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      08-23-2019, 12:37 AM   #1
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Clutch Bleeding

Bleeding the BMW hydraulic clutch system is known to be a pain. I've recently removed my Clutch Delay Valve, and the difference in clutch action is amazing (see this thread: https://f87.bimmerpost.com/forums/sh....php?t=1625114), but the purpose of this post is to address the topic of bleeding the system, because that's necessary if you remove the slave cylinder.

Background
As most of us know, the clutch hydraulic system shares the reservoir with the brakes, and is therefore topped up in the same way. The ISTA+ directions for bleeding the clutch say to use a pressure bleeder system like the Motive or Schwaben. Many people use these positive pressure tools without filling the container, and simply keep an eye on the fluid level in the reservoir, refilling as needed.

In order to save some money, I purchased the Motive European filler cap fitting only, and connected this to the small air compressor that I use for air-brushing, which also has a moisture trap and a regulator that I could easily set to 15 psi.

Unfortunately, positive pressure bleeding without extra fluid in a tank doesn't work for the clutch. The other thing that doesn't work (unless you're really careful) is gravity bleeding by pumping the clutch pedal. I also tried using the Mityvac to vacuum bleed the system, but this also didn't work, for the same reason.
The Root Cause
The root cause of the problem is that the brake / clutch fluid reservoir is designed so that if the clutch were to leak, the brakes wouldn't be affected, and vice versa. The brake system contains more fluid than the clutch, and is more important, so a larger reservoir is dedicated to the brake system.

The problem with bleeding happens because the clutch reservoir is really small, about the size I've coloured in Blue in the diagram below; the Yellow outlet goes to the clutch master cylinder:


So the reservoir volume for the clutch is tiny, and to fill it the level in the reservoir must be nearly over-flowing.

If you try to bleed the clutch system by pumping the pedal, positive pressure or vacuum, before the system is full, the fluid in the reservoir will drop below the baffle, and the small volume of fluid will be drained out! If you use a pressure based system as I did, you'll totally purge the system!

To make matters worse, if you don't look really carefully at the reservoir, like with a light under the back edge, you'll think it's full but the clutch section will be empty!

The total amount you can push through without re-filling the reservoir to the very top above Max is only 30ml, equal to only about two pumps of the clutch pedal
The Solution
If you're not reverse bleeding (see below), the most important thing to do is to keep topping up the reservoir. Also do not bleed to fast because even if the reservoir fluid level is high, it takes time for the fluid to flow from the brake side to the clutch side of the reservoir.

My understanding is that the positive pressure bleeders from Motiv and Schwaben effectively push fluid into the reservoir, keeping it full at all times. This is why BMW recommends this approach, but you must fill the bleed tool container.

I was able to successfully bleed my clutch by opening the bleed nipple on the slave cylinder, and fully pressing and lifting (slowly) the pedal twice, then refil the reservoir, then pressing and lifting the pedal twice, then refilling etc. I think I probably did this about 30 times and it worked! Once the system was full, I did apply positive pressure to the reservoir, being very very careful to look at the reservoir level. I'm not convinced this did anything, because I also removed my BMS clutch stop at this point as well.
Reverse Bleeding
Many people have bought into a myth about how air bubbles are constantly rising, and have resorted to reverse bleeding - pushing fluid up to the reservoir through the system. I actually tried this with three tools, but none of them worked for me and simply resulted in a mess over the garage floor:
  • Marinating syringe
  • Trigger action oil can
  • 15 PSI airbrush compressor through a Mityvac container in reverse
Reverse bleeding should work, as long as you have enough fluid to fill the system, but it's not because of the bubbles rising issue. I was never able to get enough pressure going up through the system to get any fluid into the reservoir, but if you can overcome this, it should be a good solution.
Anything Else?
If you have installed a BMS clutch stop, remove it before pumping the pedal. The clutch stop may not prevent clutch disengagement, but it will prevent full bleeding! You can re-install it once the bleeding is done, but only if you bleed fully.
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      08-23-2019, 06:48 AM   #2
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Great post!
Thanks, and sounds like a royal PITA.
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      08-23-2019, 12:12 PM   #3
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Quote:
Originally Posted by BroDoze View Post
Great post!
Thanks, and sounds like a royal PITA.
It was... initially... It took me about 6 hours to work out what was going on to be honest.

As I said, I did this because I was removing the clutch delay valve, and that part of the process (removing the slave cylinder and removing the CDV from the inlet) took about 30 mins, including putting the car on the Quickjack.

