Master Cylinder bleeding question

[Patrick_S]

I am planning to completely replace all the brake lines and also the master cylinder on my Super Beetle 1303. The master cylinder is leaking and at least one brake line is pitted from rust, the brakes still work perfectly fine though. But this is the first time I have ever worked on the brakes of a car. I have done a good bit of research by now, but there is one part I do not know how to do properly, the bleeding of the Master Cylinder. I came across this awesomely easy way of doing it.

Link


Rob and Dave's website have a similar idea, http://www.vw-resource.com/alternate.html

I assume this is a good way of bleeding the MC, assuming I am going to do it slowly and keep pushing till no more bubbles rise to the surface. But I have one big question now. After I have bled the MC in this bath of brake fluid, how am I supposed to move the MC towards the car, and how must I screw on the new, and empty, brake lines? My MC did not came with any plugs or a kit to bleed the brakes. It only has the switches and reservoir tubes screwed in. The holes for the brake lines are open. Do I need to plug the brake line holes before taking of the MC from the bath? If so, I was thinking of buying a set of these Brake Line Fittings. and finding a creative way of plugging those. What do you people think? And then secondly, fitting the new empty brake lines after the MC has been installed. How do I do this? Can I just let brake fluid leak out of the MC or must the brake line holes be plugged as long as possible??

Can anyone point me in the right direction for this?

[Mudpump]

Which is one reason I'll bet most people never bleed the master on it's own. After install, they bleed the whole system.

[Dwayne1m]

I replaced 2 master cylinders and didn't bench bleed either of them. Both work fine. I never had to bench bleed countless race car MC's either.

[birddog1]

I done many master installs, never bench bleeding the master.

It's one of those funny urban legend things. If someone was shown that method on their first and it worked, they'll swear up and down you need to bench bleed. While everyone else just puts it on the car and bleeds the system.

[Tim Donahoe]

I replaced the master cylinder on my 1974 Super Beetle (1303), using an ATE master. I did not bleed it before installation.

There is no way to transfer a messy master cylinder over to the car, attach hoses and brake lines to it, and expect there to be no air in the system, anyway.

This is what I did, after installing the new master, the soft and hard brake lines, as well as replacing new, blue brake line from the reservoir to the master--and the front drums with a disc conversion:

I installed all the parts, then filled the brake-fluid reservoir. After that, I filled a clear jar a few inches from the bottom and attached a clear plastic hose to the front right bleeder bolt. I then opened the bleeder and let that wheel gravity bleed for a good fifteen minutes.

Keep filling the reservoir throughout this procedure. Dont let it go dry!

After most of the bubbles stop going through the tube, tighten the bleeder bolt and repeat this gravity-bleeding process on the front left.

Repeat again on the rear right, then the rear left.

Because you have a dual-circuit master cylinder, you start your bleeds at the front--not the rear.

After gravity bleeding all wheels, do your final bleeds. This time, however, you start at the fronts, then do the rears, using an assistant to pump each wheel a few times, then press and hold the brake pedal as you open the bleed bolts. When you see no more bubbles, go to the next wheel.

Tim
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Richard O'Brien

[Zundfolge1432]

We never had to bench bleed them either and I started doing brake jobs on VWs in 1979. Some of the mechanics I've known over the years were trained by VW at the dealerships and they never had to bench bleed anything either. By design most other master cylinders, especially americans have a reservoir that's cast in so you can chuck it into a vice and run small hoses from the line connection back to the reservoir. You could do this to the older bus master cylinder because its made this way too. I see it mentioned so often now but other than being unnecessary it probably wouldn't hurt anything.

[Cusser]

In the fall, I replaced 4 wheel cylinders, the master cylinder, and 4 flexible brake lines in my 1970 VW which had been sitting unused for 23 years and had no fluid left in the system.

I DID bench-bleed the master cylinder before installing.

The 1970 now has firm brakes.

I always bench-bleed clutch masters and brake masters.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[Patty B.]

My mechanic had a novel idea--my new MC came with clear plugs in the holes. He used a large diameter medical seringe. Filled it with brake fluid and punctured the plastic plug and filled it up then installed. I'm sure you could do the same with a hobby or glue applicator like plastic seringe, install your MC then 'surgically' fill it up.

