Is there a brake master cylinder write-up?

[theWIFES_S70]

There's a slow leak somewhere in my brake system and brakes are slowly moving towards spongey... (All new brakes all around, two new [rubber] front brake hoses, and flushed with Pentosin Super4 two years ago.) Will definitely bleed air before tackling this, but I'm thinking master cylinder...

I've been searching, both via Google and via our own search engine, and can't seem to find much except for pieces here and there, e.g. differences in part number; getting air into the ABS and pretty much ruining everything. I've done two master cylinder jobs (on a Renualt and a Golf) and they never came out right... But granted, that was at 16 and at 18 years-old respectively, e.g., never bench bled or bled at the cylinder... Or really understood a thing about air in the brakes...

Is this because this is a pretty straightforward job, a 9 minute job Scotty Kilmer could do with one hand and pair of scissors? Thanks fellas!

[scot850]

Not sure about the details of the repair, but one of my cars started leaking fluid. Smelled it before finding the leak. The leak was from the main seal, between the master cylinder and the booster. All the fluid leaked into the booster so no obvious signs of it. Have a good sniff in the passenger cabin near the pedal area. Hard to explain the small but you will recognise it when you do.

Neil.

[j-dawg]

It's not complicated, but it can get messy, since brake fluid is dribbling from the fittings as you're trying to install the brake lines. A messy job with brake fluid always stresses me out, so once you've got the cylinder bolted in, mentally review your moves before you start unscrewing those fittings.

[theWIFES_S70]

A messy job with brake fluid always stresses me out, so once you've got the cylinder bolted in, mentally review your moves before you start unscrewing those fittings.

Yeah, me too! I remember unscrewing frozen calipers in the snow and worrying about taking too long and running my master cylinder dry...

I always imagine brake fluid to be an acid that'll eat through skin, metal, and concrete...

[BEJinFbk]

There's a slow leak somewhere in my brake system and brakes are slowly moving towards spongey...

Are you actually losing fluid?

[abscate]

It is really hard on paint. Its not good for your skin/body either. Nasty Glyoxy ethers. Nitrile gloves all the way.

The odor is best described as 'pungent' - strong chemical smell that feels like its cleaning your sinuses.

You can move the MC away from the booster to check for seeps at the rear end without breaking the lines...I think.

I sold one spare and think I have one left from my 99 part out.

[ZionXIX]

never bench bled or bled at the cylinder... Or really understood a thing about air in the brakes...

Air in the system is simply bad. Air is a gas that can be easily compressed. Brake fluid cannot be easily compressed. Air can find its way into the system any number of ways. If you press the pedal with air bubbles in the lines, your pedal will travel much further than normal before you actually get a decent amount of brake pressure applied. The air is going to compress first, then at some point the pressure is going to rise enough for the brake fluid to do its job (at a reduced capacity) and transfer force to the brake pads. If there is a large amount of air in the system, you have no brakes at all. Get the air out.

If you let the reservoir run low enough to allow air directly into the system, then the master cylinder needs to be bench bled or bled in the vehicle. Its not so much difficult as it is time consuming, especially if you are by yourself.

[theWIFES_S70]

Are these signs of internal leaks? I can't really smell anything but car... But my master cylinder has been losing a little bit of brake fluid every couple of weeks, no leaks at the wheels. Enough that when I add fluid, the pedal feels a little stiffer for a bit. I have not thought to check my clutch slave cylinder my my clutch hose...

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s70_master_cylinder2.jpg (68.29 KiB) Viewed 2538 times

[abscate]

If you are adding a bit every few weeks, somewhere there will be damp brake fluid. I don't see enough wet there to call a leak.

It could be out of the internal end of the MC in which case it can kill your brake booster.

Using brake fluid is bad. Each of my cars gets a sharpie mark on the brake reservoir and any departure from the mark pulls the car off line.

[theWIFES_S70]

Well, if you're going to check your master cylinder for leaks, make sure you do so after driving around a few miles... (Not when the car is cold, as I've been doing...)

s70_master_cylinder_kaput.jpg (83.36 KiB) Viewed 2518 times

It's official. The Master [of Disaster!] Cylinder needs to be replaced!

The KER-FLUNK will have to wait. Last time I did this, on a Renault, the car was an absolute mess from then on... Glad I have all of you this time around.

Need to put in an order ASAP, do I get a rebuilt one or do I go new? Scotty Kilmer says to always buy new... what does Robert Spinner say?

If so, is that Centric one on Rockauto any good? This absolutely blows. I was going to replace springs and do fun stuff instead of this!!!

Also, should I replace the clutch slave cylinder?