Twin-plate clutch drag (Not related to hudraulic)

[Lasse]

Hi guys,

i see that there is basically kilometers of text written about twin-clutch problems. I would like this thread to focus on possible causes for clutch drag caused by the clutch pack itself (not bad working hydraulics)

The car is a 96 MY Esprit V8 with retrofitted twin plate clutch (work probably done back in the 90's, lacking documentation), travel approx. 30000 miles.

The following is the nature of the problem:

1. Impossible to get reverse in with engine running. Hard to get other gears in as well (indicating clutch is not disengaged fully). Absolutely no problem to engage any gear when engine off.

2. Hydraulics have been fully re-furbished not long ago. Clutch line has been successfully bled. Pedal will respond nice and distinctly within a cm or so of travel.

3. Pedal travel set to 90-95mm according to manual. However, ability to select gears did not improve if the travel was increased (tested with "full travel" well in excess of 120mm with no noticable improvment).

4. Engagement point under load (gear in, point of engagement to get car moving) is approx. 30-40mm under pedal up-stop indicating good function of hudraulics and mabye also release mechanism in the clutch pack.

5. No noise under load or else indicating bad release bearring etc.

6. Friction discs inspected (not measured for flatness) - looks almost unused.

And still there is drag...

Anyone with knowledege of possible causes?

Best Regards/ Lasse, Sweden

[Advantage]

How old is the gearbox oil?

[Lasse]

It's old and due for change...

But that should not affect this problem?

Conditions for selecting gears when car stands still:

Secondary shaft stands still because wheels stands still --> Primary shaft needs to stand still to engage any gear.

If primary shaft is moving it is because clutch is not fully disengaged and this means that the synchros need to brake movement to "0" before any gear can be selected.

If the drag from the clutch is to great, the friction force in the synchros will not be big enough to stop the primary, which is why reverse can ot be selected at all...

So yes, if the oil lost all its friction properties, I would presume that even a very small drag from the clutch can produce a problem.

However, normally the clutch should disengage to such a degree that the primary axis doesn't rotate even without the help of synchros. I mean, this is how it works on all the older cars without synchromesh on reverse, working properly they will never produce gear-teeth noise when engaging reverse indicating primary axix actually standing still (="0" Clutch drag).

Is the twin-plate clutch on the V8 different in this respect? Is this mabye the reason for having synchro-mesh on reverse gear?

Best Regards, Lasse

Edited April 23, 2010 by Lasse

[freshcut]

The only other bits I can throw out to look for is insufficient lubricant on clutch splines, worn/stiff pilot bearing or some form of mechanical problem involving clutch pack or transmission splines distorted to prevent clutch disks from separating from drive plates.

As GKP mentioned, I would recommend a fresh change of gearbox oil unless that was performed recently. How long ago did you inspect the clutch disks?

[Lasse]

Hello Freshcut,

The disks were inspected a couple of weeks ago during an attempt to solve this problem. They were, as mentioned above, only inspected visually, but they looked as new.

And yes, gearbox oil is planned to be changed in the near future.

Best Regards /Lasse

[freshcut]

So the gearbox was removed during this process? If not, I'd be suspicious of the input splines. There are only a few things that can cause the input shaft to continue rotating after the clutch is disengaged.

[Lasse]

Yes, the gearbox was completely removed from the car. Splines on the input shaft looked ok.

//L

[superdavelotus]

Hi Lasse,

I've just sent you a pm telling you what your problem is.

Hopefully you'll sort it from that.

Also I forgot to tell you that on top of the other stuff I've told you, double check the pack thickness is within tollerance. The figures are in the workshop manual.

Regards,

David

[Bibs]

Why the PM? It would be in the spirit of the forum to post the possible solution online so that the next V8 owner with a dragging clutch can deal with it.

[jonwat]

Why the PM? It would be in the spirit of the forum to post the possible solution online so that the next V8 owner with a dragging clutch can deal with it.

I second that

[lotus4s]

Motion approved, all in favor say "aye"....

Edited April 23, 2010 by lotus4s

[superdavelotus]

I was told this by a Lotus specialist who told me to keep to myself. Yes I know it's not in the spirit of things.

So here's what I sent:-

Sorry you've having problems with your clutch and gearbox. It's the clutch pack not sliding on cage followed by the female splines having sharp straight cut edges dragging on the input shaft.

You have to dismantle the clutch pack and make sure the plates slides in the cage. Then you use a needle file to shamfer the female edge of spline. This stops the clutch dragging on the input shaft.

If you are unsure then you'll have to send the clutch to me and I get my garage to sort it out for you.

This is for a V8 twin plate clutch only and doesn't apply to 4 cylinders or Boxsters.

Regards,

David Walters

Edited April 23, 2010 by superdavelotus

[lotus4s]

Dave,

Thanks a lot for that info, it makes sense and will help others I'm sure.

[Bibs]

Good man Dave. I can't see why that should be secret and will no doubt save many people time, trouble and lots of head scratching.

