Mystery Plate - do I need this thing??

My LS1/944 SPEC flywheel, clutch and pressure plate package came with an alignment tool and a very nice steel plate that I have no idea what to do with....I'm thinking it may be for configurations other than an LS1.  Can someone please enlighten me?  I get worried whenever I have leftover new parts.

Thanks in advance!!

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This is a .115" shim that goes in between the throwout bearing and billet adapter plate. You must measure to see if you need the shim for your application as every car is a little bit different. The Spec clutch package should have come with an instruction sheet explaining the process.

This explains it also;

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This video from Spec kind of sucks, but it gets the point across also.

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Since the Spec pressure plate has a different mount height and throw distance, it is a must to do the measurement or you'll be removing the torque tube in no time.

Hey guys...thanks for the quick response!  When I installed the clutch and pressure plate I completely emptied the SPEC box and found no instructions...didn't think I needed them until I wanted to know the torque spec for the PP bolts...hence my other post.

Turns out its' my bad!  After TD confirmed that a SPEC instruction sheet should definitely have been included, I did some more snooping around and found the instruction sheet(s) tucked away with all the advertising stickers I've been collecting.  Likely did that when it first came in the mail and I just had to check it out.

With the paperwork, LS1Tech link and u-tube video, I'm good to go now.

Once again 944Hybrids forum to the rescue!!!! Thanks.

OK here's "the rest of the story"...I got my pilot bushing adapter and pilot bushing in, and my SPEC flywheel, clutch and pressure plate installed.

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Now to check the LS Shim Measurement to see if I need the 0.015 SPEC shim provided.

First I measured the "B" measurement from the face of the throw out bearing to the face of the billet adapter plate. (return spring removed)  Used a small square and digital calipers.

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Reading on the calipers = 2.024"

Since this is an unorthodox use of the caliper, I had to add 0.293" to get the desired dimension.  This correction is the distance from the end of the caliper to the jaw making contact with the level.

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Actual "B" dimension = 2.024" + 0.293" or 2.317"

Next is the "A" dimension which is from the back of the PP diaphragm to the transmission side of the bell housing.  Since my C5 bell housing, hydraulic slave cylinder and TT adapter plate came beautifully pre-assembled by TPC, I couldn't measure this directly.

Instead I measured from the the PP diaphragm to the block on each side using a 4 ft level and digital calipers. This is difficult as the diaphragm fingers present a relatively small flat to work off of.  The right side measured 3.349" and the left measured 3.359' so I used the average...3.354."

I subtracted this from the overall depth of the C5 bell housing which I measured to be 5.504" using the 4 ft level and my calipers.  Once again I had to add 0.293" so the actual dimension is 5.797."

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Soooo....my actual "A" dimension = 5.797" - 3.354" or 2.443"

And...the LS Shim Measurement (A-B) = 2.443" - 2.317" or 0.126"

Now...the SPEC instructions say this dimension should be between 0.175" and 0.225"   

But according to Tick Performance (see below) this dimension should be between 0.125" and 0.200"  

I think I'm good to go!!!

How to determine if a shim is needed for your setup:

During each and every clutch install you perform on a newer GM vehicle, you must measure to see if a shim is necessary for proper installation. This is done by taking two simple measurements (see worksheet):

1)  Measurement "A" is the distance between the surface of the bellhousing that meets the transmission to the tip of the pressure plate fingers. To get an accurate measurement, the clutch must be torqued properly.

2)  Measurement "B" is the distance between the throwout bearing surface to the transmission surface that meets the bellhousing. To get an accurate measurement, the slave spring must be removed and the bearing must be fully seated at the bottom of it's travel; resting on the slave's base.

Once you've got your two measurements, make sure that measurement "B" is ~3/16" to 1/8" LESS than measurement "A". If you come up with more than 1/8", add an appropriately sized shim between the slave cylinder and the transmission in order to get the measurements where they need to be.

Your “A minus B” measurement should be 0.125 to 0.200 for adequate bearing travel and to allow for clutch wear. If there is no difference between the two measurements, or if "B" is greater than "A", there could be a problem with clutch engagement which could result in premature clutch slip and eventually a total failure. Contact your clutch manufacturer before proceeding with the install.

The height of the fingers on the Spec pressure plate is different than most other pressure plates, i would consider checking with Spec to see what they say as the values given from Tick might not apply.

TD...the SPEC boundaries for the A-B dimension were 0.175" and 0.225."  My value was 0.126" which is below their designated lower limit. I don' t think there is anything I can do about that.

