Dual Disk Clutches

[ericjon262]

Not sure I emphasized it enough previously, but the Northstar build shown is *very lucky* because the stock flexplate has a large enough flat spot to just stack the flywheel on top of it. I have not seen another stock flexplate with this feature.

The F23 has a deeper bellhousing than the 282 and may be able to accommodate a spacer between the flywheel and flexplate. The F40 has a much deeper bellhousing and can definitely accommodate such a spacer. The F40 may even be able to accommodate a dual organic disk clutch.

The LX9 flexplate is pretty flat, I'll have to get some mockup parts together and see what I can make fit.

That garage less guy on YouTube has a twin disk setup from spec that I think is for an f23 in his 3800 swap. Message him

Thats an option, but I imagine it will be as much or more than the PTT parts, and I'm not a huge fan of dealing with Spec, most of my interactions with them have been way more difficult than necessary.

"Hey, I want this clutch"

"OK, we'll ship it next week"

*3 weeks later*

"Where's my clutch"

"what clutch"

[The Dark Side of Will]

Thats an option, but I imagine it will be as much or more than the PTT parts, and I'm not a huge fan of dealing with Spec, most of my interactions with them have been way more difficult than necessary.

"Hey, I want this clutch"

"OK, we'll ship it next week"

*3 weeks later*

"Where's my clutch"

"what clutch"

There is no "stock type" clutch that makes the clutch of a high powered Fiero "not a problem". The CenterFarce that Rcheee recommends was marginal with my 260RWTQ stock Northstar. The Spec St3 that could handle the torque was shit to daily drive. The Spec St3+ that gets good reviews has a full face disk that slows shifting. The vendors contribute to that generally by being imbeciles that either can't deliver the product promised or can't deliver the product WHEN promised.

That's why I went dual disk. We'll see how it turns out.

[ericjon262]

There is no "stock type" clutch that makes the clutch of a high powered Fiero "not a problem". The CenterFarce that Rcheee recommends was marginal with my 260RWTQ stock Northstar. The Spec St3 that could handle the torque was shit to daily drive. The Spec St3+ that gets good reviews has a full face disk that slows shifting. The vendors contribute to that generally by being imbeciles that either can't deliver the product promised or can't deliver the product WHEN promised.

That's why I went dual disk. We'll see how it turns out.

yeah, and the market doesn't exactly support R&D very well either, most Fiero owners won't spend the money for quality parts, and the corresponding FWD market is even worse. realistically, we're working on cars, and parts, that nobody cares about, because there's minimal money in them, or they just aren't nearly as good as they should be.

[ericjon262]

Yes, the centerbore in that unit is 1", while the centerbore in the V6 flywheel is 1.500. There's plenty of room for the V6's relatively small bolt circle.

a quick measurement with a machinist's scale on an LX9 flexplate suggests the centerbore is 1.25" not that your assessment is wrong, as 1.25" is still bigger than 1". Some preliminary measurements look promising for stacking a button flywheel on a LX9 flexplate, I need to pick up another F23 for mockup/measurements. If the F23 bellhousing is deep enough, I may be able to sneak a 3rd disc in, which would make the assembly much more durable, and slightly more forgiving if I do something stupid.

the biggest issue I currently see, is the hydraulics, I'll need to ensure that I get the hydraulics set so I have usable pedal travel, and don't over travel the pressure plate into the discs. The F23 uses a HTOB, which has an integral input shaft seal, making swapping to a different TOB more difficult. and will require some clever design ideas to either swap to a different HTOB, swapping to a smaller slave, or some other shenanigans. I do have at least one junk F23 HTOB I can take apart and use for R&D. I'll carefully dissect it and see how much area it has, and then can either develop a TOB cap to match the shape needed by the new pressure plate, or develop a means to replace the entire bearing with something more suited to the application. Ideally, I would prefer to use the stock HTOB, but I suspect this won't be easy to do. using a stock HTOB with a adapter on the end would keep replacement parts easiest, as long as the adapter is removable. it would also mean my existing clutch line could stay without any external changes. the determining factors will be total stack height, and master cylinder options. I'm not afraid to get freaky with the master cylinder if need be, but I would prefer it be some kind of off the shelf part.

