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TR2/3/3A Bleeding Technique

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frankfast

Jedi Trainee
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I'm having a hechuva time bleeding my clutch. I recently installed two new master cylinders and a new clutch slave cylinder and against the advice of some decided to use DOT 5. The brakes were bled and work fine but after bleeding the clutch slave cylinder at the bleeder valve with a Mityvac and bleeding the master cylinder with the help of of someone pumping the pedal, I can't seem to get the air out - if that is the problem. Every indication is that there is air in the line since after pumping the pedal a few times the pedal resistance is at a proper height. Could there be another reason? Is there a better technique for bleeding the clutch? If DOT5 works for the brakes, why wouldn't it work for the clutch?
 
It is not the dot 5. Bleed the whole system with the pedal. Is the bleeder on the slave pointing up or down? If down, turn it up. Have you tried both "pump,hold down,open bleeder, close bleeder, repeat" and " open bleeder, depress pedal, close bleeder, release pedal, repeat"? You can also slip a clear plastic hose over the open bleeder, place the other open end in a clear jar of fluid, and have the pedal pumped while you watch for bubbles to quit. Sometimes, and I forget why, the check valve in the m/c malfunctions to preclude bleeding in a clutch. Bob
 
The bleeder valve is up. I've tried two of the methods you've suggested multiple times. I'll try the others but am running out of patience. The brakes were easy and got immediate results but the clutch on the other hand has proven to be a challenge. I know I'm not leaking fluid because the level in the reservoir is maintained. I've heard that it is more difficult to bleed DOT5 but I didn't have a problem with the brakes.
 
Are you getting air from the bleeder or clear fluid but no initial pedal? Is the mounting flange on the slave on the front or rear side of the plate that mounts it to the bell housing? Is the support rod from the plate to the oil pan place and adjusted?I also recall that there may be two diameters for the slave piston. Check the moss catalog on this and make sure you have the right one. Seems like the "too big" one would possibly require pumping to get a pedal. How are the freeplay at the pedal and the fork?
 
Moss only sells one slave cylinder for the Girling system. It has a 1" bore. I'm not sure if the Lockheed slave cylinder which has a larger bore is interchangeable. It's for earlier cars. I'm not getting air when I bleed, only clear fluid. I've adjusted the rod according to the manual. There's air in the line somewhere. I think I might try your method of opening the bleeder, depressing pedal and letting fluid flow then closing bleeder. Air would have to eventually come out. There should be a bleeder at the top of the system not at the bottom.
 
Is your car sitting flat? Jacked up in front could trap air in the front of the slave. I believe that one of the most experienced guys on this forum bleeds his clutch by opening the bleeder and letting gravity do the work. It shouldn't be this hard. Which I realize you know. If the car is level and you are not getting air, it starts to seem like something mechanical, not hydraulic. Does the pushrod move immediately under pedal pressure? If so, does it stop moving only when it encounters resistance from the fork/pressure plate?
Bob
 
I would double-check that the slave piston is actually bottomed in the bore when checking the pushrod adjustment. Since you aren't getting any air out, it seems unlikely there is air in the system.

FWIW, I normally don't bother with the clutch bleed valve at all. Just pump the pedal up, hold it to the floor for a few seconds (for the bubbles to rise) then release it and wait 10 or 15 seconds. 3 or 4 repetitions is usually enough to get a usable clutch; the rest works it's way out over the next few days.

And that's with DOT 5. The only DOT 5 precaution I take is to take a break for several hours after adding fluid to the reservoir. That should give any bubbles time to rise to the top, so they won't get sucked into the MC from the bottom.
 
Are you bleeding from the MC itself? That's where I've been bleeding from. After pumping the pedal a few times, I crack open the front nut on the MC. Maybe I should leave it open awhile with the pedal depressed and let the fluid flow out, hopefully the bubbles with it.
 
Here is a last resort method--.
Use an old reservoir cap and mount a air valve ( like from a bicycle tire) on top of it. With a hand air pump give the valve a few pumps and bleed the slave cylinder. About two repetitions did it for us. This was after similar results as you have stated.
 
"FWIW, I normally don't bother with the clutch bleed valve at all. Just pump the pedal up, hold it to the floor for a few seconds (for the bubbles to rise) then release it and wait 10 or 15 seconds. 3 or 4 repetitions is usually enough to get a usable clutch; the rest works it's way out over the next few days."

