Fbody Pressure plate with a ZF6

[Bersaglieri]

Perhaps I missed this info during my search of the Corvetteforum, but here's a quick run down of what I'm trying to do.

I have a 450hp LT1 to go into my Corvette. It's currently in a Fbody I'm returning to stock. The Fbody has a Ram HD clutch kit and Hays Billet Flywheel. I'd like to swap the clutch stuff over with the motor, but I'm reading this from the FAQ area:


[In stock form, the ZF6 uses a "Pull style" clutch, similar to the LT1-T56 transmission. The only difference is,
a ZF6 does NOT use a sprung hub clutch disc, but rather uses a dual-mass flywheel with integrated springs between
the mounting surface and the friction surface. The OEM flywheel sells for nearly $700 US.

There are a few options for clutch replacement, other than stock. For example, you can change to a singlemass flywheel
and re-use a OEM type ZF6 clutch kit, OR use fbody clutch components, OR convert to a push style clutch.

1) If using a Singlemass T56 flywheel out of a 93-97 V8 Fbody (OEM# 10125379), you can use a Fbody sprung hub clutch disc (OEM #12551309),
but must use the propper ZF6 pressure plate for your transmission. Additionally, the flywheel must be resurfaced .090" for clearance
with the clutch fork to bell housing. This will only work on 1986+ motors with 1pc rear main seal!]



I also read this from gtsyellow of CF:

[When it comes to the pressure plate and throwout bearing, stay with the ones intended for the Corvette. They will fit to these flywheels fine, and will work with either the Corvette or LT1 Camaro clutch disc.]

But neither place does it state why the Fbody pressure plate can't be used. I know the Fbody LT1 and Corvette LT4 pressure plates are interchangeable, so wouldn't the Ram Fbody one interchange as well?

Here is exactly what I have:

http://www.summitracing.com/parts/ra...maro/year/1995 (http://www.summitracing.com/parts/ram-98516hd/overview/make/chevrolet/model/camaro/year/1995)

http://www.summitracing.com/parts/ha...make/chevrolet (http://www.summitracing.com/parts/hay-10-530/overview/make/chevrolet)

Am I going to be Christopher Columbus'ing this one? Nuckinfuts?

[Fastbird]

I wish I had some advice for you man, but I don't. I know the ZF had some difference, clutch being one, and had no clue that they were somewhat interchangeable. Just be cautious cobbling parts together in order to make it work, and definitely post up what you find.

[94Blackbird]

The pressure plates themselves may interchange, but the throw out bearings are different.
http://i.ebayimg.com/t/LT1-T56-Camaro-Firebird-Throw-Out-Release-Bearing-GM-/00/s/MzYxWDQwMA==/$(KGrHqV,!jEE6fy1WCF0BOoeJY1wTQ~~60_35.JPGhttp://i.ebayimg.com/t/89-93-LT1-LT5-ZF-Corvette-Throw-Out-Release-Bearing-GM-/00/s/MzY3WDQwMA==/$(KGrHqJ,!k4E6FGTy7DEBOoeGQgwQg~~60_35.JPG

The left pic is a stock f body throw out bearing, the right pic is a stock ZF corvette throwout bearing.

[94Blackbird]

I wish I had some advice for you man, but I don't. I know the ZF had some difference, clutch being one, and had no clue that they were somewhat interchangeable. Just be cautious cobbling parts together in order to make it work, and definitely post up what you find.

The big differences that I've been able to see are A) flywheel B) sprung (f body) vs unsprung (corvette) hub clutch disc and C) the different throwout bearings. I wish I could find the old pressure plate I have from when I did the last clutch in my car, but the throwout bearings are different from what I remember. The ZF trans may also have a larger diameter input shaft where the TO bearing rides, but I haven't been able to confirm that just yet.

[Bersaglieri]

Good info on the throw out bearing!

The obvious difference is the dual mass flywheel [which acts as a dampener] and as such the clutch disc is unsprung. The Fbody is essentially the opposite.

Here is some info I got from gtsyellow about Fbody [single mass] conversion. Mind you this is from 2002:

[i just looked into the same thing, here's the combo that will work, LT1 camaro singlemass flywheel $100 from salvage yard, ram part number c0083 is a great pressure plate under 500hp, bearing cu656 is also needed, they have a few disc options, a good one is 320m however i just used a slightly cheaper one, the HD camaro disc with a sprung hub, 30% stronger than stock they say and very streetable. i was looking for the part number but can't find it, you just want to ask for a LT1 camaro HD disc if you want to go the same way i did. also i found a nice in depth post someone made i'll repost...see following ALSO make sure your tranny is the same, i have the weirdest feeling 89-93 is one set and 94-96 is slighty different, not 100% sure on this


