Brake bleeding problem
 

Can somebody help.
I have installed a new single circuit master cylinder on my friends 912
I cannot seem to bleed the system, bubbles are coming up into the reservoir ?
I have bleed all the calipers three times each.

Likely the 'new' master cylinder is the problem...been there, done that and apparently not uncommon with the ATE cylinders now being sold.

Did you bench bleed the MC before you installed it?

Are you using a pressure bleeder?

After a quick search I found this for you, it should help get you started on the topic.

https://forums.pelicanparts.com/porsche-911-technical-forum/974851-m-c-bench-bleed-not.html

Thanks mate, will check it out

+1 on bench bleeding the master cylinder. And as long as the reservoir is above the level of the bleeder screws, gravity bleeding is an option. Open the bleeder screw, and wait for the fluid to come out. Periodically replenish the master cylinder. Repeat for the other calipers.

Thanks mate