TR4/4A Setting up Self Adjusting Slave Cylinder

[RJS]

Hi,

I have a pretty arcane question about the initial set-up for the TR4A slave cylinder which is self adjusting. I've read the Bentley Manual, Triumph Technical Service Bulletin T-66-55 (which says to use 0.3" freeplay, not 0.1") and the Moss Bulletin 596-046 on setting up the TR250 & TR6 adjustable pushrod ( https://www.mossmotors.com/graphics/products/PDF/596-046.pdf ). Each one is not entirely clear. My main question is if the slave piston is to be seated all the way home (in the back of the slave cylinder) when performing the adjustment for freeplay?

I took a shot a drafting my own step by step instructions. Let me know if you think this is correct and more clear:

1. Remove rubber cover from slave cylinder to ease adjustment of pushrod – slide it up pushrod out of the way
2. Remove clevis pin, disconnecting clevis fork from clutch actuating lever
3. Seat slave cylinder piston all the way home with pushrod (i.e piston bottomed all the way in the slave cylinder). Careful fluid does not overflow master cylinder
4. With clutch actuating lever in its natural rest position, rotate clevis fork on pushrod so the hole on clevis fork lines-up with middle hole of the actuating lever.
5. Insert clevis pin connecting clevis fork to actuating lever
6. This process should have removed all freeplay from the linkage.
   1. Alternatively, begin by creating play by screwing push rod into clevis fork. Then, remove all play b/t clevis fork and pushrod inside slave cylinder by rotating the pushrod until all freeplay is taken out of the linkage. Do this by unscrewing pushrod from clevis fork until slave cylinder piston is fully seated. The easiest way to tell is to move the pushrod in-out; when you can’t move it any more, stop. The freeplay is now zero.
7. Add 0.3” (~5/16” being 0.3125”) of play. I estimate this is 7.2 turns of pushrod into clevis fork. You can do this by a) tighten lock nut until it contacts the back of the clevis fork, b) back off the lock nut until there is 0.3" clearance b/t the nut and back of clevis c) rotate pushrod until the lock nut contact back of clevis fork again.
8. Tighten lock nut without disturbing pushrod
9. Reattach rubber cover to slave cylinder

I want to get this right since the Moss Bulletin contains a warning in bold red letters "Warning! If you totally eliminate the freeplay in the clutch linkage you run the risk of pre-loading the release bearing, which means it is rubbing against the fingers of the pressure plate. This will cause the release bearing to fail at best, and wear out the rear thrust washer in the engine at worst."

Thanks for those who are patient enough to read through this

Bob

 

[TR3driver]

If you use your alternate (6.1) procedure, then you can leave the rubber boot in place. I believe that will be easier as well, since there is supposed to be a spring inside the slave that tries to push the piston out, which will make step 4. difficult without having the piston move and mess up the measurement.

In spite of the bold red letters, it's pretty hard to mess this up. As long as there is some freeplay, you're good to go. The release bearing is actually supposed to turn all the time (the SC spring holds it in contact with the pressure plate), so IMO their warning about premature bearing failure is an excuse for poor quality bearings rather than a real hazard. But with all freeplay gone, some or all of the pressure from the pressure plate will be on the slave cylinder and not on the friction plate, which can lead to a slipping clutch (which will quickly burn out).

All this assumes you that you have an original-type bearing. Some of the aftermarket "improvements" (eg the Gunst setup) require that the self-adjusting feature be disabled.

 

[karls59tr]

In reference to 4. I've wondered about this. So you don't push the actuating lever all the way back but connect the clevis to the actuating lever when it is at "rest" which is when it is straight up and down?

 

[RJS]

Got it Randall, thanks

Glad to hear the risk is low. So you agree the intent is to push the slave piston home and then ensure you have some freeplay? In that case, I suspect you can have have all the freeplay you want, so long as there is still enough slave travel to actually disengage the pressure plate, correct? Better that than the opposite I guess.

BTW, do you know what it is that made these "self adjusting". I'm confused, is it a self adjusting pressure plate/ clutch or a self adjusting slave cylinder?

Bob

PS: the clutch is a Borg & Beck unit from TRF

 

[TR3driver]

So you agree the intent is to push the slave piston home and then ensure you have some freeplay?

Yes, exactly.

In that case, I suspect you can have have all the freeplay you want, so long as there is still enough slave travel to actually disengage the pressure plate, correct? Better that than the opposite I guess.

Yup.

BTW, do you know what it is that made these "self adjusting". I'm confused, is it a self adjusting pressure plate/ clutch or a self adjusting slave cylinder?

In effect, the spring inside the slave is what makes it self-adjusting; combined with a throw-out bearing that is designed to run all the time and no return spring on the slave. Later cars didn't even have the adjustable pushrod. Every time you release the clutch pedal, the spring holds the piston out to just remove all freeplay and hold the TOB lightly against the pressure plate.

Earlier cars (TR2-TR4) used a return spring instead, that always pulled the slave piston all the way home. So any free play represents lost motion and they have to be adjusted from time to time to keep some, but not too much, free play. However, my experience has been that the TR2-4 clutch wears very slowly, so even then it doesn't need adjustment all that often. I'm running the smaller TR4A clutch in my TR3 now, which does seem to wear a bit faster, but I still haven't moved that adjustment since 2010 or so and it's still OK.

 

[TR3driver]

In reference to 4. I've wondered about this. So you don't push the actuating lever all the way back but connect the clevis to the actuating lever when it is at "rest" which is when it is straight up and down?

I guess I glossed over that point. The lever's "natural rest" position should actually be slightly towards the slave cylinder; and you can pull it lightly to the rear (forcing the TOB against the clutch fingers) while checking the adjustment.

If the lever hangs straight down without contacting the clutch, then odds are that you have a broken taper pin or perhaps a bad TOB. Which, come to think of it, might explain the problems you've been seeing.

 

[RJS]

This is great info, thanks

Bob