Spec clutch disk question.

HondaDustR · 08-13-2009, 04:04 PM

I think I'm going to have to replace my clutch disk, since it's out of the car, it's the old rubber centered one, and it's almost down to the rivets. I've got a WTB thread in case anyone has a lightly used disk, but if I cant get one of those before it's time to put the car back together, I may just have to cough up the $350 and buy a new one. The pressure plate looks fine and the throwout bearing feels fine, so it's just the disk.

The question I have is, Lindsey Racing sells replacement Spec clutch disks and the stage 1 disk is the same price as the OEM Sachs disk here on Pelican. It is an organic compound disk, i.e. no crazy metalic compound that may not play well with the Sachs pressure plate. Would there be any advantage in buying the Spec disk to use with the OEM clutch? Will it hold any tighter or last any longer than the Sachs? I'm willing to give it a try, unless there's a good reason not to.

Any thoughts, anyone?

John_AZ · 08-13-2009, 04:46 PM

If you enjoy a long read:

http://forums.rennlist.com/rennforums/924-931-944-951-968-forum/451563-why-is-a-clutch-so-expensive.html

GL
John_AZ

flash968 · 08-13-2009, 05:09 PM

spec makes good stuff - i haven't played with that one yet though

because this job is such a pain in the butt, there are some things to be sure of so that you don't go back in there

at bare minimum scuff the surfaces of the flywheel and pressure plate with some 400 sandpaper to remove any deposits from the old disk - if there are ANY grooves or gouges on either, replace the worn part - if the flywheel is not a DMF, balance both parts

take note of the position of the pressure plate to the flywheel to retain balance

check the fork bearing - grease with a good bearing grease - replace if there is any "notching" in the pedal

put a dab of grease on the clevis rod end (the rod that comes out of the slave cylinder)

porsche4life · porsche4life's Garage

I drove a 951 with one of those clutches and it seemed stiff to me.

HondaDustR · 07:56 PM

Well, after reading that thread, I think I'm going to try one of the centerforce disks.
http://www.centerforce.com/clutches.tpl?cart=1250221522493632&subsection=clutchselector&searchStr=csearchStr3&cstep1=step1&cstep2=step2&cstep3=step3&carmake=PORSCHE&carmodel=944&caryear=1987&carcyl=none&category=CLUTCHES&make=PORSCHE&model=944&application=380944&addeditem=y&sku=380944

Nearly half the cost of a OEM part.

Now on the subject of flywheel resurfacing, it seems like there's a right and a wrong way to do it...it has to have a certain finish with certain equipment, etc...
Can a typical machine shop do it correctly? According to Centerforce, it must only be done on a qualified flywheel grinding machine. It's also a stepped flywheel, so the pressure plate mounting rim should be cut as well to keep the pressure plate tension in spec, right?

The flywheel on mine looks really good. No burned spots or discoloration and only a very slight grooved patern. What's the possible/likely consequences of just cleaning it up with 400 grit sandpaper and throwing it back on? Does some place like NAPA do flywheels?

TibetanT · TibetanT's Garage

+1 for the CenterForce clutch disk!

I have always purchased Sachs in the past, but tried this manufacturer for a change. Very happy with the performance and it is 20% lighter.

Good luck with that job.

flash968 · 08-13-2009, 08:25 PM

i've heard of centerforce, but never used them

as for surfacing, you should use a machine shop that does engine machining - they pretty much all do surfacing - most of them do balancing

sandpaper won't remove grooves, and certainly won't do it evenly anyway

this is a pretty critical area - it doesn't take much to mess it up - it isn't as expensive to do it right as it it is to do it wrong

HondaDustR · 08-13-2009, 08:43 PM

Quote:

Originally Posted by TibetanT

+1 for the CenterForce clutch disk!

I have always purchased Sachs in the past, but tried this manufacturer for a change. Very happy with the performance and it is 20% lighter.

