Brakes intermittently fading VT V6

[commodoredave]

VT V6, Sedan ( yr 2000)
foot brake suddenly went spongy ( loss of pressure feel) at low speed on flat road after a 70km drive.
Handbrake dashboard warning light came on briefly -handbrake was not on.
Was fine for another 30 kms or so and then another brief incident with same details.
Traveled another 100kms with no problem.
brake fluid level is fine with no obvious leaks in the lines.
pads were changed 3 months ago.
if sponginess comes back a few pedal pumps seem to fix it.

All suggestions welcome. Also pls suggest troubleshoot confirmation steps with any suggestions.
eg The problem may be ABC and you can confirm this by doing XYZ.

 

[vc commodore]

Sounds like the master cylinder is failing.....

 

[the_boozer]

I reckon its a faulty booster if it was master cylinder why did it come good .
I only say that as Ive had a dud booster which made the pedal feel spongy I caused it in my case.

 

[Martbar]

VT V6, Sedan ( yr 2000)
foot brake suddenly went spongy ( loss of pressure feel) at low speed on flat road after a 70km drive.
Handbrake dashboard warning light came on briefly -handbrake was not on.
Was fine for another 30 kms or so and then another brief incident with same details.
Traveled another 100kms with no problem.
brake fluid level is fine with no obvious leaks in the lines.
pads were changed 3 months ago.
if sponginess comes back a few pedal pumps seem to fix it.

All suggestions welcome. Also pls suggest troubleshoot confirmation steps with any suggestions.
eg The problem may be ABC and you can confirm this by doing XYZ.

Mate, take it to a specialist, get it sorted. If you can't see any air bubbles in the reservoir after continuously pumping the B/pedal probably the booster as
previously mentioned. Good luck and keep us posted.

 

[vc commodore]

If one thinks back to before brake boosters were popular, how did one determine a master cylinder was failing?

 

[Martbar]

If one thinks back to before brake boosters were popular, how did one determine a master cylinder was failing?

With no obvious signs of leakage or changes to the level in the reservoir, that's why I thought it might be the booster. When l had trouble with the master cylinder it was damp at the bottom and fluid was also traveling along the rod where it was attached to the pedal. Interested to see what the
fix will be in this instance.

 

[z900collector]

I had the same issue just recently when I was towing my trailer and braking in a 70 zone downhill. After some research I decided to just bleed the brakes with new fluid and the brakes are working great.
If there are no obvious signs of a vac leak, a $20 fluid replacement might be a cheap and effective remedy.

Sid

 

[mechanic]

The brake warning light illuminating is the key here.

This indicates a fluid pressure difference between the two brake circuits - ie pressure loss somewhere. Either an external leak (easy to spot), or a failed rubber cup in the master cylinder. I can't think of anything in the ABS module that could cause these symptoms.
This would also explain the spongy feeling as brakes are only being applied at two wheels - half braking capacity = twice the force required to stop.

A failed booster would have the opposite feeling - the brake pedal feels rock hard after a couple of applications and the brakes don't feel like they work. There would also be no warning light associated with this.

Rebuild or replace your master cylinder.

 

[Pollushon]

^^ this