Relationship between Clutch and Crankshaft

Relationship between Clutch and Crankshaft

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Discussion

Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
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Hi all,

I'm currently fighting Ford as my Focus ST had a bit of an issue with the clutch pedal staying on the floor when I changed gear after exiting a roundabout or sweeping bend. Strange one, I know. The car would feel like it was in gear OK, but I would need to flick the pedal back up with my toes on my left foot.

The Ford Techs diagnosed the issue as being down to... crankshaft end float. The acceptable limits of float are 0.22mm - 0.45mm. My car was showing 1.42mm! The short block is being replaced under warranty. Happy days.

The Ford master techs are being very wishy washy with regards to how they have related that defect with the symptom I experienced, and have not submitted anything in writing to the main dealer garage techs. The tech at the garage says he understands it as the excessive play in the shaft allows it to be loaded in a certain way during cornering which causes a drop in pressure in the clutch hydraulics, thus preventing the pedal from returning. But he can't be sure, as he's never seen this before.

My concern is the garage techs are saying my clutch is 75% worn. The car is only 2 years old, 16,000 miles. Ford are maintaining that the wear is not excessive and that it has nothing to do with the end float defect.

So my question is: how can crankshaft end float in a modern car impact the clutch hydraulics in a way which would prevent the pedal from returning on its own, and could this in turn have an impact of the engaged position/wearing out of the clutch?


stevesingo

4,375 posts

188 months

Wednesday 7th November 2018
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Perhaps it is less of a hydraulic issue and more of a mechanical issue. If the end float is excessive, and the clutch is worn, then the clutch master cylinder will need to operate over a longer stroke for it to release the clutch and with that the slave cylinder and the pedal. It may be the case that that the pedal or release bearing lever is going over centre, or the slave/master cylinders are jamming at the extents of their travel.

Cluch is on the near side?

Pedal jams down on LH bends?

If so, the cornering forces are also helping the crank move to the outside of the bend and therefore away from the release bearing.

The question should be raise as to how has the end float got so large and the clutch become so worn?

Both things together suggest that the car is being driven with a foot continually resting on the clutch, applying load to the release bearing and to the crank thrust bearing.

Mr2Mike

20,143 posts

221 months

Wednesday 7th November 2018
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stevesingo said:
Both things together suggest that the car is being driven with a foot continually resting on the clutch, applying load to the release bearing and to the crank thrust bearing.
I suppose there could be a mechanical fault meaning the clutch is never fully released even with no pedal pressure applied, though I'd be surprised no clutch slip has been noted.

Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
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My left foot lives on the dead pedal, so I can rule out that the car is being driven with the clutch partially engaged. I don't expect Ford will take my word on that though. I should say that the clutch would stick when changing gear AFTER exiting the roundabout, not while cornering. So when I operate the clutch, I'm on the straight, pulling away from the roundabout The cornering loads have been and gone. Whatever happens to cause the pedal to stick down happens during the bend and before I apply any input to the clutch (which has a hydraulic release bearing, ASIUI). I've never experienced it on a left bend, but then can't think of anytime I've gone round one extreme enough to match taking the third exit on a r/b.

I've had the issue since the first 6 months of ownership, and its taken 18 months for Ford to take it seriously and come up with a proper diagnosis without fobbing me off with a fluid change. The garage have said the clutch hydraulics are themselves fine, and are not replacing or repairing anything on that system. Only the short black exchange has been prescribed, but they haven't really been told why.

Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
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Mr2Mike said:
I suppose there could be a mechanical fault meaning the clutch is never fully released even with no pedal pressure applied, though I'd be surprised no clutch slip has been noted.
Well, I've never had it slip. The garage can't make it slip. But they say the clutch is really clean, and apart from some dust which they'd expect, there's no debris in there from burning or abuse, and there's no blueing on the flywheel.

Certainly my view is that if the clutch pedal doesn't return when it should, there's no guarantee of the clutch being disengaged correctly. So every time it has stuck, I'm in an increased wear scenario. By pulling the pedal back up with my foot, it should be disengaging completely, shouldn't it?

CrutyRammers

11,144 posts

164 months

Wednesday 7th November 2018
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I think you'd struggle to wear a thrust bearing down by over 1mm unless there was no oil on it, no matter how much you rode the clutch. And if that was the case, you'd surely be seeing other problems with the engine. I'd be guessing a manufacturing fault, and I guess Ford do as well if they're offering to replace.
As to how it affects the clutch, I dunno, but I'd be interested to find out. I can imagine it not disengaging properly, but the pedal staying down is plain weird.

