Itinerant Air-Cooled

Have a new master cylinder in, going to change all the brake hoses today, and so someone please correct me if I'm wrong, but when bleeding a brake system, I start at the wheel furthest from the master cylinder and work my way to the closest wheel to the master cylinder, yes?

And one other note, when disconnecting the two brake lines from the old master cylinder, the brake fluid in the chamber towards the rear of the car was under pressure, spraying when released, unlike the front chamber. Is this an indication of constricted hoses, or is it that the small port that feeds and relieves the chamber of fluid is blocked by crud, again, probably from deteriorating hoses? The reservoir on top of the master cylinder was certainly full of black crud.



thanks, neal

ruckman101 wrote: when bleeding a brake system, start at the wheel furthest from the master cylinder and work to the closest wheel to the master, yes?

Yes, but note that it does not matter if you start at the front or the rear with dual circuit brakes so long as you do the furthest for the circuit you are working on and work your way in.

ruckman101 wrote: brake fluid in the chamber towards the rear of the car was under pressure
Is this an indication of constricted hoses, or is it that the small port that feeds and relieves the chamber of fluid is blocked by crud?

Either or both . . . could cause the above symptoms.
Colin

Thanks. Front hoses looked ok. However the new Mehle replacements did not have the extra rubber insulator that fits into the clips just outside the drum. Sliced off the old ones and put them on the new hoses.


neal

Sigh. The plug I used to block the unneeded third brake line on the new master cylinder isn't plugging. It seeps. Discouraging to have put all this effort in and the brakes are no better than when I started. I thought about teflon tape, as the plug is for a plumbing application, but I wrapped the plug in teflon tape before installing it and soaked it in used brake fluid and the tape softened and thinned after ten minutes or so. There must be actual plugs designed for this application. FLAPS?


neal

You used the proper metric tapered pipe plug (M10x1)? If you tried to use a 1/8" NPT plug, the threads in the M/C or residual pressure valve
are likely damaged, but probably fixable with a tap. It's very doubtful if any FLAPS would have metric plugs, but Googling "metric pipe
plug" turns up several on-line sources. Other possibilities: a (shortened) M10x1 bolt with sealing washer; an old brake line end
cut off short, crimped and filled with solder; an old brake lite switch.

I don't know if it actually matters, but VW/Bentley actually went to the trouble to specify a brake bleeding sequence of R. front > L. front >
R. rear > L. rear.

Great stuff! How the hell do you know that off the top o' your head?

Tightened way beyond spec, but the brass plug from the FLAPS seems to have done the trick. Whew.



neal

kreemoweet wrote:
I don't know if it actually matters, but VW/Bentley actually went to the trouble to specify a brake bleeding sequence of R. front > L. front >
R. rear > L. rear.

The benefit of doing the front circuit first, is that it fills/pressurizes the end of the master cylinder, giving you better "push" for the longer path of the rear circuit.
Colin

Amskeptic wrote:

kreemoweet wrote:
I don't know if it actually matters, but VW/Bentley actually went to the trouble to specify a brake bleeding sequence of R. front > L. front >
R. rear > L. rear.

The benefit of doing the front circuit first, is that it fills/pressurizes the end of the master cylinder, giving you better "push" for the longer path of the rear circuit.
Colin

Perfect sense. Even more so for acclimatizing a new master cylinder to the system, along with four new brake hoses. Bertha Bus did well on her first run into town yesterday. Even under a moment of panic and heavy application. Still, it itches at me that I should do one final bleed of the system. My experiences with the recently purchased vacuum brake bleeding tool at this point are overwhelmingly disappointing.


neal


neal

ruckman101 wrote:My experiences with the recently purchased vacuum brake bleeding tool at this point are overwhelmingly disappointing.

neal

They are by their very design wrong. Do NOT apply a vacuum through a pressure system. A pressure bleeder with a very modest 3-5 psi from the reservoir on down is perfect.
Colin

6 psi pressure bleeder on the Squareback, and the brakes were fine on that fateful day without windows or latches. It's a handy way to do it alone.

Have never had an issue using a Mighty vac when bleeding brake/s on a VW.

Mighty vacs have never done it for me. Put your spouse or a friend in the driver's seat and have them work the pedal. If you don't know how ask. A pressure bleeder works good too for one person bleeding and they aren't all that expensive. A really good Mighty Vac can be ruined by brake fluid.

sgkent wrote: ↑

Wed Jul 19, 2017 9:17 pm

Mighty vacs have never done it for me. Put your spouse or a friend in the driver's seat and have them work the pedal. If you don't know how ask. A pressure bleeder works good too for one person bleeding and they aren't all that expensive. A really good Mighty Vac can be ruined by brake fluid.

Yep been there done that! I prefer the tried and true helper pushing the brake petal while I drain each brake cylinder. "Push......Hold.....Push....."

Vacuum bleeding technique can be rendered useless by loosening the bleeder screw too much, to the point where the vacuum apparatus starts to suck air from around the bleeder threads. Many people do this and have miserable results. I've seen it done poorly, and done well, and I absolutely think there is more skill involved with that technique.