[How-To] Clutch Damper Valve Delete

[Zee199969]

We do not have one at the m/c. There is a flow restrictor in the slave cylinder. To my knowledge, Islandborn is the only one who has modded the slave cylinder to remove it.

 

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I also have the flow restrictor at the slave cylinder removed. 25k+ miles with no issues

[smash209]

The damper on the 5th Gen is unique. Most of the other Subaru's with dampers have them located directly on the master cylinder, thus the smaller size as shown in covertrussian's pics above. Ours is a separate unit...

Of the dozens of guys on here that have done the damper delete, no one yet has broken an axle or popped a transmission as a direct result of this mod...

 

We do not have one at the m/c. There is a flow restrictor in the slave cylinder...

 

Thanks for the detailed response GTEASER and other folks! It's much clearer now what I should do ! Do you know if the flow restrictor in the slave is directional or restricts fluid movement in both directions?

[cww516]

Pretty sure it's directional, that much I remember. Wide open on pedal down, and restrictive on pedal up.

[GTEASER]

Thanks for the detailed response GTEASER and other folks! It's much clearer now what I should do ! Do you know if the flow restrictor in the slave is directional or restricts fluid movement in both directions?

 

No problem.

 

Here are islandborn's posts on the slave cylinder mod. They are in this thread but not easy to find.

 

I have very little time until summer but wanted this done. So I ordered the part and chatted it up at my Subaru dealership service guys. (they are all part of the Houston Subaru Group - run modded STIs and WRXs ) Of course it was a interesting thing as the STI and WRX set up is very different from ours - of course.

 

After looking at the AMAZING pics in the front of the tread, they did the delete quite fast @ 40 minutes. ALSO, they removed a spring set up that controlled the oil from the slave cylinder - common mod they do.

 

Results: Totally love it. This is old school clutch working. I can FEEL the slight vibrations thru the clutch pedal as I press on it. I'm running a Competition Clutch Stage 2 and would get frustrated getting into 1st gear. All the sponginess and guessing would leave me riding the clutch just to get going. Drive-Thrus KILLED me (I get a green tea from Starbucks every AM) as I would feel like a tool over-revving. IMHO this mod makes the shifting drastically better - even better I would say than the stock set up.

 

reeg240 - Well done with those picts. Even the guys at the dealership was quite impressed with how you got those so clean.

GTEASER - fantastic job on the explaining of "why do it" and the hunting you do so well for part look ups....(I swear you are independently wealthy and never work so you have time for all this stuff )

 

Its on top of the slave cylinder - all contents behind the big bolt need to be removed - plastic piece, spring, and a valve of some sort with lots of little holes with a rubber stopper. I forgot them at the dealership so I'll go today to pick them up and take a pic for all

[GTEASER]

Now I'm thinking I should do this too the next time the intercooler comes off.

[cww516]

Now you have an excuse to finally install that GS TMIC!

[BigBopper]

Islandborn is the only one who has modded the slave cylinder to remove it.

 

Hey, don't forget me too!

 

I removed both also.

 

http://legacygt.com/forums/showpost.php?p=5100783&postcount=337

[brandon.mol]

The damper we are all removing doesn't limit clutch drop speed anyway since there is no flow limiter in it and return pressure comes from the slave cylinder. Therefore, it would add zero protection to clutch dropping. Its meant to just numb the shit out of the pedal feel by increasing the volume of the hard line under pressure.

 

Remove it. Don't look back. Its useless and counterproductive. Clutch last longer without it.

 

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[Sarang]

That is significant! If it adds no protection whatsoever than it's useless.

[GTEASER]

A lot of engineering effort went into disconnecting the driver from the car.

[jertfunk]

You guys reminded me I still have this part laying around and might finally get it installed since it's starting to get warm. Since I'm pulling the intercooler should I go ahead and order the Perrin hose in case my factory one is fubared?

 

 

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[DrD123]

The damper we are all removing doesn't limit clutch drop speed anyway since there is no flow limiter in it and return pressure comes from the slave cylinder.

There are two things you can put in this type of hydraulic system to help keep pressure transients manageable - a pressure damper and a delay valve. The thing folks are eliminating in this thread is a pressure damper - it is designed to smooth pressure spikes (from fast engagement/disengagement). The other type of regulator is a delay valve - that is essentially a restriction that slows the rate of pressure rise/drop in a hydraulic system. A delay valve can be simple - like an orifice. In any event, these are pretty common things in many hydraulic systems - not something Subaru cooked up specifically to make life difficult for folks.

 

In any event, a pressure damper absolutely impacts what happens when you dump the clutch or when you slam it in really fast.

[foxrider28]

You guys reminded me I still have this part laying around and might finally get it installed since it's starting to get warm. Since I'm pulling the intercooler should I go ahead and order the Perrin hose in case my factory one is fubared?

