Poor brake performance on cold start (Std. VT II brakes)

[VT_SS_II]

Hi All,

As per the title, on approximately every 2nd cold start I have poor brake performance until the engine comes up to temperature. When it happens I'm guessing there is about an extra 10mm to 20 mm of brake pedal travel required before the brakes start to grab.

Brakes are standard and fluid level is OK. Everything is standard/original except pads/rotors/brake fluid.
My initial guess is maybe components of the booster (or other) have hardened due to age (16 years) and the heat gets them moving again.

Anyone had this happen before or can suggest things to check before I take it somewhere to get checked as the problem probably wont be able to be replicated at a workshop without a o/night stay.

Thanks

[white lie]

Have you tried giving the brakes a quick pump before you take off?
How old is the fluid? If it's got a bit of air or moisture in the system it may have a slightly spongey pedal.

[macca_779]

Bleed them. There may be air in the system

[VT_SS_II]

Thanks for the replies.
I'm having the fluid replaced later this week as it's about 3 yrs old so will see if this fixes the problem.
Haven't tried pumping the pedal BEFORE startup, only afterwards bit this had no effect.

Seems strange to me that symptoms are only present on cold startup hence me asking here.

[amckiwi]

Is the car auto (assumed)
Maybe the idle is high until it warms up and it is pushing on the converter

[VT_SS_II]

Yes it's an auto but it doesn't seem to be idling any higher than usual.
Also the 'poor performance' is due to the extra travel in the brake pedal before the brakes start to grab.

[Micks]

3yrs is a bit long without changing fluid, is hygroscopic & not good for the steel internals of the braking system. Being a VT also check the vac line feeding the booster & fitting that attaches as well.

[white lie]

As Micks says, it's sounding like a possible lack of vacuum on startup...and after 3 years, the fluid is probably close to 10% water.

[macca_779]

It doesn't sound like a vac problem. No vac will give a hard pedal.. Not a long pedal

[Micks]

It doesn't sound like a vac problem. No vac will give a hard pedal.. Not a long pedal

What about partial vacuum?

[IJ.]

Occasionally you can get a failed Booster and that gives a long pedal but you get uncontrolled braking at the same time so doubt that's it.

[macca_779]

What about partial vacuum?

What do you mean a partial vacuum. The booster should always be under vacuum. If the booster was stuffed the pedal would be hard just like if you pump the brakes when the engine is off to deplete the chamber.

[Micks]

What do you mean a partial vacuum. The booster should always be under vacuum. If the booster was stuffed the pedal would be hard just like if you pump the brakes when the engine is off to deplete the c amber.

Think I have been working on Holdens long enough now & not interested in keyboard wars mate! What I eluded to in post #7

[macca_779]

Think I have been working on Holdens long enough now & not interested in keyboard wars mate! What I eluded to in post #7

WTF!! Not trying to start a keyboard war. Just trying to get my head around what your talking about. The OP says he has a long pedal.. Not a hard pedal. In my mind and having also worked on Holden's for to bloody long. A vac problem isn't the issue here going off the symptoms provided.

What you said in post 7 would allude to a failed check valve and thus a leak of the booster or a lack of vac supply due to a split line. Again, that would give a hard pedal, not a long one

[Micks]

Oughta know by now we can't diagnose someones vehicle over the net Though Ops problem goes away when the vehicle warms up & IMHO is pointing towards booster or vac line problem. The more I think about it too could also be an intermittent faulty ABS or Master cylinder too
But as always look forward to Op's solution & changing his 3yr old fluid too!