412 brake bleeding issues

[so.manc loz]

Ive just replaced my rear wheel cylinders with a pair of off the shelf gsf type 3 items, as recommended on here. turns out one of the wheel cylinders was leaking badly, and the other was rendered innoperative by a closed off flexy hose. the car was 'MOTd' at the start of feb anyway, new cylinders on, new hard lines made and fitted both sides with brand new unions, and new flexys fitted both sides. I hadnt expected to need the flexys, so had to press a pair of late bay hoses (i think?) that i had in the garage into service. These are now 13inches long, as opposed to the original 10" hoses, but fit ok with no possibility of chafing.

so, i freed of the bleed nipples on the front calipers as well, thinking i might as well give both circuits a flush/bleed. Now, when bleeding using an easy bleed (pressure approx 15psi), or using the age old two man method (cheers dad!) you can bleed each corner until it is completely air free, but shortly afterwards there is no pedal pressure whatsoever, and if you go round bleeding again there is air in the system. Clearly there is air entering the system somewhere.....

however, ive inspected all unions, the master cylinder, front piston seals, and then even taken the drums off and checked the new wheel cylinders again, and there is no sign of fluid leakage whatsoever. so wheres the air getting in?

i have the brake bias valve, does this need bleeding? could it be leaking past the seals in the master cylinder? have you had the same problem? how did you overcome it? HELP!!!!!

Loz

[Lahti411]

It's very typical for these cars to get corrosion inside the master cylinder. As the master cylinder is located under the dashboard it doesn't get ventilated with air flow. This is what causes water to condense inside the master cylinder which again causes corrosion. You'll need to take the master out, hone it and polish it with 600, 800 and 1000 grit sand paper and see if you got rid of the corrosion. If the master cylinder is badly pitted inside, you'll need to get a better one. After polishing the cylinder you'll have to change the seals -beetle seals from same period will fit. Only check that the seal kit for corresponding master: Ate seals for Ate cylinder, FAG seals for FAG cylinder.

[so.manc loz]

It's very typical for these cars to get corrosion inside the master cylinder. As the master cylinder is located under the dashboard it doesn't get ventilated with air flow. This is what causes water to condense inside the master cylinder which again causes corrosion. You'll need to take the master out, hone it and polish it with 600, 800 and 1000 grit sand paper and see if you got rid of the corrosion. If the master cylinder is badly pitted inside, you'll need to get a better one. After polishing the cylinder you'll have to change the seals -beetle seals from same period will fit. Only check that the seal kit for corresponding master: Ate seals for Ate cylinder, FAG seals for FAG cylinder.

brilliant, cheers mate! ill pull it out tomorow and assess the condition. beetle seals will definately fit then? im sure ive read on here that rebuild kits arent available?

cheers loz

[Lahti411]

Yes, the seals from a rebuild kit for beetles equipped with dual circuit brakes will fit (model years 1972-1977, 19,05 mm cylinder). I have used them several times. Don't buy the complete rebuild kit (with pistons and springs etc.) as you will only need the seals. A seal kit should only cost something like £5 or so.

[so.manc loz]

just removed and stripped the master cylinder, the bore is totally corrosion free, however i will be ordering a new seal kit and rebuilding now its apart, just one less thing to worry about eh? thanks for the advice mr lahti

assuming rebuilding the m/c does not cure the fault described above, any more suggestions anyone?

[Lahti411]

If there are no leakages anywhere you shouldn't get air into the system -not even if the master cylinders seals were letting the fluid pass the seals. Worn seals in the mc should only cause soft, sinking pedal. Are you losing any brake fluid?
These cars brakes can be little tricky to bleed especially if every component isn't in perfect condition. It might take even four times to bleed the whole mechanism to get all the air out.

[shawn71]

I've also heard it suggested to let gracity assist the bleeding by leaving all nipples open to allow fluid to drain out of them, I can't vouch for this as I've never done it though.

I've also heard that it can help to raise the rear end in an effort to eliminate air traps, again can't vouch for it...

