AP clutch rebuild/recon services
Discussion
Jhonno said:
Worth speaking to ClutchFix also, they have done a few now with great success.
Great looking discs from ClutchFix at a very good priceSlightly thicker than spec at 7.5mm rather than 7.1mm, so I will have to be sure the clutch releases properly before fitting the gearbox
Not a disaster if there's a problem as I have a second pair that are worn to about 6.8mm each anyway
ukkid35 said:
Jhonno said:
Worth speaking to ClutchFix also, they have done a few now with great success.
Great looking discs from ClutchFix at a very good priceSlightly thicker than spec at 7.5mm rather than 7.1mm, so I will have to be sure the clutch releases properly before fitting the gearbox
Not a disaster if there's a problem as I have a second pair that are worn to about 6.8mm each anyway
ukkid35 said:
Slightly thicker than spec at 7.5mm rather than 7.1mm, so I will have to be sure the clutch releases properly before fitting the gearbox
Just refitted the clutch along with skimmed flywheel (probably didn't need to be), and it releases perfectlyVery pleased indeed, so would definitely recommend ClutchFix
ukkid35 said:
Follow up:
The clutch releases fine, but the bite point is now very high indeed, which I am finding tricky to cope with
I think this must be because the discs are slightly thicker than spec, and considerably thicker than before
Did they re-line your existing plates or supply new ?The clutch releases fine, but the bite point is now very high indeed, which I am finding tricky to cope with
I think this must be because the discs are slightly thicker than spec, and considerably thicker than before
High bite point is not a factor of thick plates, quite the opposite; the biting point rises as a clutch wears. If not much movement is required to disengage it, then it's almost on the point of disengagement/slipping when at rest. Have you tested for free play at the master cylinder?
In a hydraulic system the bite point shouldn't really change much at all irrespective of plate wear.
As plates wear the diaphragm fingers come further out, which pushes the release bearing further out too, but the important point is the release bearing is always in slight contact with the fingers no matter what the wear on the plates is, and the distance the release bearing needs to move the pressure plate and thereby release the friction plates stays roughly the same no matter what their thickness (small variations in leverage ratios notwithstanding).
However, if you have a friction plate with a lining and cusioning plate which is very compressible then the distance required for the pressure plate to move to release the plate is more. This would typically give you a clutch pedal which releases the clutch near the bottom of it's travel because you need to move the diaphragm and hence pressure plate a long way to allow the friction linings and cushioning plate to expand before they are no longer in contact with the pressure plate/fywheel.
Conversely, a friction and cushioning plate which had no compressibility would not require the pedal to be moved far at all before the clutch released, so the bite point would be near the top.
As plates wear the diaphragm fingers come further out, which pushes the release bearing further out too, but the important point is the release bearing is always in slight contact with the fingers no matter what the wear on the plates is, and the distance the release bearing needs to move the pressure plate and thereby release the friction plates stays roughly the same no matter what their thickness (small variations in leverage ratios notwithstanding).
However, if you have a friction plate with a lining and cusioning plate which is very compressible then the distance required for the pressure plate to move to release the plate is more. This would typically give you a clutch pedal which releases the clutch near the bottom of it's travel because you need to move the diaphragm and hence pressure plate a long way to allow the friction linings and cushioning plate to expand before they are no longer in contact with the pressure plate/fywheel.
Conversely, a friction and cushioning plate which had no compressibility would not require the pedal to be moved far at all before the clutch released, so the bite point would be near the top.
...but there should be a bit of 'free play' (for want of a better phrase) in the system bringing the dis/engagement point to a 'comfortable' place in the pedal's range, neither too high nor too low. Wherever or however that free play occurs, whether in the pedal/ linkage/ master cylinder before pressure is built, or in the levers of the diaphragm before they release the pressure plate, the clutch shouldn't disengage with the first couple of mm of thrust bearing travel.
There doesn't need to be any free play, all that needs to happen is when the master cylinder piston comes back it uncovers the recuperating valve and releases the pressure in hydraulic line. Free play isn't required for that.
There is some slop in the pedal / clevis / link rod / master cyl piston assembly but that doesn't have to be there, it's more that the tolerances are large because they don't have to be tight and it's of no consequence.
Paul just said his pedal biting point was high, not that it released within a couple of mm .. and I was just trying to explain how that might happen if the new friction plates were of a less compressible design. The compressibility of the cushioning plate is used to give a progressive take up and this happens over a longer pedal travel / bite point period. It makes a nice easy progressive clutch for Mr Average to cope with. By their nature they will release later in the pedal stroke than plates with no compressibility thereby giving a lower bite point than plates which don't compress or compress little.
