Air in Master Cylinder

[PWS]

Brake pedal is very sluggish, can be pushed all the way to the firewall. Prior to discovering this problem, I did all of the following: installed 4 new wheel cylinders, installed 4 new rubber brake fluid hoses, removed and reinstalled brake fluid reservoir, installed new brake light switch. After having done all this, I used my Motive Products power bleeder to replace all old fluid with new. At each of the 4 bleeder valves I extracted 1/2 cup of fluid. Following the advice of an online video, I unscrewed the connection on the MC that leads to the left front cylinder, snapping the line in the process (note the plug in the photos). I then pushed the brake pedal all the way to the firewall, held it in place with a brick, went to the MC and removed the plug, hopefully allowing air to escape, then reinstalled the plug. I did this several times until fluid flowed out of the port, and there was some improvement in the pedal action. I am now able to push the pedal in about 1 inch before encountering any resistance. Then, applying a bit more pressure, I push it another 4 inches, it stopping about 3 inches from the firewall. An improvement, but probably falls way short of what it should be.

To do this right, I'm wondering if I should bench bleed this? I think that with al my maintenance I've allowed air into the MC. Any suggestions greatly appreciated. Photos are attached.

[Bobs67vwagen]

Bench bleeding may have made it easier but now that it's all together I would first fix that brake line, then adjust each wheel so the brakes are fully adjusted. Then bleed each wheel and you may have to do several times. I use a mitey-vac hand held pistol grip bleeder. With this there is no pumping of the pedal, just vacuum bleeding at each wheel. It works very well and I do it by myself. Keep at it until you get a firm pedal.

[viiking]

[PWS]

Thanks for the suggestions. I recently installed new brake shoes and drums on the rear and adjusted the brakes there as well. Front also adjusted recently. My power bleeder, like the Mityvac, allows me to bleed without pumping the brakes. My Bentley manual says bleed 70-80 cc per wheel (80 at RR)--about 1/3 cup. I went with 1/2 cup. So, you're suggesting I go through the bleeding procedure another time, or even two more times? Beats having to take out the MC.

[slayer61]

For several reasons, I don't have drum brakes, but I have read over and over about having the shoes adjusted all the way out tight against the drums before attempting to bleed drum brakes.

Good luck Sir.
_________________

[PWS]

Thanks Slayer61. I remember reading this in another post, but forgot to do it. Before I bleed again I'll make sure all brake shoes are tight to the drum.

[viiking]

[PWS]

Yes, pipe is broken, plug inserted. I ordered a new, German 200mm brake line this morning. Once received, I will remove plug and install new line. Then tighten all brake shoes, as suggested, and proceed to fully bleed the entire system. Then check for brake action and bleed one more time, if necessary. I'll report back. Any tips on how to bend the new brake line?

[Cusser]

[zerotofifty]

Good gawd man. That is dangerous. dont drive with that messed up tube. Make darn sure the brake tubing is in perfect condition. No hack fixes like you have there. If that fails, you loose your brakes.
_________________
Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[Bobs67vwagen]

I do not think the OP is trying to drive the car like this, I think he was just continuing the bleeding process after the line broke by plugging the opening.

[PWS]

Please, be assured that I would never drive the car in this condition. The plug was simply a stopgap measure to prevent contamination of the fluid within the MC. Also, unproductive to think of bleeding the brakes before I've replaced this brake line. So, everything is on hold until new line is installed, probably later his week.

[EVfun]

Did you replace the master cylinder? They usually in no better condition than the wheel cylinder.

One quick test (that covers one possible failure mode) is to push the brake softly and feel if it continues to slowly drop under foot. If it does the cup is failing. Compare that to a where the pedal stops if you give it a hard stomp like a panic stop. If that stops higher than the first test it’s failing. You can also have just the top of travel fail from internal corrosion. Air in the system gives the pedal a springy feeling.
_________________

[PWS]

No, I didn't think of replacing the MC, although it does make sense to replace it as well. I can probably perform your "quick test" as long as the plug stays in place. However, the "hard stomp" will have to wait until brake line is replaced. If there really is air in the system, will these two tests still be valid to perform?

[zerotofifty]

Consider upgrading to the dual master cylinder, much safer than that outdated single cylinder.
Good time is now to do it,
_________________
Sorry About That Chief.

Give Peace a Chance.

Words to live by.

[EVfun]

[PWS]

Reporting back. Replaced broken brake line, completely bled all the brakes, having adjusted all brake shoes as tight to the drums as possible beforehand. Upon applying the brakes, pedal no longer goes all the way to the firewall as it did previously. Here are the new measurements: horizontal distance from firewall (carpet turned back) to forward edge of rubber pedal pad: 8-13/16". When pushing very hard with hands, forward edge of rubber pedal pad deflects 4-13/16", that is, pad is now 4" from firewall. I measured free play at 5/16". If I pump the pedal multiple times, the 4-13/16" remains unchanged--so, hopefully, no air in the system. No leaks in the system. Have not yet readjusted the brakes from their very tight position. This car has not been driven for 3 years, so I have forgotten what the brake pedal should feel like when I brake. When depressed to 4" from firewall, I get a nice, hard pedal. But I'm wondering if that 4-13/16 deflection is more than it should be? Car is not yet registered, so unable to drive it at the moment. So, what do you think?

[zerotofifty]

[viiking]

The distance to the firewall should be just at or under 8 inches. Yours is too much and can do with improvement.

The free play is good albeit marginally high. I assume you used your hand to feel this and not your foot? The freeplay should be about 1mm at the MC to pushrod which equates to about 7mm free play (3/16 to 9/32").

You can help by reducing this freeplay closer to the minimum to help with the "drop" on your pedal. Of course you do this at the brake pedal stop plate NOT the pushrod. See your Bentley for the procedure.

So adjust your pedal stop plate to try and reduce the distance to the firewall first.

The pushrod should not be adjusted. In some Bentley books there will be a distance that the pushrod should be set at. In other Bentley's they don't indicate this. Have a look at your Bentley and see if there is a measurement for this. I can quote a figure but it may not be correct for your model. Have a read of this. There is a pushrod distance quoted here, but there is also a procedure for adjusting the pedal.

https://www.thesamba.com/vw/forum/viewtopic.php?t=713865

As zerotofifty says re-adjust the shoes. Even though you first jammed them up tight, the brakes have a tendency to have to readjust to the centre after they have been applied a number of times. So you need to recheck that they aren't spinning and you don't rely on thinking you did it once a while ago. Sometimes they come loose.

Also as been mentioned if the volume you need to displace now with new wheel cylinders and hoses etc has increased, then the pedal will drop to compensate.
There are a number of brake cylinders on the market. You need to make sure the diameter of these are suitable for your car. You haven't mentioned a year model.

If all these check out, I still think a drop of nearly 5" is way too much.

"Something is rotten in the state of Denmark".
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[PWS]

I have readjusted my brakes successfully. I removed the stop plate, cleaned everything up, and re-positioned it as far as it would go toward the front seat. (The adjustment notch in the stop is 7/8" long).

First photo shows original position, third photo shows new position. Second photo shows little tab at base of clutch pedal resting against the stop. Although I was able to move it slightly from its original position, there was virtually no change in distance of the brake pedal to firewall. The stop seems to have no effect on brake pedal. The two pedals seem to move independently from each other. Position of stop affects position of clutch pedal, but position of brake pedal seems fixed. So, I am at a complete loss. Still have this 8-7/8" distance to firewall for the brake pedal.