September 17, 2019, 10:15:31 AM

Author Topic: Clutch not fully disengaging? Bigger master cylinder?  (Read 702 times)

Offline AZieger

Clutch not fully disengaging? Bigger master cylinder?
« on: June 03, 2019, 03:12:03 PM »
During my LS3 swap I replaced the clutch with a new LUK aftermarket OE replacement unit and an Exedy chromoly flywheel.  Also a new LUK slave cylinder, pilot bearing and throwout bearing.  Using a new Wilwood 7/8" MC and a braided stainless line.  Also using a TICK remote speed bleeder.

Clutch engagement point feels pretty good, maybe 1-1/2" from the floor.  "Normal" I would say.  Adequate free play at the top - about 1/8".  Starts to build resistance early in the travel - maybe about 1/2" past the freeplay.  So far I have about 300 miles on the setup altogether.

But ever since day one, the 1st to 2nd shift has been harsh (TR6060).  Other gear changes can be harsh as well, but 1-2 is the worst.  Even when shifting slowly, there is a prominent "thunk" sound and it can be felt through the chassis.  Also when putting the car into 1st sitting still with the clutch pedal fully depressed, I can feel the car move slightly and feel a little "thunk".  So obviously the input shaft is still spinning for some reason.

I have bled and re-bled the system three times.  I used pressure, vacuum, and both.  Standard and reverse bleed.  Bench bled the MC too.  I am 99.5% sure there is no air in the system.

In an attempt to solve the issue, I have unscrewed the clutch switch nearly all of the way, and also have the master cylinder clevis sitting near the end of its adjustment range.  As a result, the clutch pedal has a lot of travel compared to other cars that I have owned - it sits about 1/2" higher than the gas and brake.  It is also one of the lightest pedals of any car I have had.  And it still drags.  This leads me to wonder: What about a larger bore master cylinder?  Maybe 15/16"?  I wouldn't mind a heavier pedal with reduced travel. 

A quick search of the subject suggests that 7/8" is plenty, and that a larger bore could actually over-stroke the slave if one is not careful.  Is this true?  Should I be looking for other solutions?  It is possible that my pilot bearing is bad somehow and causing the input shaft to never stop turning?

Offline AZieger

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #1 on: June 03, 2019, 03:15:10 PM »
Also FWIW, I did not shim the slave cylinder as I was not aware that this might be necessary.  Although given the fact that the pedal builds pressure so early in it's travel I feel like this is not likely to be the issue.  When the engine is off I can hear a faint "creaking" sound of the clutch diaphragm spring moving throughout most of the pedal stroke, starting near the top when the pressure builds so I don't feel like much of the movement is being wasted to clearances.

Online MPbdy

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #2 on: June 03, 2019, 04:48:42 PM »
FC or FD?

With an FD I moved to a 3/4" master as the engagement was actually much too fast with a 7/8" and my twin disk clutch.  It bit very aggressively and was difficult to drive smoothly.

Was your pushrod modified to be longer?  Hinson did this with the old 7/8" wilwood kits.

Offline tai-lun

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #3 on: June 04, 2019, 05:20:46 AM »
I'm having the same issue with my Hinson modified 7/8", I'll be trying the clutch pedal adjustment you did when my car is back from the bodyshop to see if there is improvement but I'm a bit stuck in the same boat. Hopefully some solution can be found for this clutch issue soon..
Tai - 93 LS2 Ronin Widebody FD
Build Thread: https://www.norotors.com/index.php?topic=9172.150

Offline largeorangefont

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Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #4 on: June 04, 2019, 10:23:16 AM »
You guys may need to measure and shim the slave.

That said, have you ran a T56 or TR6060 before? Was yours used? Generally if the clutch is dragging, you won’t be able to shift with these transmissions.

If you double clutch does the thunk go away? It can be normal to get a mild clunk going into gear with these transmissions. The input shaft is not going to stop spinning the moment you depress the clutch.

If you have the clutch set to disengage too high in the travel, sure, it is possible to over stroke the clutch that depends on your clutch and shim setup. If your clutch is indeed dragging you are not over extending it obviously.
« Last Edit: June 04, 2019, 10:35:18 AM by largeorangefont »
Quote from: cool
Sell it to spacevomit.  He'll finish it.

