DIY - Swap clutch slave cylinder and hydraulic line for improved feel and control

[Phantobe]

Originally Posted by 504

So I also installed the smaller slave cylinder a couple days ago with pedal adjustment and clutch assist spring removed and I must say its REALLY nice. To be completely honest, it doesn't feel any heavier, almost feels lighter actually haha for some odd reason. This may or may not be true but it feels like there is a greater pedal range for where the clutch touches and engages completely so it leads to smoother matching of rpm between shifts and hence a smoother experience. Its definitely more clear where the touch point is now and overall it is really nice.

This coupled with MTEC assist spring and pedal adjustment could be the perfect combo for any long distance daily drivers IMO

I think the clutch is heavier, however it only took a short period of time to adjust to the feeling. So now it feels light again, just my opinion.

Easiest way to see if it truly feels heavier is to drive a stock clutch then drive your modded one, I think you'll notice the weight difference.

[Ultramaroon]

There is a 17% decrease in leverage so imagine choking up on a ratchet handle by 17% of its length. Same thing. Gotta pull harder.

I've been thinking about it and wonder if they didn't choose to source the bigger slave because:

1. The prototype fa20 had a turbo. (it did)
2. They expected people would boost the engine and require heavier aftermarket clutches? Meh, not sure about this one. Maybe, though...

[Koa]

Originally Posted by Ultramaroon

There is a 17% decrease in leverage so imagine choking up on a ratchet handle by 17% of its length. Same thing. Gotta pull harder.

I've been thinking about it and wonder if they didn't choose to source the bigger slave because:

1. The prototype fa20 had a turbo. (it did)
2. They expected people would boost the engine and require heavier aftermarket clutches? Meh, not sure about this one. Maybe, though...

Should make a note in the first page about keeping the bigger slave if FI is in their future plans huh.. Some people who may not realize it has value if running a heavier clutch would off-load their parts to off-set costs, lose it, feed it to their dogs, etc so it may be something worthwhile to note

[Dipstik-sportech]

I have the heaviest single disk they make for our cars and I'm still considering this upgrade. If the slave has a smaller diameter doesn't that mean it will also travel further ? I wonder if this will help with the synchro issues people are having......?

[Koa]

Originally Posted by Dipstik-sportech

I have the heaviest single disk they make for our cars and I'm still considering this upgrade. If the slave has a smaller diameter doesn't that mean it will also travel further ? I wonder if this will help with the synchro issues people are having......?

The clutch fork either gets engaged or not, right? Wondering how it'll help synchro issues people report (which may or may not be actual issues, but people's perceptions of issues relating to stiff/locked out gears with new transmissions, cold weather drivers, new manual drivers, or those not used to tight-tolerances).

If there are known synchro issues aside from those then do tell!

[Ultramaroon]

Originally Posted by Dipstik-sportech

I have the heaviest single disk they make for our cars and I'm still considering this upgrade. If the slave has a smaller diameter doesn't that mean it will also travel further ? I wonder if this will help with the synchro issues people are having......?

That's exactly what it means/does.

Originally Posted by Koa

The clutch fork either gets engaged or not, right? Wondering how it'll help synchro issues people report (which may or may not be actual issues, but people's perceptions of issues relating to stiff/locked out gears with new transmissions, cold weather drivers, new manual drivers, or those not used to tight-tolerances).

If there are known synchro issues aside from those then do tell!

It will have zero effect on other transmission issues, real or imagined.

Now we could consider issues resulting from people's inability to properly adjust their clutches but that's a whole different topic.

[Dipstik-sportech]

If said problem is caused by a dragging/not fully disengaging clutch then yes it could be fixed by this mod. I for one believe the clutches on these cars don't quite release fully causing the synchros to work harder than normal. Feel free to look at my thread on the synchro design @Koa have you not seen the hundreds of threads on the topic and the fact that Subaru is replacing them due to synchro failure....? I've had these transmissions apart and the synchro design is horrible.

[Koa]

Originally Posted by Dipstik-sportech

If said problem is caused by a dragging/not fully disengaging clutch then yes it could be fixed by this mod. I for one believe the clutches on these cars don't quite release fully causing the synchros to work harder than normal. Feel free to look at my thread on the synchro design @Koa have you not seen the hundreds of threads on the topic and the fact that Subaru is replacing them due to synchro failure....? I've had these transmissions apart and the synchro design is horrible.

I just would like to see a trial or series of tests analyzing disengagement of the clutch under normal use. Not that easy to accomplish and would need a team with a specific skillset to capture the data and analyze it. I wouldn't say hundreds of threads, but a vast majority of those threads are dealing with stiff and/or locked out gears (people not used to the triple cone; cold transmissions; people who just are learning to drive manual).

I've put in two RA gearsets in the non-sti 5MTs (and had Mike at PIA of Auburn do the tolerances.. I'm not that technically affluent )- I also know what bad synchro design looks like. The 5MT SOA put in their bugeye Impreza WRXs were, and still are, based on antiquated designs that this transmission just scoffs at.

