Master Brake Cylinder

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afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Master Brake Cylinder

Postby afeltein742 » Fri Aug 30, 2019 2:11 pm

Hi,
I've got weird symptoms recently with '67 420G (LHD). In hot weather or using the brakes more intensively both front wheels get stuck after a while. The brake pedal gets hardened up, as if the brakes were activated, and indeed both front brakes are under pressure. Waiting an hour or so will make it cool enough to be released. Untightening the front break pipeline hollander (e.g. right at the master brake cylinder outlet) to just let it unpressurized for a second, will release the brakes immediately. Thus, obviously the master brake cylinder gets stuck some way.
Any idea or similar experience that may help fixing it?
Interestingly some components of the Barratt MBC refurb kit do not fit, although I'm rather sure this is the right type of MBC,the very same can be found in a couple of other cars I saw, and in photos too.
Are you aware of more MBC versions during the manufacturing interval?
BR, Attila Feltein

PPV
Posts: 542
Joined: Sat Jun 14, 2008 4:48 pm
Location: Nantwich

Re: Master Brake Cylinder

Postby PPV » Sat Aug 31, 2019 11:33 am

There could be other things causing the brake situation. Sticking pistons at the callipers, soft flexible pipes acting like a one way valve, problems with the servo actuation. Allneed checking I would suggest before dismantling the master cylinder unless you see leaks etc.
Regards,
Paul V
Mk2 3.8
Mercedes A45 AMG
Mercedes AMG GLC43

afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Re: Master Brake Cylinder

Postby afeltein742 » Sun Sep 01, 2019 5:15 am

Thanks Paul. Certainly the entire brake system is going to be checked, but caliper pistons and flexi hoses cannot be suspected in my opinion, regarding the fact that all four front pistons will work fine again after depressurizing the MBC, whatever heavy use they had before. I will check the servo actuation, although I don't really understand how the servo can produce such a wrong operation.
Thanks again, Attila

PPV
Posts: 542
Joined: Sat Jun 14, 2008 4:48 pm
Location: Nantwich

Re: Master Brake Cylinder

Postby PPV » Sun Sep 01, 2019 11:23 am

Hi, I am unsure why the master cylinder would cause such a problem as usually it leaks and then the system depressurises and the pedal goes further to the floor. If the cylinder/brake pedal goes back to its usual position then why do you suspect it? In addition if it was the master cylinder why don't the back brakes have a problem also?
I am only familiar with the Mk2 arrangement but I was thinking perhaps the servo check valve is stuck etc.
Regards,
Paul V
Mk2 3.8
Mercedes A45 AMG
Mercedes AMG GLC43

afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Re: Master Brake Cylinder

Postby afeltein742 » Sun Sep 01, 2019 12:50 pm

I'm unsure too. You may be right with the servo, but I'm still doubting that anything under can do the trouble. Forcing the symptoms will cause both fronts get equally hot as hell, and I cannot imagine what else can do that than the MBC (or servo). I wish I were more aware of MBC principles... The two pistons inside the MBC can move independently as I guess, and thus the one for the front brakes may stuck too alone. Question marks...
I go to the garage on Tuesday and hopefully we'll find out what's wrong.
Thanks,
Attila

PPV
Posts: 542
Joined: Sat Jun 14, 2008 4:48 pm
Location: Nantwich

Re: Master Brake Cylinder

Postby PPV » Mon Sep 02, 2019 10:35 am

Attila, best of luck. Where are you based?
Paul V
Mk2 3.8
Mercedes A45 AMG
Mercedes AMG GLC43

afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Re: Master Brake Cylinder

Postby afeltein742 » Mon Sep 02, 2019 10:47 am

Thanks Paul. Budapest, Hungary

PPV
Posts: 542
Joined: Sat Jun 14, 2008 4:48 pm
Location: Nantwich

Re: Master Brake Cylinder

Postby PPV » Mon Sep 02, 2019 11:11 am

Just thought if you were in the UK there are a few places that could help. Have you contacted the club's technical advisors as they may be able to help with the specifics of the Mk X etc?
Regards,
Paul V
Mk2 3.8
Mercedes A45 AMG
Mercedes AMG GLC43

afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Re: Master Brake Cylinder

Postby afeltein742 » Mon Sep 02, 2019 12:52 pm

Not sure whom you think of. I'm not in good terms with Clive, he let me down at ebay, no money, he was less than helpful when I have not received his item after a month and ever. This is another story, but I won't address him.

PPV
Posts: 542
Joined: Sat Jun 14, 2008 4:48 pm
Location: Nantwich

Re: Master Brake Cylinder

Postby PPV » Mon Sep 02, 2019 1:04 pm

Sorry to hear that. Usually club members pretty good. Brian Reid and Ken Jenkins are identified as the people giving technical advice for your car but the specialist for bodywork is Keith Parrington.
Paul V
Mk2 3.8
Mercedes A45 AMG
Mercedes AMG GLC43

afeltein742
Posts: 6
Joined: Fri Aug 30, 2019 1:51 pm

Re: Master Brake Cylinder

Postby afeltein742 » Mon Sep 02, 2019 1:14 pm

Thanks. Depending on what we find tomorrow, I may contact these chaps.
Fingers crossed for my mechanic to recover by tomorrow, he seemed quite ill today.


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