Tilton Clutch

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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The Dark Side of Will
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Tilton Clutch

Post by The Dark Side of Will »

Earlier this evening I was on the phone with a Tilton engineer about how to fit a Tilton clutch to my Northstar. I had pretty much decided on a 7.25" unit before I talked to him. I just wanted to sort out PP load & ratio, # disks and friction material.

He said there are two characteristics that define the limits of a clutch: torque capacity and heat capacity.
Torque capacity is obvious.
As far as heat capacity goes, the smaller and lighter the clutch the less heat it can absorb before its temperature rises to damaging levels. Therefore the smaller and lighter the clutch, the less it can be slipped.

Tilton offers three friction materials: sintered iron for road racing, cerametallic for rally and a setup with one organic disk and one cerametallic disk for street use.

The major factor affecting the modulability of the clutch is the compressibility of the disk. Marcel in a conventional street clutch spreads the engagement load over a wider range of engagement travel than flat disks. Tilton disks are not available with Marcel. The organic friction material is more compressible than the other two, which is why it is the most streetable. It also has the lowest grip and lowest heat tolerance.

The cerametallic and organic disks are significantly thicker than the sintered iron disks. The result is that a two disk cerametallic packages in the same setup height as a three disk sintered iron.

On a scale of 0-10 for modulability, 0 being a light switch and 10 being an OE street clutch, the sintered iron is about a 2 and a cerametallic is about a 4. A carbon-carbon clutch is about an 8, but I don't have the money for that, so I'm going to pretend it doesn't exist for the sake of my sanity.

We settled on the 2 disk cerametallic for my application. He spec'd the 66-302UORA pressure plate. This is an ultra-high ratio (lighter pedal effort than merely high ratio) unit with 600 ftlb capacity (not the softest, but on the softer side of what they offer).
Page:
http://tiltonracing.com/product/7-25-in ... ng-clutch/
Installation drawing:
http://tiltonracing.com/wp-content/uplo ... I-7.25.pdf
Installation instructions:
http://tiltonracing.com/wp-content/uplo ... Clutch.pdf

For the 282 with 25mm x 14 spline, he suggested the 64185-7-AA-12 disks. The -12 at the end is the code for that particular spline.
Page:
http://www.tiltonracing.com/content.php ... &id=83&m=d
Installation instructions:
http://www.tiltonracing.com/pdfs/36.pdf

Measuring from my somewhat worn Centerfarce I have 2.25" of total engaged stack height. Wtih 1.37" of engaged stack height on a new Tilton, I have 0.88" in which to package a N* flexplate and a button to bolt the clutch to. I think I can do that, but I need to look at the flex plate a little more closely as I believe it has some contours that will get in the way.

The Tilton has a max throw of 0.250", but when new should be fully disengaged with 0.160" throw. Disengagement load will be about 500#. Tilton runs a 1.2 sqin piston area hydraulic TOB with 3/4" diameter (0.44 sqin) for a hydraulic ratio of 2.7:1. When used with a 5-6.5:1 pedal, this results in 13.6 - 17.7 overal ratios, or pedal loads of 28.3 - 36.8 lbs. I'll have to run the numbers with the Fiero clutch mechanism to see what I can come up with. Does anyone know the MC and various slave cylinder diameters right off?

The clutch can tolerate a total of about 0.030 of wear in all the friction components before requiring new disks and steels. Since the diaphragm spring in the ultra-high ratio pressure plates operates at a 5:1 ratio, this will mean 0.150 additional stack height at the TOB, so the throw out mechanism needs to be able to tolerate a clutch height of 1.52"... which feeds back into acceptable button thickness, which has dropped to 0.73".

The diaphragm fingers require a radiused face TOB. The ideal contact diameter is 44mm, but they can be used with up to 50 mm. Throw out bearing remains to be figured out, but I'll probably send him a spare that I have so that he can come up with a good match for it.

I will eventually convert to the hydraulic throw out used in the later 282's, but for now the setup has to work with the mechanical throw out mechanism.

Based on experience with his 1st gen RX7, he estimates that I could see 40K miles on the clutch if I hone my technique to make sure that it's fully engaged within a carlength or so from a dead stop. Drag strip use will be harder on it, but he said heat is the big enemy for that and the clutch will be fine if I give it time to cool between runs.