[joey1320]

I've replaced 6 acvw master cylinders over the last 6-7 years, not once did I bench bleed them. I have also replaced 15-20 ABS pumps and 4-5 master cylinders for my daily job and same, not once did I bleed before install.

For the last VW I did I also replaced the hoses and wheel cylinders (I'm about to do so in my personal car this week) and this is what I did. I installed all the components and just opened up all four bleeder screws at the same time while placing some cardboard pieces and rags under each corner. I filled the reservoir to the top and went back in the house for a beer.

After the brew, I went back to the garage and filled the reservoir again. And had myself another frosty one since I deserved it. By the time I came back all four corners were "pouring" brake fluid so I closed all four bleeders, pumped the brake pedal and did a final bleed front to back using the one person method.

For the one person method, you need a clear bottle and about a 2ft of clear hose that fits unggly over the bleeders. You drill a hole on the bottle cap for the hose to fit snuggly. You push the hose all the way down and add brake fluid to the bottle to cover the hose and a bit past. Install the cap and now you have a one person bleeder.

What this does is not let air back into the system. So you attach the hose to an opened bleeder screw, fill the reservoir and slowly press the brake pedal a few times. There is no way for air to get into the system, so once you don't see bubbles on the hose, you're done. Move onto the next.
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1971 Super - Sold
1984 Puma GTC - Sold
1971 Campmobile

[joey1320]

Link

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1971 Super - Sold
1984 Puma GTC - Sold
1971 Campmobile

[ldj1002]

Why bleed front first? Front and back are completely separate.

[Zylinderkopf]

I've replaced several master cylinders over the years without bleeding them.

I'm currently fighting with my '63's brakes. Replaced all shoes, mc, wheel cylinders, soft lines and metal lines and a couple of drums. I'm still getting no pedal after hours of adjusting and bleeding. So now I'm at a point where I'm thinking maybe sometimes that mc has to be bleed after all.

I like Rick Higgins' technique: he bleeds the cylinder after it's been installed by opening the metal lines at each port while a helper pumps the brake pedal (same as the procedure at the wheel cylinders).
http://www.bugmevideo.com/volume4.html
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1963 Beetle
1966 Beetle 1300
1970 Karmann Ghia Coupe
1971 Super Beetle
1974 Thing


"A lot of people never use their initiative because no one told them to."

[Zundfolge1432]

Go straight to the Bentley manual and what do you find? That's right no mention of bench bleeding anything. VW used the two man method whereby you have some poor sap in the car pumping the pedal while the other guy opens the bleeders and you'll see there is a difference in procedure between single circuit and dual. You'll also get a mention on using brake paste when rebuilding components. If you rebuilt something and used it within a few days you can build by using brake fluid as well. Follow the directions in the Bentley and you won't have a problem. Many years ago I was that sap in the car and it was on a lift, believe me in the summertime the temp was hotter up there and I couldn't wait to get the job done and get back on the ground.

[Cusser]

I've purchased clutch masters and brake masters for other vehicles which had instructions inside the box stating to bench-bleed them before installing.

Believe me, the technology is quite similar from vehicle to vehicle.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[Zundfolge1432]

I thought by posting the manual reference it would help, but to compare other makes and models of autos is a stretch bottom line if it helps you to sleep better go ahead and bleed per your Ford truck manual,it won't hurt anything.

Since we are stretching I'll tell you this. During part of my career I worked in a hydraulic component rebuild shop, we did all types of actuators, landing gear,flight control,snubbers etc. we used a fluid called skydrol and assembley paste to build em up. Next each part went to a test cell where a working pressure of 3000 psi was applied to extend and retract several cycles. The components were then drained cleaned externally,bagged and shipped ready to be installed on the aircraft wherever that might be in the world. All those parts are bled after installation and that means exactly nothing compared to working on VWs.

[Cusser]

[Zundfolge1432]

Uncle

[60ragtop]

[wcfvw69]

I certainly don't understand why the need to bench bleed a VW master cylinder. In 35 years of VW ownerships, I've never bench bleed one. The last one I bought was a "German" one from Wolfsburg West. I bleed it with a hand pump pressure bleeder. Once the air was out and the brakes were adjusted correctly, I had a HARD brake pedal that was perfect.
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[Cusser]