TR2/3/3A 56 TR3 Master Cylinder Issues

[mgedit]

Having issues with recently rebuilt Lockheed master cylinder on my 56 TR3. Initially could not get system to bleed. Bought a suction type bleeder and that did not help. Took cylinder out of car to look at on bench. The piston was not returning after being pushed into bore on brake side (clutch side working just fine). Pushed the piston out with a little compressed air and checked for ridges or other issues in bore. Nothing that I could feel or see (it was resleeved in brass several years before I got the car but never installed). On bench was working fine with many repetitions of pushing in the piston and having it return normally. Back in the car. Bled system with suction bleeder (no need to move piston) and all seemed OK till I got to rear of car and one wheel cylinder was leaking. Ordered new copper washers for banjo connector, and while I waited for parts system enough fluid leaked to empty brake side of master cylinder. Started over again, and now can’t get system to bleed and piston is sticking yet again. Disconnected pipe at brake light switch and used a little compressed air to push piston back to fully retracted position thinking this would get me back to previous state where I had success. However, now can’t get system to start bleeding again. Gentle movement of piston created some air bubbles in MC reservoir. After 3 or 4 gentle strokes no more air, only some fluid being expelled into reservoir so I assume little or no air in MC now, but still won’t bleed.

I am sort of at a loss as what to try next. I can take the MC out again and check it once again for internal issues, but don’t want to do that if I just end up at same stage yet again. Am I missing something? Any ideas on what would cause the piston to not return? This worries me as I don’t see why it should not be pushed back by spring. Was wondering if there is some sort of pressure build up that is overcoming the push of the spring. Ideas and suggestions most welcome and definitely appreciated. Cheers, Mike

 

[TR3driver]

I see that you are using DOT 5. I have heard similar symptoms with a freshly re-sleeved MC blamed on the use of DOT 5; apparently the new sleeve gives more resistance than the original bore and the DOT 5 doesn't lubricate as well. Might be worth trying to shine up the bore a bit (which would make the seal last longer anyway). Or maybe just working the piston back and forth a few times on the bench (using compressed air to blow it back) would free it up enough. In normal operation, the brake springs will push the piston back most of the way anyway.

 

[TexasKnucklehead]

Mike,

I will not claim to know anything about this issue, but noticed items 26, 27 & 28 in the parts blow-up of your attachment. It seems they might be used to move the assembly forward and backwards, and one reason to do that might be to get the piston to return the whole way home for the begining of the stroke. Maybe the whole thing needs to move towards the front of the car?

But, looking at that diagram, I wonder if the brake/clutch is on the same side for a left hand driven car as a right hand driven?

good luck,
Jer

 

[sp53]

Yes I am just kicking out theories also. It does look like the internal spring on the clutch side would be under more pressure and perhaps return better. On the old Girling pistons there was a second place to put a felt ring or perhaps a small O ring towards the front and once I put one on and that slowed the whole system down and I got the problem you are describing. I note this because it looks like there are two rings on the piston assembly. If it was me, I would if possible pull the front one off and see if that freed up the system. I would also replace the spring and see if that helped.

 

[mgedit]

Thanks for the suggestions. Randall, on the bench the piston seems to work OK, but it is possible that the DOT5 is part of the issue. I'm thinking once the system is bleed everything may work OK. Jer, it is not entirely clear to me how those parts are ideally adjusted. Did not find the manual all that clear on that point, but as far as I can tell the piston is not covering the inlet hole for fluid to piston area. Brake and clutch would be on same side whether RHD or LHD as brake pedal is in centre in both cases. sp53, spring replacement is one of the possibilities I wondered about (or at least switching the two I have to see if that makes any difference). Cheers, Mike

 

[mgedit]

Just to add to the confusion, the diagram I posted above of the MC parts appears to be wrong ... internal parts from brake and clutch pistons are reversed. That one was scanned from the parts book, this one (below) is from the repair manual. Since I worked from the repair manual I think I rebuilt correctly, but interesting that the two BL books are different! Assume that this is the correct diagram of how parts are to be assembled. Cheers, Mike

 

[TR3driver]

There is a comment in the workshop manual to the effect that the clutch side doesn't have a check valve, so the second diagram must be right. The SPC also identifies the extra components as "brake side only".

