Clutch fork throw

[Zed Head]

37 minutes ago, rcv said:

II don’t love having to resort to the washers under the pivot, but I think that’s my best shot at this point. 

But given that the pressure plate and disk are sold as a kit, it would be pretty weird for this to be the case right?  My 91mm stack up number doesn’t have anything to do with the clutch disk, so maybe there is something wrong there. 

If you decide to do this, make sure you use thread sealant on the pivot ball threads.  The hole extends in to the oil cavity inside.  I had one that leaked and it was a real puzzle to figure out.

Never assume that aftermarket parts are correct out of the box.  If you have an old disc you could compare.  Or take a measurement and maybe somebody will have one out here.

[rcv]

3 minutes ago, Zed Head said:

If you have an old disc you could compare.

Ask and ye shall receive.

New disk: 8.31mm

Old disk: 7.79mm

[Zed Head]

1/2 mm.  Now we need to figure out how far the 25 mm of slave travel moves the pressure plate fingers and how that translates to the pressure plate moving.  Would be a pretty cool math problem, for high school algebra.  Seems like a lot of work now.  Don't forget that clutch disc has a wave spring inside that compresses.  Can't remember the name of it.  Cushion spring?

It doesn't seem like it would be the problem.  1/2 mm is less than a groove in the disc.  Might be worthwhile to let all of this new info stew inside your brain for a bit.  Something might come to you.

 

[Zed Head]

Checking back.  Curious if you went ahead and installed it.  With extra washers and things.

I was going to suggest that you could make a lever arm, extension, for the end of the clutch fork to see if the clutch releases with that amount of throw.  A piece of pipe with the end hammered flat could be made to slip over the end of the fork and you could work it by hand.

[EuroDat]

It is a strange problem you have and I can't think of anything else but the flywheel. Is it the same flywheel you had on the old clutch?

If you want to test the clutch, that is simple. Just remove the rubber boot and use a crowbar in the space between the fork and bellhousing. Use a small piece of wood between the crowbar and fork at the slave cylinder rod position. Depending on the size block of wood, you should get a full stroke with little effort. Be carefull the crowbar doesn't slip, fly out and hit your knee. Don't ask

If you do use the washers on the pivot ball, don't go more than 4mm. You want enough thread over to provide support.

The only other thing I can think of to correct the fork position is the make a spacer ring between the collar and throw out bearing at position of the arrow. I wouldn't go any more than 4mm.

If you do one of these two modifications than 4mm will move the fork approximatly 7.5mm forward at the slave cylinder rod. Do both mods and you would move the fork 15mm forward.

Try the washers and see if you get 25mm movement with the crowbar before the fork hits the back of the bellhousing. You can always make a pushrod to suit.

[rcv]

 

2 hours ago, Zed Head said:

Curious if you went ahead and installed it

I gave up work for the day right after I sent the last clutch picture - had to get on with my other weekend chores unfortunately ?.  I really don't like adding on the extra washers without understanding why I'm having this problem in the first place. I'm worried I'm screwing up something more fundamental that's going to bite me if I just hack around it.

 

3 hours ago, EuroDat said:

Is it the same flywheel you had on the old clutch?

Yup, same flywheel. 

 

I think I'll try actuating the fork with a crowbar just to see if it actually has enough throw.  I'll make sure to keep my knees well clear!  After that, I think I'm going to try installing the original clutch setup (collar and all) just to validate that the original setup didn't have this exact same problem somehow.

[Zed Head]

On 7/11/2020 at 2:42 PM, rcv said:

Here’s the best pic I have of the pivot ball:

 

I just realized something that might be the main clue.  All of our advice has been for the 71B type transmission.  Yours appears to be something else.  I don't see the front cover of the 71B.  I noticed in some of your other pictures that the transmission was more rounded, didn't have the distinct features that the 71B has.

You can probably start over, not sure where though.  Identify your transmission.  Is it a "monkey motion"  71A type?

Sorry I didn't say something sooner, when I noticed the odd roundness.

Here's the roundness.  I even copied it and reposted.

Edited July 14, 2020 by Zed Head

[Zed Head]

On 7/3/2020 at 1:22 PM, rcv said:

I’m nearing the end of my veeery long rebuild project on my L24 and I finally bolted on my original F4W71A.  I’m using the original throw out collar and fork, but installed this new clutch kit from zcarsource: link.

