427Hotrod

I've had several C-2's and C-3's over the years. Depending on clutch setup, some "felt" right..some didn't. I really like a clutch that I can "feel" release and I want it to be released somewhere in the mid travel area so that full "to the floor" pushing isn't needed.

Mine worked pretty well with the Centerforce in it, but I had already done some playing. After getting throwout bearing height set properly with the stud in the scattershield, I played with a couple of different throwout arms but ended up staying with the stock one. One had quicker release, but arm came too close to floor when depressed fully. I had also previously drilled the "upper" arm of the z-bar or crosshaft to speed the ratio up. This was done by drilling the hole for the rod from the pedal approx. 1" lower on crosshaft. If you try this, find a machine shop with a mill.....regular drill bits won't make a dent in it! Anyway, this did help speed up release and since the Centerforce has pretty low effort anyway, it didn't feel like excessive effort was needed to push pedal.

I've also played with the adjustable pedal position on the '65-66 type pedals to increase ratio. It does help some too.

But, since I'm now using the Mcleod Dual Disc Street Twin that I had built with a little extra pressure, I found it just wasn't the way I really wanted it to feel. Still seemed like it took a lot of pedal travel to get clean release. And with the new G-Force 5 speed, I want it to be perfect!

So I removed crosshaft and took a small Dremel to the two tack welds holding the "upper and lower" shafts on the crosstube. This takes a couple of seconds and the arms can be tapped off the tube with a punch and hammer.

I then swapped the arms so that the longer one was on the bottom side going to the throwout arm, and the shorter one was on the top side where the rod from pedal attaches. I stuck it back in car and played with angles before welding arms to find the best compromise between travel and effort. Really, the arms were only slightly re-angled from their stock locations, with the majority of improvement being the difference in the lengths of the arm being exerted on, and the length of the one being moved at the bottom exerting movement to the throwout arm. This also improved the angle of the rod going from crosshaft to the throwout arm.

The net effect was that by lowering my pivot point on the upper arm, and increasing the length of the lower arm, I ended up with much more throwout arm/bearing movement for the amount of pedal travel inside the car.

After all this was figured out and working, I decided to go nuts and do some reinforcing. I added one small angled brace to each arm to limit any deflection that might occur. Didn't see any there, but figured a little overkill is OK!

When it was all done, I had my wife come out and operate pedal. She always wants to make sure she can still easily drive any of my mods. She likes to cruise in this dude. She pronounced all OK. The Street Twin Clutch is actually pretty easy to push with a low staic pressure stock of 1400#'s. Mine is set to 1600#'s. The low pressure is possible because of having double the surface area. Much better than the old Hot Rod style 2800-3200# stuff from the old days! Just for reference, current race car slipper style ones only use around 900#'s maybe and use centrifugal assist to help hold it.

One last thing I found. I did notice some flexing in the rod from the pedal to the crosshaft. It was moving slightly right where the threads start. This was probably magnified by the slightly increased effort on it due to the geometry changes, but once again, this clutch isn't that stout. I used a piece of 3/8" steel tubing to slip up over threads and tapped it down over shoulder right past threads. I then just ran another nut up the shaft to press it tight. It is absolutely amazing what this did for what I was already considering a good pedal feel. I still have plenty of adjustment room left and the pedal is very strong feeling now.

Prior to all this, I also worked on welding up and redrilling any worn pivot holes to remove any slop.


I now have a pedal that is very solid and firm feeling. It releases cleaner and is fully released by mid pedal travel. This will help give more leeway in situations where the clutch might get a little warm (5000 rpm side steps!) and swell a little bit. If you are having clutch linkage issues, you might do some real looking at what you have going on. If you have changed from a stock diaphragm style one, you might benefit from a little geometry change. The welding is simple if you have one, or if not you can work it all out and then take it to be welded. Either way, all of this is a good days project where you will feel the improvement everytime you drive the car!


JIM
_______

BacaBill

Ok 427, question,,,
I have a '79 with 4spd & right now have to push the pedal ALL the way to the floor to engage the clutch. When in gear, clutch "down", the slightest movement upward (like 1/4"), will begin to move the car forward. Are you saying that this "could" be the way to get the clutch further up on its travel to do its thing w/out having to mash it to the floor every time? If so, thank you, but I guess I'm an idiot, I need a little more info, maybe a couple pics.

427Hotrod

You've got it. First make sure there is NO slop in any linkage. A little really messes things up.

Look at you throwout arm where it comes out of bellhousing. It should be angled slightly forward toward front of car when pedal is NOT pushed. If not, you will run out of travel early. It may require a different length stud or bearing, but this is critical to making it work right.

Then, past that, anything you can do to improve ratio will help. The closer you move the rod from the pedal to the centerline of crosshaft, the "faster" it will be. You will get more movement of throwout arm for any given pedal movement.

Then conversly, the more you move the bottom lever AWAY from the centerline will move the throwout arm further for any given pedal movement.

The two of them both being moved makes a big difference! Just be careful, an inch either way is a lot! You don't want to give up all your leverage and make pedal too hard to push or have something bottom out. A little goes along way.

Again, have someone push it and REALLY look for any flexing. A little eats up lots of travel.