Oh yeah, the unit weighs 8.2# or so. With the flex plate and button, the total weight for the whole shebang should be less thant he stock flywheel by itself (14#).
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Post by Shaun41178(2) »

I think the getrag slave bore is 1-3/8th. tHe isuzu is smaller, maybe 1 inch or something. Dont' quote me as I am pretty sure I am wrong.
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Re: Tilton Clutch

Post by Series8217 »

The Dark Side of Will wrote:Does anyone know the MC and various slave cylinder diameters right off?
Slave sizes:
Isuzu: 13/16"
Getrag: 15/16"

Master cylinder: 11/16"

You can also mix and match clutch arms to tweak the effort ( viewtopic.php?t=2986 ).

The slaves are interchangeable by knocking out the studs on the Isuzu so it can be mounted with bolts. You also may need to shorten/lengthen the pushrod. Just cut down an old rocker arm pushrod. It's the same diameter and material as the slave pushrods..
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Post by The Dark Side of Will »

Thanks.

Does the Muncie have a bigger MC? I heard somewhere that it does...


The Centerfarce that I have now is plenty streetable, but it's very marginal with the Northstar. The CF can hold the N*'s torque if it's fully engaged, IE, the coefficient of static friction is high enough to hold that amount of torque. However, the coefficient of dynamic friction is NOT high enough to give it this capacity. This means that when feeding the clutch for a dragstrip launch, if I get to the floor with the gas before the clutch is fully engaged, it WON'T engage and I have to back off and start over.
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Post by BigRedDeckSpoiler »

The Dark Side of Will wrote: ...the coefficient of dynamic friction is NOT high enough to give it this capacity. This means that when feeding the clutch for a dragstrip launch, if I get to the floor with the gas before the clutch is fully engaged, it WON'T engage and I have to back off and start over.
Are you certain it's not centrifugal force from the high RPM, and the pressure plate fingers being forced "over center" when the pedal is depressed, actually causing the clutch to not engage? The Centerforce is supposedly designed to prevent just that, but you never know...

Obviously, I'm not there. If the clutch actually hits, then goes up in smoke, then yeah. Nevermind.
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Post by Kohburn »

yes the best holding force for a clutch is one with dynamic friction high enough to overcome the peak torque output of the engine
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Post by Series8217 »

The Dark Side of Will wrote:Does the Muncie have a bigger MC? I heard somewhere that it does...
Nope. Both the early and late MCs had the same bore.
Also, the Muncie uses the same slave and arm as the Isuzu.
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Post by The Dark Side of Will »

Woops... I meant to ask if the Muncie uses a bigger slave, but if it uses the same slave as the Isuzu, then I guess not.

Ahh... I remember what was tickling my memory now... does anyone know the diameter of the later FWD slave for the internal throw out arm? I think wcapman used that on his car to reduce slave cylinder travel.
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Post by The Dark Side of Will »

BigRedDeckSpoiler wrote:Obviously, I'm not there. If the clutch actually hits, then goes up in smoke, then yeah. Nevermind.
The FWD CF does not have centrifugal assistance... there's not enough room in the bellhousing.

And yes, that's exactly what happens. If I screw up feeding the clutch and get to WOT before the clutch is fully engaged, the clutch goes up in smoke. It CAN NOT pull the engine back down.
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Re: Tilton Clutch

Post by The Dark Side of Will »

Series8217 wrote:
The Dark Side of Will wrote:Does anyone know the MC and various slave cylinder diameters right off?
Slave sizes:
Isuzu: 13/16"
Getrag: 15/16"

Master cylinder: 11/16"

You can also mix and match clutch arms to tweak the effort (http://realfierotech.com/phpBB/viewtopic.php?t=2986).
Areas:
MC: 0.371 sqin
Isuzu slave: 0.518 sqin
Getrag slave: 0.690 sqin

Area ratios:
Getrag slave: 1.86:1
Isuzu slave: 1.40:1
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Post by Mach10 »

Tilton... Wasn't that the one about the reporter with the cowlick, a small white dog, and an alcoholic sailor?

Sintered Iron disk... I never quite understood this one. Is it a particular iron alloy that can be used as a friction surface? Does it have bits embedded in it? I'd like to know how it works :)
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Post by The Dark Side of Will »

Sintered iron is iron powder heated enough to get soft and then squeezed into shape under high pressure. The particles are hot enough to get soft and squeeze each other into shape and not let go, but not hot enough to melt and fuse into a single sheet of iron.
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Post by Series8217 »

The Dark Side of Will wrote:
BigRedDeckSpoiler wrote:Obviously, I'm not there. If the clutch actually hits, then goes up in smoke, then yeah. Nevermind.
The FWD CF does not have centrifugal assistance... there's not enough room in the bellhousing.
Press your clutch pedal in and rev to 5-6k. You don't feel the pressure on your foot change? I sure do with my Spec Stage II..
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Post by Series8217 »

