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Discussion Starter · #1 ·
Good afternoon,
The clutch of our BMax (34Kkm, 2016) fails to function but only from time to time. The clutch does not seem worn (tested in different ways namely with hand brake).
The only interesting circumstance is that the issue probably started appearing when the front brake pads were close to totally worn. I added Dot4, brought it for maintenance (oil refresh and new front brake pads). I also asked to check for leaks and purge the clutch circuit.
This has been done one week ago and since then the clutch failed 3 times (on a total of 40km mostly town trafic).
So, I had a look myself today and did not detect anything abnormal. Before bringing it back to the garage, challenge the purge and considering changing the emitter or receptor I would like to purge the receptor by myself. I am however puzzled by the purge unit since it is made of white plastic and not a classical metallic unit. I hesitate to turn it, fearing to brake it.
Any advise on how to open this plastic purge unit at the clutch receptor ?
Thanks a lot,
Steven
(Belgium, so left hand driven car).
 

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Discussion Starter · #3 ·
I managed to turn this plastic purge and get DOT4 to come out. I did not use a transparent tube so could not see if air was getting out. It did not look like it. In any case it does not seem to improve the clutch (the pressure felt seems to vary a bit and once in a while the pedal comes back slowly). Without taking the battery out, I tried to get my hand to the part of the the emitor that comes in the engine compartment. I could not feel any purge there.
Does anyone know if there is also a purge on the emitter (hydraulic cylinder that is activated by the clutch pedal) on this model ?
Thanks a lot !
 

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plastic parts in clutch hydraulics is common nowadays.
as far as I can tell, you remove the rubber cap, connect a tube, and the bleed nipple is just a quarter turn.

but if you just paid for servicing you should ask them.
 

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"Does anyone know if there is also a purge on the emitter (hydraulic cylinder that is activated by the clutch pedal) on this model ?"
the clutch master should auto bleed when the pedal is fully released.
 

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Discussion Starter · #6 ·
Thank you Gremlin. Indeed. However, I will probably need to wait one week before having an appointment at the garage, so I would like to test 2 or 3 things myself.
Thanks.
 

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Discussion Starter · #7 ·
Gremlin,
the clutch master should auto bleed when the pedal is fully released.
Does “auto bleed” mean that the air potentially contained in the clutch master would be automatically evacuated ?
Even if the clutch master seems to slightly go down from the pedal to the engine boot ?
Thank you.
 

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Gremlin,

Does “auto bleed” mean that the air potentially contained in the clutch master would be automatically evacuated ?
Even if the clutch master seems to slightly go down from the pedal to the engine boot ?
Thank you.
in normal use any air in the master cylinder should escape though the fill tube, and then via the reservoir this happens because when the clutch pedal is fully released, a port is open to allow fluid into the the circuit (to compensate for any clutch wear etc) and let any air out.
but if air has been pumped a little way through the hoses it may not do this. in which case re-bleed the whole clutch system using the bleed nipple on the slave.

translation
bleed nipple/ bleed screw == purge point
slave cylinder == clutch receptor
master cylinder == emitter
 

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Discussion Starter · #9 ·
Thank you Gremlin.
Extremely clear. Sorry to have reinvented some technical terms in English… Thanks for the translations 😉
Based on your experience, is the slave cylinder difficult to bleed from any air contained ?
  • 3 to 4 bleeds (3 to 4 times maintaining pedal pushed in and open then close the nipple, pump 3-5 times and again) and stop if no air is coming out or 10 to 15 ?
  • is it sometimes needed/recommended on the BMax to do a reverse bleed (pumping DOT4 into the slave cylinder bleed nipple) ?
Thank you !
 

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Thank you Gremlin.
Extremely clear. Sorry to have reinvented some technical terms in English… Thanks for the translations 😉
Based on your experience, is the slave cylinder difficult to bleed from any air contained ?
  • 3 to 4 bleeds (3 to 4 times maintaining pedal pushed in and open then close the nipple, pump 3-5 times and again) and stop if no air is coming out or 10 to 15 ?
  • is it sometimes needed/recommended on the BMax to do a reverse bleed (pumping DOT4 into the slave cylinder bleed nipple) ?
Thank you !
I have not needed to do the job myself, but I believe ford recommend using a 'Brake/Clutch System Pressure Bleeder/Filler' ie pressurise the reservoir to push the fluid through. and also to pump the pedal a few times after having bleed the system.

