Just rebuilt my rear calipers with seals from PMB Performance. Using a vacuum brake bleeder I started with the right rear caliper lower bleeder screw ( I have two screws) and initially pulled about an inch of brake fluid with lots of bubbles and then zip. I get zero brake fluid now.

What could cause this? I have no signs of any leaks and the brakes were not bad before I rebuilt the calipers. I read somewhere that I might need to bleed the proportioning valve or even pump into the caliper some brake fluid through the top bleeder ?

I ordered a Motive pressure bleeder which arrives in a few days

Chances are the brake fluid drained out of the master cylinder. I had that, had to pressurize the fluid reservoir and have someone pump the brake at the same time. Problem solved. Maybe try it on the front calipper first just to take the proportion valve out of the mix. Best, Mark

could you elaborate? I had a full Master cylinder reservoir. How do you "pressurize" do I need to have a pressure bleeder

Are you saying also do front calipers first?

Yes I would try the fronts first...I know that is not the correct way, but just to get fluid coming out. I did not have a pressure bleeder so I just carefully covered everything up around the reservoir, wrapped a rag around the top of it and shot some air in (air compressor) while my buddy pumped the brake peddle.

Okay I will try fronts first I have the Motive pressure bleeder ordered so if it does not work I can try pressurizing the Master my air compressor is not available at the moment
Thanks

On a caliper with two bleed nipples, the top is the bleed, and the bottom is a drain; only bleed with the top nipple. Air bubbles rise you know.
When bleeding the system, keep checking the reservoir to be sure it is full by removing the cap and looking down inside. The reservoir is divided by a half barrier into front & rear so an external glance may not reveal that the other half is empty. If a half does empty, then you will have to do a long bleed to ensure any air introduced at the reservoir is removed.
Pedal bleeding ensures that high pressure is able to be achieved, and it also crushes bubbles and helps them move through the system; keeping them from being trapped within things like the pressure regulator. So I like to finish a bleed with pedal bleeding after using either a vacuum bleed or an air pressure bleed method.

The other thing that I would add is that for whatever reason pumping the brakes seems to work better in situations like this then using a handheld vacuum pump. If you don’t have access to a system that will pressurize it then offer to buy someone a pizza and have them actually the brake pedal.

I like to use pressure (motive @ 5-10 psi) followed by pedal bleeding. You can also replace the bleed screws with speed bleeders to make things a one-person job. Some people say you shouldn't use speed bleeders with the motive, but it's worked fine for me. Here are two videos which may help as well...

"Bench bleeding" master cylinder while in the car:
https://youtu.be/OOSer774NqM

Bleeding brakes:
https://youtu.be/ymHHD6uKhfc

Okay the first problem was my master went dry because it was so discolored from ATE super blue that I thought it had fluid. How do I bleed now .. do I need to bleed the master?

Get some speed bleeders. One for each caliper. Installed in the upper holes. A LONG piece of clear tubing and a catch jar.

I would. Since it's gone dry, i'd just start from scratch...

– Bleed the master (in the car is fine...see video link above). Use pedal only...and put a block or something down to make sure you don't hyper-extend the pedal and damage the seals inside the MC). When no bubbles are coming through...

– Put a quart of fluid in the motive, hook it up and pressurize to 5-10 PSI. Use a rubber mallet to rap on the caliper and dislodge air bubbles while bleeding.

– Bleed from the top screws LR, RR, RF, LF.

– Finish with a pedal bleed all the way around.

If you don't have a firm pedal, do it again until you do. If it's firm enough to drive, but not perfect, that's kind of typical. Just carefully drive it on a bumpy road for a bit, then bleed again.

Good luck and be safe!

Thanks, Ian! Keep the videos coming they're great btw!

I bled the Master using your video as a guide. Then I bled with the Motive pressure bleeder and very few air bubbles came out. My pedal is firm but not hard. I have not pedal bled yet. I was thinking test drive around then bleed again with the Motive pressure bleeder. It only pressurizes to 5-6 psi I wonder if that is 914 specific or whether mine is defective although seemed to work

And make damn sure when you're doing all of this you don't let the fluid go low in the master cylinder reservoir. Keep it topped up as the fluid level gets low.

I tried a motive bleeder on a 914 once and didn't have much luck with it. That may just be me. Operator error, who knows. I prefer the old fashioned two person method.

I had no luck vacuum bleeding the 914, couldn't get past the proportioning valve for rear. Pressure bleeder or 2nd person does the trick.

Are you pressurizing the Motive bottle before opening the bleeder screw? or opening the screw then pumping the Motive handle.

I usually pump up to 7-10 lbs then open the bleeder.

