The how and why of the famous Spec Stage 1 clutch whine and chatter.

[Blank Redge]

Maybe you guys already know this. I searched around and found plenty of complaints about the whine and chatter that the Spec Stage 1 clutch produces but I haven’t found any explanations as to why this happens. Adding to the confusion there seems to be a respectable sample size of people that report that they had no problems with their stage 1 disks after years and 30k+ miles of driving. Well when I bought my SVT back in May last year it came with a stage 1 that was just starting to whine after about 5k miles put on by the PO. I’ve put about 3k miles on it since then and I’m really tired of the whining so now I’m changing the clutch out for a standard LUK clutch. When I tore the whole thing apart and got the clutch disk out, it was apparent to me why it whined and chattered (please see attached pics).

What I have shown is a Spec Stage 1 clutch disk with the contact side of a Spec pressure plate (blue powder coat paint on the front side) that is part of the kit that the PO had put in, along side the standard Ford SVT flywheel. The other pictures show the uneven wear on the contact surfaces of the Spec clutch disk and a side-by-side comparison with a new OEM SVT Luk clutch.

For some of you this might seem familiar and fairly slight but there is actually a significant problem here. For starters the stage 1 clutch has a surface area that is way too big relative to the standard Ford SVT flywheel and even the Spec provided PP. Every other problem related this follows but I’ll explain more about that later. This is an obvious misapplication and I’m not sure how this happened. Did Spec put the wrong clutch disc in their Contour kits? I took some measurements of the widths of the contact surfaces using a digital slide caliper (Starrett 723). Here are results I obtained:

Width of the friction material of the Spec clutch: 1.75 inches
Width of the friction material of the Luk clutch: 1.36 inches
Width of the SVT flywheel contact surface: 1.49 inches
Width of the Spec branded pressure plate contact surface: 1.60 inches
Width of the Luk branded pressure plate contact surface: 1.60 inches

Thickness of Spec clutch friction material, pad-to-backing, worn surface: 0.125 inches
Thickness of Spec clutch friction material, pad-to-backing, unworn surface: 0.133 inches
Overall thickness of Spec clutch, pad-to-pad, worn surface, no marcel pressure: 0.306 inches
Overall thickness of Spec clutch, pad-to-pad, unworn surface, no marcel pressure: 0.334 inches
Spec rivet to pad surface distance (worn, PP side): 0.049 ~ 0.057 inches
Spec rivet to pad surface distance (worn, FW side): 0.053 ~ 0.063 inches

Thickness of Luk clutch friction material, pad-to-backing: 0.130 inches
Overall thickness of Luk clutch, pad-to-pad, no marcel pressure: 0.310 inches
Luk rivet to pad surface distance (new): 0.060 inches (consistent)

The fundamental principles in materials science are consistent in stating that whenever an application calls for an expendable friction material to be used with a durable iron material surface, the surface of the friction material shall not exceed the operational boundaries of the durable iron material surface. The reason for this is not purely economical in the sense that material could be wasted when it is not used but mechanical because as the friction material wears, sooner or later, the unworn excess material will intrude into areas that it was never designed to go. The academic question from analysis point-of-view usually follows: what happens next? The answers usually observed is: nothing good. In short, violation of this rule causes negative interaction in the boundary areas between the worn and unworn friction surfaces as it engages and disengages with the durable material. Specifically excessive vibrations due to a combination of forced and free oscillations from the aforementioned interaction typically causes all sorts of premature wear on the friction material, material carrier, and application system. This is why we don’t see brake pads larger than the rotors they arrest or clutch disks larger than the flywheels and pressure plates they have to work with (oh wait, opps).

So the whining and chattering were the symptoms of the vibrations, I have no doubt. Left unchecked, the oscillations can get so bad that they work the marcels like bending a paper clip back and forth. Sooner or later the marcel may crack. Uneven wear on the material caused by vibrations only makes the problem progressively worst as spikes of torque force may only be applied to a narrow concentrated arc of the disk versus to entire disk as an even whole. This could pop rivets and springs in the torsen carrier assembly. Finally, perhaps, the vibrations transmitted from the splined hub to the input shaft could cause accelerated wear on the bearings and seals of the transmission. The TOB could also be affected by vibrations transmitted by the PP. I have no idea what could be happening crank side, hopefully the flywheel has enough dampening power to overcome the effects, then again maybe not, it all depends and not the least factors like mode and frequency.

