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I never tried this with any of the old clutches. But understanding how the clutches work, I'd imagine they all do this to a point.
No, they are not supposed to. With the clutch disengaged there should be enough space where the clutch is making contact on either flywheel or pressure plate and not both. At low rpm there may be contact, but not enough to make it to the back wheels. Increase RPM and the wheels may start turning. That is not normal.
No, they are not supposed to. With the clutch disengaged there should be enough space where the clutch is making contact on either flywheel or pressure plate. Not both. The reason to try this in higher RPM is to ensure the clutch is not dragging. At low rpm there may be contact, but not enough to make it to the back wheels. Increase RPM and the wheels may start turning. That is not normal.
Hmmmm. I may have to go with a 7/8 slave cylinder then. I found one, gathering specs now.
But, it only takes contact with either the PP or FW to spin the trans input shaft. Add in 2 floating discs and it's even more likely.
Although, I do like the idea of a 7/8 slave cylinder swap.
How does it shift? Do you feel more resistance when going into gears? How does it feel when shifting into reverse?
This. Shifting is notchy, more so than before. Reverse is very tough. It will go in to reverse, but it takes effort.
I'm waiting to hear back from Dorman Tech support on details for another slave cylinder; CS37793. This one is for a 2.5L Jeep (~$20 @ Rock Auto). This one has a very similar bolt pattern as the Fiero one. But, I doubt they are the same size. It too has a bleeder, but this one has the hydraulic input on top with the bleeder instead of on the bottom.
I can make another adapter plate, but I want to know the hydraulic fitting size before I go too far with it. Plus I can get the parts ordered all at once.
What would be awesome is if the fitting and bolt pattern match the Fiero. LOL. That would make this a direct bolt in swap! I won't hold my breath though.
What makes this attempt easier is that I now have an AN3 fitting on my clutch line. So adapting any slave to it should be much easier. But, knowing the mounting pattern and the hydraulic fitting size before hand makes things a bit easier.
Yeah that's usually a sign of a dragging clutch I'm afraid..
Yeah, I know. It's not dragging enough to smell. So that's Good. And it's my daily and I need it, so it'll have to do until I get the other parts in and fabbed up.
I was already researching the 7/8 slave cylinder, I just didn't want to admit it yet. Lol. Denial. Lol
I got the details about the 7/8" Slave Cylinder back. Dorman Part Number CS37793
Here are the specs we have.
Center to Center mounting hole distance is 56mm (2.2”)
Mounting hole diameter is 9mm (0.354”)
Pressure port is 7/16-24.
Bore size is 22.2mm (7/8”).
Rod is 114mm long (4.49”).
The mounting holes are the right size and distance apart to possibly bolt right to the adapter I made for the Fiero slave. The hole diameter is ~.041" larger than the AN5 bolts I'm using, and the distance from mounting hole center to mounting hole center is .035" larger than the Fiero cylinder. That's about .023" per side of wiggle room. At worse, I'll have to open up the Mounting holes on the new slave to get it to bolt up to the Fiero adapter.
The Pressure port, I found a 7/16-24 IMF to AN3 adapter and a 90° AN3 coupler. I should have all the parts in by next weekend.
My only concern is total throw now. PP throw is going to be .610" Vs stock of .472". Currently I'm at .537" (which should be good, but isn't quite enough for the McLeod Street Twin). I'm adding .078" to the PP throw. I'm glad I shortened the T-Bolt.
Well you may have it with the 7/8 slave...you are doing this reverse what Mcleod would do (larger MC with stock slave) but you say it is a 2 way street to get more stroke. Either larger MC or smaller slave.
Perhaps double clutch "up shifting" will be OK until you get the new slave as like SSR says you are basically pushing your syncros harder than they want to be. Keep off the bitch slap shifts until you get enough disengagement
My $.02 is you will absolutely love the twin disc clutch. It doesn't like slipping or it wants to chatter. You will adjust your driving technique on RPM & clutch release and all will be fine. At that point it will be just like driving a stock organic disc clutch in terms of street manners. 1st gear boiling tire smoke, 2nd gear continues laying 2 stripes, 3rd barks and leaves tire marks, 4th chirps. :-)
Well you may have it with the 7/8 slave...you are doing this reverse what Mcleod would do (larger MC with stock slave) but you say it is a 2 way street to get more stroke. Either larger MC or smaller slave.
Perhaps double clutch "up shifting" will be OK until you get the new slave as like SSR says you are basically pushing your syncros harder than they want to be. Keep off the bitch slap shifts until you get enough disengagement
My $.02 is you will absolutely love the twin disc clutch. It doesn't like slipping or it wants to chatter. You will adjust your driving technique on RPM & clutch release and all will be fine. At that point it will be just like driving a stock organic disc clutch in terms of street manners. 1st gear boiling tire smoke, 2nd gear continues laying 2 stripes, 3rd barks and leaves tire marks, 4th chirps. :-)
Yeah, I'm not the only one to take the slave cylinder route with the street twin (found another forum where someone else did a 7/8 slave cylinder). This route is so much cheaper, lol. And easier now that I got that line replaced.
I really only need the clutch for 1st and reverse. Once I'm moving I don't need the clutch at all. Also, when down shifting I rev match. I'm not too concerned about hurting the syncros.
