Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.

New Posts Contact us

Just Commodores Forum Community

It takes just a moment to join our fantastic community

Register

VX Loss of Brakes

mirrabucca

Well-Known Member
Joined
Nov 26, 2019
Messages
335
Reaction score
257
Points
63
Age
72
Location
Canberra
Members Ride
VX S pack (Devil Yellow)
Cool! The fact that he didn't just replace the master cylinder and then bleed the brakes says he isn't a rip off artist.
Good outcome, and thanks for letting everyone knwo the outcome.
 

commodoredave

Active Member
Joined
Dec 3, 2018
Messages
184
Reaction score
31
Points
28
Age
64
Location
sydney
Members Ride
vt
Hi All.
I was driving along braking normally in traffic the other day, then suddenly the pedal went spongy and I had
to pump the brakes. I plenty of space to pull right off the road, then got under the bonnet and the car to look
for any obvious fluid leaks from the master cylinder and the wheels. There were none.

After waiting 40+ minutes on the phone for roadside assistance, and doing another leakage check, I tried the
brakes on the road shoulder. They worked as normal, without having to pump them. I managed to get back to
my place (about 20 km) at reduced speed, without any brake issues at all. I haven't used that car since then.

The question: Given that description, what should I start to look for? In addition. I intend to renew any worn pads
and shoes and flush the old fluid and add new.

Thanks, M.
Had a very similar situation after driving down from the Blue Mountains. Did a full brake fluid flush and problem ( so far) has gone away. from memory Holden specify changing brake fluid every 2-3 years or every 50-60K's. My brake fluid was way beyond that and black. Make sure you do the rear passenger wheel bleed first and the drivers side front wheel last. The order you bleed them is important. The order of bleeding may be different with newer ABS systems so berst to check. Be super pedantic on making sure even the tiniest froth bubble is bled out.
 

bluehighway

Well-Known Member
Joined
Nov 13, 2021
Messages
202
Reaction score
292
Points
63
Age
58
Location
Taupo
Members Ride
VX Calais International
Glad to see some folk are flushing and bleeding their braking system, I did this just before I took my car in for a warrant of fitness last time (nz) and the tester thought the master cylinder was dry because the new fluid I used is clear... lol....the bonus to it all is the bleed also rebalances/synchronizes the front and rear discs...you notice it straight away because the car stops better and the pedal sits nice and high and feels firm ..... ;)
 

Skylarking

Well-Known Member
Joined
Feb 3, 2018
Messages
9,993
Reaction score
10,317
Points
113
Age
123
Location
Downunder
Members Ride
Commodore Motorsport Edition
Glad it’s sorted :cool:

Most brake fluids such as DOT 3 and DOT 4 are hygroscopic. Being hygroscopic means they will absorb moisture when exposed to air. Such moisture can be absorbed through brake lines, through seals or via the brake fluid reservoir. Such occurs even when the vehicle is not driven. That’s why manufacturers provide a time based schedule for brake fluid replacement.

The main enemy of brake fluid performance as such is moisture absorption. But not in the way some think… It’s not because water within the brake fluid suddenly turns the fluid into a compressible liquid, that’s impossible as all fluids are incompressible. The problem with water in the brake fluid is that water boils at 100C while brake fluid boils at 230C.

So with a few applications, even long light applications, lots of heat is generated within the brake system that ends up in the brake fluid within the caliper.. With the likelihood of the water within the brake fluid decreasing boiling point over time, ultimately yje water within will boil away and turn to vapour. The more braking, the higher chance of the water boiling and turning into vapour

And that’s where the problem is, when water boils it turns into water vapour which is highly compressible which results in brake fade…

As a side, DOT3 dry boiling point is 205C while its wet boiling point, that is 3.7% water within the brake fluid, is lowered to 140C. (3.7% can relate to 2 years of service)…

Dry Boiling PointWet Boiling PointComposition
DOT 3205°C/401°F140°C/284°FGlycol Ether
DOT 4230°C/446°F155°C/311°FGlycol Ether/Borate Ester
DOT 5260°C/500°F180°C/356°FSilicone
DOT 5.1260°C/500°F180°C/356°FGlycol Ether/Borate Ester

The more water within, the lower the boiling point and the easier it is to suffer brake fade…

1655103006971.png

Even with dry DOT5.1 brake fluid, which boils at 260C, drive as if you’re on a track and you’ll put lots of heat into the system and you’ll suffer brake fade.

So, if one sufferers brake fade, always check for fluid loss and if there is none then suspect moisture contamination and change fluid as the first corrective action. And if one still has problems, one can then look master cylinder (low line pressures?) or brake booster (vacuum?) or even driving style (if they think they’re Fangio) as the cause…


 
Top