280Sl 4 speed manual clutch biting point very low

[lamakdaddy]

Hi

My 280sl 4 speed finally arrived.  The clutch feels strong but the biting point is very low (near to the floor).  The pedal sometimes sticks a little.  In my previous cars the problem when the clutch or hydraulics are faulty is that the biting point is usually very high off the floor.  Any tips or guidance would be much appreciated.

Thanks

Kamal

[George Des]

Check the adjustments on the clutch slave cylinder. There is a spec for the gap between the pin and the throwout arm. You'll need to get the spec since it may be different between the various model.

George

[w113dude]

Hi Kamal,

It sounds like the clutch master cylinder is bad, that is the only thing that will have any sticking action, most likely the rubber seals inside has disintegrated or just broken in to pieces not creating enough compression and also causing the piston to stick, Check your fluid level in reservoir if low and you see some evidence of oil in driver side floor then that is a sure sign of a bad master cylinder.

[GGR]

Try to find out if the clutch was worked on recently, and if so what were the parts used.

Try pumping the system by activating the pedal several times. If the biting point goes up, the the system is at least in need of bleeding (air trapped).

I think that if your master and slave cylinders were bad, the car would start moving with clutch fully pushed down while engage in 1st gear. Internal leaks would have the clutch pressure plate engage even with the pedal to the floor. 

If your master cylinder was replaced by one with a smaller inner diameter (as commonly found on later models) less fluid is being pushed which would explain a low biting point. It would also explain the sticking pedal as back pressure would not be enough to counter act the pressure of the "assisiting" spring on the pedal assembly.

As a (temporary) cure, you could try adjusting the slave cylinder rod as already mentioned (but then make sure pressure on the rod is fully released - you can feel it by wiggling the rod) when the clutch pedal is released. You could then loosen the "assisting" spring on the pedal assy by loosening the adjustment at the front side of the spring so that back pressure can overcome the spring pressure more easily.

[lamakdaddy]

The gears are engaging very well and the cylinder on the gearbox (slave?) etc look new. the clutch is also very light.  Its just the low biting point that makes it difficult to modulate the clutch.  There is also alot of travel (say 1.5 inches) before any resisitance is felt in the pedal. I will start with the adjustment of the slave..

[lamakdaddy]

Well I looked at the slave cylinder today and could not find any way to adjust it. It seems to have a well installed boot and looks new or recently replaced? My car is a 71 280sl. Can someone send a picture to show adjustment? Thanks

[georgem]

If you carefully pry the boot off the body of the slave cylinder you should hopefully find the adjustment mechanism - you will need two spanners to loosen the lock nut and then rotate the rod until you get the desired free play then nip it up again with the lock nut. It may also have a large spring that goes between the clutch actuating arm and the body of the slave cylinder - disconnect this before you make any adjustment.

Cheers

[Benz Dr.]

I've seen some 280SL slave cylinders that have no adjustment and they simply use a push pin. Proper adjustment is critical for proper function. Once you have the adjustment correct it will self adjust as the disc wears after that point.

I always thought that the two master cylinders used the same diameter pistons. The outer portion of the housing is different as far as the mounting goes, with one being solid and the later one having an aluminium housing with a rubber bushing. Not clear to me why they changed this but there must be a reason. MB always has a reason for everything.

[GGR]

I always thought that the two master cylinders used the same diameter pistons.

I had the r107 or W114 model in mind when I mentioned later models. I did use an r107 master cylinder on my 5.6L project so as to match it with the 3.5L slave cylinder and clutch I've been using. The inner diameter is smaller and guess what? the pedal was sticky. I had to loosen the spring on the pedal a bit to get everything back to normal.

Depending on what may have been used on Kamal's car for price or availability reasons (in case it was replaced), this may be the reason for his sticky pedal.

[lamakdaddy]

I've seen some 280SL slave cylinders that have no adjustment and they simply use a push pin. Proper adjustment is critical for proper function.

Thanks but how is the adjustment made in the first place if there is no adjustment?

[Benz Dr.]

The length of the push pin determines how much free play you will have. If the pin is long enough there won't be any play. I've never set up a slave cyinder with the fixed position push pin as all of the ones I've seen had an adjustment on them.

Normally, you would adjust the pin so that there's a small amount of free play between the end of the pin and the throw out fork. What you're looking for is the least play possible so that the fork isn't pushing on the he throw out bearing. If it is, the bearing will wear out from constant turning. Set p properly, the bearing should last as long as the clutch plate. The return spring on the clutch slave helps to keep the fork pulled all the way back to its rest position.

When the pin is set up properly, the free play at your clutch pedal should be about 19 - 25 mm. There is also an adjustment on the push pin for the master cylinder. It should be set up so that you have a small amount of play so that the piston in the MC reaches its upper limit. If it's too tight the clutch won't release and if it's too loose there will be a lot of free play in the pedal.

Check under the car first and adjust the play there. Normally, the adjustment on the pedal inside your car never changes or never gets changed because the MC is replaced without disturbing this setting. 

[Naj ✝︎]

Hi, Kamal,

This thread may help explain further:

http://www.sl113.org/forums/index.php?topic=9338.0

It may be just a case of the slave cylinder has a pocket of air thats causing you issues.
Attached factory procedure for bleeding the hydraulic system.

Good Luck
Naj