Bleed that clutch slave cylinder!

[CO AVANT]

I have only ever bled my calipers and never my clutch slave cylinder like the idiot I am sometimes even after I installed the new clutch a couple months ago. I was getting a squishy feeling about the last inch when depressing my clutch pedal to the floor. Bled the clutch slave cylinder today after bleeding my calipers and the engagement for the clutch is much improved and the brakes are putting more pressure on the pads giving me even better stopping power! So IMO if you ever bleed your brakes, bleed the clutch slave cylinder at the same time. The bleed valve has a rubber nipple on it just like the brake caliper and is located on the bell housing drivers side above the axle. Takes a 9mm wrench/socket...

[Capt. Obvious]

Do you bleed it like you do the brakes (someone presses down, you open the valve, watch for bubbles, close it, then they let up on the pedal)?

[CO AVANT]

Yeah just like the brakes....I'd pony up and buy a motive power bleeder though if I were you. So much easier, less time consuming, and you can do it by yourself.

[absolutegtr]

+1 on the motive power bleeder. After jacking up the whole car and removing the four wheels and setting up the power bleeder, it took me literally 10 minutes to bleed all four brakes and slave cylinder.

[Capt. Obvious]

What's the order we're supposed to bleed the brakes on our cars? It's different than usual IIRC.

[CO AVANT]

Drivers front, passenger front, drivers rear, passengers rear, clutch slave cylinder

[Kittrell]

With all of the work you have put into your car, and the know-how to do it, this managed to escape you until now? Must be the thin air.

[CO AVANT]

completely forgot about it until today, drrrr lol

[orb]

did you cycle the pump w/a vag-com? or is that not needed? i've read yes and no.

my brake light will beep when taking right handed turns hard, from low brake fluid, but the fluid is topped off. do you think bleeding the clutch would stop the alarm from coming in? i had ss lines put on, and now i get that alarm, never had it before they worked on the brakes.

[DeanUW]

When you bleed your slave you should bleed A LOT! I can't remember the exact amount off the top of my head but you need to bleed it more than each caliper. I think I bleed like a half a quart from the slave...

[mike-2ptzero]

What, you haven't left for your driving trip to CA yet?

[rxrep]

As mentioned, our sequence for bleed is OPPOSITE of what we all learned on other cars. Ours goes from closest to furthest.
On the clutch slave, it calls for increased PSI on the bleeder, like double what is required for the brakes. Not sure of it exactly; I'd have to look it up on Bentley but I swear it's like >25psi.
Also, Bentley requires 100cc minimum bled out of clutch slave.
Finally, the last trick, and I learned this the hard way, is to have a really long bleed hose for the clutch slave, as the length you use for the brakes will work but will prolly squirt fluid everywhere while you hold your container up in the air to catch it.
Oh, and finally, nothing is needed with VAG COM.

[F16HTON]

The reason for the increased PSI is that the slave has quite a few pockets that can trap air.

Also, when you flush your brake fluid, the fluid in the slave will remain, when I do mine at Eurocode, they showed me to drain it and actually prefill it with new fluid, this way you do not have to bleed off quite as much.

Tappping it a couple of times also helps remove bubbles out of the air pockets.

[dougyfresh]

What, you haven't left for your driving trip to CA yet?

I was thinking the same...

Unless he's got one of those fan-dangled iPhones like some of us have

[DeanUW]

The reason for the increased PSI is that the slave has quite a few pockets that can trap air.

Also, when you flush your brake fluid, the fluid in the slave will remain, when I do mine at Eurocode, they showed me to drain it and actually prefill it with new fluid, this way you do not have to bleed off quite as much.

Tappping it a couple of times also helps remove bubbles out of the air pockets.

Hey Greg could you please explain more as to what Eurocode told you as far as the draining and prefill? Thanks!

[CO AVANT]

taking off Thursday night and driving straight through

[mike-2ptzero]

taking off Thursday night and driving straight through

So its less then a 24 hr drive straight?

[CO AVANT]

Did LA to Denver in 12.5hrs, so I'm sure I'll get there in good time.

[mike-2ptzero]

Did LA to Denver in 12.5hrs, so I'm sure I'll get there in good time.

Thats not too bad, thats about the time it took me to go from socal to NM but I made a few stops since I had the woman and kid with me.

[absolutegtr]

I think I will rebleed the slave cylinder tomorrow....does anyone know for SURE what is the pressure I should set thepower bleeder at?

I think what Lee said (~25psi) is WAY too much. I set it at ~19-20 psi when I bled the slave cylinder after my clutch install. ....but maybe I should have jacked it up to 25psi...

[rxrep]

Direct from Bentley:

*Allow at least 100cm3 of fluid to drain out.
*Working pressure is 2.5 bars which I think is about 36psi? (Can't remember exact conversion)
*Bleeder valve torque is 4.5nm

[CO AVANT]

I had to drain out a whole bottle, seriously, so many bubbles. Yes ~37psi is 2.5bar per Bentley manual. I did it at ~28psi and had no problems. I was shocked when I saw the bleeder valve torque. Isn't that like hand tight or what? Anyone's bleeder even go above 30psi?

[ridelikeme]

where is the slave cylinder, and does anyone have a pic? and does it share fluid from the brake system? sorry for the rookie questions boys but i have not done to much work on brake systems (other then installing new rotors and pads)

[CO AVANT]

shares same master cylinder as brakes. The bleed valve for the clutch slave is located above the drivers side front axle on the top of the bellhousing (transmission) There is a little rubber nipple on it like the brakes have. Remove the coolant reserior for easier access.

