Brake Bleeding

[Wicker Francis]

From doing a search on this topic, much has been discussed but I find nothing that addresses this current issue. After a complete rebuild of the brake system (new lines, rebuilt cylinders and calipers) I am filling the system for the first time with brake fluid and beginning the bleeding process. There is now evidence of fluid in both front and rear calipers and I thought to let it sit for a while for air bubbles to settle out of the fluid before a final bleed.
What is curious, however, is that as the after most reservoir is filled (the one that supplies the master cylinder) and the brake pedal is pumped, the fluid level raises in the foremost reservoir (the one the supplies the slave cylinder attached to the vacuum unit). It seems the fluid is being pumped from one reservoir into the other.

Could this be a incorrect positioning of seals and/or components in the slave cylinder or is something else going on? Or is this normal displacement with this system?

[Wicker Francis]

Neglected to mention that this is a 65 FHC.

[MarekH]

It means that fluid is passing from one brake circuit to the other at the brake booster. The seal in the middle of the brake booster shuttle isn't sealing. Hard luck.

kind regards
Marek

[Wicker Francis]

Thank you Marek. That seems to make sense. I rebuilt that booster and it's very possible that I got the seal wrong or didn't install it at all or it was a bad seal from the kit.
I'm wondering if this issue would not be a problem once the brakes are bled out and the system is closed. Thoughts?

[MarekH]

It may or may not persist.

One thing which may work, would be to drain and pack the relevant brake reservoir with red grease and then rebleed the brakes. You'll know whether it leaks because the red colour will appear at the wrong bleed nipple. That'd also by definition have injected some lubricant past the seal, which may respond positively.

If at the end of the day the seal was round the right way, the bore was smooth and the seal undamaged, then packing the booster shuttle with red grease and/or fitting a newer more flexible well lubricated seal is the next move.

Failing that, it'll get expensive.

To look on the bright side, if you are not losing fluid, then the brakes will still work (as it is a sealed system), but you will eventually end up with brake fluid on the engine bay paintwork, perhaps sooner than you thought.

kind regards
Marek

[Wicker Francis]

Thanks again for your thoughts, Marek

Not so sure I need to color the fluid because the excess fluid can only come from one place. Since this is such a new installation I'm inclined to try and bleed brakes again and possibly the seal is setting. Otherwise no big deal to take the booster cylinder out and check that the seals are in the right place or there at all.
Tomorrow is another day.

The winter salt is on the road so this car isn't going anywhere until Spring.