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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Post by The Dark Side of Will »

Since the Isuzu slave is smaller and the Getrag arm is shorter, you must have had a VERY fast clutch on your hands. That would not be acceptable on this clutch because it would probably give me >100# of pedal load (aside from the fact that I can't use the Isuzu arm with the Northstar water manifold).

Basically, I think that the slave is the easiest part of the system to change, so I'm going to see what I can change my slave to in order to get the effort down to something reasonable (70# is not reasonable for a street clutch).

Since 0.250 of throw out travel can damage the clutch, I'd like to limit my travel to 0.200-0.225 or so. I need to take a look at how far the pedal moves and go from there.

500# * 0.200" = 100 inlbs of work to disengage the clutch. Getting that streetable shouldn't be hard.
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Series8217
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Post by Series8217 »

The Dark Side of Will wrote:Since the Isuzu slave is smaller and the Getrag arm is shorter, you must have had a VERY fast clutch on your hands. That would not be acceptable on this clutch because it would probably give me >100# of pedal load (aside from the fact that I can't use the Isuzu arm).
Yeah, it was stupid fast and hard. FWD Getrag arm is about half the length of the Fiero Getrag arm. Anyway, I just wanted to make the point that my real world experience indicates that if your pedal load was less than or equal to what I got with my old setup, then you'd be fine..
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Post by The Dark Side of Will »

With my tape measure butted against the firewall so it passed by the vertical center of the pedal pad at full depression and full extension, the pedal went from a little more than 2 to a little less than 9. I'll call this 7" of pedal travel. With 0.200 of TOB travel being my goal, this is an overal ratio fo 35:1 and should result in about 15# of pedal load. This is VERY streetable. The longer pedal throw will spread the engagement out over a longer pedal travel and result in greater modulability.

Ok, in order to get this 35:1 overall with 4:1 pedal and 0.96:1 throw out ratio, I'll need a 9.1:1 hydraulic ratio. This will require a 2.07" diameter slave cylinder.
That's a big slave, folks. I wonder if anyone actually has a 2 1/16" slave cylinder, or if there's a generic hydraulic cylinder with brake fluid tolerant seals that I can pirate from something.
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Post by The Dark Side of Will »

Hehe... Idea...

2 1/16 is well into the range of brake caliper pistons. I can find a caliper with a piston the right size, acquire one and modify it to suit or cut down the piston and machine a new housing.
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Post by Series8217 »

2 1/16" is hayyuugeee.
I would look for a smaller master cylinder and maybe look into increasing the length of the throwout shaft arm to the max that will fit.
Doesn't sealing become a problem with large bores and extremely low line pressures (like in the clutch system)? Those brake piston seals are encountering many orders of magnitude greater pressure..
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Post by The Dark Side of Will »

Well... 1 order of magnitude. I'll be seeing about 160 psi in the clutch circuit with the 2 1/16" slave.

I don't see why a caliper piston seal should leak at low pressure. Your brakes don't leak when you're crawling around a parking lot, do they? That's considerably less than 1/10 of peak pedal force, and thus less than 1/10 of peak line pressure.
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Post by The Dark Side of Will »

Oh yeah, cost.
The pressure plate and floater disks as a package MSRP for $495.
The cerametallic disks with 25mm x 14 spline MSRP for $260.
I'll need a Tilton TOB, but that will come in <$50 for a mechanical.

As I said, I'm trying to find the right PP on ebay. If I can pick one up there for $100, I'll have this done in a heart beat.
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Post by The Dark Side of Will »

I had a dozen ideas last night about how to make the slave, so I don't think that will be hard.

I'm worried about the Getrag throw out fingers with 500# of throw out load. Has anyone had any experience with high load clutches and throw out mechanism problems?

Basically, do I have to reengineer the throw out fingers, or will the stock setup be fine?
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Post by Series8217 »

The Dark Side of Will wrote:I had a dozen ideas last night about how to make the slave, so I don't think that will be hard.

I'm worried about the Getrag throw out fingers with 500# of throw out load. Has anyone had any experience with high load clutches and throw out mechanism problems?

