Don't put off brake fluid changes

[grannyknot]

I don't have any willing helpers so I install Speed Bleeders on all my cars, makes flushing the system much easier. The sealant on the threads keeps the air from sneaking around.

Screenshot 2022-05-29 at 17-07-57 Brake Bleeder _ Brake Bleeding _ Speed Bleeder Products _ USA.png (105.56 KiB) Viewed 646 times

[flybobbie]

So my soft brake problem has come back.
Pedal moves a long way down before any useful brake force becomes active.
Not lost any brake fluid.
Turn engine off and pump brake get about 3 strokes and vacuum all gone, that seems normal.
But then apply force and pedal slowly moves down, with enough force seems to bottom out.
It's like the master seals have gone, or at least say the rear.
I wonder if the black stuff in the fluid was the rear brake master cylinder seals rotted.
I did use DOT 5.1, but not recommended for the Z i recently find out.

From past experience i think i need to replace the master cylinder.

[enuff_zed]

So my soft brake problem has come back.
Pedal moves a long way down before any useful brake force becomes active.
Not lost any brake fluid.
Turn engine off and pump brake get about 3 strokes and vacuum all gone, that seems normal.
But then apply force and pedal slowly moves down, with enough force seems to bottom out.
It's like the master seals have gone, or at least say the rear.
I wonder if the black stuff in the fluid was the rear brake master cylinder seals rotted.
I did use DOT 5.1, but not recommended for the Z i recently find out.

From past experience i think i need to replace the master cylinder.

Had the same issue on old Capris. The internal seals in the master cylinder fail (often due to manual pumping of the pedal during bleeding, which runs them past their normal range of travel). Then the fluid simply moves from one side of the piston to the other.

[flybobbie]

Same on TR7, every year changing seals, new cylinder was too expensive at the time.

Well checking prices for E85's cylinders they cost £25.
Price for Z4 E89 £300 upwards, what a surprise.

So just bought 2nd hand cylinder complete with servo from breakers, £40.
I will try that cheap enough to replace the lot, or choose best bits.

Just ran the abs bleed through again no difference. But you can hear what sounds like fluid going past the seal as you push the lever down.

[flybobbie]

Well all sorted.
Just fitted the secondhand master cylinder.
So there must have been something wrong with the original.

[TomZ4]

Thanks for the tip. what's the best way to check the quality of my break fluid? or just give it to the garage on service?

[Mr Tidy]

I think BMW recommend changing it every other year, so hopefully that will fit in with oil services.

And if you have a manual gearbox it's a good time to get the CDV removed!

[flybobbie]

Well drove car home tonight.
Not 100% happy with it.
Brakes ok, but pedal still seems to move a inch or so before brakes come on.
You sort of forget what normal is.
Might give it few weeks and bleed again.

[wanderer]

Thanks for the tip. what's the best way to check the quality of my break fluid? or just give it to the garage on service?

You can get a brake fluid tester off Amazon or Screwfix.
I got mine from Amazon.

https://www.amazon.co.uk/dp/B07H5HXNLS? ... 6Z4R36XNTG

[flybobbie]

Can't understand if brake fluid hydroscopic, why is the reservoir not sealed air tight with say rubber bellow, like on my motorbike.

[Smartbear]

Can't understand if brake fluid hydroscopic, why is the reservoir not sealed air tight with say rubber bellow, like on my motorbike.

As the pads wear & the fluid level drops, if the reservoir was airtight the movement of the fluid would create a vacuum?
Can’t think of any other reason.
Rob

[SonnyA85]

I think BMW recommend changing it every other year, so hopefully that will fit in with oil services.

And if you have a manual gearbox it's a good time to get the CDV removed!

My mechanic said the maximum you should let it go is 2 years also.

For the cost of brake fluid I just get it done yearly. My mechanic charges £30-£40 per hour depending on how long you have been using him for.

[flybobbie]

Well ran the abs bleed several times more and much better now.
Basic change don't probably need to bleed but if removing master cylinder and reservoir then seems to need quite a few cycles of bleed routine.