 

 

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I would suggest yes, simply because it's cheap reassurance. The stock hose is bound to fail eventually if it hasn't started already. This was the first 2 "mods" I did to my car, well this plus AEM filter, milk jug delete, and the HKS intake funnel.

[brandon.mol]

There are two things you can put in this type of hydraulic system to help keep pressure transients manageable - a pressure damper and a delay valve. The thing folks are eliminating in this thread is a pressure damper - it is designed to smooth pressure spikes (from fast engagement/disengagement). The other type of regulator is a delay valve - that is essentially a restriction that slows the rate of pressure rise/drop in a hydraulic system. A delay valve can be simple - like an orifice. In any event, these are pretty common things in many hydraulic systems - not something Subaru cooked up specifically to make life difficult for folks.

 

In any event, a pressure damper absolutely impacts what happens when you dump the clutch or when you slam it in really fast.

 

In, yes. Dropped , No. It doesn't. It only affects what the pedal does. The clutch pushes out the pedal, not the other way around.

 

The damper is straight pass through and creates no restriction of flow in the line and therefore, if you sidestep the clutch with or without this valve in place, the same thing happens on the clutch side of the hydraulic line.

 

It only affects what the clutch does if your foot is modulating the engagement rate, I.e. normal use.

[DrD123]

In, yes. Dropped , No. It doesn't. It only affects what the pedal does. The clutch pushes out the pedal, not the other way around.

What? The clutch pedal actuates the clutch master cylinder, which in turn applies pressure to and actuates the slave cylinder, which actuates the clutch. Look where the damper is located - it's in the line between the master and the slave - it damps pressure transients in the line between the two - that includes in the positive (increasing pressure) and negative (decreasing pressure) directions - it's not a one way valve, it's a damper that forms part of the fluid volume between the two. In simple terms, it gives the transient something else to act on than whatever is at the other end of the line (remember - hydraulic fluid is incompressible - you are passing a pressure wave through it, and it's changing how the fluid volume responds in terms of propagating the wave - so adding what is essentially a dynamic volume on the line impacts what it does)

 

the clutch pedal actuates the master cylinder - when you press it in, you apply pressure to the fluid (pressure moves in the positive direction) and when you release it, you decrease the pressure (pressure moves in the negative direction) - the damper impacts the magnitude of both transitions (the pressure doesn't magically go between positive and negative/zero - things have to move, etc.) - so yes, it absolutely, positively impacts things in both directions.

 

You can see through it because it's not acting like a restriction to prevent passing a pressure wave - that's a delay valve.

[brandon.mol]

You must not understand my point.

 

I'm quite aware how it works during normal use when the lines are pressurized because you have your foot on the pedal.

 

My point is if you side step the clutch, on purpose or by accident, the pedal is free floating and there is virtually zero pressure in the line and the damper does nothing to reduce their rate of clutch engagement.

 

So I don't know why you keep writing long descriptions of how the part dampens pressure variations. There are no pressure variations when your foot isn't on the pedal.

 

My entire point is that the part does not offer any protection from accidental clutch dropping, say because your foot slips off the pedal. And therefore, its not some kind of safety net against damaging the clutch.

 

And therefore, there is no argument for keeping it on the car and removing it is always a good idea.

[FLlegacy]

The clutch felt much smoother before I removed the damper, that's an argument to keeping it...

 

[DrD123]

You must not understand my point.

No - I understand, you are just incorrect.

I'm quite aware how it works during normal use when the lines are pressurized because you have your foot on the pedal.

 

My point is if you side step the clutch, on purpose or by accident, the pedal is free floating and there is virtually zero pressure in the line and the damper does nothing to reduce their rate of clutch engagement.

Ok - I'll keep it simple. The damper acts on transients - quick changes - those happen when you stomp on the clutch (goes from low/zero to positive) AND when you sidestep or lift quickly from the clutch (goes from positive to low/zero/negative)

 

rate is primarily regulated by a delay valve (which you still have - only seen one person remove that here)

 

I'll not get into what the pressure is doing in the line between the master and slave when you sidestep the clutch, as you aren't getting the fact that it's not a binary shift between high pressure and zero.

[ripstik]

My point is if you side step the clutch, on purpose or by accident, the pedal is free floating and there is virtually zero pressure in the line and the damper does nothing to reduce their rate of clutch engagement....

...My entire point is that the part does not offer any protection from accidental clutch dropping, say because your foot slips off the pedal. And therefore, its not some kind of safety net against damaging the clutch.

 

And therefore, there is no argument for keeping it on the car and removing it is always a good idea.