Basically, do I have to reengineer the throw out fingers, or will the stock setup be fine?
You might want to PM emod19 in case he doesn't see this thread. He's selling a quartermaster 2 disk race clutch setup that appears to be used so I imagine he's used it with the Fiero transmission...
http://realfierotech.com/phpBB/viewtopic.php?t=3283
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Post by Series8217 »

Will, I was browsing through the Coleman Racing catalog and noticed they sell master cylinders in a variety of diameters. The dedicated clutch MCs only go down to 3/4" but they have brake MCs for the same price that go down to 5/8".. which gives an area of .307 sq in. That's a 2.25:1 ratio with the Fiero Getrag slave.
It might be something to look into if you are going to replace your MC anyway while you're doing this. These are cheaper than the GM cylinders..
http://www.colemanracing.com/catalog/pr ... ts_id=7719
EDIT: That's a Tilton part, by the way. They have the brand in their print catalog but not online.
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Post by The Dark Side of Will »

Thanks for the info.

I'm fine with keeping the Fiero MC. It'll be easier to do that and build a new slave from scratch than it will be to adapt a Tilton master AND and new slave.

I need a 9:1 hydraulic ratio to get the travel up and the effort down to the levels I'd like.

Really... the slave won't be that hard to make.
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Post by The Dark Side of Will »

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Post by The Dark Side of Will »

Spoke with a QM rep today. The QM blue spring, which is what CK and Tina both used, has 575# of release load, which is more than the Tilton spring that the Tilton engineer recommended has. So I know the mechanical throw out mechanism is safe to 575# of throw out load, which means it's safe to 500# of throw out load.

Spoke with the Tilton rep again. He said that I'll want to design the throw out mechanism to stroke the pressure plate the full 0.250. The reason for this is that as the clutch is (ab)used and the disks get hot and warp, it will take more stroke to release the clutch, so the throw out mechanism needs to be able to provide the full safe stroke of the pressure plate.

In upping my throw from 0.200 to 0.250, I go from 35:1 overall ratio to a 28:1 overall ratio and from 15# pedal to 18# pedal... probably still lighter than stock. My slave cylinder diameter requirement drops from 2.07 to 1.800. I may go to 1.875 as a convenient size and to account for flex in the system and for other factors like the initial take-up of the master cylinder--the initial 1/4" or so of pedal travel in which the master moves no fluid.
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Post by Series8217 »

Will, just to save you some leg work when making your new slave here are the dimensions of the Getrag slave so you can design yours to be a direct replacement:
http://www.fiero.com/forum/Forum2/HTML/073274.html
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Post by The Dark Side of Will »

I'll most likely redesign the bracket to match the new slave. I can have it laser'd out of 1/2" plate easily enough. I also wouldn't be able to go as big as I wanted within the confines of the stock bracket.

Judging by this thread
http://www.realfierotech.com/viewtopic.php?p=47685

Maybe I should make a billet steel replacement for the stock fabbed steel slave...
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Post by Series8217 »

The Dark Side of Will wrote:Judging by this thread
http://www.realfierotech.com/viewtopic.php?p=47685

Maybe I should make a billet steel replacement for the stock fabbed steel slave...
I would certainly buy it if it didn't cost significantly more than the Coleman slave but bolted up to the factory Fiero stuff. The Coleman Racing slaves would require another bracket and a line adapter. It actually might be easier to just build the adapter for a Coleman slave. Either one would be a viable solution..
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Post by Shaun41178(2) »

You can't use a Hyd TO bearing with the Tilton setup?
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Post by The Dark Side of Will »

I perhaps can, but right now I'd rather use the Fiero throw out mechanism. KISS.

I have some of the parts to build the nicest 282 ever built, and one of those is a later bellhousing for hydraulic TOB. I'll switch to hyd TOB when I get that transmission together.

It's MUCH easier to make a slave cylinder than a hyd TOB, as well. I need to do some research and see if I can get the right overall ratio with hyd TOB.

I'd still need a 7:1 hyd ratio, which implies a pretty large hydraulic part of hyd TOB.
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Post by Shaun41178(2) »

ok yea I knew the later model 282's came with a Hyd TOB so I thought you could use one of those. Seems simpler then trying to find a huge ass slave cylinder, fab up a bracket, and a pushrod, then test it all out and hope it works the first time. But thats just me. Also when doing that, you gain some clearence room for other things with no slave hanging out.
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Post by The Dark Side of Will »

Hehe... I'm not finding a big slave... I'm FABBING one...

I understand what you're saying... but the slave & mechanical throw out mechanism is what's good right now.

As I said, getting the hyd ratio right with the hyd TOB will be a trick.
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