I have a flywheel on the way, I was going to hold off on ordering one for a bit longer, but it just made sense to press forward towards something permanent. I'll need to find a drawing, or measure the crankshaft pattern to cut into the new flywheel. first thing I'll do when it gets here is lay it on my flexplate and see how it stacks up. if that looks good, I'll drill the pattern, then bolt it to a crank and see exactly what that gets me for a final stack height of the "flyflex"

[The Dark Side of Will]

The Northstar pilot is 1.108" or so... not a lot of extra material in the flywheel to deal with that.
Why TF couldn't GM have made ONE bellhousing package for FWD cars and left it alone? They've used the same 142T starter ring gear since 1980, but nothing else has stayed the same inside a FWD bellhousing.

I conceptualized a "hydraulic ratio adjuster" that would work with any Fiero transmission to adjust the final throw out distance/force to work with the dual disk clutch. I haven't done any design work yet.
I don't think a MC small enough to work with the stock HTOBs to reduce travel down to what the dual disk clutch can handle is practicable. The bore would be so small that the risk of pushrod angularity hitting the sides of the bore would be pretty high.

[ericjon262]

yeah, it's an oddball thing for sure, there's at least 3 different crankshaft bolt patterns, for no other reason than just because. its also odd that the N* bellhousing is just barely different than the Metric pattern, why make them so similar when you could just make them the same.

as for the hydraulics, I haven't explored them much yet, a step down setup sounds like a PITA to bleed, and I imagine it would make bleeding the HTOB or slave even more difficult. If there's one out there, a smaller master, with the pushrod moved higher on the pivot, or the pivot moved down, could significantly reduce the fluid displacement as well.

[The Dark Side of Will]

The Northstar bellhousing pattern has the one bolt different because the "barrel" on the 4T80E trans is larger than what the FWD bellhousing was originally designed for.

I think I have something about small bore MCs earlier in this thread... Without going back to check, IIRC, Wilwood has a smaller than stock MC, but it doesn't have enough travel to do this job.

[ericjon262]

PTT flywheel fits ok, on the LX9 flywheel



This is primarily because the LX9 flexplate has a reinforcement plate on it that spaces the flywheel away from the flexplate. part number 12579453



the PTT flywheel can't stack on a LA1 3400 flywheel



it doesn't have the reinforcing plate. so it doesn't sit flat.

the flexplate is only part of the problem though, it also needs a means to center on the crankshaft. The reinforcing plate on the LX9 flexplate pushes the flywheel out far enough to only contact the flexplate at the mating flange, but it also puts the entire flywheel beyond the register on the end of the crank. so I need to find a way to keep center the flywheel. the fastest, simplest solution is to make a centering ring, much like the hub centric ring used on a wheel, the issue with that, is that can lead to stacked tolerances and sub par alignment.

one of the other ideas was to machine the flexplate side of the flywheel down, but leave a ridge at the ID to register on the crankshaft. the ridge could fit inside the ID of the reinforcing plate, and around the OD of the crankshaft register. I'm not super fond of this idea, unless I could talk PTT into making me a blank flywheel with a thicker mating flange. I'm going to take some more accurate measurements and call to try and talk to one of their engineers and see what they say about that plan.

I'm OK with modification of both the flexplate, and to a degree, the flywheel, the flexplate is a brutally simple part, that doesn't really wear out, the flywheel, requires machine work to fit the engine either way. I do not want to modify a crankshaft in any way to fit this. at this point, a centric ring looks preferred, the cut required to make the reverse register on the flywheel would be pretty meaty, to go the full depth of the reinforcement plate, the cut would be about ~2.5mm, on a flange that's only ~7.25mm to begin with.

anyone have another idea?

also, fwiw, PTT flywheel, resting on a LX9 flexplate, has a stack height of about 1.05"

this information should be pertinent to any internal balance 60V6, but my information thus far is based on an LX9 3500.

[The Dark Side of Will]

anyone have another idea?

I'm kind of thinking about updating the PTT flywheel design so that a flexplate could be bolted to the engine side of the clutch mounting ears/flange using the clutch mounting bolts. If nothing else, I could get them to do a run of 5-10 for me. That combo would work in ANY GM FWD platform that uses the 142 tooth ring gear, just by drilling the right bolt circle and boring the right pilot in the flywheel... and it would also do all the same things as their current blank flywheel does.