Renewing Brake Master Cylinder

Need some help with a technical problem - ask away and let's see if we can all help.

Moderators: hot66, impmad2000, Nige

markm
Put a fork in me, I'm done!
Posts: 1866
Joined: Thu Aug 23, 2007 2:55 am

Renewing Brake Master Cylinder

Post by markm »

Going to replace the brake master cylinder on the S as I don't seem to be able to get a firm pedal anymore. Before you ask, done brake bleed several times, calibers refurbed so thinking its the master cylinder.

So my question, when you fit the new one, do you need to put some brake fluid in it first or do you just fit it and then bleed the brakes to get the air out of it?
72 2.4s
96 993 RS
Series 1 DDK membership card
jwhillracer
Me and DDK sitting in a tree! KISSING
Posts: 2618
Joined: Fri Apr 18, 2008 5:58 pm
Location: Sunny Somerset, just above the water....

Re: Renewing Brake Master Cylinder

Post by jwhillracer »

Just fit it and bleed the brakes through.
Before you change it, have you bled both nipples on your "S" front calipers????
The sad voice of experience from years ago ............ :roll:

JW
Life's a single timed run with no practice....
1970 914/6 2.4E/Webers
1970 VW Beetle project
1972 911 Hillclimber 3.2 MFI. Part of the family for 30+ years!
2006 Hymer Merc Starline 630
2000 T4 Van LPG
2000 Golf V5 Estate GT (Greyhound Transport!)
markm
Put a fork in me, I'm done!
Posts: 1866
Joined: Thu Aug 23, 2007 2:55 am

Re: Renewing Brake Master Cylinder

Post by markm »

I have about 4 times now, still no better. Has the calipers refunded last year, pedal was fine before that but don’t seem to be able to get it back

No leaks evident anywhere, so thought good place to start would be the master cylinder
72 2.4s
96 993 RS
Series 1 DDK membership card
Ian Comerford
I luv DDK!
Posts: 768
Joined: Fri Apr 01, 2005 8:51 am
Location: Harston, Leics

Re: Renewing Brake Master Cylinder

Post by Ian Comerford »

I would always bench bleed it before fitting a new one to the car. It’s easy, gets rid of 90% or so of the air in the new MC which means you are not pushing all that air into the system at the start and having to ensure you get rid of it all. I did this last year on mine and only had to go round once bleeding each caliper.
markm
Put a fork in me, I'm done!
Posts: 1866
Joined: Thu Aug 23, 2007 2:55 am

Re: Renewing Brake Master Cylinder

Post by markm »

Job done, brakes are like night and day now, from very spongy to very hard pedal. Off for a drive now to try them out
72 2.4s
96 993 RS
Series 1 DDK membership card
jwhillracer
Me and DDK sitting in a tree! KISSING
Posts: 2618
Joined: Fri Apr 18, 2008 5:58 pm
Location: Sunny Somerset, just above the water....

Re: Renewing Brake Master Cylinder

Post by jwhillracer »

Excellent!!

JW
Life's a single timed run with no practice....
1970 914/6 2.4E/Webers
1970 VW Beetle project
1972 911 Hillclimber 3.2 MFI. Part of the family for 30+ years!
2006 Hymer Merc Starline 630
2000 T4 Van LPG
2000 Golf V5 Estate GT (Greyhound Transport!)
sladey
Nurse, I think I need some assistance
Posts: 8632
Joined: Sat Apr 23, 2005 9:08 pm
Location: Nottingham, UK

Re: Renewing Brake Master Cylinder

Post by sladey »

Fantastic news.
The simple things you see are all complicated
I look pretty young but I'm just backdated yeah
deano
I luv DDK!
Posts: 753
Joined: Wed Jul 22, 2020 11:34 am

Re: Renewing Brake Master Cylinder

Post by deano »

I have to fit a new MC too - never done it before, or bled brakes before! :shock: Sounds like fun!

I don't see a seal on the parts diagrams, where the MC mounts to the bulkhead, but I feel like it should have one - can anyone say for certain whether it needs a seal please?