These transmissions get a lot of bad rep, but my experience at least has been they are a cut above compared to most others I've driven. That list isn't exhaustive, and I'm no pro driver, but this is my findings from driving scores of different manuals throughout the years. Even my STI 6mt wasn't as nice shifting after I adjusted the clutch pedal on the Aisin- and I had quite a bit of mods that I felt enhanced that STI tranny.

I'm not saying you're wrong or that I don't feel like these transmissions are the golden egg @Dipstik-sportech... Would love to see your analysis and perspective on the synchro designs, I'll check it out. I just have seen what forums do to exacerbate problems- specifically transmission problems. Before we could go further in this topic we need cold, hard data such as:

I) How many transmissions were replaced by SOA/Toyota due to bad synchro(s) or clutch throw-out bearing (easiest to get, given transparent and full access)

II) How many people have reported transmission problems related to their synchros FAILING- not just being stiff or 'locked out' when cold or trying to shove it in first above 10mph (harder to quantify, even with forum tools)

III) Videos and data showing the engagement/disengagement of various clutch setups (Hardest to do, imo. Lots of specialized gear and competent people needed to set up and carry out the trials)

[Dipstik-sportech]

I never said it would solve it I said I WONDERED IF it would. Mine was never hard shifting but at higher rpm it was difficult to get into gear at times and ultimately I ended up with pieces of the synchro on the transmission magnet. Now before you go saying it was abuse I have been driving a manual since I was 16 so I've had some practice. This is the first trans I've ever had that has blown synchros and I'm not alone in this issue. It would be worth looking at if it could resolve the hard shifting issue and synchro wear and I plan to do this swap when the snow melts.

[Koa]

Originally Posted by Dipstik-sportech

I never said it would solve it I said I WONDERED IF it would. Mine was never hard shifting but at higher rpm it was difficult to get into gear at times and ultimately I ended up with pieces of the synchro on the transmission magnet. Now before you go saying it was abuse I have been driving a manual since I was 16 so I've had some practice. This is the first trans I've ever had that has blown synchros and I'm not alone in this issue. It would be worth looking at if it could resolve the hard shifting issue and synchro wear and I plan to do this swap when the snow melts.

I'm all about improvements.. would love to see if the synchros could be better engineered. This is a lot of car for $25k MSRP, so things do indeed have to be compromised or engineered smarter.

[Ultramaroon]

Originally Posted by Dipstik-sportech

I never said it would solve it I said I WONDERED IF it would. Mine was never hard shifting but at higher rpm it was difficult to get into gear at times and ultimately I ended up with pieces of the synchro on the transmission magnet. Now before you go saying it was abuse I have been driving a manual since I was 16 so I've had some practice. This is the first trans I've ever had that has blown synchros and I'm not alone in this issue. It would be worth looking at if it could resolve the hard shifting issue and synchro wear and I plan to do this swap when the snow melts.

You're far from alone. We've read about many people's issues with bum trannys attributed to "quality control" at Aisin. I dunno. There seem to be less reports of issues since later in the first MY.

I must admit I am mystified by issues like you and many others experience with grind at high rpm. It doesn't make sense because the relative difference in speed of the decoupling-to-coupling gearsets remains exactly the same. I am paying close attention to this and have almost 9K on my ticker. No issues yet. <fingers crossed>

Still, it's not the clutch. I shared a trick with @Phantobe a while back and told him I wouldn't mention it here for fear of being flamed. It's much easier than jacking up the car to verify and you've probably already accidentally done it many times.

At rest, try shifting halfway into first gear. Ease it just past the synchro then slowly lift the clutch pedal. With a tiny bit of pressure, you'll feel exactly when the clutch begins to engage and hear the familiar sound that makes us all cringe. Believe me, unless there's a serious problem with the clutch itself, when it's disengaged, it's really disengaged.

edit: The lightbulb just came on. ...I think. The speed ratio between the 2 gearsets remains the same but there is a greater difference in rpm at high speeds. It does make sense that the synchro failure would first be noticed shifting at high speed. Just had to wrap my tiny head around it.

[surcy]

Changed mine an

[surcy]

Changed the clutch slave cylinder as recommended and results are as advertised.


Thanks for the recommendation.

[Calum]

Hey guys, I saw someone reference this thread the other day and came looking. I think I've read everything but I've got a couple questions.

First though, anyone looking for the part might want to check rockauto.com. The prices discussed here seem amazing, but they would be basically impossible where I'm at. So rockauto.com is for those in area like me, not you guys in the US.

My question is why not remove the bolts before you remove the line? Of course you'll have to loosen the bango bolt slightly before you remove the bolts, but you might save some mess and some fluid this way.

My other question was, has anyone tried bleeding the system by manually manipulating the piston on the slave... Yes I know how that sounds... But that's how I've bleed other clutch systems in the past, just hold it lower than the master and stroke it until you get all the air out.