Single-mass flywheel conversion

The ZF S6-40 transmission behind the engine of a ZR-1, as well as that of a LT1 or LT4 Corvette so equipped, comes accompanied by a two piece cast iron "dual mass" flywheel. Camaro's equipped with the LT1 engine however come with a solid "single mass" cast iron flywheel that weighs about half as much. They use the T-56, an entirely different transmission that allows them to utilize this cheaper approach with a conventional sprung hub clutch disc. The Corvette's dual mass flywheel does not allow room for this conventional sprung hub clutch disc, and replaces the function anyway, so a simple solid hub disc is used on Corvettes. The same Valeo pull-type pressure plate is used in both cars, with variations appearing to be perhaps the clamping ring thickness and clamping pressure. Flywheel thickness is about the same, and both use a standard 26-spline transmission input shaft. Except for crankshaft bolt pattern differences between the LT5 and the others, the idea of reducing rotational mass by changing to the Camaro flywheel looks quite possible, but why is the dual mass flywheel there to begin with?

The dual mass flywheel has a primary and secondary component, the two masses of reference, coupled by a sealed bearing. The primary side fastens to the crankshaft and the secondary side to the pressure plate. The secondary component also acts as the front face for the clutch disc to engage against. The secondary side is allowed to rotate about 20 degrees relative to the primary, on a limited rotationally sprung mechanism. This allows slight rotational freedom between the engine and transmission, to damp mostly no-load idling engine harmonics and smooth engagement. Smaller transmissions don't need such a mechanism since their gears do not significantly resonate with idling engine harmonics. But the inertia of the ZF's components is such that it carries engine harmonics when idling in neutral with the clutch engaged. So to make a world-class car for the masses, GM felt it best to filter out this noise rather than be subject to complaints.

The problem with the dual mass design is weight, about 38 lbs worth. There is much potential for increased performance by simply reducing the mass of the flywheel, changing to a single mass flywheel. The LT5 has enough low-end torque that the lost flywheel inertia will not impact drivability. Doing so would allow the engine to rev faster, giving the illusion of more power and the reality of faster acceleration. Indeed there is no change in outright engine performance, but the reduction in inertial mass means less of an obstacle to overcome and more efficient use of power.

If a person wanted to convert a LT1 Corvette to a single mass flywheel, all they have to do is buy a stock or aftermarket replacement LT1 Camaro flywheel and clutch disc, and exchange simply those components alone. But the LT5 has a different crankshaft bolt pattern and so specially made aftermarket flywheels are the only choice. There are three options on the market, produced by DRM, McLeod, and Fidanza. The materials, designs, and philosophies behind each are a little different, but the true difference in performance between them is small and all seem quite durable.

The single mass flywheel sold by Doug Rippie Motorsports (DRM) is actually a partially processed stock LT1 Camaro flywheel, an undrilled blank that is machined instead for the LT5 crankshaft bolt pattern. This cast iron flywheel incorporates a lightened casting design, and so weighs about 20 lbs. It is the cheapest of the three options at about $300, and has been used with much success. It is also available from Star Performance Engineering Clutches (SPEC).

The McLeod single mass flywheel is solid aluminum with a removable steel friction surface. This design makes little effort to reduce weight, weighing in at about 18 lbs. One thought about this though is that the mass of aluminum acts as a good heat sink for the clutch disc and perhaps extends disc life. This flywheel is sold by McLeod and LPE, priced around $600-700.

Fidanza Flywheel Corp. makes a lightened aluminum flywheel, also with a removable steel friction surface. They actually offer to custom anodize the flywheel if desired, with an array of colors from which to choose. This design, much like the stock LT1 flywheel, scoops out the front side in the thick area to yield a weight of about 13 lbs. The craftsmanship is superb and it is popular. Price range is $400-$500, available from dealers like Jeal, SPEC, SGC, and WRP.

In all cases, conversion requires shorter flywheel bolts due to the standard recessed hub. 7/16"-20 thread grade 8 bolts, 1-1 ¼" length are typical. You'll need eight bolts for an LT5. Star or flat washers are recommended, especially with aluminum, and Loctite 262 threadlocker should be used in all cases.

The function of the recessed hub is for the use of a sprung hub clutch disc. A sprung hub disc is technically mandatory based upon any solid flywheel clutch design, and highly suggested, but many have done this conversion while retaining the Corvette's original solid hub disc. It is a good idea to use a sprung hub to allow for some freedom in rotation between the engine and transmission, much like that of a dual mass flywheel, but primarily it will minimize shock and provide smoother engagement. Sprung hub discs don't have much impact on the transfer of engine idling harmonics.

In selecting a sprung hub disc to use, there are many choices available and care must be taken. The disc must be originally intended for the LT1 Camaro/Firebird to properly work with the pull-type pressure plate. The stock LT1 disc's hub is too large to clear McLeod and Fidanza smaller recessed hubs without custom machining, but is of course intended to be used with the DRM flywheel. Centerforce, McLeod, Clutchnet, and SPEC produce smaller sprung hub discs for the LT1 Camaro application that will easily clear the smaller recessed hubs. These have six small hub springs and can easily be differentiated from the original with its five springs. The stock disc can be bought from SLP for $90.