227bhp

10,203 posts

94 months

Wednesday 7th November 2018
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CrutyRammers said:
I think you'd struggle to wear a thrust bearing down by over 1mm unless there was no oil on it, no matter how much you rode the clutch. And if that was the case, you'd surely be seeing other problems with the engine. I'd be guessing a manufacturing fault, and I guess Ford do as well if they're offering to replace.
As to how it affects the clutch, I dunno, but I'd be interested to find out. I can imagine it not disengaging properly, but the pedal staying down is plain weird.
No that's not correct, if there is constant pressure on the end of the crank it will wear it out. They're only splash fed, so need the end pressure releasing in order to replenish the oil film.
I'm guessing at a clutch fault if the OP drives it like it should be done.

Edited by 227bhp on Wednesday 7th November 20:33

Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
quotequote all
To be honest I'm not so concerned about the issue with the short block, as I'm not being asked to pay for that - it could be a manufacturing issue that means it should never have left the workshop, it could be something I've done, it could be a random failure. Either way, its been found and sorted and presumably there's been enough cases in the past to justify that this will sort the problem of the clutch pedal sticking down, even though no one I speak to at Ford is making that justification forthcoming. This I'm fine with.

I'm just having a hard time accepting that the actual clutch hasn't suffered as a result of this being present, which is what Ford are claiming. They reckon I'm just really unlucky that the clutch has worn as much as it has in such a short time (which is rare, they say, but still just wear and tear), while also suffering from an extremely rare crankshaft condition too.




GreenV8S

28,818 posts

250 months

Wednesday 7th November 2018
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Wrathalanche said:
I'm just having a hard time accepting that the actual clutch hasn't suffered as a result of this being present, which is what Ford are claiming.
If the master cylinder pushrod was adjusted too long or some other fault prevented the master piston coming back far enough to open the circuit to the reservoir, the clutch hydraulics would still be a sealed system while you have your foot off the pedal. This means that it could be holding a slight pressure on the clutch release bearing, and the amount of pressure might be temperature sensitive. It might not be enough to unload the pressure plate far enough to make the clutch slip (producing all the evidence you're looking for), but it would only take a slight sustained pressure to wear out the thrust bearing.


Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
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GreenV8S said:
If the master cylinder pushrod was adjusted too long or some other fault prevented the master piston coming back far enough to open the circuit to the reservoir, the clutch hydraulics would still be a sealed system while you have your foot off the pedal. This means that it could be holding a slight pressure on the clutch release bearing, and the amount of pressure might be temperature sensitive. It might not be enough to unload the pressure plate far enough to make the clutch slip (producing all the evidence you're looking for), but it would only take a slight sustained pressure to wear out the thrust bearing.
So are you suggesting that perhaps the master cylinder issue could be the culprit for the whole thing? That it could, in theory, lead to wear of the thrust bearing within the block? I was happy enough to go with the garage's view that a manufacturing defect in the short block was the root cause, but perhaps not? If a thrust bearing was worn, would they really replace the whole block, or would they not just replace the bearing? (Presuming the block itself wasn't goosed).

I'd really like to think that after 4 days of trying to find the fault, and calling in the master techs, that the master and slave cyls would have been checked before someone came up with the idea of checking the float on the crank shaft.

I never had a single problem with the clutch when in a straight line, which makes me weary of pinning the root cause on the clutch hydraulics. You'd never know anything was wrong with it unless you took a right on a roundabout. Which is kind of why I believe them when they say the clutch hydraulics are fine in isolation and don't need replaced.

What is it about turning, while there's excessive end play in the crank shaft, which could cause the clutch pedal to subsequently flop several seconds later during a gear change, while causing no damage to the release bearing? Ghosts?

Mignon

1,018 posts

55 months

Wednesday 7th November 2018
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Strange one. If the thrust bearing has worn by over 1 mm I'd expect the crank to be shot because I doubt if there's any white metal left on the thrust bearing. I also don't see this as a fault that could be related to cornering. Pressure plates take a lot of force to operate so every time you pressed the clutch it would take up all that thrust play regardless of what direction the car is heading in.

GreenV8S

28,818 posts

250 months

Wednesday 7th November 2018
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The fact it's influenced by cornering forces does seem to point away from the clutch master problem I was suggesting. The only way I can think of for cornering forces to have any effect is if the crank has a lot of end float ( you said it does?) and the crank is floating under cornering loads.

If the crank floats away from the clutch then it would be possible to pump the clutch and draw extra fluid into the circuit so that the pedal feels normal although the release bearing has now traveled much further than normal. It might stay like that for a long time, until cornering loads make the crank float back towards the clutch. If you don't have your foot on the clutch at the time, it would simply push any excess fluid back into the reservoir so the hydraulics won't resist the movement.

Next time you try to use the clutch it has to take up all the float before it meets enough resistance to disengage, so you feel the long pedal travel.

This doesn't explain why you ended up with the excessive end float but does sort of fit the symptoms once you have it.


Wrathalanche

Original Poster:

696 posts

106 months

Wednesday 7th November 2018
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Interesting stuff, GreenV8S. Feels like we're getting somewhere, but the described scenarios aren't quite right yet.

