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Clutch Hydraulics Problem


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Hi all

Kind of a bit puzzled with a clutch hyrdraulics problem probably as I’ve never done one before.

Please bear in mind all of the components are new until we get to the clutch cross shaft arm with the 3 holes.

Now I’m not sure whether the master cylinder is 0.7 or 0.75 as the only thing on the side other than TRW is AM-03.

So the problem is that when the clutch pedal is depressed the push rod does push out but just does not return to its original position when the pedal is released.

Now this happens whether the slave pushrod is connected to the cross shaft arm or not. It’s not that the cross shaft is stiff in its movement it moves smoothly and easily through its arc.

So to return the pushrod I have to push it back and as far as I know this should just happen.

But should the crosshaft “push” it back or should the hydraulics pull it back?

The clutch and shaft bits are all new or modified, pin, bearings etc.

So any ideas as what to try next as I’m kind of stuck at the moment.

Cheers    Keith

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Some slave cylinders have a light spring in the bottom, which pushes the piston (and the rod) outwards, also when the pedal is not pushed. The purpose is to eliminate free play.
The travel should be around 16 mm, and with a new clutch the lever should. E vertical if not pressed (but can move fwd against the little springforce in the slave).

Earlier cars Like TR4 do not have that spring iirc. 
 

The spring on the clutch cross shaft does not aid clutch action, it is just an anti ”floating” spring and it moves the shaft fixed to 1 side.
Waldi

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9 hours ago, Keith66 said:

Hi all

Kind of a bit puzzled with a clutch hyrdraulics problem probably as I’ve never done one before.

Please bear in mind all of the components are new until we get to the clutch cross shaft arm with the 3 holes.

If all components are new has the system been bled?  

Now I’m not sure whether the master cylinder is 0.7 or 0.75 as the only thing on the side other than TRW is AM-03.

So the problem is that when the clutch pedal is depressed the push rod does push out but just does not return to its original position when the pedal is released.

Now this happens whether the slave pushrod is connected to the cross shaft arm or not. It’s not that the cross shaft is stiff in its movement it moves smoothly and easily through its arc.

By hand, push the lever to one end of the arc and then push harder- does the lever go further?  Now do same at other end of the arc?  If the lever goes further it could indicate the cross shaft fork attachment pin has started to fail.

So to return the pushrod I have to push it back and as far as I know this should just happen.

But should the crosshaft “push” it back or should the hydraulics pull it back?

The clutch and shaft bits are all new or modified, pin, bearings etc.

So any ideas as what to try next as I’m kind of stuck at the moment.

Cheers    Keith

Cheers.  Peter W

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Hi all

Ta for the replies, but as you can see from my answers I’m puzzled.

But firstly can I say I’m making a huge assumption here. I press the clutch pedal, it pushes the SC pushrod out, moving the crosshaft lever to disconnect the clutch and when I release the clutch everything returns back to its original positions, engine running or not.

Mike, the cross shaft spring is ok and in place, although I’m not sure what the diaphragm spring is.

Waldi, I’d read that some SC’s had springs in them but most new ones not now and as it’s just to take up any slight slack would not seem to be the issue. I’d also thought the cross shaft spring was to aid lateral location and does not affect rotation, hence movement of the lever on its end.

Peter, Yep system has been bled, with at least three master cylinder reservoirs full of fluid is flushed through and getting zero air bubbles for ages. Everything clutch side is new, including new pin, bearing etc. and the car has never moved under its own power since so a pin failure would be almost inconceivable.

So I’ve got the following movement.

When pushrod connected and clutch pedal depressed 12 or 13mm at the lever.

But it then just says there zero return.

When pushrod is disconnected from lever I get the same 12 or 13mm movt.

AS for the crosshaft lever. It moves smoothly and easily either way with no roughness or stiffness. The total movt by hand is about 20mm. But it does not spring back either way just stays where you put it.

The pushrod can be manually pushed back into the SC, but when it is as far as it will does not line up with the crosshaft lever but it does bounce out by about 5mm. Once it has come out that 5mm it does more or less (1 to 2mm) line up with the middle hole.

But after this I still get the same 12 or 13mm on pressing the clutch pedal and once the pedal has been pressed and the pushrod moved its 12 or 13mm it just stays where it is.

Cheers    Keith

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Keith, the clutch operating lever should move freely from about 'twenty to ' to 'half past' where the lever is pointing approximately vertically downwards. At that point the clutch release bearing meets the fingers of the clutch spring (diaphragm spring) and you can't push it any further backwards by hand. The slave cylinder on a '6 is supposed to be self-adjusting and does not fully retract, it just goes as far back as the lever pushes it and the spring inside the cylinder then holds things so that the release bearing is just in contact with the clutch. It is the clutch spring itself which pushes everything back when you release the pedal.  

The first time you press the pedal after connecting things, there should not be much pedal resistance initially as the system will take up any clearance. The slave piston will not return to where it was because it will have self-adjusted. Subsequent pedal presses should feel harder and operate the clutch from the new 'zero' position. Perhaps that is what you are seeing?

