Haynes roadster build with donor Sierra part, progressing well but now problems with brake bleeding.

I have filled my master cylinder with new brake fluid and bled each bleed nipple in turn with a vacuum bleeding kit attached to my air compressor. I have read extensively about the process, but this is the first time I have actually done it, so I may have made some stupid error.

However I think I have done everything correctly; I put PTFE tape around each bleed nipple, the calliper bleeding points are at the top and I built the flexible hoses very carefully.

The vacuum bleeding system seems to work well but I cannot get air free fluid to come through. All four wheels (Discs at the front and drums at rear) still have air bubbles coming through the fluid despite bleeding continuously for about 15mins each. I then found two leak points (one around the brake light sensor and one of on a fixed line connection), I sorted these and re-bled whole system, but again I can't get it bubble free. I have seen on videos that cavitation can produce fine bubbles through the bleed nipple itself, but I still have bigger bubbles.

I plan to test the suction system through a bleed nipple alone, immersed in brake fluid to see if the air could be coming in around the rubber connection from the vacuum bleeder to the bleeding screw. Also I thought I could test each flexible hose, but I am loathe to take all the connections apart on the whole system without being clear what might be happening.

The brake pedal pushes in fine and applies brakes well (although I am only testing it against me pushing the car inside a garage). There is no leak of fluid anywhere. The pedal travel is less than when the Master cylinder was empty (presumably correct?). Handbrake still not holding back wheels (separate issue I think)

Could there be a leak at the master cylinder? Grateful for advice from more experienced builders, please.

put the vacuum bleeder away and do it manually. put a tube on the nipple then the other end into a glass jar submersed in a brake fluid.

get in the car and press down on the pedal. whilst pressing down on the pedal get a friend to open the bleed nipple. the pedal will drop to the floor. when it hits the floor hold it there and get your helper to nip the nipple closed. once the nipple is closed raise the pedal. give it a pump or two on the pedal then repeat. do this on each calliper one at a time until you see no air.

never failed me in 20 years.

Here's what I would do;

1. Get rid of the PTFE tape. I seem to remember it's an IVA fail to have PTFE tape anywhere in the system.
2. Wedge the brake pedal down with a large block of wood or similar, and leave it overnight. The continual pressure in the system has a tendency to collect all the frothy bubbles together and into the highest place (which is either a caliper nipple or the master cylinder).
3. Get a pressure bleeder rather than a vacuum bleeder, I believe using pressure rather than vacuum makes it easier to keep the bubbles out (hence the old school method of using the brake pedal still being preferred by many). I prefer Gunsons eezibleed, just remember that the pressure settings in the manual are wrong and it will work with half the pressure stated.

To be fair, the fact you already have pedal pressure means that just number 2 should finish the job. Although I'd still do number 1.

As above... PTFE tape is a pretty bad idea!!

Get rid of it and make doubly sure no flakes have got into the pipework.

Then get a decent pressure bleading system...halfords used to sell a Gunson one for around £20...

the gunson bleader works very well and was the only thing that could blead my landys complicated brakes, used it may times now with no issues. Connect to a half inflated tyre and NOT to your air compressor or the fluid will blast out or you blow the bottle up too

Thanks everyone. I have taken Ash's advice and bleed them by two man method and all air bubbles have disappeared. Good pressure on foot brake, but handbrake still not holding? Any further suggestions on that.