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1G Clutch disengagement issues/ Recommended Clutch

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Anfurnyy

Supporting Member
678
799
Jul 4, 2020
Rapid City, South_Dakota
I know there's about 5 thousand posts about this but im kind of at my wits end and out of options and every post i read is pretty much all conflicting information. Ive read just about everything can find, and watched all the videos if Kurts (bastarddsm) explanations and recommendations, etc and I cannot get this setup to disengage completely to shift at high rpms without grinding. Im shifting at around 9k rpm, car is making PROBABLY 750+whp, and 550+ft/lbs

I have reached out to Tim Zimmer through his site on recommendations, and waiting on reply.

Clutch setup CURRENTLY is:
ACT 2900
ACT Solid Hub Disk
ACT Streetlite flywheel
Comp Clutch forged clutch fork
New OEM TOB and clip
Pivot ball is shimmed with 2 washers (i think about 3 mm?)

2g OEM slave cylinder (with speed bleeder), .812"
White Shed Speed Wilwood Master cylinder .700" bore
Welded Pedal assembly
OEM Clutch Hardline, with shorter braided steel slave line
White Shed Speed Billet Shifter mounts

The car has been through:
2 1g OEM slaves
1 2g OEM slave (currently installed)
2 OEM Master cylinders
1 Wildwood master cylinder (currently installed)
1 OEM hard-line (currently installed)
1 OEM braided steel from Master to Slave
1 act 6 puck sprung (RIP)
1 act 6 puck solid disk (RIP)
Countless bleeding sessions, manual 2 person, vacuum bled, 2 sets of speed bleeders, adjusted the master rod every way to Sunday.

Both the Sprung and Solid Hub disks have yeeted all the material off the disks, Pressure plate and flywheel look damn near perfect.
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I have NOT:
Pulled pressure plate and test disengagement on a press with feeler gauges to measure for disengagement

ANY ideas on anything else that could be the problem or what else to try Besides just replacing the pressure plate? Is there another single disk setup that seems to work better for people at this level?

I have a QM 8 Leg Street setup that I about to just jump ship to to get around all these disengagement issues but also dont because i dont want to hurt the stock gearset faster.
 
The slave cylinder likes to trap an air bubble that doesn't come out easily. Bleed it out like normal from the pedal, as the bleeder is open push the slave all the way in by hand, hold it and then close the bleeder.

Also your shim sounds like too much unless your flywheel has been machined a few times and/or the fork/pivot ball are worn.

Can you snap a picture of where the clutch fork sits in the bellhousing cutout? Also, if you have the trans removed, a pic of the pressure plate with it torqued to the flywheel and the angle of the PP fingers (concave / flat / convex).

Edit - do you have all the trans bolts tight including the crankwalk bolt (the one that goes from the block side to the trans side)?
 
The slave cylinder likes to trap an air bubble that doesn't come out easily. Bleed it out like normal from the pedal, as the bleeder is open push the slave all the way in by hand, hold it and then close the bleeder.

Also your shim sounds like too much unless your flywheel has been machined a few times and/or the fork/pivot ball are worn.

Can you snap a picture of where the clutch fork sits in the bellhousing cutout? Also, if you have the trans removed, a pic of the pressure plate with it torqued to the flywheel and the angle of the PP fingers (concave / flat / convex).
I'll try that bleed method next time the trans is in the car.
Flywheel has never been turned. Both ball and fork are new. The whole clutch setup has less than probably 400 miles on it. Clutch, clutch fork, pressure plate flywheel all went in at the same time. Now, if I remove those shims I would actually LOSE travel,
right?

Terrible picture but this is where it was sitting a few days ago. It is very slightly to the LEFT of the middle of the fork window.
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This is how the fingers sat with the fresh, solid hub disk after the pressure plate was torqued down.
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Edit - do you have all the trans bolts tight including the crankwalk bolt (the one that goes from the block side to the trans side)?
Yes, all of them Always blue locktited as well.

In total, 2 14mm on top, 1 long 14mm on the front by the slave, little 10mm right next to the turbo, the flywheel inspection cover bolts and the rear 12mm by the motor mount, right?
 
I'll try that bleed method next time the trans is in the car.
Flywheel has never been turned. Both ball and fork are new. The whole clutch setup has less than probably 400 miles on it. Clutch, clutch fork, pressure plate flywheel all went in at the same time. Now, if I remove those shims I would actually LOSE travel,
right?