 

 

Edited by RobH
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The SC mounting to the bracket and the bracket to the gearbox/engine flange is critical, it would seem that the slave is not actually pushing the clutch shaft rearwards enough to open the clutch internally.

I dont have the exact positions for the slave and the bracket, but I'm sure others can help here.

Make sure also that the slave has its bleed screw at the top for best bleeding.

Perhaps you could post a picture of how your sc and bracket are mounted.

John

Edited by John L
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Some good ideas in previous replies.

Some more :

1) Is the flexible new ?

If it's an old flexible, it can play as a partial or total anti-return valve.

2) Do you use Silicone fluid in your system ? 

It can cause a serious seal expansion by chemical reaction with the rubber, then won't allow the slave piston to come back as it should.

The list goes on....

 

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Hi All

Thanks for the replies.

Flexi pipe is new. Everything from the crosshaft lever to clutch pedal is and fluid id DOT4.

But what RobH says makes absolute logical sense to me, that the movt of the SC pushrod pushes against the clutch plate diaphragm fingers to disengage the clutch and that’s what returns the SC to its original position. But its just way to heavily sprung to move by hand.

So I’m assuming that when the pushrod is connected to the lever there should be no play so the half inch of movt generated by the SC pushes against the clutch cover fingers.

Clearly mine is not so I’ve got something wrong.

Time to look again, just hope its not a GB out.:(

Cheers   Keith

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Hi All

Its true there could be wear at the pedal end, but not knowing what the movement should be I really don’t know.

However I’ve read that the movement at the SC should be at least 0.40 to 0.50 inch and I’m getting 12 or 13mm that seems about correct.

Waldi say that the crosshaft lever should be vertical but will move fwd about 16mm but will not move by hand past the vertical. Exactly as mine is.

Now hopefully the SC is in the right place, see pic, and it seems to be from other pics I’ve seen and I can’t see how it would fit otherwise.

But the pushrod just does not reach the lever unless it is fully extended and then of course pressing the clutch does not move the pushrod further, so something must be wrong.

Now it seems that the simple way to confim if things are in the right place is to compare the distance between the SC and the lever.

On mine this is 11.75cm from the ally rubber join on the SC and the lever in its vertical position.

Is this too much as it seems to be and what might be causing this to be out,

 

Cheers    Keith

SC Position (2).jpg

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The SC assembly is in the right order but is the backplate mounted at an angle to the engine backplate? Maybe it's just my interpretation of the photo.

I can't help you with the measurements as I'm a long way from my car at the moment.

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I agree with Mike. Something doesn’t look right there!

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EDIT:  post removed as the info was probably not right. 

Two people obviously didn't like it, but it's a pity they didn't bother to post to  explained why, which isn't very helpful really.  

 

Others seem to have had a similar problem to the OP in the past:

 

Edited by RobH
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2 hours ago, RobH said:

Two people obviously didn't like it, but it's a pity they didn't bother to post to  explained why, which isn't very helpful really.  

Are you serious. You of all people should know why more and more people avoid posting. 

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8 hours ago, Mike C said:

The SC assembly is in the right order but is the backplate mounted at an angle to the engine backplate? Maybe it's just my interpretation of the photo.

I can't help you with the measurements as I'm a long way from my car at the moment.

Hi Mike and Dave

What do you mean by an angle?

Its flat on the backplate and the SC seems parallel to the chassis not up or down left or right, at least as far as I can tell lying on my back underneath, lol.

Rob I’ll certainly be reading those two post to see if I can get any more info on my prob.

Any other suggestions gratefully received and if anyone knows the correct distance between the SC and lever that would be great.

Cheers  Keith

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Ok- there is no angle- "Its flat on the backplate and the SC seems parallel to the chassis not up or down left or right, at least as far as I can tell lying on my back underneath, lol."- that's the correct mounting.

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Keith

I think you are missing something here, the clutch lever should be pushed rearwards, the rod from the slave should be connected to the middle hole, the fluid will fill the SC at this position, pushing the pedal will then push the clutch shaft rearwards and open the clutch inside.

As the clutch wears it will push the SC piston back into the SC itself, this is the auto adjustment.

As long as the piston doesn't come out of the SC when the clutch pedal is pressed its fine.

I think the black bracket should be mounted flat to the gearbox flange, it looks as if there is a nut under the bracket, try and get the pushrod to be pushing straight to the clutch shaft, and so not allowing the SC piston to rub too hard on its sides.

Its difficult to write it in words.

John

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Oh dear! It seems to be getting a bit bitter. I commented on the picture it looked like the two faces are not flush!

so to that end........ goodbye!

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3 hours ago, stuart said:

I presume you have the right length pushrod then?

Stuart.

Stuart

To be honest i don't know. It would have been thew old one from the old SC, so i've just assumed its correct.

Is my gap of 11.75cm from the end of the SC to the lever ok or to big.

I'm assuming that if the bits are ok and in the right places i have a more fundemental problem i need to sort.

But i'm kind of stumped.

1825823148_SCtolevergap.png.009e253c0d959a28900433cd673b212e.pngCheers   Keith

 

1825823148_SCtolevergap.png.009e253c0d959a28900433cd673b212e.png

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