Brake bleeding, Nothing but air from rear brakes Options

[draganc]

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.

[Medtner3]

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

[davep]

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

[Medtner3]

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

[Medtner3]

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.

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.

[Medtner3]

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.
'

[Frankvw]

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

[Gint]

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

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.

[davep]

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.

[mb911]

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.

[iankarr]

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!

[mb911]

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.

[Medtner3]

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

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.

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

[Medtner3]

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.

The Master is fine it was just air in system still

[Medtner3]

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.

The Master is fine it was just air in system still but I have yet to try gravity bleeding. I intend to bed the pads in as soon as I am comfortable with the pedal firm enough