I received the following advice from an engine builder:


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That said, be very careful to check your clutch adjustment. We do not want to over center the pressure plate and it fails. This happens when the pressure plate spring is depressed and it gets "sucked in". This moves it too far and the allows the heavy face that applies pressure to the disc when the clutch is released to go off center. At about 2.2lbs., this will cause the clutch to blow up.


How do we adjust a "self adjusting" hydraulic clutch? We want to limit the travel of the t/o bearing so we disengage the clutch as little as possible but still get a good clean shift.


We do this by limiting the travel of the clutch master piston. You have 2 options, #1 install an adjustable stop on the floor to limit the clutch pedal travel or #2 Add free play to the clutch pedal push rod. This give you more "slack" at the top of the pedal travel, but reduces the total travel of the clutch master piston so the clutch travels less.


The stock free play is about 1/16-1/8". I would try about 1/4" and see if you feel a difference in the shifting. If no difference, you should be good. Adjusting the travel is easy. If you find the push rod attached to the clutch pedal you will see the jam nut on the push rod itself. Loosen this up and turn the rod. The more the pedal moves before the rod touches the piston the more free play. Remember to get a feel for how much travel you start with so you can add about 1/8" to 1/4" more.

Our goal is the least travel without making it hard to shift.
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Just as a personal preference, and to hopefully be easier on synchros, I have my clutch pedal adjusted to get as much throw as possible (clutch grabs higher off the floor). But that is contrary to the advice above.


I'm not sure I buy it, though. The pressure plate bolts to the flywheel, so it can't move off-center. and the clutch disc slides on the trans input shaft. it sounds like they're suggesting the ring on the inside of the pressure plate can go off-center, but not sure if that's realistic...?

 

That depends which clutch you have. If you have an OE/OE-style then you typically adjust to the factory service manual clutch pedal measurement specifications unless they tell you otherwise in the instructions. If you have a racing style 7.25” or 5.5” mini clutch this becomes much more critical and they usually tell you to either have an adjustable stop added if needed and adjust using that style or similar method as you described. Typically that becomes much more critical on the smaller or flat racing style pressure plates.

 

Just to give you idea, this is the recommended pedal throw for the Tilton 7.25” (assumes 3/4” MC bore) and 5.5” (assumes 5/8” MC bore, same as factory RX8 MC bore) carbon clutch; very short. They give you a procedure for setting adjustment for anything outside this range.

 

bumping this, anyone know or heard of a hydraulic release bearing setup for the OE RX8 transmission input nose? I seem to recall that Eric Meyer claimed to have one, but am not sure if it was a purely custom deal or not.

 

got a lead on one made for the NB Miata AZ6 6-spd trans, looking into that ....

 

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I think I saw that before when someone said they had run one on their pro series race car. How much do those go for?

 

very reasonable, $380 for what you see. A 7.25” or larger clutch will likely require a larger (3/4”) master cylinder. While the release bearing is a round-face QM part, it’s 44mm dia. contact. A 38mm is generally preferred for a 5.5” clutch, but it’ll work though with slightly higher pedal effort. The hydraulic release usually reduces pedal effort some on it’s own. The pedal was light already with OE setup.

This is for an AZ6 Series 1 6-speed trans. I’m going to size it up to see if it will fit an S2 6-spd, but am doubtful. I know a race shop is working on one for the S2, but not sure how far out that may be regarding availability. I suspect it may cost more.

I’ll have a new race release bearing and Feed larger ID slave cylinder FS soon. Another “why didn’t I just use my head and do it this way in the first place“ scenario.

I want to put a dry-break coupler on the clutch line so that hydraulic fluid isn’t running all over the place when the transmission comes out or re-bled when it goes back together, and a good mating pair (Staubli) costs almost as much as the release setup, that’s crazy.

 

any other advantages of hydraulic TOB over traditional setup?

 

I'm hoping it will lessen the amount of clutch stop length needed, which then translates into finer pedal control to lessen the on/off affect some.

That's why I had purchased the Feed larger ID slave cylinder, but this now replaces that..

So I did find a -3AN Titanium dry-break connector pair on Speedway Motors for $80. They also have an aluminum one for same price and both are rated for brake fluid contact, but they look to have been made in WuhooFluLand. I'm wondering how long it will hold up, but will likely choose the Ti version and hope that it holds up long term.

 

i see, you're looking for longer clutch pedal travel for better clutch modulation. wow $80 is cheap for dry break fittings. they would be great for remote reservoir shocks.

 

there are other benefits. It’s already a hydraulic system, this eliminates the additional mechanical side of the OE system along with the wear/monkey motion associated with it. A number of brands/vehicles come with this standard from the factory now.