B8.5 A5 - Clutch Bleeding Help

[avimore]

Hi all,

I was bleeding the brakes and clutch slave cylinder today. I use a Motive brake bleeder and find that it works really well.

I've bleed the brakes a couple of times in the past already with no issue and the brakes went smoothly this time around also. I tested the brake pedal after and it is rock solid. But when I went to bleed the clutch slave cylinder I ran into some issues...

I used the same process as the brakes, except I pumped up the Motive bleeder to 2 BAR as per the factory manual. I attached the bleeder bottle hose onto the bleeder screw, and opened the bleeder screw. The fluid started to flow into the catch bottle as expected, but then just as I got around 50ml of fluid out, I got a gush of air flowing out from the slave cylinder, and it started to sputter and then the fluid stopped flowing all together.

I closed the bleeder screw and started the process again from the beginning, but the same thing happened again: got a little bit of fluid out and then it started to hiss/sputter and then no fluid came out. I tested the clutch peddle and it went straight to the ground.

Does anyone have any idea what I did wrong here? I followed the same process as the brakes, except pressurised the Motive bleeder to 2 BAR instead of 1.

Any recommendations on how I can fix this?

Also, not sure that it matters, but I use the dry pressure tank method when bleeding the brakes. I use the Motive for pressure only and do not put fluid in the tank. Instead of dumping fluid into the Motive bleeder and pressurising it, I fill the master cylinder reservoir to max, screw the Motive adaptor on and pressurise it.

Thanks in advance.

[old guy]

I believe your dry method is causing your problem.

As you know, the brake fluid reservoir serves both the clutch and brakes. However, the clutch and brake are partially separated in the reservoir. There is a separate open internal container that supplies the clutch. it fills from the top. As long as the brake fluid level is above the top of the container it remains full.

Once the fluid level goes below the top of the internal container the two systems act separately. This is a safety feature. It prevents a catastrophic brake failure from occurring if you happen to lose your clutch hydraulics.

By pressurizing your master cylinder and "dry" bleeding, your brake fluid level dropped below the top of the internal container supplying the clutch and consequently you drained it completely. Thus a complete loss of clutch hydraulics while still maintaining a stiff brake.

[avimore]

I believe your dry method is causing your problem.

As you know, the brake fluid reservoir serves both the clutch and brakes. However, the clutch and brake are partially separated in the reservoir. There is a separate open internal container that supplies the clutch. it fills from the top. As long as the brake fluid level is above the top of the container it remains full.

Once the fluid level goes below the top of the internal container the two systems act separately. This is a safety feature. It prevents a catastrophic brake failure from occurring if you happen to lose your clutch hydraulics.

By pressurizing your master cylinder and "dry" bleeding, your brake fluid level dropped below the top of the internal container supplying the clutch and consequently you drained it completely. Thus a complete loss of clutch hydraulics while still maintaining a stiff brake.

Hey old guy, thanks for your help that makes a lot of sense.

If I run the bleeding procedure again using the normal Motive method, would this fix this issue? Or do I have to do any additional steps given that I have now completely drained the clutch line?

[old guy]

Hey old guy, thanks for your help that makes a lot of sense.

If I run the bleeding procedure again using the normal Motive method, would this fix this issue? Or do I have to do any additional steps given that I have now completely drained the clutch line?

Yes it should fix the issue. No additional steps necessary but it may take a while to get all the air out.

[avimore]

Yes it should fix the issue. No additional steps necessary but it may take a while to get all the air out.

Gave this a try again today with no luck.

I started with a full brake fluid reservoir, the clutch pedal was all the way out (as far away from the floor), filled up the Motive bleeder with brake fluid and pressurised it to 2 bar. I opened the clutch bleeder screw and nothing happened. I thought I would be able to hear some air coming out but couldn't hear anything or see any fluid coming out. I waited a good 15 minutes and then stopped as I didn't want to push it, but the bottle kept pressure the entire time.

Is it possible I have to wait even longer for the air to get out? When opening the bleeder screw, i gave it around 4 quarter turns but didn't want to go further as I felt that should have been enough to open the line.

Am I missing anything?

Thanks.

[old guy]

Try depressing the clutch pedal up and down multiple times about an inch or two. That should get the fluid flowing.

[avimore]

Try depressing the clutch pedal up and down multiple times about an inch or two. That should get the fluid flowing.

Success! Thanks for your help, Fletcher. You were right, the clutch pedal needed to be depressed quite a few times to get all of the air out and get the fluid flowing.