Brake fluid!

[SD1too]

Can you can help further with this please Brian?

Originally Posted by marinabrian

If a "fault condition" occurs, such as failure of one of the primary circuits ...

Can you confirm that you mean an open brake line caused, for example, by the well known corrosion?

... the associated shuttle valve will operate to minimise fluid loss ....

To which solenoid valve are you referring Brian? How does the ECU detect this fluid loss?

This can result in air being trapped in either accumulator ...

This suggests that you are referring to the outlet solenoid valve opening. Since the wheel has not locked, what trigger would cause the ABS ECU to do this?

... you will have 40ml of old fluid left in the system ...

Are you referring to the short fluid channel downstream of the non-return valve (shown within 12 in RAVE 70-20) and outlet solenoid valve?

Thanks in advance for your assistance.

Simon

[COLVERT]

Originally Posted by Ross R75

An interesting story, but without a source link, unfortunately it's a "my mate Dave".

Brake fluid has 2 boiling points. We know it absorbs moisture over time, so it has a "dry" boiling point for new untainted fluid, and a wet boiling point for old fluid 2-3 years old. In the case of DOT4 brake fluid that will be in most of our cars, the wet boiling point is 60 degrees C lower than the dry boiling point. That's a huge difference.

When the brake fluid boils, any water in it turns to steam. Steam/vapour can be compressed, which means that effort at the pedal isn't reaching the brake caliper pistons and braking performance is reduced.

I'll continue doing mine every time I buy a used car, and every 2 years thereafter. Others may differ, as is their right.

Bon Jour Monsieur ROSS.

Your comment above. If the brake fluid BOILS then whether it has water in it or not you still have no brakes.---



C'est vrai ???---

[Rp61973]

Thanks Brian. My 75 is overdue for a bleed. I will follow your recommendations.

[alanaslan]

Originally Posted by SD1too

Can you can help further with this please Brian?



Can you confirm that you mean an open brake line caused, for example, by the well known corrosion?



To which solenoid valve are you referring Brian? How does the ECU detect this fluid loss?



This suggests that you are referring to the outlet solenoid valve opening. Since the wheel has not locked, what trigger would cause the ABS ECU to do this?



Are you referring to the short fluid channel downstream of the non-return valve (shown within 12 in RAVE 70-20) and outlet solenoid valve?



Thanks in advance for your assistance.



Simon

I have always changed my brake fluid every 2 years or 20,000 miles which ever came first. These days it is every two years. Retirement has reduced mileage. I use a 2 litre pressure system. A bit like a garden weed spray unit.
I fill up the pump unit fasten the lid to the cars fluid bottle and bleed all round at about 25 psi. I usually flush about three litres through the system. The old fluid looks disgusting and has a high water content according to the probe unit.
I have always done this with all my cars and for the past twenty years on my 75s.
I was under the impression that flushing at 25 psi got the ABS circuit. Have I got this wrong.?
Alan


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[Dawn]

My brothers ZT hasnt been done since it was about 5! Not according to records. It is booked to be changed with belts and every other service item in June with Lates. For me its not worth risking for the cost!

[Ross R75]

Originally Posted by COLVERT

Bon Jour Monsieur ROSS.

Your comment above. If the brake fluid BOILS then whether it has water in it or not you still have no brakes.---



C'est vrai ???---

Correct! I'd rather it boiled 80 degrees higher, which is why I change my brake fluid regularly! Has the penny dropped yet?

[VVC-Geeza]

What quantity of fluid is required for a change?

[bl52krz]

Hi Dawn. I think you will be suitably impressed when visiting Lates emporium. Don’t forget the chocolate biscuits. I suggest you get a quote from a dealer first on how many hours it takes to change the belts. Then see how long it takes Lates to change them.

[COLVERT]

Originally Posted by Ross R75

Correct! I'd rather it boiled 80 degrees higher, which is why I change my brake fluid regularly! Has the penny dropped yet?

Whoops. I think you misunderstood my post.---

It really doesn't matter how often you change your brake fluid.

Even if REGULARLY meant every week.

If it boils you have no brakes.---

Now has the penny dropped ????---- Brakes failed and he went that way.---Ouch.

[Ross R75]

Originally Posted by COLVERT

Whoops. I think you misunderstood my post.---

It really doesn't matter how often you change your brake fluid.

Even if REGULARLY meant every week.

If it boils you have no brakes.---

Now has the penny dropped ????---- Brakes failed and he went that way.---Ouch.

I understood what you meant first time, and I'd agree with you but then we'd both be wrong.

If the fluid boils, you have no brakes. I agree completely. Changing the fluid makes no difference, I disagree entirely.

So we're agreed that you have brake failure with boiling fluid. We're also agreed that brake fluid is hygroscopic, it absorbs water over time... Yes? Old brake fluid boils at a temperature 80 degrees Celsius LOWER than new brake fluid. Therefore, you have a greater chance of suffering total brake failure with old fluid, than you do with new fluid. It's really not a difficult concept.

Clang!....... Ah yes, NOW the penny has dropped