In closing, the Spec Stage 1 clutch disk itself seems fairly robust and well built. I have no qualms about its material and workmanship. 8k miles or so hasn’t been too bad on this thing. But then again I really babied this thing (because I didn’t like hearing the whine) and the PO wasn’t hard on it either. Regardless I just don’t know what application this clutch was originally designed for. It certainly wasn’t for the Contour or at least not with the stock flywheel or pressure plate. Perhaps there are aftermarket flywheels for the Contour that have contact widths greater than 1.75 inches. Does anyone know what a Fidanza width is? What really troubles me is that the Spec provided pressure plate is also too small for clutch disk. Now what is up with that? I think we all might be hard pressed to find a pressure plate with a contact side that wide for our ‘tours. Does anyone know differently? The important lesson to walk away from this may very well be: if you’re going to replace your clutch, make sure it “fits” your flywheel and pressure plate setup.

Just thought you should all know...Comments, suggestions, advice anyone?

 

[BrApple]

First, that was a very well thought out and presented information. I follow what you are talking about.



I can't tell if its the light or not but the wear on that flywheel does not look good. looks like it might have been overheated or not cleaned well or something.

here is mine after 7k miles on a new SVT flywheel and spec stage 3+ clutch.

Also spec just uses OEM Luk pressure plates. not sure if they use the whole PP or just the housing, but they appeared identical to me.

And just for good measure, the pressure plate.

As for what can happen with the dust from the clutch disk, may not apply to the stage 1 as I don't know if its ceramic or not, but it can get into the TOB and cause it to make noise.


I had and had not noticed the difference in clutch material area between the stock and spec clutch. I wonder if that is why at time the clutch grabbed very low to the floor and other times it did not. I can imagine that the are not worn, because it was larger then the friction surfaces, could catch on the inner edge of the pp or flywheels, and once it wore it wouldn't do that.

 

[SHOgoFast]

Best explaination I've found. Nice work. I would love to see a spec 3 clutch disc compared in this fashion. I totally agree with you Brian, the 'lip' created could certainly lead to early engagement.

 

[RFcsvt]

hopefully the flywheel has enough dampening power to overcome the effects, then again maybe not

So would a lightweight aluminium flywheel have less dampening than the stock one which may actually create a worse situation for the Spec clutch and maybe cause transmission issues sooner? That's kind of what my initial thought is.

Also I just pulled my stock flywheel after 36k miles on a stock LUK clutch and it looked very similiar to the picture Brapple posted, it did not have the same looking wear that the OP's flywheel had.

 

[BrApple]

Also I just pulled my stock flywheel after 36k miles on a stock LUK clutch and it looked very similiar to the picture Brapple posted, it did not have the same looking wear that the OP's flywheel had.

yes that flywheel looks like it has hot spots on it. My oem se flywheel with 95k on it looked similar to the pictures I posted of my 7k SVT flywheel.

 

[amc49]

I don't run these specific parts but after putting in quite a few clutches I can say it's better when the parts are correctly matched. Having said that it's obvious a mismatched part sold here simply to get sales? A lot of them do that but not quite the degree of the worst disc shown. Clutch disk does not wear that much before considered dead, check the reject thickness number. If I saw that situation I would seriously consider relieving the ID of the pressure plate in a radius to get some more life out of parts if still fairly new. Or throw disc up on lathe and cut a relief groove there to fake out plate to think material ends there. Just an effort to get away from the lip dragging there. Early on there will be no trouble since any edge riding will result in unusual wear right there on the disc, but as the step gets larger could result in problems. Certainly not best practice.

Virtually ALL flywheels show hotspots eventually if they get any more than old granny driving. It is a FRICTION based system after all, and testosterone runs high in our pack..........

 

[Blank Redge]

I'll be posting more pictures but it just so happens that I have another SVT flywheel that I'm getting machined *again* because it wasn't machined flat correctly the first time (too much material left near the step edge of the contact surface...maybe due to using worn or beveled stones). To get it right the second time, they asked for me to bring in the Luk clutch and pressure plate and mounting bolts so they can measure and make sure it all fits. I thought that was kinda strange, don't they just follow the book or some conventional specification when machining? But anyway I agreed and handed it all over to them, anything to help get it right. But now I'm wanting them so I can take side-by-side pictures.

Yes, that flywheel is well burnt and unevenly at that. The hardness of those areas would have changed if it transitioned to clementite or martensite making it harder and "slippery" vs the softer iron surrounding the spots. Several questions popped into my head seeing that:

1) Was this flywheel like this when the PO had the Stage 1 kit installed, or was it resurfaced prior to installation?
2) Are these hot spots purely the effect or also a contributing cause of the vibrations?