I started this at about 9pm, and by 10pm I had everything back together ready to bleed, and this is where I ran into problems.

By 2am, having poured nearly a quart of brake fluid through the system and got some in my eye, drips over my shirt face and hair, and most over the garage floor, I gave up. By that time I'd tried (and failed) positive pressure at the reservoir (without fluid in a container), vacuum at the slave nipple, and reverse bleed using the marinade syringe.

Before going to bed I ordered the Motive pressure bleeder from Amazon for same day delivery before 9pm, figuring by that point that I wouldn't be going to the office that day.

In the morning, I borrowed my wife's car and picked up another litre of brake fluid and a pump oil can from Harbor Freight. I spent about 2 hours trying reverse bleed with the oil can, but eventually found that if there is any back pressure at all, the pump in the can just stops working.

At this point I tried reverse bleeding by using the container from the Mityvac connected to my airbrush compressor. about 10ml went in initially, but I had to start increasing the pressure to force more fluid in. The Mityvac container is designed for vacuum though, and with pressure, the cap doesn't seal well and the best I could get was about 15psi, and this only flowed about another 10ml upwards; not nearly enough to get to the reservoir.

I stopped for lunch and planned to give up again, and wait for the Motive unit to arrive. After lunch though I decided to go back and give regular pedal pump bleeding another try, paying careful attention to the level in the clutch section of the reservoir, and as you know for my OP, this worked.

Now that I know all of this, I don't think it is a PITA at all, but knowing it was what made it so.

My colleague has a BMW and wants to come over and do this work to his car. Now that I know the process I'm sure it will take 1 or 2 hours tops.
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      08-23-2019, 01:42 PM   #4
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So, just to be clear: An Eazybleed canister attached to the bleed nipple and just pumping the clutch pedal (much like bleeding the brake solo) does the job?

If so, there's a CDV or two about to be removed from the F87 and E46...
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      08-23-2019, 04:05 PM   #5
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OP, when you were trying to reverse bleed, did you have the bleeder screw open 3-4 turns? I found this to be necessary when I reverse bled mine. I initially tried operating the bleeder like I normally would (60ish degree swing of the wrench) and no fluid was moving. It didn't even start to drip without a turn or two.
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      08-23-2019, 04:46 PM   #6
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Quote:
Originally Posted by wellvrsd View Post
OP, when you were trying to reverse bleed, did you have the bleeder screw open 3-4 turns? I found this to be necessary when I reverse bled mine. I initially tried operating the bleeder like I normally would (60ish degree swing of the wrench) and no fluid was moving. It didn't even start to drip without a turn or two.
I did, yes. I hope I didn't give the impression that reverse bleeding wouldn't work. What I hoped my post said was that reverse bleeding is a viable method if you can get it to work... but I couldn't.

The other thing I wanted to get across is the reason reverse bleeding works, because I kept reading that it was to do with bubbles rising etc, which is not the reason at all.

I tried reverse bleeding in 3 ways:
  • Meat marinade syringe - leaked out the bottom of the syringe under any back pressure
  • Harbor Freight Oil Can - Stopped pumping as soon as there was any back pressure
  • Mitevac containter (in reverse) with airbrush compressor - worked fine initially, but air leaked out of the cap once the pressure was increased
I think some people had used a large (non-leaking) syringe, and this is probably capable of more than the ~10psi that I could achieve with the Mitevac container.

By the way, what approach did you use for reverse bleeding?
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      08-23-2019, 05:11 PM   #7
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I used this syringe: https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

The tubing that came with it didn't work, but I had some that did, probably 3/16 or 1/4 inch ID. I just pushed it onto the tip of the syringe until it made a seal. At first, I tried doing it with the removable tips that were included with the syringe, but I couldn't get a good seal that way. I had to push the fluid in really slowly to prevent it from blowing out the seal at the syringe or the slave cylinder. Excruciatingly slowly. The pedal wound up feeling even firmer than when I started though.

I also took a brake fluid bath figuring this all out.
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      08-23-2019, 05:27 PM   #8
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Quote:
Originally Posted by wellvrsd View Post
I had to push the fluid in really slowly to prevent it from blowing out the seal at the syringe or the slave cylinder. Excruciatingly slowly.
This explains a lot. A large syringe (150ml in your case) that doesn't leak, and can take a steady sustained pressure. If you had to slow down to avoid blowing off the pipe, you must have been putting quite a bit of pressure in, which explains why I wasn't able to with only 10 psi.
Quote:
I also took a brake fluid bath figuring this all out.
It stings if you get it in your eye, and I rushed to the sink to rinse it out. Brake fluid is odd stuff though, because it feels like oil, but is really water soluble.