Terrible picture but this is where it was sitting a few days ago. It is very slightly to the LEFT of the middle of the fork window.
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This is how the fingers sat with the fresh, solid hub disk after the pressure plate was torqued down.
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Your clutch fingers look like mine. I am extremely curious what your fix ends up being. Does it fail the clutch drag test? Clutch in, flat surface, rev to 7k?


I'm subbing to the thread so I can follow/steal advice and fixes.
 
Your clutch fingers look like mine. I am extremely curious what your fix ends up being. Does it fail the clutch drag test? Clutch in, flat surface, rev to 7k?


I'm subbing to the thread so I can follow/steal advice and fixes.
Yeah Everytime I try it it starts failing around 7k. I'll be honestly I didn't do the drag test after adjusting the master a few days ago but trying to shift at 9k with and without NLTS it clunks/grinds into gear.
 
Yeah Everytime I try it it starts failing around 7k. I'll be honestly I didn't do the drag test after adjusting the master a few days ago but trying to shift at 9k with and without NLTS it clunks/grinds into gear.


I know it's easier said than done, but just for giggles have you measured step height of the flywheel? Paul Volk and a few others have all had issues with new ACT Flywheels being out of spec and causing issues.

I can't say for certain mine is stepped incorrectly, but if I get the new(pre-checked and verified) flywheel from Tim Z and it fixes my issue, I'll add myself to that list.
 
I know it's easier said than done, but just for giggles have you measured step height of the flywheel? Paul Volk and a few others have all had issues with new ACT Flywheels being out of spec and causing issues.

I can't say for certain mine is stepped incorrectly, but if I get the new(pre-checked and verified) flywheel from Tim Z and it fixes my issue, I'll add myself to that list.
I haven't but I will. I'm not sure how crazy it needs to be checked though. Do I need to bust out the dial gauge or are calipers sufficient?
 
That 8 leg twin will shift like butter at 9k, or mine was. Just adding to the thread not suggesting.
 
I'll try that bleed method next time the trans is in the car.
Flywheel has never been turned. Both ball and fork are new. The whole clutch setup has less than probably 400 miles on it. Clutch, clutch fork, pressure plate flywheel all went in at the same time. Now, if I remove those shims I would actually LOSE travel, right?
Terrible picture but this is where it was sitting a few days ago. It is very slightly to the LEFT of the middle of the fork window.
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This is how the fingers sat with the fresh, solid hub disk after the pressure plate was torqued down.
You must be logged in to view this image or video.
Yes, by removing the shims your fork would sit more to the passenger side in your pic, so the slave would be further extended at rest. Not exactly the position you need. IMO your fork looks pretty good like that (because it's shimmed). The bigger question is why you need a shim. If everything is new from the clutch fork to the flywheel, and the trans sits tight against the block without flex, all the measurements *should* be within OEM spec without a shim. What's not in spec? Biggest variable is the FW step, and that jives with the pic that shows how flat your PP fingers sit. Beyond that, the thickness of the disc could be another culprit or even the design of the PP. That's not to take into account a warped PP or disc.

I found this post from JackM to be pretty informative:

I really wish I could see an entire thread of pics of multiple people's clutch, where the fingers sit after PP torqued, and if they had disengagement issues. I always forget about taking pics of my stuff, but IIRC the fingers always pointed outward.
 
The 2900 is tough to make work but it does. Log your up shift times just use the upper pedal switch. I've seen 280ms on a 2900 with a solid hub street disc at 9500RPM and a beat up old trans.

The ACT discs are very soft and the chunk out like that if you don't have good release and you try to slip them with your foot. They are soft but they are the best friction material in the regard that they have VERY high friction, and they keep it. They do not get glazed easy like all the other "ceramic/feramic/ranobuzzwordoftheweek" types.

My car made over 550ft*lbs on the engine dyno and a 2100 and act puck disc holds it just fine. Even with 75% missing from all the pucks.

If you keep the act discs plan on a freshy every race weekend. Sucks, but you are trying to put a lot of power through a small clutch this is the way it goes.

A street disc will last longer but not hold as much as it puts more heat into the pressure plate/flywheel - it's hard on them.

A qm twin might work for you, but if you abuse it the discs glaze, and you will also destroy all of your driveline parts.

Lastly, if the step height is within +/- 0.020" IT DOESN'T MATTER. You need to chase down other issues.

