VS Commodore BRakes

[Ralph1Malph]

I am trying to get to the bottom of my VS ute brakes.
They fade on the first stroke nearly every time, but then rock solid until next application.
So far, I have changed fluid and bled - twice and changed the master cylinder so ruled that out too.
It does have ABS so maybr a problem there.
I am tempted to change the wheel cylinders next as maybe theres some internal leakage there.

Any clues?

Ralph

[Davehoos]

VS is 4 wheel disc.not known for positive pedal with cold pads.

some utes have rear load pressure limiter--lever connected to diff to adjust max rear pressure.

for a normal ute 1085-1086 pads
in the dealer we used a shandy pads for the front--different compound inner outer,one suits colder application.VN VP wouldn't stop when cold and last VR=VS I drove was much the same.the disc is different,but they have a different booster setup.

work been buying stealth pads-it has a soft backing for noise reduction that allows the pad to twist in the holder..they also been chewing out the inner pads and have a dreadfull feel.rego brake test is ok when new pads.

[justinc]

some of the worst feeling brakes i have ever encountered, cold in a v8 auto they are bordering on dangerous. don't know how these vehicles pass safety standards

jc

[Ralph1Malph]

Maybe I misled y'all
Maybe I used the wrong descriptor .
Instead of fade, I should have said that the pedal slowly/bit faster than slowly travels to the floor on the first application, almost feels like air, but as I said, none in it at all. I'll check again coz maybe there is a slight leak but I am not losing any fluid, nor can i see any wetting.

After the fluid change and bleed, the brakes are great, except for the floor travel which I was trying to fix!

The proportion valve is working but it doesn't feel like that is the cause.

The fluid was very (200000+) old and had goobers in it. I changed the master cylinder as it is common for fluid goobers to restrict the non return/pressure valve leading to these exact symptoms.

Maybe those same goobers have gummed up the pressure valves in the ABS module as I now notice that first application in the morning, the ABS gives a little flutter or shudder. mmmmmm


And yes, I only have the POS because it was free!

Ralph

[Davehoos]

piston seals.hoses.

not had to work on ABS units-with old age.the electric side often had failed by 200 000Km.

I replaced hoses a few times as the expanded when you applied----but it didn't fix it.

always had good results replacing calipers--normally upgrades.
not unusual for single piston caliper to flex or the pedal.

[Ralph1Malph]

Thanks Davehoos,
Yes my feelings exactly. It has done 340000 all hard km!

I will systematically change the flex lines, then pistons (maybe calipers) I just have to get to the bottom of it!

Cheers
Ralph

[Ralph1Malph]

I came across an old post on a commodore forum which suggested that the ABS modulator was not able to be bled 'manually'. IE one has to bleed it via the diagnostic computer. I could believe this as nanocom includes a bleed function on Disco ABS! Reading further, one chap said he had success with a less scientific method. He continued to work the ABS by braking on a gravel road, in order to force any air trapped in the ABS module to be expelled.

I tried it and the results are encouraging. I'll bleed a few more times and activate the ABS a few more as well and let y'all know how it went.

Ralph

[Ralph1Malph]

All fixed! I am chuffed. I am staggered by the amount of air hidden in one dodgy commodores ABS module.

All fixed!
Ralph

[Davehoos]

did you bleed at the module pipes or at the calipers.

[Ralph1Malph]

Fair question. I had a young apprentice do it at work. Not his fault at all, but they are taught to bleed at the calipers. Unless the manual or diagnostic comp says otherwise. We had neither a manual nor diagnostic comp!
That said, I went to many holden/commodore fora and only one post about working the ABS module.
In hind sight I should have realised. After all, we do the ABS module on LR brakes
All good now tho.

Cheers
Ralph