Something strange when vacuum-bleeding clutch - need advice

[Orange Crush 1LE]

Guys,

I recently dropped in a new 416 and added a brake pressure sensor, and car has a fresh full flush with Motul 600. Now my clutch goes to the floor after a couple of hot laps at the road course. When the car cools, it goes away. Hoping it's just air in the clutch line, I used the method described in the factory service manual to pull air out of the system. This is not a typical bleed procedure, everything is done at the reservoir cap. See details in the photo of the service manual, but in summary:

1. Fill reservoir
2. Attach a Mityvac metal vacuum pump (this is a hand-held pump) to the reservoir using a cap bleeder adapter (just a reservoir cap with a fitting on it for the vacuum hose).
3. Pull 15 - 20 in Hg vacuum, which will pull any air out of the clutch fluid line.
4. Release vacuum, and refill brake fluid as necessary.
5. Repeat steps 3 and 4 until the fluid level is full and no longer drops and air bubbles can no longer be seen in the reservoir.

I went to the auto parts store and bought a Mityvac and hooked it up to my reservoir using a cap bleeder adapter that came with my brake bleeder.

I had strange results: Although the fluid level didn't drop, which suggests that there were no bubbles, it did pull a couple of inches of fluid out of the reservoir. Is this normal / expected? You would think that the method in the factory service manual would be flawless, and would not pull fluid up unless there's something wrong with the system. But maybe it sucked my brake pistons in, as evidenced by the soft brake pedal which required pumping after this procedure. I wonder if something is wrong with my master or slave cylinder, or something else?

I took it for a test drive and the problem didn't surface, but I didn't have an opportunity to get on it at all, and so the problem still may be there when driven hard and things get hot.

Any thoughts? Anyone else use this method?

[X25]

This is pretty interesting. It would be great if we could get the air out of the system without having to get down under the car! I suppose you should follow this up with a full on brake bleeding to ensure you don't pull on those, either (though I doubt there would be much of a movement, if at all). Does the Mityvac come with the right cap adapter? If not, where do you source it? I actually have a similar cap adapter from my Motive power bleeder, but I'd rather not use it for this purpose, since screwing the hose back and forth is not fun.

[402]

Pretty common, by doing this you can also pull your brake caliper pistons in causing "extra" fluid to come up the tube.

I am not fond of this method.

[Orange Crush 1LE]

Originally Posted by X25

This is pretty interesting. It would be great if we could get the air out of the system without having to get down under the car! I suppose you should follow this up with a full on brake bleeding to ensure you don't pull on those, either (though I doubt there would be much of a movement, if at all). Does the Mityvac come with the right cap adapter? If not, where do you source it? I actually have a similar cap adapter from my Motive power bleeder, but I'd rather not use it for this purpose, since screwing the hose back and forth is not fun.

In thinking it through, I realized that although I've regularly flushed my brakes with Motul 600, I've never bled the clutch fluid, so the original old Dot 3 is in there. That may be the culprit right there. I'm going to do a full clutch bleed before I hit the track this weekend.

The Mityvac doesn't come with the right cap adapter. However it comes with a hose and a small cone fitting that can be jammed into the bottom of your power bleeder's cap adapter fitting. You can see this in the first picture.

[Orange Crush 1LE]

Originally Posted by 402

Pretty common, by doing this you can also pull your brake caliper pistons in causing "extra" fluid to come up the tube.

I am not fond of this method.

Yes that appears to be what happened, as my brake pedal had to be pumped after this procedure. It seems like this method would work well if I had a seperate clutch reservoir, but not so good with the common brake/clutch reservoir.

[X25]

Originally Posted by Orange Crush 1LE

In thinking it through, I realized that although I've regularly flushed my brakes with Motul 600, I've never bled the clutch fluid, so the original old Dot 3 is in there. That may be the culprit right there. I'm going to do a full clutch bleed before I hit the track this weekend.

The Mityvac doesn't come with the right cap adapter. However it comes with a hose and a small cone fitting that can be jammed into the bottom of your power bleeder's cap adapter fitting. You can see this in the first picture.

I see. I might just get another hose/adapter from Motive for this purpose, then, since with my bleeder, I never put fluid into the bleeder (but rather use it as a pressure generator), and I don't want to contaminate it with fluid.

My car is actually fine, but my brother's clutch pedal ('13 1LE) doesn't feel as good as mine; we might try this out before trying anything harder.

[TransAm-98]

Todd, I've never been a fan of the mighty vac method for any system. If you're going to bleed it it just buy a pressure bleeder from Motive. Summit has them, you still have to get under the car but it works a lot better than the mighty vac method. It will make bleeding your brakes a lot easier too.

-Ryan

[tw78911sc]

Make sure you take the car out and pound the ABS to get the fluid out of that unit and flush again.

[X25]

Originally Posted by tw78911sc

Make sure you take the car out and pound the ABS to get the fluid out of that unit and flush again.

Or just let it cycle itself next time at the track : ) granted, it might be a while at this season, though.

[Orange Crush 1LE]

Originally Posted by TransAm-98

Todd, I've never been a fan of the mighty vac method for any system. If you're going to bleed it it just buy a pressure bleeder from Motive. Summit has them, you still have to get under the car but it works a lot better than the mighty vac method. It will make bleeding your brakes a lot easier too.

-Ryan

Thanks Ryan,

I've got a pressure bleeder but wanted to try the Mityvac method because it was in the service manual. I'm now not a fan of the Mityvac either, LOL

[LagunaSecaZL1]

Todd, I have a separate clutch reservoir mod and use ATE Super Blue Dot4. I also have the Motive Bleeder to push the fluid from the reservoir out the calipers. I do like my Mity-vac to suck all the old fluid out of the reservoir first. Refill with the reservoir with clean fluid, pressurize the reservoir and bleed each caliper. You do have to take off each of the wheels though.

[h018871]

the only issue i've experienced with the Mityvac and it is a small one. you need to coat the bleeder port threads with grease so the you can move fluid through the brake/clutch lines.
i've never used the motive pressure bleeder, so i can't make a comparison.

bottom line is you need to bleed them both often if you drive the car hard

[IDEALG]

Never try to vacuum bleed the system, Pressure bleeding is the best way. we use the Mityvac pressure bleeder it works great every time

[X25]

Originally Posted by IDEALG

Never try to vacuum bleed the system, Pressure bleeding is the best way. we use the Mityvac pressure bleeder it works great every time

What is being mentioned here is a bit different. We are not talking about vacuum-bleeding brakes. It is very hard to bleed the clutch system since the bleeder is very hard to reach. This is a quick procedure to get that air out of the end of the line. If it works, I think it is very useful.