If I didn't do your pedals, you probably need to be on a stock 1g 0.75" slave. Back the upper clutch switch all the way out and raise the pedal as far as possible. You need the TOB to move farther. It's not rocket appliances.
 
I really wish I could see an entire thread of pics of multiple people's clutch, where the fingers sit after PP torqued, and if they had disengagement issues. I always forget about taking pics of my stuff, but IIRC the fingers always pointed outward.
Jack is the only one besides me that ever actually went after a solution, but he stopped short.

End of story is that if finger position step height or shimming effects your release you do not have enough travel.

All you have to do is bolt together a few clutches and open them up with a bolt/nut/washer/tob and the problem shows right up.
 
The 2900 is tough to make work but it does. Log your up shift times just use the upper pedal switch. I've seen 280ms on a 2900 with a solid hub street disc at 9500RPM and a beat up old trans.
When using NLTS I'm showing 219ms going off the bottom clutch switch signal. I don't have track days YET, the car sees mostly street time and pulls here and there.
Lastly, if the step height is within +/- 0.020" IT DOESN'T MATTER. You need to chase down other issues.
Is there a spec that it needs to be or just all within .020" of each other?

If I didn't do your pedals, you probably need to be on a stock 1g 0.75" slave. Back the upper clutch switch all the way out and raise the pedal as far as possible. You need the TOB to move farther. It's not rocket appliances.
I'll try to go back to the 1g slave. I'm assuming smaller diameter means more fluid TRAVEL but not necessarily more Fluid in general
Both stitches are physically out as fas as the pedal will travel. I've set the clutch switches/ stops accordingly as well.
Be very careful you don't overextend things and break shit. Run pedal with hand while adjusting.
Yeah, I have been. Followed your instructions as well as I could. Only recently learned about just barely extending the master rod just enough that it doesn't cover the reservoir hole.
 
I could see from Jacks post that it could need shimmed if the pressure plate thickness is physically thinner than an OEM plate. That's about all I got for guesses LOL
I agree, if the entire Pressure Plate is thinner or if the Flywheel is thinner.
 
I agree, if the entire Pressure Plate is thinner or if the Flywheel is thinner.
I think I just so happen to have an OEM pressure plate here and these are the difference in height. I just set them on a table with some aluminum flat stock running across the middle of the fingers. Not super scientific but oh well.

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I really wish I could see an entire thread of pics of multiple people's clutch, where the fingers sit after PP torqued, and if they had disengagement issues. I always forget about taking pics of my stuff, but IIRC the fingers always pointed outward.
I'll make a thread asking just that, or someone else can. I would also like to see that. Title it "show me your PP!" for extra points.
Both switches are physically out as far as the pedal will travel. I've set the clutch switches/ stops accordingly as well.

Same on mine.
 
From my experience as I had been using the ACT2900 for long. With the 2900, whatever I did with the clutch adjustment it would move the car around 7000 rpm by the clutch drag test. I couldn't make it higher. But if it was somewhere between 6500-7000 rpm, to be honest I had no issue with shifting even above 8000 rpm. But after I went with a 67mm turbo (when it started to exceed 750 hp in VD, I think like where you are at now), at the beginning it was fine but the grinding was getting more significant and harder and harder to shift at higher rpm. Then at that moment, I gave up with the 2900 and I went with the QM 8 leg triple disc w/3000-3300 psi diaphragm spring, and the ppg gearset. I just installed them and did the clutch drag test with the same clutch adjustment and the same cylinders. The car didn't move at all even at 8000 rpm.
So maybe it's simply time to go with multi plate clutch, if you would like to stick with manual.
 
Use the upper switch. A solid hub street disc, or a solid 4 puck WILL shift faster than a twin. The discs have less inertia. Your measurements with the calipers tell you nothing. you need to measure the disc thickness, pp thickness, spring thickness, and fulcrum to mounting surface. Or do it right, measure the clamp vs deflection and put it where it should be, just past peak clamp.
 
Use the upper switch. A solid hub street disc, or a solid 4 puck WILL shift faster than a twin. The discs have less inertia. Your measurements with the calipers tell you nothing. you need to measure the disc thickness, pp thickness, spring thickness, and fulcrum to mounting surface. Or do it right, measure the clamp vs deflection and put it where it should be, just past peak clamp.
Do you break in these solid hub pucks? I didn't this last one. Maybe half our of normal driving and then pretty much went nuts. I've been told by ACT that you just basically wear out the high spots on the disk and then good to go.
 
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