20% lighter...and 50% cheaper!

There is a machine shop nearby that does engine work. Does the pressure plate mounting rim need to be cut as well?

John_AZ · 08-13-2009, 08:51 PM

A good machine shop in PHX quoted me $40 to do the FW. Some went as high as $50 when you say Porsche and stepped disc. The stepped "rim" is done on a lathe. The FW surface is ground. Call around and find out who knows how to do a Porsche FW correctly and get to the outter edge under the rim. You will see it is tapered IN. You do not want your new disc at the outter edge to ride on a FW with a ledge at the outter edge. In the WSM is a FW thickness chart min/max.

The Centerforce FAQ says NO Blanchard style grinder on the FW surface. I am not a machinist to explain why.

Balancing is another $50-$75. A good machine shop will balance the FW first---and use it as the arbor for the PP. I have suggested and did do both in the past. I have read more recently and a lot of people just have the FW surfaced and cross their fingers. Most of the time they have no clutch vibration problems. You really have to have good references and your trust for the machine shop to do the balancing right.

A couple of past posts suggest just sanding FW and PP as you mentioned if the surface did not have any disc rivet gouges or deep bluish burn in marks.

GL
John_AZ

HondaDustR · 08-13-2009, 09:12 PM

I think I'll have the flywheel resurfaced and just sand the pressure plate. I'm pretty sure I could still see the original machining marks on the PP surface and there is virtually no detectable surface damage.

How critical is balancing? I mean, the flywheel had to have been balanced at some point before it ever got on the car at the factory. What could happen to it to cause it to go out of balance?

John_AZ · 08-14-2009, 04:20 AM

Centerforce ----requires per FAQ---to have the FW resurfaced. Check the PP TO fingers for any wear caused by the TO. Using the PP twice has been done by many members.
See post 18 from SoCal Driver== Potential expensive drivetrain klunk

Balancing both pieces will let you shift up to 3500rpm and beyond and not have an annoying drivetrain vibration. Even with the balancing, on our 20 year old cars the TT bearings have worn and the motor mounts may need replacing. Both may contribute to an additional vibration.

GL
John_AZ

Schumi · 08-14-2009, 06:43 AM

As far as paying attention to the orientation of the PP to the flywheel before taking it off...

I do not think the flywheel is balanced with the PP attached. I'd be willing to be that if the flywheel is balanced at the factory, it is without a clutch and PP attached.

With that said, I will wholly admit that when I took off my PP and swapped clutch discs and reinstalled the PP, I did not even think about the PP orientation. It has 9 bolts, 3 sets of 3, and I just lined it up and torqued them down. Nothing seems like it vibrates more than it used to. It's probably indistinguishable, and there was a 33.3% chance of getting it in the original orientation on accident.

flash968 · 08-14-2009, 07:11 AM

engines are not generally balanced at the factory, and almost never to the level we would like - they have much looser tolerances - they balance some when they are too far out, but not the others

since it is really impossible to balance a pressure plate without a flywheel, if you have ever changed the pressure plate, the balance will be off and need to be redone

you will not necessarily feel the vibrations - they can be below that threshold - the problem is that they are there and do the damage to the bearings anyway

if you have a DMF, this absorbs the vibrations at the expense of power lost in that process - same thing with a harmonic balancer, though it is much more limited in its ability, as it is on the other end of the engine - one thing to remember is that any energy absorbed by these is energy not getting to the wheels - these devices are there to calm things down without having to go to the time and expense of balancing - do you really want to give up that power?

the other hidden added bonus of balancing is that it frequently allows for higher and smoother revving

do not reuse any pressure plate or flywheel bolts - these are heat stretched and will not torque the same - this is potentially very dangerous - having seen the result of a pressure plate ripping loose, and watched the guy learn how to use his new leg, i would not recommend it

John_AZ · 08-14-2009, 08:29 AM

I'm glad flash brought up balancing again. Many brand new 3 piece Sachs kits are badly out of balance. It may have improved over the years, but earlier new Sachs PP needed to be balanced with the balanced FW.