Thanks for reading and hopefully someone can answer... :cyclopsani: :bounce:
Dean
1973T Targa MFI 334 met blu- under restoration https://www.ddk-online.com/phpBB2/viewt ... 28&t=67060
1980 924 Turbo, blu/grn tartan - restored
911hillclimber
Nurse, I think I need some assistance
Posts: 18858
Joined: Mon Mar 10, 2008 6:26 pm
Location: West Midlands

Re: Renewing Brake Master Cylinder

Post by 911hillclimber »

Never fitted one on my '73T since the first rebuild in 1989. Does seem odd that there is no gasket there mind.
With the splash shield in place, that whole area is very well defended from road splash, so maybe Porsche thought a gasket pointless?
Easy to make one from a suitable material so why not fit one?
73T 911 Coupe, road/hillclimber 3.2L
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
sladey
Nurse, I think I need some assistance
Posts: 8632
Joined: Sat Apr 23, 2005 9:08 pm
Location: Nottingham, UK

Re: Renewing Brake Master Cylinder

Post by sladey »

deano wrote:I have to fit a new MC too - never done it before, or bled brakes before! :shock: Sounds like fun!

I don't see a seal on the parts diagrams, where the MC mounts to the bulkhead, but I feel like it should have one - can anyone say for certain whether it needs a seal please?

Thanks for reading and hopefully someone can answer... :cyclopsani: :bounce:
I’d recommend getting one of the pump-up pressure bleeding kits made by people like Sealey. Makes the whole process easier and very much a one-person operation
The simple things you see are all complicated
I look pretty young but I'm just backdated yeah
Lightweight_911
Nurse, I think I need some assistance
Posts: 16794
Joined: Wed Nov 12, 2003 10:48 pm
Location: Worcs/W Mids border

Re: Renewing Brake Master Cylinder

Post by Lightweight_911 »

sladey wrote: Fri May 19, 2023 5:12 pm
I’d recommend getting one of the pump-up pressure bleeding kits made by people like Sealey. Makes the whole process easier and very much a one-person operation
I'd second this - makes brake bleeding a doddle ...

.
Andy

“Adding power makes you faster on the straights;
- subtracting weight makes you faster everywhere”
Nine One One
Put a fork in me, I'm done!
Posts: 1619
Joined: Fri Mar 01, 2013 11:45 am
Location: Kernow - good old Cornwall

Re: Renewing Brake Master Cylinder

Post by Nine One One »

Lightweight_911 wrote: Fri May 19, 2023 5:51 pm
sladey wrote: Fri May 19, 2023 5:12 pm
I’d recommend getting one of the pump-up pressure bleeding kits made by people like Sealey. Makes the whole process easier and very much a one-person operation
I'd second this - makes brake bleeding a doddle ...

.
BUT remember to seal off the air vent pipe to the side of the brake fluid reservoir, otherwise when you pressurise the reservoir, it will p155 all the fluid out of that vent pipe, into the front frunk area!
deano
I luv DDK!
Posts: 753
Joined: Wed Jul 22, 2020 11:34 am

Re: Renewing Brake Master Cylinder

Post by deano »

Nine One One wrote: Fri May 19, 2023 6:38 pm
BUT remember to seal off the air vent pipe to the side of the brake fluid reservoir, otherwise when you pressurise the reservoir, it will p155 all the fluid out of that vent pipe, into the front frunk area!
I probably would have discovered this the hard way, so great tip!! I think I will fit a seal too :cheers:
Dean
1973T Targa MFI 334 met blu- under restoration https://www.ddk-online.com/phpBB2/viewt ... 28&t=67060
1980 924 Turbo, blu/grn tartan - restored
Gary71
Nurse, I think I need some assistance
Posts: 10228
Joined: Wed Mar 31, 2004 1:27 pm
Location: Cheshire
Contact:

Re: Renewing Brake Master Cylinder

Post by Gary71 »

I made a little paper gasket, probably not needed as Graham said.

As for the vent tube… no one would be stupid enough to make that mistake with a pressure bleeder would they… :)
markm
Put a fork in me, I'm done!
Posts: 1866
Joined: Thu Aug 23, 2007 2:55 am

Re: Renewing Brake Master Cylinder

Post by markm »

sladey wrote: Fri May 19, 2023 5:12 pm
deano wrote:I have to fit a new MC too - never done it before, or bled brakes before! :shock: Sounds like fun!

I don't see a seal on the parts diagrams, where the MC mounts to the bulkhead, but I feel like it should have one - can anyone say for certain whether it needs a seal please?

Thanks for reading and hopefully someone can answer... :cyclopsani: :bounce:
I’d recommend getting one of the pump-up pressure bleeding kits made by people like Sealey. Makes the whole process easier and very much a one-person operation
Alternatively, you could just bribe a 19 yr old lad to sit and respond to on/ off, I find this works well but does cost a couple of £££ each time
72 2.4s
96 993 RS
Series 1 DDK membership card
Post Reply