When it comes to the pressure plate and throwout bearing, stay with the ones intended for the Corvette. They will fit to these flywheels fine, and will work with either the Corvette or LT1 Camaro clutch disc.

The price for converting to a single mass flywheel is amplification of no-load engine harmonics, the sound of marbles rattling together when the engine is idling with the transmission in neutral and the clutch engaged. How much of a problem is this? In my experience, and that of most others, it is not a problem at all. With the radio at normal listening level, the noise typically can hardly be heard. Some however seem to have much more significant noise problems. It doesn't seem specific to a certain flywheel brand or material. Changing to a sprung hub clutch disc when converting to single mass is a good idea, and could have an impact on these problems. But I believe it is more the result of engine, clutch, or transmission imbalances or other irregularities, or perhaps simply a low idle speed- or sensitive person.

Though I don't feel it is warranted, the transmission noise at idle can be reduced or eliminated by increasing idle speed to 1000 RPM, and/or changing to a synthetic transmission lube. Of course another option for similar gains without noise would be an aluminum dual mass flywheel, but the effort and cost are really unnecessary. A single mass flywheel and sprung hub disc are an effective, minimally invasive modification that will leave you asking why you didn't act sooner, I highly recommend it!]

Here is what I've got from the FAQ area:

[ZF6 Clutch Specifics:

In stock form, the ZF6 uses a "Pull style" clutch, similar to the LT1-T56 transmission. The only difference is,
a ZF6 does NOT use a sprung hun clutch disc, but rather uses a dual-mass flywheel with integrated springs between
the mounting surface and the friction surface. The OEM flywheel sells for nearly $700 US.

There are a few options for clutch replacement, other than stock. For example, you can change to a singlemass flywheel
and re-use a OEM type ZF6 clutch kit, OR use fbody clutch components, OR convert to a push style clutch.


1) If using a Singlemass T56 flywheel out of a 93-97 V8 Fbody (OEM# 10125379), you can use a Fbody sprung hub clutch disc (OEM #12551309),
but must use the propper ZF6 pressure plate for your transmission. Additionally, the flywheel must be resurfaced .090" for clearance
with the clutch fork to bell housing. This will only work on 1986+ motors with 1pc rear main seal!

2) If using a Singlemass 4+3 flywheel (OEM# 14088646), you can use an OEM type ZF6 clutch kit, but due to the lack of a dual mass flywheel
OR sprung clutch hub you will get some gear noise.

3) You can use a Singlemass 4+3 flywheel with an OEM type 4+3 PUSH clutch, but NOT with the ZF6 hydraulics!
You need to convert to a hydraulic throw out bearing (such as Howe 82876 for Black Tag ZF6 with a 1.375" TOB). LD85 has completed
this swap and has added the following information:

"Essentially, I use a 4+3 FW , PP and Disc, .100" spacer between the BH and Block, and a Hydraulic Howe Push Type slip on TOB,
a Wilwood 3/4" bore Master Cylinder, and a Clutch Pedal travel stop."

Expect to pay about $160 for the TOB, $160 for the master cyl, and another 40-50 in materials to make the spacer + pedal stop.


AGAIN, A DUAL MASS or A T56 flywheel will only work on a 1986 AND UP MOTOR WITH A 1PC REAR MAIN SEAL!]


I've also read conflicting information about the throw out bearing being different between the black tag and blue tag ZF6's transmissions. It seems that Carolina Clutch is a place many people get referred to for clutch kits, etc for C4 Vettes. I'm hoping that calling them tomorrow will yield more results than I got from Ram today.

[94Blackbird]

I think where the confusion is coming is because the black tag trans has a larger input shaft diameter than the blue tag. Black =1.375 Blue= 1.311. As far as I can tell the throwout bearings are the same though.

[Bersaglieri]

Hmm, more good info that I don't have to measure with a caliper later, thanks.

What's the T56 diameter?

I sure hope this works out, the only possible hitch of this whole swap is with the clutch stuff. Everything else is cake.

[94Blackbird]

Sorry, I don't have that information.

[Bersaglieri]

No problem man, you've been more help than anyone else so far.

[94Blackbird]

No problem man, you've been more help than anyone else so far.

I am swapping a ZF into my trans am.

[Bersaglieri]

Ah I remember now... honestly I think that it's an excellent upgrade. I drove my T56 car last week and it was horrible sloppy compared to the ZF6. The ZF6 shifting changes the driving experience by itself.

