Variable Clutch Cover Height or Thickness Availability

[zKars]

So I discovered something interesting over the past week regarding the age old issue of clutch throw out bearing collar height selection.

We have discussed many many times how to determine what height the throwout collar has to be to achieve the now well accepted total 92 mm total height, based on your particular choice of clutch cover. What I remember in the many discussions I heard, is how the struggle to get a long enough collar almost always comes up.  This lead me to assume that all that was available in new parts are clutch covers that are much thinner than the old stock 240z covers.

What is new here, is that I have definitive measurements on two popular Exedy Clutch kits with very different heights! You can now choose the one that most closely matches your existing cover, and not worry much about finding a “matching” collar.

In my recent experience of replacing several clutches for various cars, I have been buying the 280z spec clutch, 06009 part number, and it is much thinner (requiring a longer collar) than any of the stock OEM 240 clutch covers I’ve seen in the past (requiring a short-ish collar).  

My parts hoard has accumulated several of the shorter collars, and I’m always struggling to find longer collars to go with the thin pressure plates. I’ve even considered designing a two piece adjustable length collar to handle any situation.

Well it turns out I ordered a 06029 kit the other day for a customer after having an old age brain fade, spec’ed for 240 and early 260. Got it out of the box and found the clutch cover is nearly 3/8 -1/2” inch taller than the 06009 kit.  I will add the exact height of the spring finger tips with the cover bolted to a flywheel (yes, it very different) to use in your 92mm collar selection calculations shortly.

Clearly Exedy has it straight since most 240 owners would have shorter collars, and need a thicker cover. 280’s have longer collars, needing thinner clutch covers.

Not sure how I missed this, but what it means, is that there is a choice in clutch cover heights out there, you don’t always have to go hunting down the right(er) length collar. Just by the right clutch!

I should note that the clutch disk in both kits are identical. Technically they have different part numbers, I can not see or measure any difference in the disks. 

Note this handles only the 225mm clutches, not the 2+2 240mm clutches. There were no 240mm spec clutches for 240z. 

It would be great to have a database of all the popular clutch brands and their clutch cover heights, something you can’t find in their published specs.

So every time you replace your clutch, measure the cover height and record it here. Thank you.

[zKars]

Here are some pictures of the two covers.

 

[Patcon]

The difference in the fingers is amazing too!

Why would they be so different?

[EuroDat]

On 29-1-2021 at 1:58 AM, zKars said:

What is new here, is that I have definitive measurements on two popular Exedy Clutch kits with very different heights! You can now choose the one that most closely matches your existing cover, and not worry much about finding a “matching” collar.

In my recent experience of replacing several clutches for various cars, I have been buying the 280z spec clutch, 06009 part number, and it is much thinner (requiring a longer collar) than any of the stock OEM 240 clutch covers I’ve seen in the past (requiring a short-ish collar).  

My parts hoard has accumulated several of the shorter collars, and I’m always struggling to find longer collars to go with the thin pressure plates. I’ve even considered designing a two piece adjustable length collar to handle any situation.

Well it turns out I ordered a 06029 kit the other day for a customer after having an old age brain fade, spec’ed for 240 and early 260. Got it out of the box and found the clutch cover is nearly 3/8 -1/2” inch taller than the 06009 kit.  I will add the exact height of the spring finger tips with the cover bolted to a flywheel (yes, it very different) to use in your 92mm collar selection calculations shortly.

The famous 92mm height measurement is based on several conditions that need to be the same through all the pressure plate manufactures.

The diaphragm releases to a certain height. That is determined by pivot point of the diaphragm and inner radius of the clutch cover where the diaphragm contacts.

I had a 350 chevy engine with a saginaw close ratio box and a webber (different company) performance clutch / throw out bearing collar. The old and new pressure plate heights were competely different, I can't remeber what they were going back 34 years, but once I bolted them to the flywheels (new clutch had a lightened flywheel), they were the same height.

It will be interesting to see what the assembled condition height is. It is the only relavent measurement. 

[Trnelson]

Saw this and wanted to compare what I pulled out with what I purchased. New one is on the left. Does this mean I need to send this unit back and get the correct size?  I would assume so. Still have a month or so before I’m ready to install 

[grannyknot]

@Trnelson, can you drop a ruler down the center of both the old and new clutch cover so we can see the difference if any of the height of the spring fingers?  The cover height is obviously different but the finger height could be the same but hard to tell from the photo.

[zKars]

The height of the fingers with the clutch cover bolted to the flywheel (with the disk in place) is what is really needed to properly compare. The free height of the springs may or may not be useful as noted above, the way the fingers move is determined by internal geometry of the moving parts. 

The fingers on the left cover sure do stick up more than the ones on the right, or so it appears, AND the cover itself appears thinner.

[zKars]

I have to note while we are here.

There is also another way to get whatever clutch cover and throw out collar you have to work.

There is an adjustable length push rod clutch slave cylinder option and a matching clutch fork with a hole. 

I’ve found cars with very long collars and very thick clutch covers who’s clutches were working just fine with a very short push rod on the slave courtesy of the adjustable length rod arrangement. The Rule of 92 isn’t as hard and fast a rule as I’ve gone to great lengths to champion.

BTW these slaves are spec’ed on the 70 Z’s if you’re looking for one on Rock-Auto. 

Nothing stopping you from just hack sawing off your fixed length rod as well. Just more of a trial and error thing.

[Zed Head]

Most people with collar problems either find that the fork hits the back of the transmission hole before full clutch release or that a too long collar jams the pressure plate fingers causing a slipping clutch.  You can't fix either of those with an adjustable rod.  The rule of 92 is the "guaranteed" method, for those that want to do the job once.  

I think that some pressure plates probably release with a shorter stroke also.  More precise design, shorter levers on the diaphragm springs, thinner cushion springs, stuff like that.  So the odds probably depend also on the clutch kit overall design.

Interesting topic for sure.  

Here's the Rockauto pages for the two types.

https://www.rockauto.com/en/catalog/nissan,1971,240z,2.4l+l6,1209158,transmission-manual,clutch+kit,1993  (goes through 1975!)

https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,transmission-manual,clutch+kit,1993 (options are growing - racing clutches)

 

[Trnelson]

I had measured the finger height when I had the parts out this morning and there was only 1/16” difference if the new one being shorter. Sounds like that may or may not be indicative of its compatibility with the other components that I have.  I’m not in position to install the clutch etc as I’m finishing up engine assembly and it’s on a stand, maybe in a few days.  I did check my current slave cylinder and fork. It appears that I already have the adjustable version, albeit crusty, on the car.  My plan as of now is to install the new clutch with the slave cylinder setup that i have, sounds like it will need some adjustment but should work. 

Thanks

 

Tom

[Trnelson]

@Zed Head, our posts must have crossed paths!  Well now I’ll have to do more measuring when I finish up the engine and bolt up the clutch. Stay tuned 

[Zed Head]

Posting just to get some key words in this thread.  I searched "zkars pressure plate" and nothing came up.  It should now.