I guess those are questions where I'll never completely know but I can't help wonder. I see the production bevels on the step edges of the flywheel that leads me to believe that it has never been resurfaced. But then again, I don't know for sure. I can understand how a badly vibrating clutch disk and/or a disk biting harder or early in some areas opposed to others due to uneven wear can cause a flywheel to overheat in localized concentrations. But what do the hot spots themselves do regarding the Spec disk wanting to play the trumpet? Probably nothing good but I don't know how bad. I was wondering why the Spec pressure plate looked eerily like Luk brand. After ~8k miles it doesn't look bad. How come it doesn't have as many hot spots as the flywheel? Then again, the amount of excess clutch material PP side is significantly lower than it is FW side. This could mean more opportunities for premature gripping and biting FW side due to mass and leverage differences in the boundaries of contention...but this is still speculation.

The thought did cross my mind to "remove" the excess clutch material on the Spec disk to try to salvage it but I decided against it for the following reasons: In terms of cutting and removing I don't have any precision tools, only a dremel so I can't do it precisely. The overall surface wear on the Spec disk is uneven. I found that out after cleaning it and measuring the rivet depths. They all vary greatly so either the rivets have random thickness or the surface is not flat anymore. Spec also seems to use a metal reinforced backing for the friction material in addition to the marcels. Those would also have to be cut without cutting the marcels. Finally I really want to see how this disk performs natively to its intended application. The Stage 1 has over 22% more surface area then the stock SVT clutch. If all this area could be utilized with the same clamping force then it would be a clutch to contend with for sure (could we possibly ever need a stage higher than this done correctly?). I just like to know where I can get the right parts to do this for a Contour. Now that I *think* I know what the problem is, I'm wiling to give another chance to the Spec Stage 1. Please, somebody help me find the right PP and FW for this thing!

 

[amc49]

Forget measuring rivet depths, waste of time. They all end up at different heights. Only thing that counts is disk thickness and that will not be exact either even on brand new part.

I strongly suspect that much of the friction difference in new (or reground) and used flywheel or plate is actually small amounts of friction material ground into metal surface similar to disc brake rotor problems. Meaning new surface gets as new fairly even grip if it was not previously severely overheated.

I think much of the lopsided overheating comes from pressure plate that does not lift clean all the way round at once. Meaning loose parts in plate or springs not even, or surface not dead flat. I remember much screwing around with shims trying to get that on our AMC twin disc drag cars. When they released clean all the way round you could run the setup a year and teardown revealed the ink stamped part number still pretty much intact on friction material. It was all or nothing at all when it came to lockup on those.

 

[CSVT1214]

Excellent post Blank Redge! I've wondered for years what could have caused the noise from the clutch. I'm running a SPEC Stage 1 with SVT flywheel and I've got over 60k miles on it and it still grabs like new. It engages slightly higher, but does not slip in any gear.

If it wasn't for the noise, I would run this clutch again, but the noise is extremely irritating and embarrassing. I'll most likely be returning to a stock SVT clutch in the next year.

 

[Blank Redge]

Sent an e-mail to Spec tech support regarding this issue with the their SF371 kits for the Contour V6. I hope to see what they say regarding appropriate alternatives.

 

[Blank Redge]

More side-by-side comparison between the OEM Luk and Spec clutch setups...

 

[svttour]

Fantastic write up! Im eager to hear what spec has to say about this issue. I want to add that I am almost 100% sure that the pressure plates from SPEC and CLUTCHNET clutches for that matter are LUK brand if you look closely you can see LUK stamps on them.

I am running a spec stage 3+ and it only has about 3k miles on it. I havent driven the car in a very long time but I do remember it being very noisy. Alot of chatter and I may have had some moaning one or 2 times.

 

[CSVT#49]

Someone should make the same measurements from the ClutchNet setup... maybe I'm nominating myself since I have a brand new stage3 (red) 6 puck clutch in the box in the basement...

 

[dukeofsho]

I have Spec II that chaters and whines at times. I'll be taking it apart in a few weeks due to another noise inside of the trans. Wouldnt it be something if its all related.
I was told by Terry to buy a Ford TB but I used the spec instead. I wonder if thats could also be the problem. The other probelm is I can't find a Ford TB.

 

[SHOgoFast]

Or throw disc up on lathe and cut a relief groove there to fake out plate to think material ends there. Just an effort to get away from the lip dragging there. Early on there will be no trouble since any edge riding will result in unusual wear right there on the disc, but as the step gets larger could result in problems. Certainly not best practice.

I just installed a spec 2 for a forum member and removed material from the clutch disk to prevent the lip from forming. I'll be sure to get feedback from the owner and see if there are any noticable differences in experience.