New Clutch questions

[89esprit]

Well I finally had to give in and replace the clutch in my 89 Esprit Non SE.  I got the clutch  out without pulling the shafts, thanks to all the advice from the folks on here. Now I have a few questions.  I think I've read somewhere that the spec for the diameter of my friction plate is 9.25 inches and the one for the Citroen trans is 9.5 inches.  When I took out the clutch I found that the friction disc is actually about and eighth of an inch from the outside edge of the Pressure plate. Is it possible for me to put a 9.5 inch clutch in instead of the 9.25? Is more better in this case?  The same thing on the flywheel.  All of the raised section of the flywheel (where the disc rides) isn't being used, again about an eighth of an inch all the way around.  That brings me to another question.  I'm going to get the flywheel resurfaced.  Does anyone have the spec on how high the raised portion of the flywheel should be?  I thought I read on here it should be .5mm but I can't find the thread where I read that.  Thanks for your help

Kenny

[Chillidoggy]

It's 0.5 - 0.6mm step, and a minimum of 12mm thickness for the flywheel.

Why do you want to increase the clutch size? Did you have problems with the original one?

[89esprit]

Just thought if it was larger it may last longer and get better performance.  I think the one I pulled was original but its hard to say. Last driving season it was getting worse and worse.  I did some laps (behind a pace car) at Watkins Glen International and the clutch was slipping under load.  I was constantly adjusting it trying to find the sweet spot but never did.  Once I got it out last week, it was down to the rivets on the flywheel side and not much better on the pressure plate side. No wonder it was slipping.  I figured as long as it had the room for the larger one why not? Not a good idea or ???

Also, how thick should the disk be?  I read here that its 8.6 mm do you agree?

Edited March 7, 2016 by 89esprit

[Chillidoggy]

 I'm sure there'll be someone along soon that can help.

[sailorbob]

The specified diameter of the OE friction plate is 228 mm (9.00 in).

[Chillidoggy]

In addition to Derek's post, according to the service notes I have, a new clutch friction plate thickness is 7.7mm (+/-  0.3mm), and the service limit is 5.9mm.

[89esprit]

Unfortunately, my service notes don't say what the thickness is... however it does state the diameter is supposed to be 235mm or 9.25 inches.  Hmmm I wonder what the differences are.

 

I appreciate all the help. Thanks!

[sailorbob]

The 235 mm friction plate has been superseded by the 228 mm friction plate.

[89esprit]

Do you have any idea why they would go to a smaller friction plate?  Doesn't make too much sense to me... But I'm no expert.

[sailorbob]

As the pressure plate is unchanged reducing the area increases the pressure. Maybe that's the reason for the change

[Chillidoggy]

I'm not sure it's as simple as that. I think there are other considerations in the clutch equation. There must be an optimum pressure to friction-surface area, maybe @CHANGEScan advise?

[sailorbob]

It's not as simple as that but I was trying to indicate that a reduction in diameter doesn't necessarily equate to a reduction in torque capacity. The real reason for the change was probably financial.

[CHANGES]

Sailorbob and ian29gte are correct, it is not that simple.   Looking at it purely in Lay mans terms we have 3 main influencing factors to consider..  1. The driven plate's overall diameter.  2. Clamp load from the cover assembly. 3. Surface area of the friction faces on the drive plate.   These together will provide a given torque..

With the same clamp load, two different diameter driven plates can provide similar torque figure. The larger of the two has the advantage of greater radial gyration, but with its greater surface area will reduce the coefficient of friction. This is a sort of trade off.  However using an increased clamp load with the larger plate will show noticeable torque capability increase. Down side of this is peddle loading and inertia factors with reduced rpm limit for driven plates. 

There are so many permutations, but without going into details that will hopefully answer the question..  

 

On 07/03/2016 at 16:48, 89esprit said:

I was constantly adjusting it trying to find the sweet spot but never did. 

  Ken, the reason you could not find the sweat spot is because the clutch system on the Esprit is not adjustable.. It is not uncommon for owners to try and adjust the clutch with the screw on the actuating arm, but that is only there to centralise the slave cylinder so it does not deck out during stroke or clutch ware..   You can change your hydraulic cylinders and peddle fulcrum to achieve different characteristics when fitting custom clutches, but on a standard unit the system provided is very capable.   

[Chillidoggy]

Does it for me, Dave.

I remember in the distant past an acquaintance with a GT40 using the theory that machining off some of the friction plate material would improve the clutch torque capacity because by doing that the pressure on it was increased. It didn't work, in fact it was worse.

[89esprit]

Thanks for all your help guys!  Well I got the clutch all in and after a short ride yesterday It seems perfect! I will give it another shakedown later this week.  I was just too beat to take it for a longer ride.  I wound up getting a custom clutch built for me a shop that specializes in clutches and brakes.  I sent them my clutch and pressure plate and they completely rebuilt them. He offered me 3 choices, the original fiber disc, a 12 button cerametalic disc or 16 button cerametalic disc.   I had them put 16 cerametallic buttons on the disc.  8 per side. He explained that the 16 would engage a lot smoother vs. the 12. The disc is 9 inch by the way and 8.5mm thick.

They also resurfaced and rebuilt the pressure plate. 

I also had the flywheel resurfaced.

I paid $288 USD for this. What do you guys think?

[MrDangerUS]

Great job,

and sounds like a bargain.

What is the name of the shop did you use? Where?

Edited March 22, 2016 by MrDangerUS

[89esprit]

I used a company in Buffalo, NY. Oddly enough their name is  Buffalo Clutch Inc. When I was starting out as a mechanic I worked for a neighborhood garage in Buffalo, and we had put two clutches in a 454 Corvette within a 3 week period. The guy was very hard on that car. So finally the old timer that owned the place said we'll fix this thing once and for all. We pulled out again and took it to these guys at Buffalo Clutch, told them what was going on, and they rebuilt it a lot beefier.  Never gave that guy another bit of trouble. 

Then I worked as a mechanic for a drilling company there, and I took tons of clutches from the drill rigs to them. That was back in the early 80s. That's when I started using the cerametalic button clutches. 

When I talked with them, I told them, what the flywheel was like, with that 0.5-0.6mm step up where the disc rides and the thickness that the disc should be, and they built it from there. http://www.buffaloclutch.com/