Does that mean you're not bleeding anything?
 
frankfast said:
"FWIW, I normally don't bother with the clutch bleed valve at all. Just pump the pedal up, hold it to the floor for a few seconds (for the bubbles to rise) then release it and wait 10 or 15 seconds. 3 or 4 repetitions is usually enough to get a usable clutch; the rest works it's way out over the next few days."

Does that mean you're not bleeding anything?
Click to expand...
I do either pre-fill the MC, or loosen the outlet fitting and bleed enough to get the MC mostly full of fluid (so it will pump up). But that's all, for the clutch.

Brakes are a different story, too many ups and downs; plus the residual pressure valve (if it hasn't been disabled).
 
I recently replaced my clutch MC and slave on my TR4a, and used DOT 5. With my wife’s help, I used the “pump pedal, hold, open bleeder, close bleeder” method and it worked fine. However, as Randall mentions above, I also verified that the slave rod was pushing the slave piston all the way home. Moss has a video describing this:

https://youtu.be/uj1dMdYgRK4

The only issue I ran into is that I found, after it was bled and adjusted, the slave cylinder did not push the release lever as far as some others have observed. Turned out not to be an issue as the clutch worked fine.

Jim
 
Mounted on the same same side as the one taken off. The fact that the pedal must be pumped to get resistance and to get the pedal at the proper height before resistance seems to indicate that there is air in the line. I can't imagine what else would cause that problem.
 
Sometimes pumping DOT5 just makes the problem of air bubbles worse.
If you can push down w/o pumping you may have better results...but first wait a few hours for the air bubbles to reunite.
 
Do you have a return spring hooked up? If so, try unhooking it. If that makes an effect for the better then try a weaker spring. I am convinced some of those aftermarket spring are too strong.
 
frankfast said:
Mounted on the same same side as the one taken off. The fact that the pedal must be pumped to get resistance and to get the pedal at the proper height before resistance seems to indicate that there is air in the line. I can't imagine what else would cause that problem.
Click to expand...
Consider what would happen if, for example, you had about 1/4" freeplay at the slave; like would happen if the taper pin had sheared. The return spring would eventually pull the piston back into the slave (displacing fluid into the reservoir) and then when you step on the pedal, most of the pedal travel is taken up by moving the piston out until the fork touches the TOB. You would feel essentially no resistance until the TOB actually starts to compress the pressure plate springs, at the very end of the stroke.

But if you pump it up, the spring doesn't have time to return the piston and you wind up with it out far enough to eliminate the freeplay. The clutch appears to work normally; until the return spring pulls the piston back again.

I actually drove that way for several months when my taper pin broke. I learned to keep my left foot on the clutch pedal just enough to keep the return valve closed, so I didn't have to pump the pedal the next time. But if I forgot and took my foot off ...

Probably would have worked as well to just remove the return spring. Without it, there is nothing to push the piston back into the slave and it should stay extended by just the friction of the seal in the bore. ISTR Geo said he drove this way for some time (perhaps still is?) But it didn't occur to me at the time to try it.

The reason everyone asks about the slave cylinder mounting is that the photo in the workshop manual (and many other places) is wrong! It shows the Lockheed arrangement, which was different. So it could well have been wrong when you got the car.

3ya68rs.jpg
 
frankfast said:
Are you bleeding from the MC itself? That's where I've been bleeding from...
Click to expand...

That seems a doubtful approach. If you are going to open a bleeder I would think the one on the slave cylinder is what you'd want.

I have only cracked open the master cylinder connection if I was having trouble getting a bleed started - don't recall ever having to do that on the TR clutch.
 
I started bleeding from the slave bleeder with a MityVac and when I was getting clear fluid took the car off the jack stands. Still had problems so remembered that air rises in a system and started pumping the pedal and cracking open the output nut on the MC. Did initially get some air out but then all clear.
 
SP3 and TR3 - Now I'm confused. On the Girling system, is the slave cylinder mounted in front of the bracket or behind? My manual shows behind but the illustration above shows in front which is the way mine is located and the way it came out. In that location there seems to be a lot of pressure on the return spring.
 
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