Brake master Cylinder

zombiebug · Posted: Wed Apr 16, 2014 4:49 am Post subject: Brake master Cylinder

How hard is to change one? Ive never had one fail on me before so ive never had to do it. The reason I ask is the rubber grommets in the top section of mine are failing causing it to leak from both top grommets. Also my switches are leaking and as far as I know the rubber grommets in the top and one of the switches are the same it left the factory with. I figure I would change the original out for a new one to prevent it failing any other way. So I ask you, how hard is this to complete?
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'74 Super

volksworld · Posted: Wed Apr 16, 2014 5:26 am Post subject:

like anything else...depends on your patience and skill level...the 2 bolts that hold it to the firewall run through sleeves that float in their holes....if you slide the bolt out completely the sleeve can fall into the chassis and is not fun to get back out...yes you need them or the bulkhead will crush....then your next challenge is to re-attach 3 brake lines without cross-threading them....I leave the master loose till I get the lines threaded in,then I bolt it down..at this point a helper to align the master while you bolt it down from inside(ratchet,long extension,13mm flexsocket) wouldn't hurt....I slice the rubber hoses off the supply tubes so I don't damage the upper pieces...always replace the supply hose....check and adjust pedal free play when done or you wont be able to bleed it properly....it is not necessary to pull the gas tank to do the job but as a first timer you might find it easier cause there's not much room to swing a wrench under there....and if you have a main brake to the rear that's really rusted ,manhandling it to get it on and off the master can break it...then you wonder why you cant get a good pedal as its dumping a pint of fluid under your carpet...have fun...

volksworld · Posted: Wed Apr 16, 2014 5:29 am Post subject:

sorry...just saw you have a super....so ignore my comments about pulling the tank....you only have 2 lines to deal with and more room to work....but everything else still applies

[email protected] · Posted: Wed Apr 16, 2014 5:44 am Post subject:

Master cylinders hold up a lot longer than rubber grommets. A old good german master cylinder is much more reliable than a brazil import. I would be include to rebuild the old rather than buy new.

As long as your replacing brake bits you should also consider replacing the rubber brake lines at each wheel. Don't forget to at least inspect all the wheel cylinders seeing as that rubber is probably just as old as the master cylinder rubber.

LeninCas · Posted: Wed Apr 16, 2014 8:28 am Post subject:

If you DO decide to change it, I strongly suggest using a Varga TRW one.

It will save you trips to Auto Zone, hours of work, and a huge headache.
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zombiebug · Posted: Wed Apr 16, 2014 8:33 am Post subject:

Thanks for the replies everyone. All the rubber lines have already been replaced as I have been doing them bit by bit as I could and the rubber line from the reservoir to the master cylinder has just been changed in January when I had the body off and the floors replaced. I've always thought the German one was better but didnt know there was a rebuild kit for them.
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'74 Super

zombiebug · Posted: Wed Apr 16, 2014 2:59 pm Post subject:

Does anyone know what parts I will need to replace with the master cylinder once its off? I cant find any part numbers for the top grommets or any information on the other parts of it besides that of the switch.
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'74 Super

Cusser · Posted: Wed Apr 16, 2014 4:02 pm Post subject:

volksworld · Posted: Wed Apr 16, 2014 5:20 pm Post subject:

I always swore by the german ones till I got a bad batch of them a couple of years ago...been trw/varga ever since...go german on the brake light switches

zombiebug · Posted: Wed Apr 16, 2014 9:23 pm Post subject:

volksworld · Posted: Thu Apr 17, 2014 5:45 am Post subject:

unfortunately a bad master isn't just a case of dried out rubber seals....brake fluid is hydroscopic (attracts water)...so the water content of old brake fluid rusts and pits the inside of the bore so the seals don't seal...so you have to hone every last pit out (fun in a blind hole) and hope its perfectly straight and not oversize when you're done....restoration rebuilders bore them oversize and press in stainless or brass sleeves to save ones that aren't available new....but yours is....believe me its not worth rebuilding cause the risk is too great if you don't do it right

zombiebug · Posted: Thu Apr 17, 2014 3:30 pm Post subject:

Tim Donahoe · Posted: Thu Apr 17, 2014 8:59 pm Post subject:

I bought a really good German master cylinder from Wolfsburg West. It was not cheap. But I didn't even bench bleed and that sucker was a one-time installation deal.

I hate buying cheap but funky parts and have to do the job twice.

Tim

Hyperspace · Posted: Thu Apr 17, 2014 9:47 pm Post subject:

I installed brakes for someone, it went fast and rock hard.... then a few days later his master bled out. I warned him about the master before hand. Brought me a second OG master.... been around the car 3 times now... can't get last bit of air out. Driving me nuts.

Something to remember about kits... the rubbers probably come from China. Also, with most cars today, the kit costs almost as much as a master, or rather thediffirence in time to just swap out, in labour costs, makes new cheaper.

Fixing them is something you only do in a bind.
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zombiebug · Posted: Fri Apr 18, 2014 5:00 am Post subject:

Tim, That was what I was looking at. WW is expensive but im 100% sure its German and it will last. So I always look to them when I need a crucial bit.

Hyperspace, Yea I have had air in the lines for ages. Its just another thing to me now lol.
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'74 Super

fred69vert · Posted: Fri Apr 18, 2014 7:03 am Post subject:

zombiebug · Posted: Fri Apr 18, 2014 7:06 am Post subject:

Fred, Yea its recommended that you use a power bleeder to get the air out of the system. I found a friend that has one so if it fits my super beetle reservoir I am going to do that. That's should get the air out.
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'74 Super

Tim Donahoe · Posted: Fri Apr 18, 2014 7:37 pm Post subject:

Zombie, when I put in that German MC I had mentioned earlier, I also installed new front rubber and metal lines and a disc brake conversion.

I did gravity bleeds, first, because almost everyone said to bench bleed the MC first--and I didn't feel like it, so ...

... I gravity bled each wheel, starting in the rears, then the fronts.

Then, since the new MC was a dual circuit, I did the pump-and-hold method (my daughter did the pumping and holding), starting with the fronts, then the rears. That's ass backwards, I know. But dual circuits seem to prefer that way.

It was all easy that way--and no air ghosties the next day. Of course, throughout the entire bleeding process, I was constantly watching the reservoir and filling it when needed.

I suspect the slow-going initial gravity bleed, fills up the MC better.

I believe Wolfsburg West says to bench bleed, but it's not necessary if you gravity-bleed, first.

Tim

Greezy Joe · Posted: Sat Apr 19, 2014 7:36 am Post subject:

There is one sure fire way to damage a new MC. That is pushing the pedal all the way to the floor when bleeding the system. It won't happen every time but is something to avoid doing.
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zombiebug · Posted: Tue May 06, 2014 8:37 am Post subject:

OK I got a new German master cylinder. Started taking thing apart and the nuts for the lines wont come off. The way this car reacts to things coming off, I think these brake lines haven't moved since they left the factory. Anyone know a good way to get these off? I really don't want to be bending new lines today if I can help it.
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'74 Super


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