So are you planning on doing the same, running single mass flywheel/Fbody PP/Fbody sprung clutch? If so, looks like we'll be working together on this one. Hopefully if there isn't a sand storm I'll be tearing things apart after work today. I should be able to get spacing and measurements as I go from both transmissions/clutches.

[94Blackbird]

Ah I remember now... honestly I think that it's an excellent upgrade. I drove my T56 car last week and it was horrible sloppy compared to the ZF6. The ZF6 shifting changes the driving experience by itself.

So are you planning on doing the same, running single mass flywheel/Fbody PP/Fbody sprung clutch? If so, looks like we'll be working together on this one. Hopefully if there isn't a sand storm I'll be tearing things apart after work today. I should be able to get spacing and measurements as I go from both transmissions/clutches.

I'm going to be converting over to a push style clutch for this one. The ZF slave sits a little higher than the t56 slave cylinder does. Unfortunately you have all the info that I have.

The reason I chose to go ZF over having my t56 built is because the ZF is a straight cut gear box, and far stronger than the factory rating. The guy who built my 8.8 for me has put over 1000 flywheel horsepower through one, bone stock, and still hasn't opened it up and has no plans to unless something starts going wrong.

[93M6Formula]

What clutch was used in the 91-92 Firehawks?? They used a ZF-6 in those as well. Don't know if it will help at all but just thought I would add to it.

[94Blackbird]

What clutch was used in the 91-92 Firehawks?? They used a ZF-6 in those as well. Don't know if it will help at all but just thought I would add to it.

I believe the same clutch set up was used in the 91-92 hawks as the ZF equipped vettes. They also had a special bellhousing that it would take an act of congress and half the gold in fort knox to get a hold of. SLP made a very limited run of the conversion kits for 3rd gens after they quit making the thirdgen hawks.

[Bersaglieri]

I hate to link other sites, but here's the thread on CF I made as well: http://forums.corvetteforum.com/c4-tech-performance/3225147-searched-fbody-pressure-plate-with-zf6.html

Looks like we're slowing but surely getting somewhere. I may just need a ZF6 throw out bearing and to shave the flywheel .090"... I could deal with that!

[94Blackbird]

That sounds about right.

[Bersaglieri]

I've got the stock ZF6 throw out bearing, but it's a good possibility it's got the same 165,xxx miles the body of the car does... hmm.

Here's a picture of my Ram pressure plate and throw out:
http://i116.photobucket.com/albums/o4/roadtrip120/347da9e8.jpg

Looks like the fbody style.

[94Blackbird]

It is, here's a pic of the pressure plate from my corvette pull out I bought to get the trans.

[Bersaglieri]

Corvette guys came up with measuring the ZF6 setup to the pressure plate teeth, then comparing that to what the Hays/Ram measures and cutting the difference.

Also here is an excellent source they came up with for clutch stuff: http://www.powertorquesystems.com/Corvette/CorvetteMain.htm

They list two different throw out bearings for the ZF6, just as you showed the two different shaft sizes of black vs blue tags. Looks like my best bet might be to buy a new TOB from there with a fluted pilot bearing and have the flywheel machined as necessary after measurement.

[Bersaglieri]

Talked to Jim at Power Torque Systems and that guy knows his shit on ZF6 transmissions. I can't recommend him enough for sourcing parts, getting info, and having everything in stock. He actually works on what he sells and has first hand information and experience in these transmissions. I've got a throw out bearing and fluted pilot bearing on the way from him.

We also talked about the possibility of a factory flywheel not being strong enough to take the clearance without coming apart, so that should be noted as well. He's not much of a forum guy but I'll be sending him this link to see if he can find any inaccuracies or provide any more help for other people doing the same.

[Bersaglieri]

Well I'm taking the flywheel in today to have it machined. I called Carolina clutch to double check my measurements but they said they have 'no idea about any of that, we don't machine anything here'.

I took a straight edge and measured the distance between the face of the block where the trans mates and the face of the flywheel where the clutch meets. The difference is ~.130". I figure after having the single mass resurfaced and .090" taken off the crank side it'll be nearly the same. I did not have the opportunity to measure to the throw out bearing yet, I'll be doing that shortly.

I called Doug Rippie, mailbox full. I left a message with ZR51 Performance.

That's the update. I hope to reinstall everything this weekend.

[Bersaglieri]

Update: Didn't take it in, I'm waiting on a confirmation call from Doug Rippie Motorsports. Sounds like it needs taken off the CLUTCH FACE of the flywheel not the crank side.

That being said, several Corvette clutch people have told me the factory Valeo friction should hold the ~375rwhp I'm expecting to make. So I may sell the Hays/RAM combo and see how the factory stuff holds.

PS I called SPEC since they sell a flywheel already machined and the tech told me to pound sand as I asked my questions. Yet another reason I'll never run their product.

[Bersaglieri]

Wound up running a stock Corvette clutch, so far it's holding fine. Will update later.