The reason you should not pump it to more than 10 lbs is that the lines from the reservoir to the master are attached with hose clamps on rubber hoses and can blow off under high pressure.

I have the bleeders closed and it goes to about 6 psi have not tied to pump it much higher it stalls there

I could not get the vacuum bleeding to work either

Your lines from the reservoir to the MC are probably not tight enough to hold more than 6 PSI. They weren’t designed to be pressurized. But 5 PSi gets the job done on my cars.

I could never get the brakes bled properly until I installed speed bleeders.
Those combined with using the motive at the reservoir to pressurize the system followed by a pedal bleed was the ticket for me.

If you've got all of the old fluid out you could run clear tubing from the bleeder all the way back to to the reservoir. That way you're not wasting fluid, you're just circulating it until the air is out. Run the tubing such that you can see it while you're pumping the brake so you know when the air bubble are gone.

Assuming you are not in a rush to drive the car I would
use gravity bleeding and let physics work for you.

I replaced ALL lines, master, prop valve and all four calipers
and couldn’t get any fluid to bleed.

Bought clear silicone tubes at HD, connected them to the
nipples and it was done after 3hrs, without even touching it.

Just make sure you have no leaks, your fluid level is on point
and the end of the tubes are at or above the reservoir level.

Damaged master cylinder or impatient? I put on speed bleeders and pumped two to three inches of fluid through each caliper staring with the traditional right rear and top bleeder only. First with Motive pressure bleeder until I did not see bubbles, then a pedal bleed, although I could not see whether bubbles came out or not. Neither one firmed up the pedal. And the Master did not go dry.

I’m wondering did I ruin the Master by pushing to the floor accidentally? !? I only did that once
??
Or is there still air in the Master or possibly proportioning valve? Confused never had so much trouble bleeding: I read another thread where more than one person said it takes four trips around the car with pedal bleeding to get a firm pedal on the 914

Have you correctly set the venting clearance on the rear calipers? IIRC, the correct value is half of the value printed in the books.

I set them at .008” there is a slight drag

I have run about 2 liters through the system I know it's crazy. The old
ATE blue fluid was a nasty blue/charcoal black and it's all out.

I used speed bleeders and could see the fluid running through the clear tube but
hard to tell on the bubbles since I was at a distance. I pedal bled around the car four times.

UPDATE: Pedal bled four times have a pedal now it's not that great but
I think at least with brakes I can drive the car around and take Ian's advice
that will work more bubbles up. Then I will try another Motive pressure bleed and a
a pedal bleed and see where I am at.

At least I have a pedal I don't think the Master is damaged at this point we shall see.
'

I understans it is very frustrating yes. Keep up the good work and keep us informed. Be safe driving with half a pedal !

This last time I did this, I followed that advice and set them to .004 instead of .008. Worked much better that way. I intend to do the same with my current 914 as it needs the restored PMB calipers venting clearance set. One of these days...

Drive it for a while. Give the pedal an extra pump first when stopping. Sounds like you have an air pocket somewhere. And try tightening up the rear venting clearance.

http://www.914world.com/bbs2/index.php?showtopic=34527
Use .004" for venting clearance
You can search for posts by Cap'n Krusty and "venting clearance"
I also second the recommendation to drive it cautiously to get bubbles freed, and the seals to get set properly. The internal mechanisms and the rubber seals both act to pull the pistons back when you release hydraulic pressure. They often need a little exercise to get them in just the right place to have the correct venting clearance so that you have no drag but fast response to applied pressure.

Kind of have the same issue.. The entire brake system is new and I still can't get a good pedal.. Hope I didn't damage the new MC.

How would you have damaged the MC? It's unlikely, unless you pushed the pedal to the limit while bleeding. Easy to avoid by putting a wood block behind the pedal.

When the system is new, it definitely takes a bit of work and several round-trip bleeds to get the pedal firm. I also found it helped when I took a syringe and shot brake fluid up through the lower bleed screws (and out the tops). Speed bleeders help a lot, as you can use them alone, or in conjunction with a pressure bleeder like the motive. Took me nearly 2 liters of fluid to get the pedal firm.

Also, if you've got new pads and rotors, they need to be bedded in...and that will affect your braking power. See the procedure on the PMB site. Eric also has a great writeup on gravity bleeding... https://www.pmbperformance.com/914tech.html

Be safe and enjoy!

I am concerned it pushed down too far. I have a very soft pedal. Will try to bleed again soon.

Okay . I am thinking possible the proportioning valve but if I drive for a while and careful I should be good to bleed again. I can also try the .004 " clearance if the .008" does not seem good enough

The Master is fine it was just air in system still