K-series clutch release bearing

[John Vine]

I've just replaced the clutch release bearing on my 1999 1.8K. The old one looked like it had been spit-roasted and then knocked about with a large sledgehammer. It was black and covered with all manner of gunge. The inner plastic slider had become detached from the rest of the circular plastic carrier, and the whole caboodle showed signs of violent seizure.

 

When I came to reconnect the clutch cable, there appeared to be no end float or play in the cable at all. This seemed to be due to the return spring in the pedal box pulling the top half of the pedal backwards, and applying a light tension in the cable at all times.

 

It occurred to me that this would cause the CRB thrust face to be in permanent contact with the diaphragm springs on the pressure plate. Am I right? And if so, could this permanent contact lead to premature CRB failure due to the CRB rotating permanently at crank speed?

 

JV

[Peter Carmichael]

The bearing should cope. The bearing itself is fine according to your report (and all the ones I've seen) but the carrier is toast. If you don't have the spring, the clutch cable will regularly unclip itself from the release arm.

[Rob Walker]

John,

 

I think your reasoning is correct. I have had two release bearings go exactly the same way and now after talking to some other unfortuate Seveners have come to the same conclusion. Len Unwin also comented on this problem in an earlier posting. He suggested setting up a counter spring reduce this effect but said it was difficult to get the counter spring rate just right. I also think using increased revs and stronger springing in the AP clutch cover may be a contributory factor.

 

Rob.

[John Vine]

Thanks for your feedback, chaps...

 

Far from being fine, however, the bearing is also toast, and burnt toast at that! It gives every appearance of being totally foutu. For example, when I spin it, it flops about like a rag doll, and feels like it's running on a bed of coarse grit. There's evidence that it's suffered a violent seizure. For example, the circular plastic carrier (the bit with the spring clips) has worn away to half its original thickness, the two points where it contacts the actuating arm have disappeared altogether and the arm has been running directly on the metal bearing housing (which means it's been rotating when it shouldn't), and the grooved plastic slider has become completely detached from the rest of the plastic carrier. Given that the plastic bit isn't supposed to rotate at all, but simply slide merrily up and down the input shaft sleeve, I can only surmise that it got ripped up when the bearing itself seized.

 

Len's given me good advice in the past, and a counterspring looks like a solution. I can see that a light tension stops the cable becoming detached from the actuating arm, but wouldn't a clip of some sort do the job better? (I seem to recall from my Sierra days that the cable was indeed clipped this way.) Len seems to be saying that there's a design flaw in the current set-up. I think I'll pose the question to the engineering guys at Dartford (in writing, this time, as they still haven't returned my call of last Thursday!). Btw, do you know where I can find Len's post?

 

JV

[John Vine]

Following Len's advice, I spent a hour or so today setting up a counter-spring on the clutch pedal. I used Caterham p/n 1454217, and it seems to offer precisely the right spring rate, as it (just) takes the tension off the clutch cable. As I'd ordered two of these springs, I used the other one on the accelerator pedal to apply a slight tension to the throttle cable.

 

JV

[CHRIS CLARK]

John.

 

I was under the (false?)impresssion that you really needed to take the pressure off via the operating arm. Yes/no ?

On the pedal it would need to PUSH the cable to keep the bearing from touching the spring leaf faces. Not possible.

[John Vine]

Chris,

 

Yes,I think your idea would be the ideal solution, but presumably would mean cutting a hole for the spring in the rubber cover on the bellhousing, and then finding a suitable mount for the fixed end of the spring (on the bellhousing, or gearbox top plate perhaps?). I have to admit I was looking for a simpler "solution", albeit less effective perhaps. The spring can't "push" the cable, but it does reduce the tension, and this (I hope) will introduce enough slack to encourage the CRB to back off slightly from the diaphragm springs (which, I recall, was Len's original proposal). Maybe this is just wishful thinking though? I suppose time will tell.... I'm certainly keen to avoid lifting out the engine again just to replace a £10 part!

 

JV

[Rob Walker]

I think it must be possible to fit a spring at the point where the clutch arm exits the bellhousing pulling the arm and bearing away from the clutch fingures. The spring on the peddle could still be retained.

[John Vine]

Going back to first principles, presumably the tensioning spring on the clutch pedal is there solely to prevent the other end of the cable jumping out of its locating slot in the operating arm? If so, perhaps a simpler solution would be to clip the cable end onto the arm in some way? I seem to recall that certain Sierra models were set up this way. Then you could remove the spring altogether (or at least reduce its rate considerably). Or would that simply create problems with the CRB (such as alignment, and angle of presentation to the diaphragm fingers), or the rest position of the clutch pedal?

 

An alternative solution might be to insert a coil spring over the exposed length of cable between the arm and the plastic bush in the bellhousing. I guess you'd need to experiment quite a lot to get the correct spring rate, and also choose a pitch that would allow the spring to compress without binding up.

 

JV