Non-adjustable slave cylinder on 280SL

[roadsterdude]

Back to my slightly slipping clutch.  On a 250 mile drive last week, I did encounter my slipping clutch somewhat in 5th gear at 75-80 mph.  No big surprise, I knew it, but kind of postponing action.....Researched a thread where someone fixed the exact same problem by adjusting the slave cylinder to 4mm free play, so worth a try.  My 280 has a non-adjustable slave and of course the free play is 0. My question (before doing a winter project of clutch/pressure plate/throw-out bearing/flywheel surfacing, and God knows what else (once I am "in there") - could I install an older 250SL adjustable slave cylinder with some free play and see if my situation magically disappears like the post I found?

If the answer is "no" (as I suspect), then is there a post somewhere that documents a clutch job on a later 280 somewhere on the forum?  One twist is that this car is refitted with a ZF 5-speed, so I'm not sure if there would be any difference in the clutch set-up.  I know the drive shaft length etc. is different.  Any advice is appreciated!   

[Tyler S]

If it was refitted with a zf trans then it is entirely possible that the wrong style old slave cylinder from the 4 speed was used? If it will even bolt up.  It all depends on what style clutch was installed. A 3 finger design or the one with the diaphragm.. The ladder being self adjusting internally.
Here is a good thread
http://www.sl113.org/forums/index.php?topic=9338.0

[roadsterdude]

Tyler, thanks for the link.  I think I understand more now.  I must assume that the slave is either the 4 speed one or one that came with the zf.  In either case I believe the clutch is the later diaphragm style since this is a '69 280, so I guess my idea of refitting a 250 type adjustable slave is a non-starter since that was obviously used with a different type of clutch.   I will either have to live with the occasional slip at high rpm high gear (torque induced), or bite the bullet and do the clutch job.  Any links to help on the clutch job would be appreciated.  Thanks again! 

[Benz Dr.]

I have a 230SL with a 250SE engine and a ZF trans. This set up is using the later pressure plate but I found that a 280SL style throw out bearing wouldn't fit on the front cover of the ZF trans. I had to use a 230SL style brearing and an earlier adjustable slave cylinder to make it all work. I doubt that ZF made two different front covers for only about 1,400 units supplied to the various different models that used these rare transmissions and not likely something different for a hand full of 280SLs.

 

[Tyler S]

If an adjustable slave will bolt up and the pin will reach then maybe it would work. In the mean time you could always loosen the 2 slave mount bolts and see how much foreward tension there is before disengagement of the clutch. Would tell you if that peticular slave is not giving enough freeplay and is bottomed out in the bore.

[ctaylor738]

There should be an eccentric BOLT where the push rod attaches to the pedal.  You can turn it to make a limited adjustment in the free play.

Also, doesn't the master cylinder need to "vent" fluid up into the reservoir as fluid expands as engine heat increases the temperature of the fluid?   If it can't vent, it might put enough pressure on the clutch to make it slip.   You might try adjusting the resting point with the eccentric nut to see if this helps.  Also, the o-ring in the master cylinder can swell from contaminated fluid and block the little vent hole.

[roadsterdude]

I will try this.  In the meantime, I have checked for the 230/250 type slave cylinder 0002951907, and they are out there from $63 to $300+ but none of them appear to come with the threaded rod or return spring - and I will need both.  I may try and find a used unit somewhere just to see if it bolts up and works.  In the meantime I'll have a look at the pedal.  Thanks!

[ctaylor738]

The rod is 111 295 07 33, spring is 111 993 11 10.

You can also make a custom-size rod out of an M6 (I think) bolt.

[roadsterdude]

Is this the eccentric nut you mentioned?  Not sure how I can adjust anything here, but I may be looking at the wrong thing (it's pretty tight quarters for a 200 pounder).  Don't want to turn something that does not need turning - BTDT!  Also took a pic of the slave.  When I say "zero" free-play, I mean it does seem to be free to spin in the hole and does not feel under pressure, but no play - if that makes any sense.  I am going on a two week vacation Thursday, and will probably have to postpone parts seeking etc until I get back, but I'll post results of whatever I end up doing.  Just may be awhile.  Thanks for the responses so far!!

[ctaylor738]

Yes, that's it.   But my bad - I should have said "eccentric bolt."  Will correct my original.

If you can turn the pin, it's probably not exerting pressure on the clutch.  But the $64 question is what is it like with a fully warmed-up engine?

[Tyler S]

If the slave cyl piston is bottomed out in its bore then adjusting the pedal freeplay inside the car will do nothing to help the slipping issue.

[tel76]

It is very unusual for the slave cylinder piston to bottom out but this is very simple to check out.
Using your hand or a screwdriver, try to move the clutch throw out arm in towards the slave cylinder, if the arm moves into the cylinder then your piston is not bottoming.

[Tyler S]

If his rod is too long pushing on the throwout bearing/fork and the piston is bottomed out then the clutch is not fully releasing = slipping
Freeplay measurement should be taken when the piston is bottomed out. This is where it starts its travel to release the clutch. The spring should pull it to the bottomed out position. If it wont move back the there is pressure on the line or the master is mis-adjusted.
If the rod is too short then the slave starts its movement too far up its bore and can either pop out or not let the clutch fully disengage.

[tel76]

On the self adjusting clutch there is no return spring fitted,( although the release fork still has the facility), therefore the piston does not always go to the bottom of the cylinder.
If there is a return spring fitted then it is the adjustable type and free play is adjusted with the piston at the bottom.
With the above in mind I have seen that because there is the facility on the release fork for a spring to be fitted a previous repairer fitted a spring to the self adjusting clutch, this caused numerous problems with selection.