similar data from the MkV would align with the ITS, but I will say that the difference in the MkV seemed even more pronounced than the difference in the ITS. That could be down to the amount of torque being put down amplifying the effect. Anyway, here's the data in a chart:

The diamond at the bottom indicates the initiation of travel and the dot at the top represents full travel. There's a bit of a bounce at the end. The lag in getting started even with a full delete is likely down to friction, pressures equalizing, and a rubber hose if I had to guess.

So all this science on something that's NOT a Supra. How was the clutch released for the test? side stepped or leg release?
Every cdv system has it's own parameters.
Phil

 

[Spart]

Everyone point and laugh at phil!

I met someone once who told me some very sage advice about engineering. I'll try to quote verbatim although this is from memory, but it left an impression.

"When I was starting out as an engineer, some of the best engineers I met could just look at something and tell me how it would work (or not work.) But it turns out, those are the worst engineers. You don't know if a thing works until you test it. If you know a thing works and you can't explain how a thing works, then you don't actually know that thing. You believe in that thing."

Phil definitely believes the CDV does nothing.

 

[tracer bullet]

Phil definitely believes the CDV does nothing.

Eh, but he's right to question it. I too think he might believe a bit strongly about something without having all the details, sure, but haven't ever actually met him so I can't judge his personality. But pointing out that the info presented is for a different car is not at all something he should be given any grief on, it's entirely accurate and worth noting.

 

[swrdply400mrelay]

@Spart

If possible I'd like to see this in a Supra before and after CDV delete.

I did CDV pretty early on so I can't remember for sure, but IIRC even after the clutch pedal was completely unreleased and up, it felt like the clutch was still not completely engaged for a second.

 

[lucky phil]

Everyone point and laugh at phil!

I met someone once who told me some very sage advice about engineering. I'll try to quote verbatim although this is from memory, but it left an impression.

"When I was starting out as an engineer, some of the best engineers I met could just look at something and tell me how it would work (or not work.) But it turns out, those are the worst engineers. You don't know if a thing works until you test it. If you know a thing works and you can't explain how a thing works, then you don't actually know that thing. You believe in that thing."

Phil definitely believes the CDV does nothing.

Not actually true. I believe it's there for giving the driveline a bit of relief in extreme circumstances like side stepping the cutch. It's obviously there for a reason but isn't something that would affect normal drivers in normal clutch use on a road car. That's why one particular patent I read for a CDV system it was patented as a clutch "anti abuse" system.
Us engineers also like data, "relevant data" that is. Then backed up by a user "blind test"


Phil

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