Need Input on Clutch Issue

[Jack B]

I recently installed a Spec clutch on an excellent flywheel. For whatever reason, the clutch does not release immediately. In other words, it drags a bit which keeps the input shaft turning and slows down the shift. If you shift slow and keep a firm pressure on the shifter it is hardly noticeable, but, if you try a fast shift it is difficult to make the shift, it is like hitting a wall.

I have bled the cylinder multiple times. The clutch now has approximately 500 miles. I know it is not the trans because it shifts into gear easily with the engine off or if you wait for a few seconds for the clutch to spin down.

What I need if anyone can help is the finger height off of the flywheel on a stock clutch , with the clutch bolted down. This will have to be done fairly accurately. I believe the Spec clutch has a finger height and fulcrum that will not allow the clutch to totally disengage. If anyone has seen this same issue, I am open to all suggestions.

 

[FATHERFORD]

I read over at the alley that spec recently has been putting the stickers on the wrong side of the clutch disk. Causing the hangup you are talking about.

You might want to look into that.

 

[dave6666]

I read over at the alley that spec recently has been putting the stickers on the wrong side of the clutch disk. Causing the hangup you are talking about.

You might want to look into that.

That would REALLY ****!

 

[Nadine UK GTS]

Hi Jack, do you still need this measuring? I have an old OE one in the garage, I could dig out and measure if helps. I can measure accuratly...I've recently done such measurements converting a 10.5" clutch and fork set up on my Cobra over to an internal hydraulic release bearing and 7.25" twin plate clutch!

 

[Jack B]

Hi Jack, do you still need this measuring? I have an old OE one in the garage, I could dig out and measure if helps. I can measure accuratly...I've recently done such measurements converting a 10.5" clutch and fork set up on my Cobra over to an internal hydraulic release bearing and 7.25" twin plate clutch!

Nadine:

you would have to bolt it down with a the disk installed. I am going measure mine this weekend. This can give us a baseline so that we know what is correct for our cars.

I found something very interesting and bothersome. I had four throwout bearings (from previous clutch changes). I measured the length between the contact surfaces, three measured identical at 2.161 and the fourth was 2.064. That is scary since there is not a great amount of travel to begin with.

 

[Nadine UK GTS]

Oh Jack, I've been a norty, norty girl! I forgot to go measure :-(
It's Tony 1 : 1 's fault, I got distracted thinking of his special measure tool he posted about
I can say that I checked some HRBs I had removed, and yes there are differences, I fully agree with you, this is of concern! I have disassembled one to renew the bearing though (no probs) but tech says its not servicable! It's a bugg*r in the maths when working out distances of stroke etc. as you say theres not a lot there to begin with, and taking into account fingers-play once worked and relaxed etc... Have you put in a pedal stop (I did) wasn't sure if OE would overstroke otherwise?

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[SNKBYT]

Hey Jack--- I had the same problem with a spec clutch. It was there stage -3 clutch. i used it with a lightweight segmented flywheel. It would drag and not release especially at higher rpm. Spec said it was the flywheel. Flywheel said it was the clutch. I went back to the stock flywheel and stock clutch. Everything is fine. I have a roe blower and 700RWHP.

 

[Jack B]

Hey Jack--- I had the same problem with a spec clutch. It was there stage -3 clutch. i used it with a lightweight segmented flywheel. It would drag and not release especially at higher rpm. Spec said it was the flywheel. Flywheel said it was the clutch. I went back to the stock flywheel and stock clutch. Everything is fine. I have a roe blower and 700RWHP.

They seem to be willing to help, so I won't make a judgment yet. What is really confusing is the fact that the clutch releases about two inches below the free-play, in other words near the top. That would seem to suggest that it is releasing.

The one missing element is that no one seems to know is how much travel one full pedal depression gives us. I have taken several dimensions and will post these once I am finished. I can tell you that with the spec clutch, when the transmission is bolted in, the seat (trans side) of the throw-out bearing is approximately 1/2" away from the top of the slave ram when it is fully retracted.

 

[Nadine UK GTS]

Hi Jack, taken some measurements, with a good used OE flywheel and used OE clutch plate, and new non-OE disc (obviously all torqued down).

From the face of the flywheel against the crank, to the fingers point of bearing contact was 3.48"
The thickness of the flywheel (from crank face to clutch disc face) was 1.26".
So the measurement of the whole clutch, off the face of the flywheel to the fingers bearing contact point is 2.22".
For reference the disc thickness was 0.322"

The OE slave casting is marked AP...(AP racing was a UK sister company to Tilton) I wonder if they could tell us the max stoke of the slave?
I've always gone on freeplay needing to be 0.2" when you set it up. Did I read right, you have 0.5" is this with the bearing all the way back on the spring? It must be possible given the master bore size and the slave piston size, to then work out pedal travel. Can Spec advise of stroke required to fully disengage, but not over-stroke from the point of engagement, or at rest? I was trying to measure pedal travel from point just as it starts to disengage (ie on lift, in gear and start to depress pedal, that a helper can just start to turn rear wheels with light drag) but it's real tight for space down in toe box area, I'd need to make up a tool to acuratly measure.

 

[Nadine UK GTS]

Jack this has been on my mind a little all day!
I started doing some more measures, I had several OE slaves, and with the bearing on the spring, fully retracted, there was a defference of 0.182" between them all (!!!) the years were '94 - '99. But...I have sourced other bearings to replace on the slaves. Are you measuring off the long sleeve that slips over the input shaft?

What do you think the free play measure is on OE with spring retracted? Is the bearing spring is to be full compression? I've tried to measure this before, but rember it was tricky.

I found some old notes, I 'think' distance from trans machined HRB mount surface, to release fingers was 3.48" total, if I understood my notes OK!

 

[Jack B]

Jack this has been on my mind a little all day!
I started doing some more measures, I had several OE slaves, and with the bearing on the spring, fully retracted, there was a defference of 0.182" between them all (!!!) the years were '94 - '99. But...I have sourced other bearings to replace on the slaves. Are you measuring off the long sleeve that slips over the input shaft?

What do you think the free play measure is on OE with spring retracted? Is the bearing spring is to be full compression? I've tried to measure this before, but rember it was tricky.

I found some old notes, I 'think' distance from trans machined HRB mount surface, to release fingers was 3.48" total, if I understood my notes OK!

I have a series of pictures and measurements that i will post next week. I have rethought what is important and it is the distance from the rear of the bellhousing to clutch fingers. Take a steel ruler lay it across the bellhousing and measure the distance to the fingers and subtract the thickness of the ruler.

If the fingers are too far forward there is a point where the slave goes inoperative. You really don't have a lot of room for error. The slave only moves the fingers 1/2". In addition, the slave can only adjust about 5/8" for all the dimensional variables.

 

[Nadine UK GTS]

Hi Jack, Yes, the clutch needs 0.5" stoke to disengage. But...on a twin plate I found out the wear factor to be up to 0.19" that means the max stroke needs to be at least 0.7" but it should have 0.197" free play engineered in as well. I called up AP racing UK who make the OE slave, they weren't most helpful, but said the OE slave stroke was manufactured at 0.709". When I converted over to the Tilton, I had to really get my measurements on the point, I did the calipers off a rule and subtract way too, I got within a 0.008" range off at least 6 different measure points.