1971 HLS30-14938 "Lily" build

[Captain Obvious]

And as for your clutch... Which style clutch master are you using (early or late*)? Have you got a pic?

And same thing goes for the clutch as goes for the brakes... When you're foot is not on the pedal, it is important for the master to return to un-actuated "at rest" position. If it does not return to "at rest" it will not bleed or work properly.

 

* Early has the reservoir in front of the output hard line connection, while the late style has the reservoir behind the hard line output connection. Both have a valve inside, but they operate differently.

Edited November 4 by Captain Obvious
more detail

[Patcon]

Any ideas on how to check for trapped pressure in the braking system?

Clutch master...

[motorman7]

I usually use the vacuum bleeder for clutch and brakes. The one time that the clutch didn't bleed was when the clutch hard line didn't seal with the flex line. I had to tighten the flare nut more.....took me a while to figure out the problem though. 

[Captain Obvious]

10 hours ago, Patcon said:

Any ideas on how to check for trapped pressure in the braking system?

Well if you are simply looking for a test, I would do something like this:

Hit the brakes and confirm that the rears are locked up.
Let off the brakes and confirm that the rears are still tight.
Reach behind a rear caliper and loosen the flare nut. Let some fluid bleed out.

If the rears relax when the fluid bleeds out, then you were holding pressure. If they don't relax, then it's probably something in the caliper itself that's sticking.

And if the rears DO relax, I would repeat the test, but this time let some fluid bleed out from the flare nut on the underside of the master cylinder. That will help identify where along the path the issue is.

If it's holding pressure, I would expect it to be right there at the master cyl. And if that is the case, I might be able to help walk you through removing the check valve.

[Captain Obvious]

And that clutch M/C is the later type. You can do a kinda-sorta bench bleed of the clutch master by loosening the flare nut on the outlet and just let it gravity bleed into a rag. If fluid doesn't flow, I suspect it's a problem with the linkage.

If you loosen the nuts that hold the clutch master onto the firewall, does it a) push away from the firewall, b) remain pulled tight against the firewall, or c) it's kinda neutral?

It should be neutral with a tiny bit of slop in the linkage. If it pushes away, you need more play in the linkage and may not be opening the internal valve.

[inline6]

On 11/3/2024 at 10:22 AM, Patcon said:

I am using a later master cylinder that I believe is a 280zx unit. So I shouldn't have the check valves then...

Still can't get the clutch to bleed. Not manually, not by leaving it open and not with the vacuum bleeder. I guess I will have to pull it out and diagnose it.

I recently couldn't get my clutch to bleed (just after I couldn't get my brakes to bleed), and the problem was the little slider valve found on the piston assembly.  No pictures, but the little valve for the clutch master cylinder is much easier to get to than the one on the brake master cylinder.  it has a little spring on it.  Should be easier to disassemble and make sure it is not sticking.
 

 

 

[Patcon]

I had read your posts and figured that's what I'd have to do. Thanks for the reminder

[Patcon]

The reverse bleeding is interesting

[emccallum]

7 minutes ago, Patcon said:

The reverse bleeding is interesting

It has worked for me many times, especially when I replace everything and dont bench bleed. Old BMW's were really hard to bleed, at least for me, without this method.  FWIW, mountain bike brakes are bled like this. 🙂

 

 

[Patcon]

Got the manifold gasket surface cleaned up

I don't know what gasket this is Sean sent but I like the way it looks! Nice and thick

 

Edited November 5 by Patcon

[Zed Head]

1 hour ago, Patcon said:

Got the head gasket surface cleaned up

Manifold gasket?

Hey, on the problems bleeding the clutch system - I discovered that you can push the slave cylinder back in its bore by hand from underneath or by reaching down inside the engine bay.  Crack the bleeder, push it back using the rod to remove the air.  Easier than messing with the pedal.

I also had a bad slave cylinder that I could not get bled.  I never really figured out  for sure what was wrong with it.  I think that it might have been sucking air in through the seal.  Can't understand how unless the MC return spring was strong enough to pull negative pressure.  Anyway, replacing the slave cylinder fixed it.

p.s. I remember that there was a small amount of fluid under the dust cap.  But there shoudl have been more after many pumps.  Had to be sucking air on the return. 

Edited November 5 by Zed Head

[inline6]

1 hour ago, Zed Head said:

 

Referencing this nice exploded view and my comments earlier, #9 is the valve that got stuck.  #10 is a rubber part that fits on #9.  When the rod portion of #9 seizes in #12, then the cylinder operation stops working properly. 

I don't know exactly how it works, but I think #9 works like a one way valve - it seems to close the circuit, which then allows the main piston and primary cup to move fluid.  When #9 is stuck in the "open" position, fluid just flows back and forth, and no force or movement of fluid is generated.

Edited November 5 by inline6