EDIT, to add
it would be a bad idea to reverse bleed the clutch system, because any grot will then end up in the shared reservoir and thus possibly affect the brakes!
 

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Discussion Starter · #11 ·
OK. Thank you Gremlin. I have a pressure set. If the bleed operation I just finished is not enough and the garage appointment is too far away, I might give it a try on the clutch circuit.
Thanks again for your swift replies.
 

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Discussion Starter · #12 ·
Hello to all,

Reading further on the Net, I saw different approches :
  • Ford guidelines for Ford Focus : push 120ml of fluid with a vacuum tool into the bleed nipple : nothing to do with a vacuum principle to me. Approach found as not ideal by several people.
  • Vacuum the air and fluid with a vacuum tool connected to the bleed nipple. Seems popular and easy.

Putting the reservoir under pressure is what I have done for brake fluid replacement and bleed on several cars, with success. And also what Gremlin suggested to be the Ford method. But astonishingly I did not read that on the Net. Any negative to this method if the max pressure of 1,8 bar is respected ?

Thanks !
 

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Hello to all,

Reading further on the Net, I saw different approches :
  • Ford guidelines for Ford Focus : push 120ml of fluid with a vacuum tool into the bleed nipple : nothing to do with a vacuum principle to me. Approach found as not ideal by several people.
  • Vacuum the air and fluid with a vacuum tool connected to the bleed nipple. Seems popular and easy.

Putting the reservoir under pressure is what I have done for brake fluid replacement and bleed on several cars, with success. And also what Gremlin suggested to be the Ford method. But astonishingly I did not read that on the Net. Any negative to this method if the max pressure of 1,8 bar is respected ?

Thanks !
I think 1.8bar is whey too high. more like 1.8 psi. (about 0.15 bar) or perhaps 0.18bar
 

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Discussion Starter · #14 ·
Hello,
Update :
My trusted mechanic
  • replaced the clutch
  • replaced the slave cylinder.
He says that the support where the slave cylinder pushes on the clutch was not flat anymore and that the piston most probably sometimes did not keep its 90 degrees angle and let pressure of hydraulic drop in the slave cylinder.
The clutch pedal course is improved (softer, more constant). But the phenomenon unfortunately still happens every 40/50 use of the clutch. 🥲
It happens in two pushes (from lighter clutching to not enough clutching anymore) and disappears in 1 or 2 pushes.
Back to my trusted mechanic now to try another bleeding. I personally suspect air somewhere between the second reservoir and the master cylinder.
The master cylinder does not seem to be a part often ordered according to my spare parts supplier.
More later today…
 

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Discussion Starter · #15 ·
Update :
The new bleeding done today did not evacuate more than some mini air bubbles. The phenomenon appeared again after the today bleeding.

Probable explanation of the issue according to the trusted mechanic : the fact that the original clutch operated not flat probably made that an over pressure was regularly generated inside the slave and master cylinders or punctually when the clutch once in a while blocked somewhere along its course. And that this over pressure damaged the seals (or anti back DOT4 movement valve?) in those mostly plastic master and slave cylinders.

I will do one more test so I can confirm the issue is not solved. If not solved, the master cylinder will be replaced in a couple of days.

Kind regards,
 

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Discussion Starter · #18 ·
Hello,
I tried a new bleeding today. No air seen, again.
But… during the bleeding, clutch pushed in, I jeans once the clutch mechanism releasing slowly. Exactly like when the bleed nipple is turned open. So, nearly 100% sure that the master cylinder is out (internal sealing releasing pressure once in a while during clutch operation). Would confirm the supposed cascade : clutch mechanism not operating flat damaged the master cylinder and possibly the slave cylinder, by over pressure in the cylinder(s).
Expensive joke.
And a difficult case : combination of at least 2 failures, and non permanent problem….
 

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Discussion Starter · #19 ·
Hello,

Here is hopefully the end of the story:
We have had the master cylinder replaced. LUK brand. However the Murphy law followed us and we were unLUKy again : the electrical contractor in the brand new master cylinder (for start stop and manual start) was not functioning. So we had an other new one to be placed again.

All is now functioning perfectly! 😀

Summary : failing clutch from time to time but more and more frequently. Cause : the clutch mechanism was not operating flat and damaged the master cylinder and possibly the slave cylinder, by over pressure in the cylinder(s) when operating the clutch pedal. The 3 components have been replaced with success.

Regards,
 

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Nice to know you got it sorted, and thanks for letting us all know the outcome, it may help others in the future.
 
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