Clutch slave and master cylinder "matching"

[ciper]

This might be slightly off topic but I'd rather ask around in a friendly environment before heading over to the other places.

The long story short - I'm trying to compile specs for slave and master clutch cylinders. The brake sizing spreadsheet that Legacy777 made comes to mind.

The reason I ask is that through a series of unfortunate events I'm using an 02 WRX master cylinder against a 98 RS slave on the STI swap with an ACT stage 2 clutch and I HATE IT. The engagement and peddle feel suck. Before I mess with adjusting it I want to see if the combination of the two created a mismatch in fluid volumes.

I thought the information could be useful later for those of us wanting to adjust/improve our peddle feel (assuming there are differences).

[AWD_addict]

Does the pedal feel too light or too heavy?

Get the piston diameters, they should be cast into the sides of the cylinders.

Even if the hydro ratio is decent, the clutch type could be what you dislike.

[ciper]

The peddle feels slightly stiffer, which is ok, but engagement is at the VERY top of peddle travel. The difference between a fully open clutch and engaged clutch is about 1/3 of an inch of pedal travel.

[Legacy777]

You need a larger slave cylinder piston diameter, or smaller master cylinder piston diameter.

I think it'd be cool to put a spreadsheet together that would calculate movement ratios between different size master & slave cylinders.

[93forestpearl]

I've been wondering this as well. I've been using an undamped SS clutch master and a WRX slave on my 6mt and I'm just the opposite. I engage at the very end of the pedal throw. I've been contemplating getting an STi slave.

[ciper]

I'd be glad to help find whatever information needed. If we do make a spreadsheet lets make sure to denote if the slave is push or pull.

[Legacy777]

I've got several FSM's. I could try and start putting together things.

[ciper]

I found some of the spare parts -

What I think is 98 RS master markings - 5/8
WRX master 11/16

98 RS slave 3/4
What I think is 2002 WRX slave - 3/16


So originally the car had a 5/8 pushing a 3/4 and now it has a 11/16 pushing a 3/4 . I'm impressed with myself that I could feel such a small difference!

[n2x4]

Are you sure the clutch freeplay doesn't just need to be adjusted?

[93forestpearl]

When I go home this weekend I'll have to dig up my extra SS undamped master and check out the size of it. I'm not gonna take out my slave to check its size. Thats a few hours of work for me.

[ciper]

Hehe check this thread out.... http://forums.nasioc.com/forums/showthread.php?t=243252

Also this http://forums.nasioc.com/forums/showthread.php?t=404047

It would be nice if I could find a larger slave.

When I go home this weekend I'll have to dig up my extra SS undamped master and check out the size of it. I'm not gonna take out my slave to check its size. Thats a few hours of work for me.

I bet you can see it just looking under the hood. I was able to read the size from the RS slave with the intercooler still installed.

Are you sure the clutch freeplay doesn't just need to be adjusted?

I'm pretty sure it does but even so the engagement space is still small. I'd love to get an even smaller master to increase pedal travel further than the stock one.

[AWD_addict]

You need a larger slave cylinder piston diameter, or smaller master cylinder piston diameter.

I think it'd be cool to put a spreadsheet together that would calculate movement ratios between different size master & slave cylinders.

Get some measurements from a clutch pedal to determine the mechanical ratio. That way the sheet could calculate how much the pedal effort would change too.

[Legacy777]

Yeah I could do that too.

[ciper]

It looks as if the 07 STI has the same specs as that 02 WRX.

[93forestpearl]

Looked at my extra SS master and found out it is a 5/8. The WRX master is 11/16 so I might have to try that.