I doubt I'll get 4th to chirp, between the tires, gears, and vehicle weight it just goes. Hell, trying to lay smoke is kind of a pain for me. It'll tear first loose for sure, but it'll be accelerating the whole time too. For any real smoke, I have to brake stand. Otherwise it's just a dusting of smoke.
O.k, so my parts will be here in the next couple of days. But, I was very concerned about over extending the system to where I would be hitting the PP or bottoming out the TOB against the trans. So I got to thinking, something isn't right.... this should be working as is; probably my math is off. So I did more research.
I found on a couple of forums where guys are putting in LT1/T56 stuff to other cars and they measure 4th gen MC throw at less than 1"...... I've been doing my math with 1.1" of MC throw. So I decided I should measure actual throw. I got some interesting results.
If I pull the clutch pedal aft to take all slack out of it (like you would for bleeding) I get .9375" of total travel. If I let the pedal rest I get .8325" of MC throw. And if I measure from where the pedal gets really firm (by hand, not foot) I get .7300" throw. I redid the math for .8325" of throw and got completely different results, obviously.
The stock 3/4 MC to 1" SC gives a SC throw of .468"
The McLeod 13/16 MC (assuming it has the same throw, it probably doesn't) to 1" SC gives a SC throw of .550". This can't be right because I've read (not directly from McLeod though) that McLeod specs .500" throw at the TOB and with this it'll only get .420". If the McLeod MC allows for 1" of stroke it'll get .504" of throw at the TOB. I don't see how that is possible with the limitation of the stock pedal and firewall. But I can see how the McLeod MC can be adjusted to take out all the slack in the pedal and get .9375 of MC throw. That would put the SC throw at .618" and TOB at .472"
The stock 3/4 MC to a 15/16" SC gives a SC throw of .533"
The stock 3/4 MC to a 7/8" SC gives a SC throw of .611"
I also measured the Clutch Fork to see where it would possibly contact the PP at full press. The best I could come up with was about 1-3/8" outboard of the pivot. But, with ****** having the McLeod MC and the shortened T-Bolt and not hitting I'm not too concerned with it hitting on the 7/8 SC at full press. But even if I go with the shorter throw on the McLeod MC and compare that to the 3/4 MC to 7/8 SC throw, I'm only loosing .023" of clearance at that part of the Clutch Fork. And since I shortened my T-Bolt .100" I am pretty confident it wont hit.
Of course I'll verify this once I get it all installed.
what was the gap you measured when you installed the bottom disc & floater?
mine is at .022
If to tight, the bottom disc will drag (not disengage). That is where the shims that come with the Twin come into play to adjust that floater plate gap.
assuming your measurement of stroke travel from MC is right to then determine what you get at the slave, the 3/4" slave should get you enough and based on your math more than you need. IDK if your clutch pedal has a "stop" bolt you can adjust so it only travels so far. Mine does but I have a custom pedal (B-body). My McLeod MC also has a adjustable rod and I had to adjust the pedal out to get full disengagement with it. The pedal is higher than it was with a single disc clutch
If you modified your stock MC to a adjustable rod you could get more stroke from it by raising the pedal, would be another option to try using the slave you have now.
I got .022" clearance from the floater to the bottom disc.
There are no stop bolt or adjustments to the clutch pedal assembly (hydraulics included) anywhere on the stock set up. On the stock pedal assembly, the bracket that mounts the pedal to the firewall has a little plastic piece on it that the pedal it's self will contact. That is the stop. I cannot move the pedal any further than it is without cutting the pedal or mount.
This works out for me though. Since it's just barely dragging now, and the 7/8 SC adds .078" SC throw, I don't think the clutch will drag anymore. If I had the 1.1" stroke I thought our cars had it would be .617" of TOB throw and that's what had me worried.
Well if going with the 7/8" slave gets you to much travel and you don't want to over extend the clutch accidentally you could either fab up some form of pedal stop to only allow it to travel x distance or even put a spacer/washer between slave and the mount to back it off some if you find you get more slave travel than you need.
IDK what stock F-body pedal rig is as I don't have one which is why I asked if you had any form of adjustable stop on it. I have a neutral safety switch mounted on my pedal rig and set my stop so the pedal bottoms out before the NSS completely bottoms out. That way the NSS is just a switch and not also acting as a pedal stop as it is just a plastic button type switch. It is a GM part though.
Alright, I got the 7/8 slave cylinder installed. It bolted right in. I put the stock SC pushrod in to keep the plastic ball of course. The hydraulic fittings fit as advertised too.
Did a test, works great! No grinding on the PP and it goes into gear perfectly now. No resistance. I didn't have to adjust anything, just bolted it in. I'll let you all know how the test drive goes.
Jeep 7/8 SC on the Left, Fiero 15/16 SC on the right.
Test drive went great. It's weird, but the clutch pick up is much much smoother. The pedal is stiffer than stock and there's still a bit of chatter (very small amount) at certain rpm/slip points(due the discs not being spring hub), but it mostly drives like stock now. I'm impressed.
The twin will chatter some if you slip it. You will adjust your engagement technique to deal with that. Yes the discs are non sprung so less forgiving. Some harmonics you will hear if you lug it in a particular gear sometimes.
05-15-2016, 12:26 AM
