Unfortunately during brake bleeding I let the reservoir run dry. I've bleed the 4 calipers subsequently but the pedal is still a bit soft. Can the master be bled on the car? If so, how?

Much appreciated

 

I think you just have to re-bleed everything again, starting from scratch. If your car is a manual, you may need to bleed the clutch, as well. If you have ABS, sometimes that system also needs to be bled (per reports I've read, no direct experience with this on my car).

I don't think that there's a way around a full re-do of the work, unfortunately.

Good luck

 

I've had this happen. Get a cheap master cylinder bleeding kit like this: https://www.dormanproducts.com/p-19543-13911.aspx

You can do it on the car.

 

I bought short premade brake lines from Canadian Tire and just bent them so they push fluid back into the reservoir. They were about 6" long and already had the proper brake line fittings and flare on them. It worked great to bench bleed my new master cylinder. You could you use the same setup with the master in the car. I used a Motive power bleeder to finish of the brake bleed.

 

Thanks guys. I'll see if I can find some right-sized brake line and if not, the Dorman kit. Help appreciated as always

 

If you think about... even if you perform the standard 'bench-bleed' operation, you can still have air trapped in the lines at the master.
In addition to dribbling brake fluid all over as you're installing it.
The master can be bled with the same or better effectiveness with the car's lines still hooked up.
Pump the pedal to pressure, hold it down. Crack one line at a time per pump up/hold down cycle.
If the system is essentially full, I usually give it 3-4 cycles per line to be sure the air is gone.
Some fluid will spurt out, easily caught with a rag. Rinse down with water when done, it dissipates the brake fluid way better than brake cleaner.
I've also had good success (on BMWs...) bleeding air out the ABS pressure block with the same method.