Master cylinder rebuild frequency ?

[99sh]

I hope this question isn't like asking what oil is best, but what is the expected required maintenance for brake master cyls?

I was under the impression to rebuild/replace only when it leaks, but I stumbled on an article in this month's 'The wheel' where it suggested to rebuild every season. A quick google search shows one camp of people replacing the entire unit every couple of years vs some others rebuilding pretty frequently.

Assuming fluid is replaced every season I would've thunk these would last near forever and attend to only if there are issues.

Guidance/thoughts/opinions?

Arax

Sent from my moto x4 using Tapatalk

[Purple Frog]

OK... i'll take a stab.
Racing 12 times a year.
Bleeding the brakes almost after every day on the track.
Using top grade brake fluid.
I've gone the life of some cars without rebuilding the cylinders.
Also, remember i don't use the brakes a lot. These cars are "momentum" cars.
Turn 10A at Atlanta is about the hardest i brake.

Now... if i buy a car. Then i do an inspection. Maybe a rebuild. Matters what i see.
I've got street cars daily driven with over 100,000 miles with original cylinders, etc.
and its a lot more dangerous on the street than on the track.

I am prepared to be flamed by the ASDMI (anal society of daily magnaflux inspection).

[Hawke]

My FF is 45 years old, and still has the original cylinders. Fluid is changed every 6 months, and are rebuilt every couple of years. Still OKAY for me.

[SEComposites]

I used to rebuild every year. A rebuild kit is so cheap plus it gives you a chance to take everything apart to check nuts and bolts in that area, give everything a good clean, take pedals out and re-lube pivots, bias bar etc etc. But then I’m one of the ‘ASDMI’ who likes to know their car isn’t going to fail because of lack of maintenance.

[DaveW]

I have run brake & clutch MC's for a very long time (sometimes over 10 years) w/o issues. And I use the clutch for every shift.

One of the keys to that is using a high-lubricity brake fluid like Castrol LMA (now called, IIRC, Castrol DOT 3,4 Synthetic).

[99sh]

You know it's one of those things. Do you keep the unit as-is knowing that it's proven and know it works, or do you replace it with a new seal and hope the new shiny bits are not inherently flawed. I err more to the side of demonstrated reliability, but it's a fine line I suppose.

I'm running the ATE Type 200 fluid. It may not have the highest wet/dry boiling point numbers, but then again for our light cars it'll never see those temps. At <$20 for a 1 liter can, can't be beat. Let the best brake fluid wars begin!

[DanW]

I have run brake & clutch MC's for a very long time (sometimes over 10 years) w/o issues. And I use the clutch for every shift.

One of the keys to that is using a high-lubricity brake fluid like Castrol LMA (now called, IIRC, Castrol DOT 3,4 Synthetic).

In my business there is also a phenomena of "infant mortality" The highest probability of failure is when new or just rebuilt.

After that, the Probability vs. Failure curve falls away...

[Steve Demeter]

IN 40 years I have had exactly ONE master cylinder go bad. And it was the clutch that sees far more wear than the brakes due to the long travel it experiences.

Have used nothing but Castrol GT LMA and it's successor.

Change fluid every year by sucking reservoirs dry then bleeding at each point with a mity vac until nothing but clear fluid comes out.

[Hardingfv32]

The claim of 'high-lubricity' was new to me so I went off to research how it is tested etc. SAE has a standard for this which generally sets a minimum. Could not find any tests that are on topic for DOT 3/4. Did find something on Dot 5 silicone which oddly indicated lower lubricity (this is before the noted seal swelling etc.). Has anyone seen any actual testing for lubricity.

Bosch has some new fluids they say are designed for modern ABS etc. brake systems that they claim reduces wear. Maybe there is some value in a product that is newly formulated for high activity brake systems... relative to lubricity levels.

Brian

[DanW]

The claim of 'high-lubricity' was new to me so I went off to research how it is tested etc. SAE has a standard for this which generally sets a minimum. Could not find any tests that are on topic for DOT 3/4. Did find something on Dot 5 silicone which oddly indicated lower lubricity (this is before the noted seal swelling etc.). Has anyone seen any actual testing for lubricity.

Bosch has some new fluids they say are designed for modern ABS etc. brake systems that they claim reduces wear. Maybe there is some value in a product that is newly formulated for high activity brake systems... relative to lubricity levels.

Brian

Brian,

This may seem counter-intuitive, but silicone fluids (siloxane) are known to be generally poor lubricants. I worked on a project for a medical klystron tube that spun the target plate and circulated silicone heat transfer fluid. The mechanical seal generated heat from friction was almost as much as the heat produced by the klystron.

Regards,
Dan

[DaveW]

My knowledge of the high lubricity of Castrol DOT 4 Synthetic stems back to the days of Girling LMA, which was known to prolong seal life due to its lubricity. Everything I've heard since indicates that Castrol DOT 4 Synthetic still has that property.

[swiftdrivr]

20 years without a rebuild, then rebuilt un-necessarily [discovered they were not the problem], but at least now I have "shatter and disperse" aluminum ones vs the old "steel and stuff themselves into the footwell" originals

[billtebbutt]

Seriously. My one and only Runoffs appearance (1997??) was ruined on lap 2 of the feature race by a failed front MC seal. AND it had been rebuilt the previous winter, so only a season (7 weekends I believe, no testing) of time on it.

FWIW, I got off the racing line, drove in my mirrors at 2/3s speed so I neither held anyone up or came up on anyone else, until I got to the requisite 60% laps completed for a "finish", then parked the car....

Sometimes, s5^t just happens.

Cheers,
BT