 

i think you have this a bit backward. the dampener slows pedal up, not pedal down. so if you side step the clutch before removing the dampener your clutch is going to engage slower than if it were removed. i actually thought the dampener worked great launching, but felt like garbage for everyday driving and fast shifting

[cww516]

Nope, it acts in both directions. That flexible disc in the damper (which occasionally likes to blow out and puke brake fluid on your feet, another reason to get rid of it) flexes when the line is pressurized, and the amount it flexes is proportional to how fast you push on the pedal (F=k•x). It'll still be flexed a little with the pedal fully depressed, since the pressure plate is pushing back, so if you sidestep the clutch, there is a very brief moment where the damper maintains line pressure as the disc relaxes back to its free state. GTEASER's analogy likening the damper to feeling like there's a rubber ball between your foot and the pedal is pretty much spot on as far as function, too. As DrD alluded to, there's a bunch of other stuff in the system doing the same thing (rubber and braided stainless lines, mostly), plus transients and harmonics and a bunch of other stuff that's over my head (it's a sad day when a mechanical engineer knows more about electrical than about fluid power...). Having the damper in place will damp out a bunch of that noise, which makes for smoother (but not necessarily slower) clutch engagement.

 

tl;dr- a damper is kind of like a li'l baby accumulator, so everyone is at least a little bit right.

[smash209]

I think it makes sense that the damper would affect both directions (unless there is a ball valve in the top). I will remove it as soon as I can considering there is still a delay in the slave that is "protecting" me. Have to get the new part.

 

My pedal is squishy and sort of feels like its attached to a ziptie even after bleeding well. It's probably the damper right? However, what is the likelihood that the rubber washer creating the one-way valve in the slave has bit the dust after 90k?

[brandon.mol]

Guys...If there is low pressure in the line, because the pedal is free, then the damper does nothing to the rate that the clutch moves because the master cylinder is not providing any significant resistance to to the fluid flow. The slave cylinder is free to return fluid as fast as it can and as a result, the clutch engages as fast as the slave lets it.

 

This part does not limit the flow rate of the fluid and therefore it does not reduce clutch engagement speed if you side step it.

 

Its irrelevant what is going on with the pedal. All that matters is whether something is slowing down the flow rate in the line on the way out of the slave.

 

The only "useful" thing this part does is mask clutch chatter.

[DrD123]

you need to think about what a damper does, and how it acts on a changing system.

 

maybe another way to look at it - if it doesn't do anything to the system, why does removing it change the way the hydraulic system feels? particularly for clutch engagement, where you are decreasing pressure?

[smash209]

I did the delete today. Wow! Even after everyone hyping this up, I am surprised at the difference this makes! The car really drives as it should. After 10 mins of driving I feel so much more comfortable with the engagement point and feedback. Now I know when I'm slipping the clutch and when I'm not. So much easier on hills and confidence when matching revs.

 

A few notes:

- After contorting to get my head under the dash, I decided to lay the drivers seat all the way back (and down), and lay upside-down to do this work. I can't say this was better but it worked.

- I was going to use a generic union from autozone after reading that I need to get the subi part and then grind off an ear. Don't do this. Grinding the ear was easier than expected (used air cutoff tool), and because of the tight space and mounting location it was invaluable to have a new part that fit perfectly when trying to line up the fickle hydraulic lines. I also didn't need to undo the line at the master cyl, just the two at the damper.

 

- It should go without saying that you need a flare nut wrench.

 

- After assessing just how dot3 was going to drip into my eyes, or at least be super annoying and not easy to plug up, I opted to go the route of draining ALL the fluid. Sucked it out through the slave. This worked well IMO, however required extra bleeding to get all the air out.

 

- Tips for bleeding (if you sucked in air). I used a combo of the vacuum pump (cheap plastic version mitivac) and the pedal. I also took the slave bleeder screw out and teflon taped the threads, so I know any bubbles are from the line. Bleed normally using a combo of vacuum and pedal push pull. Alternate. At some point contrary to most I've read, with bleeder open, you need to go fast with the pedal 3 or 4 times up and down. You will feel the restriction in the slave cylinder slowing the action if you do it right. I believe this is needed to fully get the air out of the system. Keep bleeding normally after this and all should be good. I used 2.5 of the small dot3 containers total.

 

If you are still debating as I was... just do it. It can always be reversed, but I doubt anyone would who likes driving stick after experiencing the difference!

[A_A_ron]

I just got this done today. I live in an apartment and I have limited tools so I figured I'd play it safe and ensure I don't melt my carpet or have a bunch of air in the system by paying a shop to do it. When I replaced the clutch I got a 6 puck and asked the guy about the damper. He said it should be easy and he'd only charge me for an hour. Took less than an hour and I paid 90 bucks to have it done which I am personally okay with since I don't have my own garage and I'm tight on time getting ready for boxerfest.

 

Even just pulling out of the parking lot I noticed a difference. As I was feathering the clutch (uphill start from a complete stop) I paused as the friction was kicking in and it remained steady. Then as I started moving into the street I let off and it engaged the rest of the way consistently. It's amazing.

 

Also if anyone else is considering this I ordered 3 of the connectors and have two extra. I will sell at cost and we'll find the cheapest shipping possible or we can meet up at boxerfest if you are going to be there.