I ran this by TPC about the same time I posted my measuring adventure and was advised that when using the SPEC flywheel clutch & PP package with the GM Hydraulic Throw out slave bearing and C5 bell housing, they have never needed or used a shim.  That's good enough for me!! Below is the finished assembly with the bell housing (or clutch housing as GM calls it) in place.  Torqued to 37 ft-lbs.

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Just one more thing.....I checked the torque on the 1/4" bolts holding the Hydraulic Throw out slave bearing to the billet adapter and one was 11 ft-lbs and the other was 15 ft-lbs as delivered.  The factory torque requirement is 71 in-lbs or about 6 ft-lbs but I don't know how long the stock bolts are.  Since the TPC arrangement can clearly handle 15 ft-lbs, I brought the lighter bolt up to 15 ft-lbs and called it good.

Also I was advised by TPC that the billet adapter bolts to the bell housing should be torqued between 36 ft-lbs and 52 ft-lbs.  They were all just shy of  45 ft-lbs. I brought them all up to 45 ft-lbs and called it a night.

The big question is which direction do the fingers migrate as the Spec clutch wears.

They move out or closer the the TO bearing. I had the same issue. With some careful grinding of the back of the TO bearing mounting flange and the plastic (composite) edge of the TO bearing sleeve itself, I was able to bring the distance to .155 +-. At least with the TO I had, the plastic had a rounded edge that I ground down flat to just were the internal lip starts (if memory serves), the portion that catches to keep the bearing from going to far forward. Spec said that distance was good enough however it will eventually cause the clutch to slip sooner at the end of its life. Generally I am easy on clutches so I called it good enough.

Jack

This is why I mic'd the D95 TOB when designing the C5 TT adapter, as it allows more clutch wear play. It's "B" dimension is and should be 2.25". One of the taller cheapbay TOBs would have caused issues even on a factory clutch....

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Wow...great feedback!  Thanks guys.

I've been surfn the net all morning for more info on the SPEC package after seeing xschp's post about the migration direction upon clutch wear...lots of pictures...no details.

However, I agree with Jack regarding the diaphragm fingers moving backwards toward the trans as the clutch wears.  This makes perfect sense as forward movement releases clutch pressure.  That said, if I only have 0.126" of travel to work with, then that's the maximum amount of clutch wear that can take place before the TOB creates interference and slippage begins to occur.

With this in mind I took a closer look at the clutch plate.

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It's a total of 3/8" thick with exactly 0.125" (1/8") of material on each face.  Of that, only 0.033" (just a shade over 1/32") of material is usable (wearable?) before contact with the rivet heads and damage occurs to the flywheel and/or PP.  

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So...doing the math once again, available clutch material for wear without damage = 2 x 1/32" = 1/16".
1/16" (0.0625") is less than my A-B dimension of 0.126" so before I get any TOB interference it will be time to change the clutch anyway.  I'm not that familiar with hydraulic slave cylinders, so unless there is another reason besides clutch wear to have a certain A-B dimension, I'm thinking I'm good to go. 

Spec mentioned there will be spring/finger break-in and use fatige that will add to your calculations but I expect that will be slight. Go for it.

Jack

Well folks, I thought I was done with this thread and was satisfied with my A-B dimension of 0.126".  But....something xschop said stuck in my craw....and that was, "This is why I mic'd the D95 TOB when designing the C5 TT adapter, as it allows more clutch wear play. It's "B" dimension is and should be 2.25". One of the taller cheapbay TOBs would have caused issues even on a factory clutch...."

So I began to wonder, do I have a "cheapbay TOB" or a GM C5 unit   The only way to find out was to tear it down and look for a PN.
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Below is all I came up with and I could not find any connection between this PN and any manufacturer. 
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Clearly the TPC provided slave cylinder/TOB combo is not a GM C5 unit and is 0.042" taller. I contacted TPC to get the rest of the story but as it turns out the actual supplier is super double top-secret but Eric assured me he has had no unit failures in over 50 builds.

While I had the slave cylinder out, I remeasured it directly and got 2.292" vs. my previously calculated value assembled of 2.317".
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This is reduction of 0.025" which added to my old A-B dimension of 0.126" gives me a new A-B clearance value of 0.151".  No too bad!

One other positive thing came from the tear down....I learned that my JEGS bell housing bolts are shorter than stock units.  555-82511 BELL HOUSING BOLTS GM LS ($16) To compound that shortfall, they came with washers which I originally used.  I elected to lose the washers this time around and re-installed them at 37 ft-lbs of torque with some blue Loctite.
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