Loss of clutch pressure (after a right hand bend!) 2005 TDI SE 85k miles

Sidbo

Sidbo

Member
I have a weird clutch problem: Quite often, (perhaps 30-40% of the time) after turning right at a roundabout or taking a sharp right hand bend, I will lose clutch pressure - that is, the clutch will still operate, but only just - instead of feeling "normal" it engages/releases with the pedal much closer to the floor and it doesn't feel as though the hydraulics are working (there's very little resistance in the pedal).

I have tested to see what then rectifies the problem and it either resolves itself after a minute or so - seemingly without intervention, or I can immediately hook the pedal upwards with my toe - as though the pedal itself has dropped towards the floor - perhaps implying that it's a pedal issue, rather than a hydraulic problem?

Of note:
  • I Just had my brake servo replaced with a new unit and some suspension work done.
  • The clutch problem 100% existed before the servo work was done
  • I think the previous owner said he had had a new clutch fitted (within the last couple of years)
  • car has done 85k
  • 2005 1.4 TDI SE
Any insight is invited !

Thanks


Sid
 
audifan said:
Check you have enough brake fluid. Bleed the clutch slave cylinder.
Click to expand...
Thanks - but the brake fluid was renewed with the servo and brake pressure is now fine.
Are the brake and clutch hydraulics shared then?
(I had assumed so and hoped that the clutch issue was related to the now replaced brake servo)
 
Sidbo said:
Thanks - but the brake fluid was renewed with the servo and brake pressure is now fine.
Are the brake and clutch hydraulics shared then?
(I had assumed so and hoped that the clutch issue was related to the now replaced brake servo)
Click to expand...
Bleed nipple for the clutch cylinder is to the right of the engine near the gearbox cables covered with a rubber cap, check reservoir is full get someone to apply steady pressure on the pedal while you open the bleed nipple & close before they release pressure, repeat until you have clean clear fluid at the bleed point.
Keith.
 
Got it - I'll definitely do a bleed and see if that helps - it does sound like it could be air in the system, but my basic (motorcycle) understanding of brake/clutch hydraulics is that air in the system would affect all of the system all of the time, not just one element (the clutch) after a given manoeuvre such as an extended right hand turn.
Maybe an air pocket at the clutch (slave cylinder) is actually isolated from the brakes....
But, I still don't get how an air bubble would have varied impact on pressure depending on where the bubble is sat in the hose?
 
Sidbo said:
Got it - I'll definitely do a bleed and see if that helps - it does sound like it could be air in the system, but my basic (motorcycle) understanding of brake/clutch hydraulics is that air in the system would affect all of the system all of the time, not just one element (the clutch) after a given manoeuvre such as an extended right hand turn.
Maybe an air pocket at the clutch (slave cylinder) is actually isolated from the brakes....
But, I still don't get how an air bubble would have varied impact on pressure depending on where the bubble is sat in the hose?
Click to expand...
It’s a separate line from the reservoir often overlooked worth a try& at least you know it’s new fluid!
 
Not only flush out any air but also old contaminated brake fluid that could be full of water. Bet the brake fluid hasn't been changed in years before new servo fitted. The slave cylinder itself could be past it also due to lack of maintenance. Fluid only good for about 2 years then needs replacing. Check the service record to see when it was last changed.
 
Hi fellow A2 owners.
I did a DIY bleed of the clutch fluid as guided here using a decent home bleed hit late in 2019 - to no effect - the odd loss of pressure after a sharpish right hand turn remained.
Today I had my local mechanic do a professional bleed and the problem remains: After a long/sharp right hand turn (never left hand) the clutch pedal loses pressure and I have to flick it back up from a suddenly low pedal position with my foot - this instantly fixes the issue.
So I am at a loss to understand or diagnose the problem.
My mechanic confirmed my assessment that if it were air (or water) in the lines, it would be a consistent/constant problem - unless the right hand turn were somehow moving an air pocket that was then easily rectified by lifting the pedal back up from the floor.
That air pocket is now ruled out after a full professional bleed.

So does anyone have any idea how/why this behaviour persists? Could it be the pedal mechanism somehow (not the hydaulics which are now ruled out?).
It appears mechanical, not electronic - because a right hand turn is the only cause of the effect.
Interestingly, the problem does not occur on EVERY right hand sharp turn -but it is frequent and only when taking such a turn.

Thanks in advance
 
Sidbo said:
So does anyone have any idea how/why this behaviour persists? Could it be the pedal mechanism somehow (not the hydaulics which are now ruled out?).
It appears mechanical, not electronic - because a right hand turn is the only cause of the effect.
Interestingly, the problem does not occur on EVERY right hand sharp turn -but it is frequent and only when taking such a turn.

Thanks in advance
Click to expand...



Pinkythelabrat said "When you get the clutch done it’s worth getting the arm and pivot bearing done as well. Apparently the little top on the pivot can wear through the lever arm and it’s only a few quid extra while they are already doing the clutch." Maybe?
 
You could also fill the reservoir higher than the full mark - say to the base of the threaded neck to see if that makes any difference.
 
Hesketh said:



Pinkythelabrat said "When you get the clutch done it’s worth getting the arm and pivot bearing done as well. Apparently the little top on the pivot can wear through the lever arm and it’s only a few quid extra while they are already doing the clutch." Maybe?
Click to expand...
Thanks, but why would that pivot bearing issue cause the clutch pedal drop only after right hand turn do you think?
 