The Dark Side of Will wrote:Ahh... I remember what was tickling my memory now... does anyone know the diameter of the later FWD slave for the internal throw out arm? I think wcapman used that on his car to reduce slave cylinder travel.
Yeah, its 1 1/4". I'm not quite sure how you would bleed that one in a Fiero though. The FWD slaves don't have bleeders on them since its a straight shot to the master cylinder. You pump until the air bubbles rise to the MC reservoir. It's a very different design.. the slave has a molded plastic body, and the line has an o-ring and a pin. It "clips" in.
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Post by Mach10 »

The Dark Side of Will wrote:Sintered iron is iron powder heated enough to get soft and then squeezed into shape under high pressure. The particles are hot enough to get soft and squeeze each other into shape and not let go, but not hot enough to melt and fuse into a single sheet of iron.
Soo... Basically a disk of rough crystaline iron particles for use as the friction compound?

I thought they used a similar process for making high performance con-rods with very exacting and even grain structure.
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Post by The Dark Side of Will »

Mach10 wrote:
The Dark Side of Will wrote:Sintered iron is iron powder heated enough to get soft and then squeezed into shape under high pressure. The particles are hot enough to get soft and squeeze each other into shape and not let go, but not hot enough to melt and fuse into a single sheet of iron.
Soo... Basically a disk of rough crystaline iron particles for use as the friction compound?

I thought they used a similar process for making high performance con-rods with very exacting and even grain structure.
Powdered metal processes use higher temperatures to melt the surfaces of the particles and weld them together.
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Post by crzyone »

An on/off clutch with a flex plate that weighs less than a stock flywheel... Man that sounds awesome! Should rev like a racecar, but doesnt sound very streetable.

Cost wise what are you looking at? For me to buy an aluminum flywheel ($400) and a replacement spec 3 ($300) it sounds like this is a pretty cool option. Not to mention it will hold 600lb/ft :thumbleft:
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Re: Tilton Clutch

Post by The Dark Side of Will »

The Dark Side of Will wrote:
Series8217 wrote:
The Dark Side of Will wrote:Does anyone know the MC and various slave cylinder diameters right off?
Slave sizes:
Isuzu: 13/16"
Getrag: 15/16"

Master cylinder: 11/16"

You can also mix and match clutch arms to tweak the effort (http://realfierotech.com/phpBB/viewtopic.php?t=2986).
Areas:
MC: 0.371 sqin
Isuzu slave: 0.518 sqin
Getrag slave: 0.690 sqin

Area ratios:
Getrag slave: 1.86:1
Isuzu slave: 1.40:1
I'm limited to the Getrag throw out arm due to the Northstar water manifold.

The later slave has 1.227 sqin and area ratio of 3.31. I'll have to get back in touch with wcapman about how his slave setup works. I'm pretty sure he used that cylinder. I'll look into it.

The center distance from the 282 throw out shaft to the input shaft is 1.783.
The center distance from the throw out shaft to the throw out arm cup is 1.715.
That's very close, but slave cylinder load will be 1.04 * throw out bearing load, or 520#.
This will result in 280# of MC load with the Fiero Getrag slave and 157# of MC load with the later Getrag slave.
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Post by The Dark Side of Will »

As near as I can measure with the pedal in the car, the C-C on the pedal pivot and MC banjo pivot is 2.5". The pedal pivot to pedal pad distance is about 10" for a 4:1 pedal ratio.

With the Fiero Getrag MC this is a 70# clutch pedal (and I thought an ACT 2600 was bad... OUCH!) and with the later Getrag slave is would be a 40# clutch pedal. This is still a bit stiffer than Tilton's recommended 18:1 ratio which would put the clutch pedal at 30# or so. Basically I need to figure out the appropriate slave cylinder (1 1/4 is very close) and come up with the bracketry and pushrod to install it.


I haven't asked about cost yet. I hear it's about $1K to set up a new QuarterMaster, but that includes paying for custom machining of the button flywheel. I'm checking ebay to see if anyone has that particular pressure plate, as that would be the most expensive part of the deal.
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Post by Series8217 »

Just a note.. I used the Isuzu slave and FWD Getrag arm for awhile. It was driveable but took some time to get used to. I wouldn't want a heavier and quicker pedal than that. I don't have time to do the calculations at the moment but you may want to just to compare the effort you might have to deal with to what I consider the limit for "streetable" effort..
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