Super Seven S2 Clutch Issues

[SENC]

The following is a note from John Watson in a thread on the now essentially defunct se7ens.net mailing list:

According to the Girling catalogue:-
LOTUS SEVEN SERIES TWO - June 1960 to October 1961 
and 
LOTUS SUPER SEVEN October 1961 on

BRAKE MASTER CYLINDER = 5/8"
CLUTCH MASTER CYLINDER = 3/4"
CLUTCH SLAVE CYLINDER = 3/4"

Cheers,
John.

I also had this in my files, from page 3 of a Girling catalog.  I'll also attach the pdf of the catalog if the forum allows me to do so.

 

 

Girling Dunlop Parts Catalogue G262.pdf

[jbcollier]

Is it a “real” Girling cylinder, or a knock off?  I think you said you put in a new one?

 

I remember you overhauled the slave.  Was the bore excellent with no wear marks or corrosion whatsoever?

Edited June 4 by jbcollier

[TEM]

Yes, I bought a real Girling.  Every thing on this car is original so I want to keep it as original as possible.  The 3/4" MC is the one I bought new, one of the mounting ears was broken off.

[TEM]

Form the brake section of the Seven manual.

 

 

I love conflicting information.

 

I have nothing in wring on the clutch MC.  Others including a fellow club member with a Seven have said they are using 3/4" MC on the brakes and 5/8" on the clutch.  Perhaps the clutch was replaced with a heavier competition clutch and thus the massive pedal force needed with the 3/4" MC.

 

More important to me at the moment is why I'm not getting full stroke from my MC regardless or piston size.  I pulled the MC and on the bench, the stroke is perfect at 1.375".  put it back in to check stroke with the slave attached but forgot the slave does not have a stop and pushed the piston out of the bore and got it stuck on the pushrod.  The seal was sticking half out so I had to cut it off to get the piston back in the bore to dislodge the slave cylinder.  I'm dead in the water until I get a new rebuild kit.

[SENC]

Yep, one of the frustrating things about old Lotus - always lots of conflicting evidence - and evidence that they really did frequently stick whatever they had on these cars!  Bottom line, I think either work for both brake and clutch, just require different pressure and different pedal strokes.

 

Don't feel to bad, I had exactly the same thing happen, though I was on the road taking an initial test drive after getting everything back together.  Mine was due to slightly missing on the setup of the dome nut, which allowed the piston too far forward when I fully depressed the clutch.  I was only about a mile from home and had my son pick me up to get some tools and a spare slave cylinder I had.  It was a royal PIA to get the stuck slave out (I had to cut the rod, too) and a new one in and adjusted on the side of the road.  But I was thankful it wasn't my Elan.

[TEM]

Yep. Mine was stuck in there real good too.  I used a long screw driver to lever the throwout arm just enough to coerce the piston back in the cylinder.  Don't want to do that on the side of the road.

[MV8]

I would not assume the installed travel is as much as the max design travel of the MC. You'd need to raise the pedal attachment point (slightly higher effort/reduced pedal ratio) and fit an offset pedal fork (to eliminate the need to raise the MC to match). Doesn't need to be as rigid as the brake fork since the pressure is just enough to move the pressure plate fingers.

[TEM]

Why would you not assume that?  The only thing to stop the MC travel is the pedal hitting the firewall or the clutch arm bottoming out in the pressure plate. 

 

The odd thing is that when I added the 0.2" preload the car was undrivable due to the clutch slipping.  So, the clutch grab point is very high.  So, why does the rest of the pedal travel not fully disengage the clutch?

[MV8]

In general, an installation should have a safety margin to prevent total hydraulic failure due to stacking tolerances. My understanding is:  1) you carefully measured the MC stroke to be 1.04", 2) you are bottoming the MC, and 3) the design stroke of the MC is 1.375". This tells me that the pedal linkage is preloading the MC piston by approx 3/8". It also won't self-bleed if the compensation port is always covered by the piston. Linkage wear and less-than-ideal operating angles contribute to a loss of MC pushrod travel.

Also, I don't know if the release bearing is the type that is designed to turn with the pressure plate all the time or just when shifting, which requires clearance to the pressure plate. A return spring on the fork suggests the latter. I've not read the mechanical adjustment procedure.

Pictures from the side of the top of the clutch pedal area (to include the MC mount) with the pedal released and fully pressed might help us to see the issue. Feedback from a second set of eyes is usually a good thing.

Edited June 5 by MV8

[TEM]

MV8

Commenting to your above assumptions.  1)Yes, MC stroke in the car connected hydraulically to the clutch measured 1.04".  2) No, I can't say that I am bottoming out the MC.  It could be bottoming out on the clutch. 3) Yes, bench testing the MC yields a stroke of 1.375.