Offline tai-lun

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #5 on: June 05, 2019, 02:49:59 AM »
My T56 was brand new upon install, F-body with a scarab clutch at the time. It now has a Z06 LS7 clutch and RAM flywheel but only recently has the foot to the floor pedal so the car moves on startup if you have it in gear and clutch pedal to the floor.

Clunk with double clutch but not all the time, I think I've got the mild clunk typical with T56's though. I'll hopefully be looking at it before weeks end but my car is still at the bodyshop where they are not so stoked on now having to push it everwhere.
Tai - 93 LS2 Ronin Widebody FD
Build Thread: https://www.norotors.com/index.php?topic=9172.150

Offline jwvand02

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #6 on: July 14, 2019, 10:16:56 AM »
Have you tried turning the driveshaft by hand, rear wheels in air, while someone else pushes the clutch?

This will tell you fairly conclusively if your clutch is disengaging or not, and where in the travel it's actually happening.

I thought for a long time that I had clutch issues but it turns out that the transmission that was supposedly in good shape was far from it.

Offline SuperSlow

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #7 on: July 23, 2019, 02:47:00 PM »
I too have this issue. Hinson modified 7/8" Wilwood, McLeod twin and GM Performance slave. Every time I have the transmission out I forget to measure for shims, just had it out a couple weeks ago :banghead:.

The car has always had a slight clutch drag but I am tired of it now.

I'll do as stated above and pull the trans to measure for a shim.

Offline SuperSlow

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #8 on: July 23, 2019, 09:14:37 PM »
Well I just pulled the trans and everything measures fine.  :banghead:

I am thinking that the henson master needs more adjustment. It has always had a drag to it but it is much worse now. Master is adjusted all the way out. Probably going to put it back together, pull the master and weld a longer rod onto it for more adjustment. Pedal has always had play at the top too so there is definitely more adjustment to be had.

Online Supe

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #9 on: July 23, 2019, 10:56:59 PM »
Well I just pulled the trans and everything measures fine.  :banghead:

I am thinking that the henson master needs more adjustment. It has always had a drag to it but it is much worse now. Master is adjusted all the way out. Probably going to put it back together, pull the master and weld a longer rod onto it for more adjustment. Pedal has always had play at the top too so there is definitely more adjustment to be had.

With a twin disc, make absolutely sure you're not overextending the clutch fingers.  I had this problem with my ACE twin disk, and needed a pedal stop.  Almost all of the twin discs seem to need a pedal stop and have a high grab point it seems.  Easy way to check is to do the wheel spin test on jack stands, but back off the pedal a bit and see if the resistance lets up.  I'll be adding a RAM adjuster to help alleviate the issue.

Offline tai-lun

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #10 on: July 24, 2019, 04:32:39 AM »
An update from my issues, I replaced both lines from the slave and inspected the MC. After reinstalling, and adding a brace to keep the main hydraulic line nice and straight, no more issues. It may have been a bit of dirt in the line, not entirely sure but I've been street driving and took it to a track day with no issues that were clutch related.

The main hydraulic line was backing out of the slave, WITH the pin in - might be something the check out if you are running a stock slave like I am.
Tai - 93 LS2 Ronin Widebody FD
Build Thread: https://www.norotors.com/index.php?topic=9172.150

Offline SuperSlow

Re: Clutch not fully disengaging? Bigger master cylinder?
« Reply #11 on: July 25, 2019, 01:17:28 AM »
Well I just pulled the trans and everything measures fine.  :banghead:

I am thinking that the henson master needs more adjustment. It has always had a drag to it but it is much worse now. Master is adjusted all the way out. Probably going to put it back together, pull the master and weld a longer rod onto it for more adjustment. Pedal has always had play at the top too so there is definitely more adjustment to be had.

With a twin disc, make absolutely sure you're not overextending the clutch fingers.  I had this problem with my ACE twin disk, and needed a pedal stop.  Almost all of the twin discs seem to need a pedal stop and have a high grab point it seems.  Easy way to check is to do the wheel spin test on jack stands, but back off the pedal a bit and see if the resistance lets up.  I'll be adding a RAM adjuster to help alleviate the issue.

Put the trans back in earlier today and had my roommate push the pedal in and out real slow while I tried to twist the driveshaft. Couldn't turn it the whole time. This was with no shims and the master adjusted all the way out.

Really appreciate the help, especially from knowledgeable people.

I plan on welding a nut or two onto the clutch pedal clasp tomorrow to get more adjustment, hopefully this will fix it. It really seems like I never had enough throw all along.