Sorry

[baby bleu]

i have remain the brake m.c. on my 412 , 2 weeks a go,, i buy a set of clear hose,(filler hose) liquid chimick proof,, and i connect the oil brake reservoir on the hose,, i seal tight the 4 hole,,,,2 for the swith and 2 for brake line,, and i refill the reservoir of the brake oil,,and i push on the piston with a screw driver,, the first pumping was easy,, in the mean time you can see the air buble in the clear hose return in the reservoir,, and i pump again,, 5-10 time ,or more ,wend the ,,m.c,, is free of air ,,you d,t can push on the piston,, extremly hard to push,,, wend it is free of air in the hose,,you do the installation on the car,, you keep the end of the hoses close,, and you connect the brake line on the m.c.,, with this tech.,,i save a lot of brake oil,,and afther the brake line was fast to blead,, with that we d,t push the air in the brake line,, baby

[Dubster]

Sorry to dig up an older thread, I have now started work on my 412, I have stripped the rear drums to find that the drivers side cylinder is leaking big time, and that the bleed nipple on the passenger side has already been sheared off - probably over 20 years ago!

I see from this thread that Type 3 cylinders are the same, but I just wanted to know if these are the same as late Beetle items?

Also, are the rear flexis the same as the later Beetles?

Thanks all

Rich

[shawn71]

Hi Rich, good luck with 412.

The rear brake shoes are the same as 1302/03 front shoes. The rear hoses are the same as Type 1 swing axle rear hoses as are the front ones on the Type 4.

As for the rear cylinders I can't remember if they are the same as those on a Type 1 but the club handbook list Type 1 front 10/57> as the repair kit so...

As for brake and clutch masters you can get them resleeved by Pastparts or have a read through this

http://www.shoptalkforums.com/viewtopic ... 2&t=133485

[so.manc loz]

the rear wheel cyclinders are the same as type three items, and although they arnt listed in the aircooled catalogue they are available at gsf, you just have to ask. i think beetle rears are similar, but when fitted, the bleed nipple will sit below the brake line, and as such youll never be able to get all the air out of the cylinder

and, as i never posted the solution to my problem, it was air leaking back past the threads on the bleed nipples as i was bleeding. bit of PTFE at each corner, and i had pedal pressure again! rebuilding the m/c was probably unneccesary, but at least i know its sound now

[Editor]

It doesn't pay to have the nipples open much, for that reason. Maybe 1/4 turn. Or get a helper to push the pedal and you release the nipple just as they do that, then tighten it before they let the bedal up. I thought I'd ruined my Golf 3 system when i couldn't get pedal pressure, but I'd let air back in by trying to do it myself, without an assistant! It has worked many times before, but not this time.

[so.manc loz]

It doesn't pay to have the nipples open much, for that reason. Maybe 1/4 turn. Or get a helper to push the pedal and you release the nipple just as they do that, then tighten it before they let the bedal up. I thought I'd ruined my Golf 3 system when i couldn't get pedal pressure, but I'd let air back in by trying to do it myself, without an assistant! It has worked many times before, but not this time.

that was exactly it for me! lesson learned eh, well know for next time

[Dubster]

Hi Rich, good luck with 412.

The rear brake shoes are the same as 1302/03 front shoes. The rear hoses are the same as Type 1 swing axle rear hoses as are the front ones on the Type 4.

As for the rear cylinders I can't remember if they are the same as those on a Type 1 but the club handbook list Type 1 front 10/57> as the repair kit so...

As for brake and clutch masters you can get them resleeved by Pastparts or have a read through this

http://www.shoptalkforums.com/viewtopic ... 2&t=133485

Brilliant info, many thanks!

I'll shuffle across to GSF in Leeds tomorrow, well I'll probably call them first, not sure if they'll keep Type 3 bits on the shelf these days, may have to order them?

[Dubster]

Brakes now rebuilt and working, the master cylinder is holding pressure, but has a small weep on to the brake pedal.

Are the seal kits for Beetles (as mentioned by Lahti411 fourth post down) the best option, or would I be best getting the MC professionally refurbed?

*UPDATE* I've been looking for MC rebuild seals on-line, but have drawn a blank, has anyone got any idea where I should be looking?

Cheers all

Rich

[kps70]

I'd bite the bullet and get a rebore/new seals from pastparts, if it starts leaking.

[Editor]

The rear seal can harden and leak. Could be that's what's happening on yours. I heard from Jim Adney (jadney at vwtype3.org) that there's a part from a ?Mercedes that is the same and is available separately, but I can't recall what model or number.

[Dubster]

Was about to send my MC to pastparts as Kieron advises, however managed to locate a NOS item in the US for £67 delivered, hope it fits

[shawn71]

Was about to send my MC to pastparts as Kieron advises, however managed to locate a NOS item in the US for £67 delivered, hope it fits

Unless its a RHD unit then it won't fit without some work...sorry to be the bearer of bad news , however if its the same make as you old one the internals could be transferred