I'm on the road traveling right now, so I don't have anyway to get a picture of it. Keep thinking about it..you're on the right track.

JIM

PRNDL

pics? Here is mine:

comp

:thumbs: on the tips Thanks

MILO

BACABill : One of my first cars was a 77 Nova with a three speed on the floor. Swapped it out for a close ratio Muncie. As far as adjusting when the clutch would engage, I had an adjustment bar where that engaged the clutch fork. I'm not too familiar Vette setup but figure it was worth mentioning. Hydraulic clutches has a similar adjustment.

71roadster

The thing I don't get is why it should ever take pressing the pedal all the way to the floor to get the clutch to release. It indicates something else is out of whack. I am trying to solve this very same problem with my car. I even sent the clutch back to centerforce for verification that the installed height was correct (which they say it is, but I have my doubts). I am using the same clutch, bearing, scattershield (but new flywheel) in my new engine as was running with the old engine but suddenly I have to mash the pedal ALL the way to the floor at stoplights or shifting from a stop.

I may consider your solution if I cant figure out why it doesnt work in the first place. Thanks for the info.

Chris

PRNDL

This is a really common problem when switching to a centerforce clutch, and we have beaten this topic to death!! (search the archives). I had the same problem. The problem is usually that the centerforce clutch requires a longer fork ball stud. The long GM stud may be too long.... most use the adjustable model. In my case, I Bubba'd the problem away by lengthening my clutch rod, so I wouldn't have to pull the trans and replace the clutch fork stud. If you were actually in contact with centerforce about the problem I am astonished that they did not mention/ask you about your clutch fork stud. It is on the orange sheet that comes with the clutch kit. MJ

here, take a look thru this old thread:
http://forums.corvetteforum.com/zerothread?id=158546





[Modified by MNJack, 9:48 AM 4/29/2004]

71roadster

I guess my problem is a little different. I didn't switch to a centerforce clutch. I was running a centerforce and everything was perfect. Then I changed engines and things went down hill. My problem is not too much play, it is that there is no play at all and I still have to push the clutch to the floor. And I have measeured and set everything down to a gnatsass per centerforce's diagrams and still nothing. At this point I am just going to try different ball stud heights. I modded my TKO a little so I can adjust the stud without pulling the tranny, hopefully I find something that works or the centerforce is out...

Chris

71coupe

Jim, do you have any pics? I aslo have a Mcleod street twin & have been thinking of modifing the linkage. when you say crossshafts, are you refering to the z-bar? Also, are you using any custom hardware like heim joints?
Thanks :cheers:

BacaBill

:thumbs:
This has been a big help people. Now I just gotta get under there & take a close look at things. I found it hard to believe that there was no adjustment, just kinda typical that you have to make MODS to do it.
:banghead:

427Hotrod

I'm traveling this week and don't have any pictures. It was just one of those projects you start on and then work it all out.

Yes some folks call it a Z-bar, some a crosshaft..same thing.

I am using basically stock stuff other than I lengthened the lower rod from z-bar to throwout arm a long time ago. It enabled me to get better angles on things as it went through travel. I think I will eventually make a new rod from pedal to Z-bar and use Heim joints for the heck of it. I think Speeddirect makes some already though.

I think if it all worked fine before, and you have set up throwout bearing height correctly, something is flexxing or there is some exessive play somewhere. Years ago I had a '64 where the pedal started coming apart where it attaches to the shaft that goes through brake/clutch pedal support. Took a while to find that one. Look REAL close for any flexxing...something is eating up your travel. The Centerforce works fine if set up right, and as you said it worked before. Something has changed or moved. How 'bout the ball stud on side of block? Is it cracked or loose after you installed new motor?


JIM

71coupe

Thanks for the detailed info :cheers:

mfendley

71roadster - did you take the t/o off the fork when you did the engine swap? I ask because there are two ways for the fork to engage the bearing (but only one right way). The fingers of the clutch fork AND the spring clips BOTH have to be in the groove of the throw-out bearing. I screwed up and had the fingers in the groove, but the spring clips behind the groove - and it required me to adjust my pedal so that it started to engage the clutch almost as soon as the pedal is coming off the floor, but there was no free travel at the top of the pedal. I made the switch and all is back to normal.

weendoggy

This is my clutch replacement page. I found the ball to be too short and got a longer one (truck) which solved a lot of issues.
http://members3.clubphoto.com/glenn2...99/guest.phtml

Also, just recently, I pulled all my linkage off, filled all the holes and redrilled to fit tightly. This got rid of a lot of play, even though there was little wear, on the linkage. My clutch releases about one inch off the floor.

One note: I think by changing the levers as you have, you would increase the pedal pressure needed to depress the clutch. You need a longer lever at the top end to make it easier. So, did you find it easier to depress after you changed the arms?

427Hotrod

Yes, what I did does increase pedal effort, but by making sure all is stiff and solid in addition to faster ratios it works so much better it's ridiculous.

But pedal effort is up the user. My 5.0 Mustang with a Motorsport replacement clutch is stout. This one is up there too, but it's a dual disc Mcleod set up with additional static pressure to make sure it can handle the 540's Hp. Can't imagine how it could be too tough with a regular clutch.

My wife came out and checked it and pronounced it fine. She requires the abilty to drive it too! :steering:

JIM