So: let's assume the car left the factory in a condition where there was end float as much as three times the maximum allowable, which has gone unnoticed.

Here's the process of events from my point of view:

I'm driving around town oblivious.

I approach a roundabout, and select second gear (gear number not important in reality). So far so good.

I round the roundabout and take the third exit. As I pull away, I step on the clutch to change to third.

The clutch pedal now feels lighter than it did when I changed gear on the approach.

With the clutch down I shift to third and release the clutch, which rises back from the floor maybe about an inch max and stays there.

The engine responds to acceleration like it's in gear just fine. No shortage of power, no clutch slip. But the pedal is still down an inch off the floor lining.

Stepping on the clutch again while in this stuck position achieves nothing.

I flick the clutch pedal up with my left foot. It doesn't take much and the clutch is back where it should be. Car is still responding to accelerator input as normal. Subsequent gear changes are completely normal and the pedal travel feels the correct weight, until the next roundabout or particularly sweeping right hander and it all repeats.

Give the car to the garage, they say clutch fluid and hydraulics check out fine. Refer to master techs who eventually ask garage to measure end float. The out-of-allowable is picked up. Master techs prescribe a short block replacement under warranty, citing past cases with the previous shape Fiesta ST. The story is just about to end there with no explanation given, but I'm then informed my clutch plate is 75% worn. Noone send to share the opinion that this could be in any way related to the above

Edited by Wrathalanche on Wednesday 7th November 23:26

99hjhm

409 posts

152 months

Thursday 8th November 2018
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The effects of cornering on a clutch/crank wear!!??

On a road car too!

99hjhm

409 posts

152 months

Thursday 8th November 2018
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My girlfriends Fiat 500 has a clutch pedal that some times sticks down, I bled the system and it much improved the problem. It’s a hydraulic issue. There would be no adjustment, it don’t happen any more. Or it’s a binding pedal if your suggesting it’s aggravated by cornering.

How’s your driving style?

I also don’t get why Ford would think of checking the crank end play? Known issue?


PositronicRay

21,697 posts

149 months

Thursday 8th November 2018
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99hjhm said:
My girlfriends Fiat 500 has a clutch pedal that some times sticks down, I bled the system and it much improved the problem. It’s a hydraulic issue. There would be no adjustment, it don’t happen any more. Or it’s a binding pedal if your suggesting it’s aggravated by cornering.

How’s your driving style?

I also don’t get why Ford would think of checking the crank end play? Known issue?
If you were peering at the engine while someone operated the clutch you'd see 1mm movement on the crank pulley.

Wrathalanche

Original Poster:

696 posts

106 months

Thursday 8th November 2018
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My driving style is pretty tame. Used to be lots of short, town only trips but now there's a 10 mile motorway commute so everything's distinctly average. Occasionally drive it quickly, but never been anywhere near a track or anything like that. Haven't even gotten round for going for an actual 'hoon'.

To be clear, there hasn't been any suggestion from those who have looked at the car that the crank end play has come from cornering loads, or anything for that matter. The garage thinks the end float has allowed for enough slop in the system that somehow the clutch hydraulics take a hit while cornering. That's the best explanation they can offer. But they admit they don't actually know that for sure. And they weren't the ones who thought to check the float and replace the block. That came from the Ford's technical department over the phone. They had seen it before on the fiesta ST.

sl0wlane

547 posts

159 months

Thursday 8th November 2018
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Does this car force you (by electronic means, like the Mrs’ Yeti) to start the car with the clutch in for safety reasons?

Crank shaft wear and increased end float can be caused by starting a car with the clutch in, putting more pressure on the crank during startup before any oil pressure is achieved.

A known problem with the Honda K20, especially with higher spring rate “uprated” clutch plates.

Wrathalanche

Original Poster:

696 posts

106 months

Thursday 8th November 2018
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It does. But so do all STs I believe. This issue is apparently extremely rare.

There has been no statement saying there has been any wear on the crankshaft or thrust bearings. In reality there probably has, but all that has been stated is that end float was beyond acceptable maximums. Could have left the factory like that for all I know. The point is, how do they go from investigating a sticking clutch pedal to looking at the crank end float?

Don't get me wrong, I'm glad they found it. But I can't follow the logic for the investigation, nor how the prescribed solution of replacing the block sorts the problem with the sticking clutch. Yes, it will fix the problem of end float, but how are the two issues related? That's the answer I can't get from anyone, other than guesses from the garage.

In essence I trust that the master technicians are right and that the new block will make the clutch pedal issue go away. There's at least one other owner who had the issue which I found on a forum who says this sorted them out. But because the dealership have just been told "replace the short block" and nothing else without knowing why, I'm concerned other areas that could have suffered are not being investigated and put right. Hence my suspicion on the overly worn clutch disc.

227bhp

10,203 posts

94 months

Thursday 8th November 2018
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Given it's all in the hands of Ford you'll never know, pointless debating any further.