I'm not sure how the MC can be pre-loaded.  The pedal is free to move before inserting the pin to hold the MC and pedal together.  Is it possible that the MC doesn't full retract?  Possible.  But I can say that I didn't see any movement of the MC rod when removing the MC form the car and motion is smooth on the bench.  But, I'll check it when I get the system back together.

 

The release bearing is in contact only when shifting (confirmed visually through the shift fork hole).

 

I Had to cut the slave seal when I accidentally pushed the piston out of the cylinder.  I will send pictures when the new seal arrives.

[MV8]

I am confused. Is the following not accurate?

Post #8: "After careful measurements, I show the following: Master cylinder rod travel = 1.04""

Post #15: "With the current pedal setup, I have no problem pushing the pedal all the way in.  It does not hit the fire wall, but it does bottom out the MC."

 

The clutch would not bottom out.

 

Your pedal adjustment should look very close to this photo of a '61.

Edited June 5 by MV8

[TEM]

Sorry for the confusion.  As I dig deeper into the issue I learn more.  When first looking into this, an observation was made that the MC was not going full stroke.  Since this MC was recently rebuilt and the observation that the clutch was not fully disengaging, the MC bottoming out was a reasonable hypothesis.  Upon removal from the car, the MC was found in good working order and could reach full extension.  Therefore, something else must be limiting the stroke.  That is where we are today.

 

My pedal setup is show below.

[MV8]

I will state the obvious if it isn't clear to all. The slave stroke is limited to the MC stroke. These are normally 1:1 (3/4 bore slave, 3/4 bore MC). You are trading a longer stroke for lower pedal effort with a 0.750 bore slave and a 0.625 bore MC. A little more effort with a 0.700 bore MC is probably your best compromise, but let's see if you are getting everything you can from the linkage.

On the car, with the red line disconnected at the MC or fluid mostly drained, what is the total MC push rod travel, measured at the entry to the MC body, from released (pedal up) to the firewall? What stops the pedal travel/MC stroke with no fluid? You can place masking tape around the shaft and mark with a pen and straight edge, then measure the distance between marks.

[TEM]

I measured the MC travel both on the bench and in the car with no fluid and I'm getting about 1.36~1.37" of stroke.  The pedal is not hitting the firewall or anything else I can see so I assume the MC is bottoming out.

 

I would agree that changing the MC from 0.625 to 0.7 would help if I were able to get full stroke from the MC with everything hydraulically connected.  But that's not what I was seeing.  Something else must be stopping the stroke.  If that is the case then a 0.7" MC will not stroke any further and only serve to make the clutch heavier.  But I will check hydraulic stroke again after I rebuild the the slave.

[jbcollier]

Cylinder bores wear.  This may mean that the effective stroke is shorter.  I have seen this many times with used and “rebuilt” masters.  I would fit a new one myself — and did when I recommission mine last year.

[MV8]

Unless the pedal does not travel as far when bled, you are getting full stroke out of the MC but I don't understand how you determined what stroke you should be getting at the slave. Piston travel is inversely proportional to the diameters squared. If you go ahead and drop out using PI, slave stroke is equal to the MC stroke X master bore squared over slave bore squared. 0.390625/0.5625 = 0.694 x 1.375" MC full stroke = 0.954" of slave stroke. What method are you using to bleed the system? How did you ensure there is no air pocket in the slave?

[TEM]

That is the correct formula for a 5/8" master and 3/4" slave.  Your results match my previous post.

 

As I mentioned, I remove the slave cylinder from the bell housing and raise it above the master cylinder.  I clamp the slave cylinder so that the piston doesn't eject itself and then bleed as normal.  This keeps the air pocket at the highest point.  I first bench bleed the master.

[SENC]

Do you have the spacer/washer in behind the circlip on the slave, to ensure it is positioned (and remains positioned under pressure) correctly?  If not, you're losing about a 16th of an inch.  Enough?

 

[TEM]

No, I do not have this washer.

 

When adjusting the clutch you are to leave a 1/16" gap between the domed nut and the arm.  Does it matter if there is a washer there?  I would think that the washer is only there because the circlip is so thin and a washer would provide better contact area with the bell housing.  It may also reduce the chance of a rattle.  But I don't think it will lead to any stroke reduction.  There is a 1/16" gap with and without the washer.

 

I check the Elan parts list (similar design as the Seven) and there is no washer there either.

 

[SENC]

I first reinstalled without it (unintentionally), and noticed the pressure on the rod forced the circlip up snug against the mount on the bellhousing, leaving a gap on the front side.  The space took up that slack, effectively locking the slave cylinder in a rearward position.  I'd have to measure it to see how thick it is and how much it actually impacts it, but estimate about 1/16.

 

I feel like I've seen a reference to it, but will have to look around to see if I can find it.  I don't remember it, either, on my Elan, but may have had a thicker circlip.