TR2/3/3A More questions concerning clutch hydraulics

[Lukens]

Gentlemen and ladies,
Some of you may recall that I was experiencing clutch related problems while vacationing in Ohio. The problem was that my clutch pedal would go "soft" at unpredictable times. I learned to pump it a couple of times and had no additional problems. I'm back in Florida now and although I don't have time to work on it now, I still have some questions. Humor and educate me please.

I think I have a grip on the workings of the master cylinder. My understanding is that when fully extended the return port to the reservoir is open. Pressing the pedal pushes the piston assembly inward, thus closing off the return port and sending all the juice to the slave.
Question #1. How much piston travel is required before that port is closed? Or more meaningful, how much free pedal travel is required before the slave is actuated?
Question #2. When the pedal is released, will the piston in the slave be bottomed out?
Question #3. What brings the slave piston all the way home? The external spring? Or the "suction" from the pedal being released?
Question #4. and probably not my last, I'm confused about the importance (or apparent lack of) the external slave spring.

As always, TIA,
Russ

 

[MGTF1250Dave]

Aloha Russ,

Here is my understanding of the clutch hydraulics regarding your questions:

1. Very little piston travel is required to close off the return port. However Pedal travel can vary depending on the adjustment of the push rod length (it should have some free play against the piston). Also over time the hole in the clutch pedal that the clevis pin goes through can oval and introduce free play. All this free play needs to taken care of before the piston begins to move.
2. Maybe, but probably not. The slave piston will move to until the pressure of the clutch operating push rod is relieved. The clutch pressure plate springs will push back against the throw out bearing moving the operating lever and moving the push rod back against the slave piston.
3. There is an external spring that brings the slave piston home.
4. The return spring is important to bring the throw out bearing back far enough so that it not in contact with the clutch spring operating levers or fingers. This is to reduce excessive wear of the bearing.

 

[Lukens]

I must be dense, I'm still not understanding the geometry between the slave cylinder and the clutch. Assume that the is pedal is up. The pressure plate is exerting it's full force against the clutch. The external spring will bring the TB aft (away from the pressure plate fingers). But here's my confusion: How far aft? Where does it stop? The rod's not against the piston because we want a gap there, something else must stop it? And what establishes where the piston stops, the same gap says the rod stops short of the piston's "pedal up" position?

 

[titanic]

Please disregard this post. It doesn't apply to a TR3.
There shouldn't be an external spring on the slave cyl. unless an adjustible pushrod has be fitted. This combination was used on TR2-4 and required periodic adjust. because of clutch disc wear. The external spring caused the pushrod to push the slave cyl. piston to the bottom of the bore when the clutch pedal is released. Starting with the TR4A(I think) the external spring and the adjustible pushrod was eliminated to make the clutch self adjusting. There is an internal spring in the slave cyl that pushes the piston in the opposite direction of the earlier arrangement. Now, when the pedal is released, the pushrod pushes the arm and TO bearing to maintain contact (or close to it) on the clutch PP. As the clutch disc wears, the internal spring pushes the piston out so that the TO bearing stays in contact with the PP.
That is the theory anyway. In practice, if the spring pressure is too light to force the TO bearing to spin with the PP, a groove is worn in the PP. The Buckeye articles on the clutch has a better explanation. I had the problem with the worn PP and went back to the earlier arrangement.
Berry

 

[TR3driver]

I must be dense, I'm still not understanding the geometry between the slave cylinder and the clutch. Assume that the is pedal is up. The pressure plate is exerting it's full force against the clutch. The external spring will bring the TB aft (away from the pressure plate fingers). But here's my confusion: How far aft? Where does it stop? The rod's not against the piston because we want a gap there, something else must stop it? And what establishes where the piston stops, the same gap says the rod stops short of the piston's "pedal up" position?

The rod does come up against the piston (under the force from the spring), normally there is no gap there. The bearing lifts away from the pressure plate by roughly the same amount as the freeplay adjustment.

In order to measure the freeplay, you have to pull the lever away from the slave, against the force of the return spring. Or use the book method, which is to unscrew the adjustment (against the return spring) until it comes up against the PP springs. Then you screw the adjustment back in by the recommended distance (0.1" for the Girling setup) to create the freeplay.

 

[TR3driver]

Please disregard this post. It doesn't apply to a TR3.
There shouldn't be an external spring on the slave cyl. unless an adjustible pushrod has be fitted.

Right. The TR4A-TR6 were designed differently, with a TOB that is supposed to run continuously. The big advantage is not having to adjust the slave occasionally. The big disadvantage is that some replacement bearings don't turn easily enough and wind up rubbing against the PP fingers. In extreme cases, the fingers wear out, ruining the PP.

I prefer the earlier setup because of that. Not that big a deal to adjust the clutch every blue moon or two. And you need to be under there occasionally to deal with other issues anyway.

 

[titanic]

Randall-I must have been having a senior moment-I didn't realize the original posting pertained to a TR3 until after I responded. The pp fingers on my 6 looked like the one on the Buckeye site, even though the TOB is the stock RHP. After replacing the clutch and reverting to the external spring&adj. pushrod, there was no wear at 30k miles.
Berry

 

[karls59tr]

Right. The TR4A-TR6 were designed differently, with a TOB that is supposed to run continuously. The big advantage is not having to adjust the slave occasionally. The big disadvantage is that some replacement bearings don't turn easily enough and wind up rubbing against the PP fingers. In extreme cases, the fingers wear out, ruining the PP.

I prefer the earlier setup because of that. Not that big a deal to adjust the clutch every blue moon or two. And you need to be under there occasionally to deal with other issues anyway.

So if you have a TR6 gearbox and TR3 clutch disc, pressure plate and TOB do you use the external return spring? Does the TR6 slave cylinder have an internal return spring that the TR3 slave does not?

 

[TR3driver]

Randall-I must have been having a senior moment-I didn't realize the original posting pertained to a TR3 until after I responded. The pp fingers on my 6 looked like the one on the Buckeye site, even though the TOB is the stock RHP. After replacing the clutch and reverting to the external spring&adj. pushrod, there was no wear at 30k miles.
Berry

As I understand it, there was a big batch of bad RHP bearings made. They worked OK, except were a little too stiff to turn, with results as you saw. Some of them even set up a howling noise as they rub against the PP (but not all of them).

Hopefully they are all out of the system by now, but you never know.

There have also been "upgrades", like the Gunst clutch, that suffer the same problem. The Gunst kit actually includes an extra spring to be installed, to force the bearing to turn.

 

[TR3driver]

So if you have a TR6 gearbox and TR3 clutch disc, pressure plate and TOB do you use the external return spring? Does the TR6 slave cylinder have an internal return spring that the TR3 slave does not?

With the TR3 pressure plate & TOB, I'd stick with the external return spring.

Actually, in my case, I'm using a TR4A pressure plate & TOB and I still kept the external return spring.

The TR6 slave cylinder is supposed to have a spring inside it, but it isn't a return spring. Instead it holds the piston out against the pushrod. The parts manuals are somewhat confused, though, and some of them don't show the spring. I've even seen a Girling instruction sheet that says to remove the spring when using the slave on a Triumph (but I assume they were talking about TR3-4).