There is some slop in the pedal / clevis / link rod / master cyl piston assembly but that doesn't have to be there, it's more that the tolerances are large because they don't have to be tight and it's of no consequence.
Paul just said his pedal biting point was high, not that it released within a couple of mm .. and I was just trying to explain how that might happen if the new friction plates were of a less compressible design. The compressibility of the cushioning plate is used to give a progressive take up and this happens over a longer pedal travel / bite point period. It makes a nice easy progressive clutch for Mr Average to cope with. By their nature they will release later in the pedal stroke than plates with no compressibility thereby giving a lower bite point than plates which don't compress or compress little.
spitfire4v8 said:
Paul just said his pedal biting point was high, not that it released within a couple of mm .. and I was just trying to explain how that might happen if the new friction plates were of a less compressible design.
I have now checked the spare old discs that I have and as you said they are slightly compressibleI didn't check the relined discs as I didn't realise they were supposed to be compressible
I have tried to compensate for the change in pedal feel by changing the clevis pin to the upper hole which I discovered when checking it for wear - which is quite extreme so I've ordered a new one
Unfortunately it has made only a very slight difference
I am not at all happy with this
The clutch is getting less unpleasant with use
That could be in part because of the clevis pin pivot point change, hopefully a new clevis pin will also help
Yesterday I was planning to remove the relined discs and replace them with my old worn discs, just so that the clutch felt right for the next track day
However today I'm inclined to leave it be, because I think the clutch is wearing in positively, and I'm too lazy to put in the 18 hours that it takes me to change the discs, and I'm running out of time
I really hope I've made the right decision, as I had to use my other car last year when the Cerb's oil pump seized on the way to this very special event
That could be in part because of the clevis pin pivot point change, hopefully a new clevis pin will also help
Yesterday I was planning to remove the relined discs and replace them with my old worn discs, just so that the clutch felt right for the next track day
However today I'm inclined to leave it be, because I think the clutch is wearing in positively, and I'm too lazy to put in the 18 hours that it takes me to change the discs, and I'm running out of time
I really hope I've made the right decision, as I had to use my other car last year when the Cerb's oil pump seized on the way to this very special event
What stops the pushrod separating from the piston?
This is where I have a lot of play which I want to remove
I have ordered a new master cylinder, but I'm unlikely to attempt to replace the entire unit
Instead I am hoping that the bore is the same so that I can replace the piston complete with seals and pushrod, while leaving the cylinder in place
This would be a preventative move as far as the seals are concerned, and hopefully will remove all play between pushrod and piston
This is where I have a lot of play which I want to remove
I have ordered a new master cylinder, but I'm unlikely to attempt to replace the entire unit
Instead I am hoping that the bore is the same so that I can replace the piston complete with seals and pushrod, while leaving the cylinder in place
This would be a preventative move as far as the seals are concerned, and hopefully will remove all play between pushrod and piston
The clutch seems to be wearing in slowly
The discs do seem to be compressible, I now have a significant range of pedal travel over which the clutch engages, I may even have to swap the clevis pin back to the original location
The other issue that confused me was that the new slave seals I fitted seemed to be quite tight, preventing the slave piston moving freely, this was particularly bad when cold
However when up to temp the pedal gets lighter and the clutch action is more predictable, hopefully this means they are bedding in as well, and cold performance will also improve
I really hope so as a couple of hours ago I was resigned to taking the gearbox off again and replacing the slave for a new one
The discs do seem to be compressible, I now have a significant range of pedal travel over which the clutch engages, I may even have to swap the clevis pin back to the original location
The other issue that confused me was that the new slave seals I fitted seemed to be quite tight, preventing the slave piston moving freely, this was particularly bad when cold
However when up to temp the pedal gets lighter and the clutch action is more predictable, hopefully this means they are bedding in as well, and cold performance will also improve
I really hope so as a couple of hours ago I was resigned to taking the gearbox off again and replacing the slave for a new one
I can't think of a logical reason why temperature should affect the operation of the slave .. the working tolerance change over such a small temperature range (typically say 15deg ambient overnight to 90degC conducted through the flywheel from the crank) would make a minimal difference in working tolerances especially with compressible rubber seals taking up the gap anyway ..
Happy to be proved wrong though, I'm not a metallurgist or rubber seal expert lol.
Happy to be proved wrong though, I'm not a metallurgist or rubber seal expert lol.
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