I looked for some health and safety documentation on the bottle, but found none, and later read that it's actually not harmful so they don't need to give any guidance on the bottle.

Cleaning up the garage floor is also a lot easier because you can just hose it down.
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      09-15-2019, 11:21 PM   #9
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So, curious... couldn't a lot of the fluid loss (and pain from bleeding) be minimized by clamping off the flexible hose before detaching it?
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      09-18-2019, 12:01 AM   #10
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Quote:
Originally Posted by ZPrime View Post
So, curious... couldn't a lot of the fluid loss (and pain from bleeding) be minimized by clamping off the flexible hose before detaching it?
I did that... The problem is that you'll still have to bleed the air in the section forward of that, and the tiny reservoir is the nightmare. Like I said, two pumps of the pedal and it's empty and you're then pushing in more air from the top.
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      09-20-2019, 01:32 PM   #11
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Thanks for the info. I need to do this.

There needs to be a YouTube video made for reverse bleeding the slave cylinder!
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      09-22-2019, 02:34 AM   #12
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Quote:
Originally Posted by chmura View Post
Thanks for the info. I need to do this.

There needs to be a YouTube video made for reverse bleeding the slave cylinder!
There is one, but I still don't think that's the correct way to do it.

I actually think there might be one way valves in the system, and you'd be pushing against them to go in reverse.

In my opinion, the best way, and the way that BMW recommends, is to use a top pressure system that continuously re-fills the reservoir.

The second best approach, and the one I used, is to re-fill the reservoir every two pumps of the pedal. I did the process on my own, by simply pumping twice, refilling, pumping twice refilling all with the bleed nipple open. I let about 100ml of fluid run through the system into a bottle, then tightened the nipple and all was great.
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      10-02-2019, 03:01 AM   #13
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The problem with any pressurized system that refills the reservoir is that you then end up making a mess when you try to take it back off of the reservoir at the end...
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      10-19-2019, 10:45 AM   #14
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Quote:
Originally Posted by ZPrime View Post
The problem with any pressurized system that refills the reservoir is that you then end up making a mess when you try to take it back off of the reservoir at the end...
That's not my experience, as long as I've let all the pressure out first before unscrewing the cap from the reservoir.

You do need to take a couple of syringes worth out of the reservoir though as it will be super full afterwards.
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      10-19-2019, 10:47 AM   #15
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Quote:
Originally Posted by Nezil View Post

In my opinion, the best way, and the way that BMW recommends, is to use a top pressure system that continuously re-fills the reservoir.
This mod has been on my mind and i was wondering if a top pressure bleeder would work - thanks for confirming!

Luckily enough i have one in the garage! :-)

I'll get this done soon!!!
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      10-21-2019, 02:26 PM   #16
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I'm having a hell of a time getting this done.

Been using the Motive system with a full tank, but I'm still getting air bubbles at the slave. When I pop the Motive cover off the reservoir, it's full to the top. Maybe I'm going to fast and it's not filling the clutch side quickly enough. Front of the car is on jacks and rear is on the ground, but I'm thinking that would help since it looks like the clutch section of the reservoir is in the rear.

Going to try to old fashion way with the pedal tonight.
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      10-21-2019, 11:22 PM   #17
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Put a flashlight under the reservoir so that you can see the level of the clutch section.

Fill up to the very top, making sure that the clutch part does really fill.

Open the bleed nipple on the slave cylinder and leave it open, but with a tube and bottle connected so that you can see that something is flowing out.

Keeping an eye on the level in the clutch section by looking through the windshield as you pump.

Pump the clutch once, check the level in the clutch side, see if you need to top up and do so if necessary.

Pump the clutch again, continuing to check the level.

Once you’ve pumped about 3oz through and out of the slave, and provided the level didn’t drop too much, you’ll be done. Tighten the bleed screw and test.

I believe there are one way valves in the system so you don’t need to tighten the bleed screw between pumps. Just leave it open until you’re done.
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      10-22-2019, 10:55 AM   #18
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In a porsche, the clutch will only pressure bleed when the pedal is down - perhaps the same with these cars.
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      10-24-2019, 02:26 PM   #19
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Quote:
Originally Posted by Nezil View Post
Put a flashlight under the reservoir so that you can see the level of the clutch section.

Fill up to the very top, making sure that the clutch part does really fill.

Open the bleed nipple on the slave cylinder and leave it open, but with a tube and bottle connected so that you can see that something is flowing out.