Something is not right here...
A right-hand turn is causing the clutch fluid volume/pressure in the clutch "circuit/system" to be lowered which causes the pedal to drop. And it doesn't just return to the previous volume when the turn is completed??? Is that correct?

The right-hand turn trigger might indicate a suspension related issue. You state the clutch-drop happened before you had the recent brake and suspension work. I have difficulty imagining some right-hand turn suspension change that is causing the motor/gearbox to move in their motor mounts that is affecting the clutch fluid volume/pressure. The only possibility I can think of is a hose being stretched which would cause the diameter to reduce and force fluid back to the reservoir and the pedal to drop?

At the same time I have difficulty imagining how a right-hand turn can affect the "closed" clutch fluid circuit related to an air bubble or air lock or contaminated fluid.
Are you loosing any fluid from the clutch circuit (do you regularly have to add fluid)?
 
audifan said:
You could also fill the reservoir higher than the full mark - say to the base of the threaded neck to see if that makes any difference.
Click to expand...
Isn't it unlikely that a reservoir gap would cause this behaviour, especially only in one turn direction.
 
Valpen said:
Something is not right here...
A right-hand turn is causing the clutch fluid volume/pressure in the clutch "circuit/system" to be lowered which causes the pedal to drop. And it doesn't just return to the previous volume when the turn is completed??? Is that correct?

The right-hand turn trigger might indicate a suspension related issue. You state the clutch-drop happened before you had the recent brake and suspension work. I have difficulty imagining some right-hand turn suspension change that is causing the motor/gearbox to move in their motor mounts that is affecting the clutch fluid volume/pressure. The only possibility I can think of is a hose being stretched which would cause the diameter to reduce and force fluid back to the reservoir and the pedal to drop?

At the same time I have difficulty imagining how a right-hand turn can affect the "closed" clutch fluid circuit related to an air bubble or air lock or contaminated fluid.
Are you loosing any fluid from the clutch circuit (do you regularly have to add fluid)?
Click to expand...

Thanks for the detailed response.
I agree: Something's definitely not right.

I am starting to rule out fluid hydraulics because as I said, I manually bled the clutch in the engine bay using my own bleed kit last year following advice from forum members (which is very much appreciated!) and then yesterday I had it professionally bled by my mechanic - neither made a jot of difference.
So again:
  • 1. It only happens after a long or sharp right hand turn.
  • 2. It doesn't ALWAYS happen though.
  • 3. It is immediately rectified by lifting the pedal back up with my foot
What points at hydraulics is the right hand turn behaviour, what negates hydraulics is a full bleed not fixing it AND being able to rectify by lifting the pedal back up.
Is there an important clue in the pedal behaviour? Could it be the pedal mechanism itself somehow?
What about the master cylinder behind the pedal itself - is that a possible culprit?
 
Valpen said:
A right-hand turn is causing the clutch fluid volume/pressure in the clutch "circuit/system" to be lowered which causes the pedal to drop. And it doesn't just return to the previous volume when the turn is completed??? Is that correct?
Click to expand...

Yes, if I pull the pedal backup with my toes, it seems to rectify immediately.
If I leave it, the pressure stays diminished and the clutch pedal bite is dramatically lowered - but still just about activates.
I think, but not certain, that if I leave the pedal alone the pressure returns, but less quickly than if I intervene with my foot.
 
The only possibility I can think of is a clutch hose being stretched which would cause the hose diameter to reduce and force fluid back to the reservoir (which it could as the pedal/master cylinder piston are at the "top"), and the pedal would drop once the hose is un-stretched and the master cylinder piston is sucked back in the cylinder by the hose diameter returning to normal? Brake hoses are very strong regarding expansion (increasing their diameter) from internal positive pressure, I am not sure of their tolerances towards their diameter being reduced from stretching/pinching.

To rule this out, I would check the routing of the clutch hose from the master cylinder (brake) to the slave cylinder (clutch) and make sure it is correct. And then I would check my motor/gearbox mounts for something that could be influenced by a right-hand turn.

I have played-with/worked-on lots of different vehicles for all too many decades, and I have never run into something as bizarre as what you are experiencing. Hydraulics are supposed to be "bullet-proof". And there is no ABS etc on the clutch...
You have certainly awakened my curiosity...

I am not sure the best way on this forum to get the attention of some of the more experienced mechanics, but A2Steve and
bretti_kivi and Pinkythelabrat may be able to engage some of the more experienced mechanical competence here to support your trouble shooting.
 
That's another very helpful response - I'm grateful.
I am glad to have given you a challenge, but I am now worried that something I thought would be basic is actually a mystery to an experienced individual such as yourself.
And that implies high repair costs.

Like you I'm not sure about how to get attention from some of the other experts - do your links to their user accounts send a notification I wonder?
 
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Hi Sid,

I had simillar effects, but when hooking a sharp left turn at a Y junction.
Clutch pedal almost to the floor and only returned by manual lifting by my toe.
I tried just bleeding the system first, with no luck

My fix was a genuine new clutch slave cylinder and quick bleed.

My car is a 2002 TDi

Cheers
Jeff
 
Hi Jeff, wow - that's interesting - I hadn't considered a faulty slave cylinder.
Your symptoms do seem almost identical (other than direction of turn!).

Thanks very much.

Sid
 
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