[Marcus3]

Hiya

Are you saying you have 30,000 miles on this clutch ? if so it's at end of it's life

by the description of your reverse gear and other gear problems, it certainly sounds like it

Also just FYI, the 2 clutch plates don't seem to wear out as fast as the intermediate plate that's between them, as this plate has both clutches wearing on it from both sides I have found that this has been the problem

hope this helps

-Marcus

[Lasse]

Hi all you guys!

Thanks a million for all the replies and your devotion to the subject. I will most certainly look into all the possible causes that has been presented here.

I've also learned that there is a known problem on very early clutches (which this is) with a possible contact between friction disc periphery and the six steel wear plates on the cover housing.

Marcus3, Yes, I will again measure the thickness and other properties, but the clutch definitely doesn't look worn out. I agree that a worn-out clutch could produce this problem if it is related to the release mechanism going bad, but the wear in itself doesn't increase the drag. It will however produce clutch-slip once the friction plates are worn down to the rivets or the slave cylinder will bottom out so the clutch can't engage anymore...

Again, thanks for all the useful input to the further investigation so far...

Best Regards /Lasse

[Günter]

sidenote:

the problem with the friction plates 'scrubbing' onto the legs (steel covers) of the clutch cage is not generally on early cars: it is more mostly related on 'reconditioned' plates. In case the recondition company could not manage to fabricate within the right diameter, or used an friction material that is to soft for the steady pressure & forces in the V8 clutch system, and starts to 'float/deform' on the outer edge -therefore the friction plate can 'grow-up' in diameter and starts scrubbing on the outer edge.. .

Bad point of that effect is that in some cases the friction plate does not move far enough with 'clutch pedal' pressed, or on opposite ways -does not engage fully with pedal up. Therefore it is under steady 'slip' and will wear out much faster ...

[Lasse]

Hello Günter,

interesting information since it seem possible that the friction plates may have been refurbished based on the fact they look brand new even though the clutch travelled probably 50.000km or so.

Next step will be to pull the tranny once again, this time ALL pieces will end up on my measurement table and be thorougly measured and examined. Service kit (pins and clips) will also be purchased for excange.

Whish me luck...

I will report back on sollution and result...

Please keep posting interesting causes and similar cases with known solutions.

Best Regards to you all/ Lasse

[superdavelotus]

Hi Bibs,

I suppose it's their bread and butter and they have to earn a living which is why I felt a bit bad. It's not rocket science and I reckon most people won't start filing their clutches and send to their specialists anyway.

Regards,

David

PS. Oh forgot to mention that OEM clutches from Lotus have a paint stripe on the housing which goes right through the plates as well. This is there to line up and make sure you reassemble them in the same way. When you have plates reconditioned, sometimes they come back with no markings at all or the plates you get aren't the plates you sent. This will cause problems with them sliding on the 6 mounting sliders on the housing cage.

This will also cause drag. In the Lotus service notes, it does advise that you shouldn't disassemble the cage and instead replace the whole assembly. We know that in most cases it's not the case due to cost. There are so many companies doing recon clutches or companies taking them apart and not knowing how they work properly.

[Lasse]

If I'm remebering correctly all clutch parts BUT the friction plates has this paint marking. Unfortunatly the marking doesn't help to mount the friction discs in the right position nor with correct orientation.

Can anyone verify that the depiction of the friction discs in the service manual is correct i.e. it depicts the actual discs in correct position and orientation?

BR // Lasse

[Marcus3]

I have a spare clutch down at LotusPBC, I will be down there this Saturday, I can take some pictures if you need

Also if you look at the friction plates, they are marked with "this side to flywheel" etc etc, if I remember correctly

Anyways let me know if you need pics of one

-Marcus

[Lasse]

Pictures would be nice.

I ask for this confirmation because one of the problems I have is that the marking of the outer friction plate is contradictory to how it is depicted in the manual. I.e. if I fit it according to the marking (flywheel side/bearing side) it will be fitted the wrong way round according to the depiction in the manual.

Having been working on Lotuses for over 10 years now I don't find such circumstances strange - they're more sort of typical

BR //L

Edited April 27, 2010 by Lasse

[freshcut]

I'm not so sure on the markings to be honest. I just replaced the clutch linings on my V8 about a month ago, and the disks matched the manual diagram with correct markings. Even the new AP disks I ordered were correctly marked. Perhaps I had an unusual set as everything seemed to go exactly according to the book, which I will agree, sometimes things are a bit backwards, but in this case everything came together as expected.

[Lasse]

The thing is that I have no history what so ever on what work has been done on the clutch earlier, mabye the discs aren't even the Lotus/AP original part... At the moment they are mounted exactly as depicted in the manual, which in this case also means that the markings are reversed.

BR //L

[freshcut]

The use of alternate disks certainly wouldn't be unusual. There are a few threads where others have cone to alternative disks, switching out the input shaft, etc. Personally, I stick with the "keep it stock, keep it happy" camp and opted to replace with OEM when I did mine. I also recall along side the markings there were markings on the new disks with the AP racing emblem painted on them as well as on the old disks right next to the "flywheel/bearing" side. I'd imagine if they're AP disks, you should have similar markings.