Keeping an eye on the level in the clutch section by looking through the windshield as you pump.

Pump the clutch once, check the level in the clutch side, see if you need to top up and do so if necessary.

Pump the clutch again, continuing to check the level.

Once you’ve pumped about 3oz through and out of the slave, and provided the level didn’t drop too much, you’ll be done. Tighten the bleed screw and test.

I believe there are one way valves in the system so you don’t need to tighten the bleed screw between pumps. Just leave it open until you’re done.
Do you have a link to the pressure adapter you used for the slave cylinder bleeding.

Does anyone make small extension reservoir that screws onto of the vehicles reservoir so that you are above the fill line so the tiny slave cylinder reservoir does not go empty?

Also would be a good idea to try to pressure bleed the clutch when the pedal is down. Not pumping.

Also you have the link/post of how you removed the CDV? I think you removed it rather than drilling through it if I remember correctly.
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Last edited by chmura; 10-24-2019 at 02:31 PM..
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      10-24-2019, 02:59 PM   #20
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Quote:
Originally Posted by chmura View Post
Do you have a link to the pressure adapter you used for the slave cylinder bleeding.

Does anyone make small extension reservoir that screws onto of the vehicles reservoir so that you are above the fill line so the tiny slave cylinder reservoir does not go empty?
I didn't use a pressure adapter in the end, I just kept manually re-filling the reservoir every other pump of the clutch.

I did order a Motive European Power Brake Bleeder from Amazon but I needed to use the car and so worked out another way. I still haven't used the Motive tool yet, but might do this when a friend with an M235i stops by.
Quote:
Also would be a good idea to try to pressure bleed the clutch when the pedal is down. Not pumping.
ISTA+ doesn't mention this, but if I have any issues when I eventually test the motive unit I'll post back here.
Quote:
Also you have the link/post of how you removed the CDV? I think you removed it rather than drilling through it if I remember correctly.
I didn't really post about it because I used the same approach in the other thread I linked to. I removed the slave cylinder completely, and fished out the rubber ring and metal CDV using a 45 degree pick if I remember correctly. I kept the parts in case of issues.

I then re-connected the slave cylinder with the CDV and rubber part removed, and there are no leaks. I'm not the first to do this, and I'm sure I won't be the last...
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      04-14-2020, 01:44 AM   #21
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Hi Nezil-

Just wondering if you ever completed the job with your buddy's 235i and if you did, if you used the motive bleeder or the method that ended up working for you.

I removed my CDV some months ago and reverse bled with the 150ml syringe. I'm not convinced I don't have a bubble in there. If I'm slamming gears at WOT, I'll occasionally feel like there's a delay--like a serious 1-2 second delay where I don't have full engagement after my foot is off the clutch. It's only happened a few times but it scares me. Could be something in the rear end too, not sure, but there's sometimes a feeling that something's slipping. I may try it your way and see if it makes any difference.

Anyway, just throwing it out there to see if anyone bites.



Quote:
Originally Posted by Nezil View Post
I didn't use a pressure adapter in the end, I just kept manually re-filling the reservoir every other pump of the clutch.

I did order a Motive European Power Brake Bleeder from Amazon but I needed to use the car and so worked out another way. I still haven't used the Motive tool yet, but might do this when a friend with an M235i stops by.

ISTA+ doesn't mention this, but if I have any issues when I eventually test the motive unit I'll post back here.

I didn't really post about it because I used the same approach in the other thread I linked to. I removed the slave cylinder completely, and fished out the rubber ring and metal CDV using a 45 degree pick if I remember correctly. I kept the parts in case of issues.

I then re-connected the slave cylinder with the CDV and rubber part removed, and there are no leaks. I'm not the first to do this, and I'm sure I won't be the last...
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      04-16-2020, 07:24 PM   #22
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a bubble in the clutch line won't lead to a delay on engagement. It will prevent full disengagement as you are using clutch pedal travel to compress the air bubble and not move the clutch towards disengagement and that can result in accelerated wear and glazing of the disk and flywheel, especially under the conditions you describe, which will in turn result in slippage. If you suspect that is the case, you should be able to test it by getting into a tall gear 4th or 5th), low speed out of boost, and standing on it. You should know if its slipping as it goes into boost.

I did the CDV removal as well. Used the motive. It does require you pump the pedal, and you will see air moving from the reservoir thru the bleeder hose. It takes a lot of pedal pumping and for a bit I was losing confidence. But eventually the pedal started to gain pressure and the bleed was successful.
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