Also, since it works on the bench (I misunderstood that part), I wonder if bleeding procedure might be the difference? The workshop manual procedure is somewhat different than what I've always used, as the book says to leave the bleed valve open while letting the pedal return. Since the return valve to the reservoir is a side port, I'm wondering if the early MC needs to suck back some fluid in order to return. If you close the bleed valve with the pedal down (which is the way I was taught to do it), the MC wouldn't be able to suck back any fluid and the resulting vacuum might hold the piston down the bore against the spring pressure.

 

[bobhustead]

Randall- That manual suggestion doesn't seem right to me. Wouldn't the open bleeder just return emitted air into the slave?
Bob

 

[TR3driver]

Randall- That manual suggestion doesn't seem right to me. Wouldn't the open bleeder just return emitted air into the slave?

No, because you are also supposed to have a hose from the bleed screw into a jar of clean brake fluid. The emitted air rises to the top, so only clean fluid gets sucked back.

At least that's the theory.

 

[bobhustead]

It will, of course, work that way, but I missed the hose in the jar part in the thread.
Bob

 

[TR3driver]

 

[mgedit]

Thanks for the further clarifications. I will have one more go at bleeding and report back. Randall, I was wondering about some sort of vacuum being part of the issue. Thanks to all for suggestions. Cheers, Mike

 

[sp53]

My spin on this is that there is some resistance in the cylinder like Randall mentioned earlier. I am curious about the inner parts. Do you have a chart for names of the parts whether an O ring or felt ring?Anyways, like a lot of these parts we get they are not up to the same quality as original. If an O ring is too thick or egg shaped, it creates resistance. I do not know if they are 3 world parts or not, but perhaps you can find a supplier in Europe that has them or perhaps contact one of the British car hydraulic rebuilders and see if they have any suggestions. I just do not believe it is avacuum problem.
I would take it back apart and have a very close look with amagnifier and perhaps do some measuring with and instrument.

 

[martx-5]

...
I would take it back apart and have a very close look with a magnifier and perhaps do some measuring with and instrument.

What would you recommend?? Oboe, tuba, perhaps a viola... :glee:

Just kiddin' around...:tennis:

 

[mgedit]

OK, so I had some time and took the MC apart again. It was assembled correctly and I cannot find anything that looks wrong or installed incorrectly. However, when I pushed the brake pedal gently to the floor (with MC reservoir empty, but some fluid in with piston) the brake piston did not return (stayed at far end of bore), the clutch piston returned smoothly as the pedal was released. Before pushing it all the way in, if I moved the brake pedal only a little the piston returned OK, about half or more up the bore, the piston returned after a bit of delay (it did not return smoothly like the clutch side). Since the only difference is the valve seat, cup, and body, I'm inclined to think that may be the root of the problem. Can anyone explain to me the function and working of this assembly? I think I have another new valve cup (part 8) and I'll replace that as I don't know what else to do. However, I'd like to better understand how this should be working to have more confidence that it will work when I re-install the MC again. Cheers, Mike

 

[mrv8q]

Mechanical, not hydraulic problem with the brake pedal itself?

 

[TR3driver]

Were the outlets connected to the car when doing this test? If not, what happens if you undo the brake connection while the piston is "stuck"?

I believe the "check" valve is actually a residual pressure valve that should hold a slight positive pressure in the hydraulic system all the time. It should allow fluid to flow out easily (under force from the piston), but block flow back into the MC until the outside pressure exceeds the inside pressure by enough to lift the valve off it's seat (something around 5-10 psi).
See https://www.freeasestudyguides.com/residual-check-valve.html

 

[mgedit]

Don't think it is a mechanical problem with pedal assembly ... was rebuilt and is operating smoothly. Thanks for the explanation of check valve operation Randall. I believe at one point I tried unscrewing the brake pipe to see if that would help, but it did not. Plus the piston stayed "stuck" when I removed MC and I had to use air to pop it out. Will check out that on check valve as well. Thanks, Mike