Hi Folks,
I'm desperate for a solution after struggling with this for over a month now.
I recently swapped out my stock ls1 clutch for a Mantic twin plate organic with steel flywheel.
The installation went fine and included a new slave that came with the kit and I installed a new pilot bearing.
I can start the car and select any gear I like including reverse with no problem and charge through the gears fine.
Problem is that under certain circumstances the clutch appears to not disengage enough to allow shifting to neutral without having to forcefully bang it out of gear. Most often this happens in low speed parking situations in 1st or reverse gear or when coasting down to low speed in any gear then depressing the clutch and having to smack it out of gear.
The baffling thing is that I have no problem then selecting any gear and the clutch start of engagement point is at about 1/3 of pedal travel.
I have about 300 miles on this clutch at present and have done the following to try to remedy the problem.
>new master cylinder ( bench bled to eliminate bubbles I trapped at top of cylinder)
>new braided stainless hose to replace the rubber original ( to minimise possible heat expansion ) and added heat shield to protect from header heat
>endless bleeding sessions using all different methods including lastly the purchase of a pressure bleeding tool. All methods have resulted in an acceptable clutch pedal feel.
Nothing I have tried has made any difference at all to this problem. Contacting Mantic has only led to the advise that " you've definitely got air or definitely got heat affecting the fluid" .
The only thing I haven't done is pull the box for inspection but would like some opinions on what could be wrong that I'm missing.
I had no problems with the stock clutch performance, only when drag racing the clutch pedal would hit the floor after 3rd gear once my mods went past 400 rear wheel hp. There was however 2 loose pressure plate to flywheel bolts found during disassembly.

 

Let me guess, your new Master Cylinder is OEM?

 

Correct. But the original worked fine on the ls1 clutch and a Tick isn't an option for me . My car is an Aussie RHD Monaro ( same as 04 gto) and tick masters won't fit.
I just don't understand why it will disengage smashing through the gears but wont come out of gear at low speeds.
I can start the car, push the clutch in and select any gear easily. I've held it in gear with the clutch depressed waiting for it to start to engage on its own due to fluid bleeding back to the master but that doesn't happen and when I lift the clutch there's about 1/3 travel before start of engagement and revs begin to drop.
I'm not 100% sure about this but even after I have to smack it out of gear with the clutch depressed I can then ease it into any other gear no problem. I'll check on that.
I don' t think it can be a gearbox problem because the clutch is definitely still slightly engaged as taking the foot off the brake the car still wants to drive

 

I know tick makes a 3/4 unit as well, I know you said it won't fit, but they make GTO specific ones as well. Might be worth a shot.

 

I've already contacted them previously when thinking about solving the pedal to the floor issue with stock clutch. They said you may be able to adapt it to fit but they didn't know. Looking at photos it won't fit. Our mc's are right behind the head. No room for the adaptor and outlet pipe at the end of the cylinder. Regardless, aussie gm cars seem to operate fine normally with the oem mc. Maybe different to the gto version?

 

I just jacked the rear up and started her up with the intention of watching the wheels to see where the initial take up point is. It's lower than I thought and will get a measure on it when I get a chance but the interesting thing is on start up with the clutch out and trans in neutral the back wheels spin for a few seconds then stop but still spin easily with a slight push. Push them backwards and they'll start rotating forwards after a second. What's going on there? I've never had reason to do this before so don't know if it's normal or some contributing factor to my problem.

 

I just measured the initial engagement height from fully depressed pedal. It's 40mm or just over 1 1/2" . Full pedal travel is 170mm or 6 3/4"
Is that too low?

 

Two possibilities. Is your slave a GM slave and not aftermarket? The factory GM slave is best and has the most travel. Second, did you measure for a shim? Non stock clutches sometimes require a shim behind the slave to take up the gap between the slave and plate.

A needed but missing shim will move the engagement point lower in the pedal stroke. Yes I think 40mm is low. 80 would be closer - halfway up or more is about right

 

I did compare the two but can't remember what the outcome was now. I'll check with the manufacturer.
Their specs are 4-6mm from fully recessed. Mine was 6mm so on the long side of tolerance.
I've come to believe through all this having mocked up a complete working master and slave with my old parts that this distance doesn't matter on the long side so long as the slave isn't pushed past its built in stop and mine certainly won't. Stock mc has 32 mm stroke and this moves the slave only 12mm - it's fixed by the swept volume of the master. The slave withdraws to the contact point as you lift the pedal then the master is pulled back to its full limit by the pedal return spring. Provided the slave seal isnt sucked back to the back of the slave you get full stroke of 12mm every time. Using a pressure bleeder as I have done ensures the seal is fully forward in the slave bore.
I understand if the gap is too short that you may get slippage as the clutch wears and diaphram moves closer.
I'm happy to be corrected if wrong about any of this. It took me a lot of thinking and observation of what actualy happened on the bench to dismiss some of the things I accepted as fact before

 

That is some very good information. The stock GM slave will travel 13mm before the seals blow. You are correct if the gap is too short you can get slippage, but if the gap is too large, you can easily get incomplete disengagement coupled with low pedal engagement. So, am I reading that your gap is 6mm? If so, I would definitely shorten that gap to .100"-.125", say 2.5-3mm. You aren't going to get that much in thermal expansion unless the parts get close to 800 degrees.

 

I measured the master cylinder push rod travel from inside the car under the dash at full pedal travel.
It's only about 26-27mm, that's 5-6mm short of max potential of 32mm and equates about 2mm less slave travel than possible.
I'm now looking at modifying the stock push rod to adjustable length to move the pedal further from the floor.
There's no other adjustability for this in my car. Everything is fixed.

 

Boy, it's too bad the tick isn't an option. That 7/8" bore would move more fluid and get that last 2mm of travel

 

Well, I tried the adjustable push rod route. Even with full travel of the slave there was no difference.
So having exhausted everything I could think of I took it to the guy that I bought the clutch from. He drove it and conceded that there was a problem that he'd never seen before.
During discussions on my installation he asked me if I greased the input shaft.
Well, I didn't. I cleaned with a toothbrush with thinners and installed the clutch dry having googled the subject and found many adamant that no grease should be applied.
Well I can tell you that heeding that advice cost me 2 months of this occupying my every waking thought.
Today i pulled the box, lubed the input shaft splines with assembly lube and problem is solved :-)

 

Sorry to hear about your headaches, but glad you've solved the issue and can get some enjoyment from the car at least. Tt's obviously not one of our clutches, but lubricating the input shaft spline is on our Installation Checklist, which should be a good reference for installing any clutch. (This one is officially for the DF017010 Dual Friction LS1 clutch, but it's a general document):

http://www.centerforce.com/images/st...0Checklist.pdf

 

Mantic really need to lift their game as far as instructions and after sales service or tech advice go here in Australia. All I ever got from them from a number of calls was " it's definately air in your system" or "it's definately exhaust heat related expanding the fluid making the clutch slip".
I guess they get used to the same old problems but didn't seem to want to listen to what I was telling them about my particular issue.
Now that I have this one working right hopefully I'll be happy to say that it's an excellent piece of gear.
Next test will be at the track to see if I can actually pull 3rd or 4th gear without the pedal hitting the floor.

 

So, basically, the disk was binding a bit on the input shaft, and greasing it freed it up?

 

That's right.

 

lubricating the spline, sparingly, is a often over looked step in new clutch install.

some use a graphite spray lube or high temp grease (sparingly)

 

That master size can also cause
considerable damage.

 

Great advice. Very few look at this area of the install.