Okay, found it, in the very first post.  I don't know for sure but the 71A might not work with the 92 mm standard that the 71B does.  

Either the 71A is different and we've been steering you wrong or the 71A is the same and you still have a problem.

[Zed Head]

The distance from the front of the bellhousing down to the top of the pivot ball would be good to get.  If it's the same as a 71B then the 92 mm number should work.  The relationship between clutch parts will be the same.  

After all of this, it might just be that the 71A needs the thick pressure plate.  The pivot ball might be deeper, farther away from the engine.

p.s. if that is the case, then adding washers to extend the pivot ball would be rational.

Edited July 14, 2020 by Zed Head

[rcv]

Ah yeah, it's the monkey motion 71A.  I probably should have reiterated that along the way.  I just called my future father-in-law who gave me this car, and he couldn't recall ever having any major issues with the clutch - certainly never having to stomp the pedal to the firewall to get it to release. I'm assuming that means the old setup is valid, so I just need to figure out where the difference is between the new and old.  I'll also try reinstalling the old clutch just to make sure.

I've been assuming that the 92mm stack-up height is correct regardless, because that's the number I measured off of the old parts.  However, in my 92mm measurements, both pressure plates have been just laying on the bench with the friction disk out of the equation. This discounts any difference in height of the pressure plate itself, and only measures the distance from the throwout ears to the flywheel-side face of the plate casing.  It's definitely possible that the difference is actually in the pressure plate itself, which had been hovering above the bench when I measured.  I'll do a side-by-side measurement of both the new and old pressure plates sitting on their respective disks and see if there is a difference.  I'll also grab a reading of the bellhousing face to the pivot while I'm at it. Any idea what that is for a 71B?  The transmission is still mounted to the engine, so I'll have to wait a few days until I have time to spend in the garage before I can do any more work.

 

 

Edited July 14, 2020 by rcv

[EuroDat]

I took some measurements of my spare transmission to give you something to go on. I can't see why the 92mm rule would not apply for the 71A, you kind of proved it with the old clutch although we don't know if it was the same as, or the original clutch.

The position of the fork in relation to the front of the bell housing is the same on the 71A/B/C.

I also did some checking on my transmission. When I position the fork at 135mm, there is very little room behind +/- 15mm. Not enough to fully depress a correctly adjusted clutch pedal. Everything being equal, your old clutch will be further forward due to the thinner disc. The diaphragm in the pressure plate has a fulcrum of about 5 to 1. So 0.5mm woulf move the diaphragm fingers about 2.5mm and the clutch fork about 4.5mm give or take a couple tenths of a mm.

Mind you, that is going out from a situation with a pddal box having little wear and correctly adjusted. A clutch will easily disengage with 15mm clutch fork movement. It will be low in the pedal movement.

Another thing to note. When I push the fork all the way back the collar almost slips over the end of the support tube. That is not good. See photos.

[Zed Head]

I wrote this yesterday before I realized the 71A thing, then didn't post it.  Overall, it seems like something is partially opening your pressure plate, jammed up against it.  Either the nose of the transmission, or the sleeve/collar, or a combination.  

There should be play behind the throwout bearing and sleeve.  In other words, the bearing and sleeve should not be contacting the pressure plate fingers or the front of the transmission, at rest.  It should have wiggle room between the two.

I went back and watched your video and when you move the fork I don't see the bearing/sleeve moving.  Only the fork. It looks like something is jamming the bearing/sleeve in to the pressure plate.  If you take it apart again make sure that the bearing and sleeve slide all the way back on the nose of the transmission.  That friction surface is often overlooked.  Even though the bearing/sleeve is held in the fork it's resting on the nose.  The noses actually get worn and break after many miles with no lubrication, just from the bearing and sleeve wearing on it.  Most old transmissions have a groove worn on the nose.

And, following up on EuroDat's last comment, maybe the collar slipped off of the nose as you were installing and is jammed in there, between the end of the nose and the pressure plate.  It might be that you just need to get it back on the nose where it can work like it should.  I think that is a good possibility.  It fits, I think.

It's at about :40 in the video.  Here's a clip from it, below.  Lots of fork movement but no sleeve movement.

 

Edited July 14, 2020 by Zed Head