[F16HTON]

shares same master cylinder as brakes. The bleed valve for the clutch slave is located above the drivers side front axle on the top of the bellhousing (transmission) There is a little rubber nipple on it like the brakes have. Remove the coolant reserior for easier access.

Shares the same fluid reservoir as the brakes (they get fluid from the same location) however it does not share the brake master cylinder.

You have a clutch master cylinder which is attached to the pedal, and a clutch slave cylinder which is located on the transmission and has a plunger to push in the clutch fork and disengage the clutch.

The way it works is that when you press in the clutch pedal, the clutch master cylinder forces hydraulic fliud (brake fluid) through a small steel line into the slave cylinder, the pressure created by forcing the fluid causes the sleve cylinder to move and in turn it moves the clutch fork. The clutch fork in turn moves the clutch diaphram and releases the pressure off of the clutch pressure plate.

The way the clutch engages is that the pressure plate clamps down on a disk that is connnected to the tranasmission via splines, when there is pressure from the clutch disk, it is mated to the flywheel and transfers the rotation of the engine to the transmission.

When you disengage the clutch (by pushing in the pedal) it allows the disk to spin freely by releasing the clamping pressure put on it by the flywheel.

The reason it is important to bleed the clutch is beacuse the size of the master cylinder and slave cylinder are very small in comparison to the amount of pressure it takes to disengage a clutch, the reason they are small is they have to be proportionally smaller than the hydraulic brake system, if they were any larger, as the clutch begins to wear, you could potentially use all of the fluid in the reservoir for the clutch, leaving none for the brakes.

Brake fluid is typically good for no more than two years if your car is driven normally, if you drive hard like I do, you need to change your brake fluid every six months or year.

High performance brake fluid (such as Motul RBF) also condenstes (collects water) very easily and should be changed after track events, canyon carving and anytime you tend to overheat your brakes.

If you bleed your clutch, you will have better performance, a longer lifespan and your third gear synchros will last longer.

[CO AVANT]

Good info Greg. I meant to say the reservior, I don't know why I wrote master cylinder since there is a clutch slave cylinder, drrr typing brain fart.....just too much on my mind right now lol See you tomorrow

[Ill 3.0]

Yeah just like the brakes....I'd pony up and buy a motive power bleeder though if I were you.

But it can still be done manually? I just bled my brakes and figured I'd wait until next year to buy a power bleeder when I change fluid again. Do you just have someone pump 3 times (valve closed obviously) with a board behind clutch pedal, then open valve?

[CO AVANT]

Not sure if it would work manually like the brakes though using the clutch pedal, the bentley procedure uses a pressurized container to 2.5bar.

[dougyfresh]

Stop posting and hit the road, SON!

[F16HTON]

But it can still be done manually? I just bled my brakes and figured I'd wait until next year to buy a power bleeder when I change fluid again. Do you just have someone pump 3 times (valve closed obviously) with a board behind clutch pedal, then open valve?

Not a good idea, the reason why is that when you depress the clutch pedal, the slave cylinder has a shitload of pressur eon it from the clutch forks and pressure plate diphram, once you crack the bleeder valve, the slave cylinder loses all pressure and it is the same as dumping the clutch. What you will do is force the piston in the slave cylinder into the back of it and it may or may not cause damage, the end result is that you will suck more air back into the system than you had before.

If you do not have a pressure bleeeder, you are better off cracking the valve and tapping the side of the slave cylinder, all of the bubbles will rise to the top and you will get it as close as possible.

The Bentley method of pressurizing the system is the best way, a power bleeder is only $25-35 dollars.

[Ill 3.0]

got it, thanks Greg.

[Toast]

i just took mine to a shop and the mechanic called saying they dont know whats wrong but the clutch is hitting the floor - you would think they would rtfm

[A4_Mike]

Yesterday, I used a power bleeder to bleed all of my brakes and the clutch slave cylinder. My brakes had relatively new fluid from last year so the fluid looked decent. I can not say the same for the clutch slave cylinder where the fluid looked really dirty and had a green hue to it. I could not believe how bad the fluid looked! Regardless, the car is using Pentosin racing brake fluid now so I am all set for a track event in early September.

In conclusion, I highly recommend to bleed the clutch slave cylinder! Thank you to the OP for bringing the topic up.

[sambrody44]

You guys think a dealership is competent enough to do this?

[CO AVANT]

i just took mine to a shop and the mechanic called saying they dont know whats wrong but the clutch is hitting the floor - you would think they would rtfm

They mess up your slave cylinder? Were they bleeding at 37psi?

I would hope a dealership is competent enough to do it lol

[sambrody44]

They mess up your slave cylinder? Were they bleeding at 37psi?

I would hope a dealership is competent enough to do it lol

Any idea how much they'd charge?

[sambrody44]

I just got quote $120. Does that seem fair?

[CO AVANT]

You could buy yourself a motive power bleeder for $30 and a couple bottles of Motul 5.1 for $14 and do it yourself. It is very easy to do, I could walk you through it if need be. It takes a whole 5 minutes.

[sambrody44]

You could buy yourself a motive power bleeder for $30 and a couple bottles of Motul 5.1 for $14 and do it yourself. It is very easy to do, I could walk you through it if need be. It takes a whole 5 minutes.

Where would i get the power bleeder? What type of fluid? Do I need a lift to do it?

[CO AVANT]

You do not need a lift. You don't even need to get your car in the air for that matter. Just google for the "motive power bleeder", they are everywhere. Motul 5.1 brake fluid if you bleed the brakes and clutch slave cylinder. If you are just bleeding your clutch slave cylinder then use what ever brake fluid is currently in there. The clutch and brakes share the same reservior.