I cannot stress enough that you have to go to a machine shop that knows Porsche. If you take it to the local NAPA---that most likely cannot do a balance--and the guy at the counter has glazed eyes and the experience of a monkey-----you get what you pay for.

GL
John_AZ

HondaDustR · 08:40 AM

okay, okay...I'll balance the damn things...

jk

(stupid project just gets more and more involved)

Thanks to everyone for the good info.

Techno Duck · Techno Duck's Garage

Just feel like adding, balancing the FW and PP and is not rocket science. It may be from a Porsche but its not much different from a Honda... if you dont want to tell them what its from just say its from a old VW or BMW. They key is to question the guy a little about his process..any place that can balance a rotating assembly on an engine can do it. I went to a few places locally trying to find one that would lighten the flywheel and balance the pressure plate and flywheel assembly. Of all the places i went to, only one of them asked me before i asked about giving them the pressure plate to balance with the flywheel. I knew immediately this was the place to goto. Funny enough it was the guy in the older shop on the corner who smells like booze in the morning and is usually not in before noon that does the best work...not the well known engine builder of drag cars in my area. They will leave witness marks on the flywheel and pressure plate so you can line everything back up at the end.

I highly recommend getting the FW and PP resurfaced and balanced at a machine shop. A few grams of imbalance spinning at 6k rpm is pretty huge and will eventually kill your main bearings. .. Think of it this way, at 6k rpm a ~3 gram imbalance will equal close to 6lbs of imbalance at full tilt. Think you can eyeball a 3 gram imbalance with some sand paper.. ? It shouldnt be more than $100 to have both done. I had everything balanced and the stock FW lightened for $200 a few months ago.. $100 of that was just the lightening.

Its not a high cost thing and can potentially save you having to do a clutch job again a few thousand miles down the road.

John_AZ · 07:41 AM

TechnoDuck quote" knew immediately this was the place to goto. Funny enough it was the guy in the older shop on the corner who smells like booze in the morning and is usually not in before noon that does the best work...not the well known engine builder of drag cars in my area. They will leave witness marks on the flywheel and pressure plate so you can line everything back up at the end."

He has a relative in PHX

Mine had a near dead old cat on the counter. The shop looked like it was in a "Deliverence" movie remake. Cash only. My receipt was on a blank piece of paper. Usually did track cars. The fancy shops would not do a balance.

John_AZ

bazar01 · bazar01's Garage

I am on my 3rd clutch on the S2. Always new parts, just resurfaced FW once this time and never had vibration issues. Checked rod and main brgs and still looked like new with no copper showing and going 240k miles. FW is balanced from factory as seen from balancing holes drilled from behind the FW. New Sachs PP has been vibration free.
Street car, no balancing req'd. Use the extra cash on something else needed. Offered just an opinion.

HondaDustR · 08-14-2009, 04:16 PM

Well, especially considering I'm a high rpm addict at every opportunity, I'll definitely look into having it done. The machine shop nearby that I had do my rear brake disks last year looks exactly like the "good" shops mentioned above...you'd never guess the place is actually anything but an abandoned shack, but several people have said they do really good work.

FWIW, the rear main bearing on my old block looked really good except for the silver stuff starting to tear away, front to back, but on only one section of it, just as if something was out of balance. It was a still smooth dark grey surface exposed, not any copper colored stuff like the trashed bearings.

I'm also considering having the crank on whatever short block I end up getting measured, poished, and possibly straightened and balanced. Don't know what kind of expense that's going to incur, but it is cheaper to do it right than to do it wrong! Can the crank be balanced independent of the rods and pistons? Is it worth the even more $$$ to have the whole 9 yards balanced? How about cross drilling the main for #2 rod bearing lubrication? Is it fine to just do the one main, or to drill all of them?