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Old 01-11-2019, 04:13 PM   #1
henrymfisher
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WR Blue Pearl

Default Clutch Delay Valve (CDV) - 2019 WRX-STI

Hey guys,

I bought a brand new 2019 STI over the holidays!! So far I love the car except the clutch. Its horrible!! Its jerky, it lets out at different engagement points, it very difficult to be smooth with.

I have owned, driven and tracked many manual cars for 40 years, so I am experienced.

Do these cars have a CDV valve in either the master or slave cylinder?
I have seen posts about early STI's ('05 ish). If it does, does anybody have a detailed mod fix (replace the slave with part# or replace the master with part #). Or do you remove said components and remove the culprit and tie off the fittings?

My old BMW 330i (ZHP) had a CDV with the exact same symptoms. Once removed the clutch was perfect. I suspect the same with my awesome new STI.

HELP please!!! Many thanks.

Henry
'19 WRX-STI (lip)
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Old 01-11-2019, 09:23 PM   #2
Lee-online
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I too recently purchased a 2019 STi. Turning off the the hill assist made a huge difference for me. I think the clutch seats after a few hundred miles and became smoother.
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Old 01-14-2019, 10:43 AM   #3
henrymfisher
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@LeeOnline - Thanks for the tip.

Still trying to get a definitive answer if the car has a CDV valve.

HELP!!!!!

Thanks,
Henry
'19 STI
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Old 01-14-2019, 11:18 AM   #4
USCBallZ
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Quote:
Originally Posted by henrymfisher View Post
@LeeOnline - Thanks for the tip.

Still trying to get a definitive answer if the car has a CDV valve.

HELP!!!!!

Thanks,
Henry
'19 STI
Not much to add in the way of knowledge, but to me it absolutely feels like it does. I too just picked up a 2019 STI (after 15+ years of BMW ownership) and there is something CDV-like if not exactly a CDV going on with my car as well.

That said, I only have ~750 miles on it, so maybe it gets better? My BRZ had the same problem, and it drove me bonkers until the day I sold the car

Hopefully someone on here with more knowledge can shed some light on how to remedy this!
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Old 01-14-2019, 11:22 AM   #5
Blktrax
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There is no delay valve on STi, there is on WRX.

The hill holder operation uses the ABS module to keep the vehicle from rolling back on hill, till the clutch is partially engaged. Disabling the feature will give more consistent engagement point due to foot timing , however obviously then the feature doesn't work.
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Old 01-14-2019, 11:24 AM   #6
anarekist
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also the way the engine is tune, most aftermarket tunes takes away that CDV feeling
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Old 01-14-2019, 11:27 AM   #7
USCBallZ
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Quote:
Originally Posted by Blktrax View Post
There is no delay valve on STi, there is on WRX.

The hill holder operation uses the ABS module to keep the vehicle from rolling back on hill, till the clutch is partially engaged.
That makes sense re: hill holder. So it's normal to have the clutch engage at different points on the pedal in these cars?
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Old 01-14-2019, 11:29 AM   #8
Blktrax
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Yes, because depending on incline and the power of brake applied, the VDC has to see Clutch switch #2 off, Brake switch off, increase of throttle, before releasing the brakes.
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Old 01-14-2019, 11:30 AM   #9
Blktrax
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Quote:
Originally Posted by anarekist View Post
also the way the engine is tune, most aftermarket tunes takes away that CDV feeling

Drive modes I, S, S# modify throttle response also make it feel differently as well.
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Old 01-14-2019, 12:55 PM   #10
USCBallZ
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Quote:
Originally Posted by Blktrax View Post
Drive modes I, S, S# modify throttle response also make it feel differently as well.
Thanks for the info! Since I'm almost done with break-in, I'll have to experiment with drive mode/hill assist configuration to see what fits my driving style best
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Old 01-14-2019, 02:18 PM   #11
bp05obxt
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Quote:
Originally Posted by henrymfisher View Post
@LeeOnline - Thanks for the tip.



Still trying to get a definitive answer if the car has a CDV valve.



HELP!!!!!



Thanks,

Henry

'19 STI


There definitely is restrictions on the factory line that are causing a lot of these issues. If you follow the hardline you will find these brass unions that are inline restrictions that act as a damper.

I know the wrx also has a damper in the slave cylinder that can be modified. As for the STI, in the past, there were also restrictors inside the slave cylinder that needed to be removed to improve engagement and operation.

I have done a Perrin braided clutch line (bypasses/removes hardline and connects directly to slave cylinder) for a 2015+ wrx (would also work for 2015+ STI) and it made a world of difference. After driving the car for a time after the line install it seemingly allowed the clutch to wear into a smoother operating clutch with a much more positive engagement.

I highly recommend a Perrin or any other like designed SS braided clutch line and any other related modification to improve the clutch operation overall.
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Old 01-14-2019, 02:32 PM   #12
henrymfisher
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@bp05obxt - Thanks for your reply and photo.

Can you direct me a little. Where did you take this picture?
Underneith at the gearbox? Or up top?

Thanks.
Henry
'19 WRX-STI (lip)
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Old 01-14-2019, 07:44 PM   #13
james-30
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Group N trans mount with polyurethane corresponding bushing around said mount, engine mounts, pitch stop, rear diff bushings and a one peace carbon fiber drive shaft will 95% cure all issues in the sti drive line play. I'd look into super pro bushing kits. I to have a 19 sti by the way.
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Old 01-15-2019, 07:25 AM   #14
bp05obxt
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You can see the brass unions if you follow the hydraulic hardline from the clutch master cylinder down along the firewall.
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Old 01-15-2019, 10:19 AM   #15
Jedi03
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+1 on the one piece driveshaft helping...also did diff and pitch stop mounts myself...i did the Prothane kit for my car...would love to disable hill start assist...i actually learned how to drive on hills with manual trans way back when lol
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Old 01-15-2019, 12:12 PM   #16
james-30
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Quote:
would love to disable hill start assist...
Its very easy to disable. there are many youtube vids on how to do so.
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Old 07-28-2021, 09:03 PM   #17
fullah
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Quote:
Originally Posted by bp05obxt View Post
There definitely is restrictions on the factory line that are causing a lot of these issues. If you follow the hardline you will find these brass unions that are inline restrictions that act as a damper.

I know the wrx also has a damper in the slave cylinder that can be modified. As for the STI, in the past, there were also restrictors inside the slave cylinder that needed to be removed to improve engagement and operation.

I have done a Perrin braided clutch line (bypasses/removes hardline and connects directly to slave cylinder) for a 2015+ wrx (would also work for 2015+ STI) and it made a world of difference. After driving the car for a time after the line install it seemingly allowed the clutch to wear into a smoother operating clutch with a much more positive engagement.

I highly recommend a Perrin or any other like designed SS braided clutch line and any other related modification to improve the clutch operation overall.
Any negative effects of deleting the clutch delay valve so far?
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