Brakes

[Adam Cole]

Hi

I've put a new master cylinder in my 72 911e and cannot get pedal AT ALL

Yes, i bench bled it...........i then got another one believing that to be the issue .....i put in same problem.

I have put temp lines off it and it pumps fluid no problem so despite suspecting the MC i don't believe its the problem.

There are no leaks in the system, checked 100 times. Friend operating pedal when bleeding says you can notice pressure drop when you open the bleeder on the rear but not the fronts. I suspect the problem is in the front brakes but for the life of me don't know what it is .....system just doesn't seem to want to build pressure.

Calipers (S) re built not long ago ..........

Anyone got any ideas, its driving me INSANE .......

[Scott Douglas]

Are all your bleeder valves at the top of the calipers?
Is there more than one on each of the front calipers?

Asking based on a foggy memory of having similar questions asked on the 912bbs forum in years past.

[Adam Cole]

Yes Scott definitely right Calipers on the right wheels

Single bleed on all and all on top

[wdfifteen]

Make there is a small amount of pedal motion before the pushrod between the pedal and the MC piston contacts the piston. This is a classic symptom of the piston not retracting fully.

[Adam Cole]

Wdfifteen

Yep done that too

Pistons in MC returning fully ....

[John Rogers]

I would suggest getting a pressure bleeder and use that. I finally got one after many years of having the wife pump the pedal and the headaches that can cause. The pressure bleeder run up to 5# or so will show where there are any issues immediately.

[wdfifteen]

^^
The only way I got rid of soft pedal on my 911 was with a power bleeder. It cost about$40 and is worth every penny.

[asphaltgambler]

Or try gravity bleeding first if you don't have access to a power bleeder.

[Zeke]

If the front lines are older than say 5 years, replace them. Common problem with the insides swelling closed. Then the front calipers don't retract and you can't bleed the system.

[Bill Douglas]

Originally Posted by Scott Douglas

Are all your bleeder valves at the top of the calipers?
Is there more than one on each of the front calipers?

Asking based on a foggy memory of having similar questions asked on the 912bbs forum in years past.

That was me :blush: I put them on upside down. They fitted up fine but wouldn't bleed, duh.

[Adam Cole]

Thanks for the tips

Blocked both openings to the MC - pumps rock hard so I know is not the MC

Just changed the front hard lines right through

Will block the rear line and bleed the fronts and hopefully it works

Tomorrow’s job now ....

[T77911S]

bleeder valves on top or bottom as asked.

open the line at the MC and let it bleed a little out.
I have done the last several brakes by myself, just gravity bleed.
start at RR.

[Zeke]

Originally Posted by Adam Cole

Thanks for the tips

Blocked both openings to the MC - pumps rock hard so I know is not the MC

Just changed the front hard lines right through

Will block the rear line and bleed the fronts and hopefully it works

Tomorrow’s job now ....

It's the soft lines....

[onewhippedpuppy]

Originally Posted by John Rogers

I would suggest getting a pressure bleeder and use that. I finally got one after many years of having the wife pump the pedal and the headaches that can cause. The pressure bleeder run up to 5# or so will show where there are any issues immediately.

Yup. Not saying it is the only issue here, but it will make life exponentially easier. It's one of those tools that after purchasing, you wonder how you ever did without.

[John Rogers]

One thing to be careful of when using a pressure bleeder is the possibility of a burst brake flex line. If they are old such as original ones on a 914 or 911 that can happen. At a vintage race at Willow Springs the mechanic was pressure bleeding the brakes on a 356 and got the rears done, no fluid from the front one so he jumped the pressure up and bam......the line burst and hit him in the face, eyes and all with fluid! He spent two days in the hospital getting his eyes fixed so he could see!

[onewhippedpuppy]

I don't know what the exact age for replacement should be, but I certainly wouldn't trust original 914 brake flex lines at the track. I'm not betting my life on a 40+ year old piece of rubber.

[john70t]

Do them in order: Front left (shortest line and closest to MC) until clear, front right until clear, rear left, rear right. i think.

Closed valve,
Apply pressure (slow pedal one time if possible, or Motive Powerbleeder, or MityVac vacuum at caliper which I usually prefer to use),
Suction should hold,
Crack open bleeder slightly until pressure almost drops so there is no air Backwash, close bleeder valve,
Pump again, crack bleeder, repeat ad nauseum.
Check reservoir regularly.

Before installing, you can get a short piece of brake line and curve it so it dumps into the reservoir.
Push the piston and pump the fluid through until the caliper is out of bubbles.
Then you know there is no air in the caliper itself to start with.

Good call on the 40yo four individual rubber brake lines, any of which could fail, and then the car won't stop anymore at the very wrong time.

[wdfifteen]

Originally Posted by John Rogers

One thing to be careful of when using a pressure bleeder is the possibility of a burst brake flex line. If they are old such as original ones on a 914 or 911 that can happen. At a vintage race at Willow Springs the mechanic was pressure bleeding the brakes on a 356 and got the rears done, no fluid from the front one so he jumped the pressure up and bam......the line burst and hit him in the face, eyes and all with fluid! He spent two days in the hospital getting his eyes fixed so he could see!

Sounds like he got lucky. You only need about 10- 15 psi in a pressure bleeder. The lines see a LOT more force than that when you step on the brakes. He saved himself a crash. Unless he's using a type of pressure bleeder I've never seen the pressure is applied at the plastic reservoir, which is not designed to see any pressure, should have blown before a brake line - even a really bad one.

[wdfifteen]

Originally Posted by john70t

Do them in order: Front left (shortest line and closest to MC) until clear, front right until clear, rear left, rear right. i think.
.

Start at the wheel farthest from the master cylinder.

[John Rogers]

If you use a pressure bleeder, AS YOU SHOULD, it doesn't matter what order the wheels are bled! Just make sure to never let the fluid level drop out of sight in the brake reservoir or you will pump air into the system.