VS master cylinder and ABS Q

[immortality]

Can i change the Master cylinder without needing to take the car to a service center to cycle the ABS unit to bleed out any air that may enter the system?

been having braking issues with this car for a while now. though it was just a sticking caliper but the problem seems deeper then just the calipers. this week i've re-kitted all the calipers and fitted new pads on all four corners. this has gotten rid if that annoying sqweek when you first drive off but the long pedal problem is still there, worse since i did the rear calipers today. there are no leaks and i'm not loosing any fluid. have bleed the system a couple of times and i'm certain there isn't any air in the system. the booster fuctions normally, with the engine off and no vacuum the pedal is fairly firm (but still has some travel), start the engine and the pedal sinks as the vacuum assist kicks in, it's the fact that the pedal goes a long way down that concerns me.

i've never done a master cylinder on a ABS equiped car before. what i've been told is that if air enters the ABS module the only way to bleed it is to have the system hooked up to tech2 so they can cycle the ABS unit to bleed the air out? is this true?

is there a way that i can change the master cylinder without needing to get the ABS unit flushed?

thanks in advance for any help

[hako]

A lot of mechanics "bench bleed" the master cylinder before fitting - this will generally ensure no air gets in the lines and you need no bleeding. Bleeding takes time and time is money! Do a GOOGLE for full instructions.
The VR/VS series always has had long pedal travel and if there is no leakage from the MC you may be going to a lot of trouble for no gain. If the pedal is hard with no vacuum then that is your best indication of no air in the lines. New pads and calipers may need a few thousand KM to fully bed in.

[immortality]

A lot of mechanics "bench bleed" the master cylinder before fitting - this will generally ensure no air gets in the lines and you need no bleeding. Bleeding takes time and time is money! Do a GOOGLE for full instructions.
The VR/VS series always has had long pedal travel and if there is no leakage from the MC you may be going to a lot of trouble for no gain. If the pedal is hard with no vacuum then that is your best indication of no air in the lines. New pads and calipers may need a few thousand KM to fully bed in.

yeah, it always did have a long pedal but i'm going a looooong way now, almost to the floor with no vacuum the pedal is hard but it still has some travel if you apply enough pressure. previously you could "pump up" the pedal with one quick pump and it would be rock solid, that was before the pads and new seals, now, that doesn't even really work. pedal isn't spongy to indicate air in the system. once you get pressure the car pulls up fine. guess i'll give it a few days to see if it improves with some mileage

edit. bench bleeding won't totally eliminate the need to bleed the entire system once the new MC is fitted as there will be some air when re-connecting the brake lines to the MC.

[VrWagz1]

You will have a little air in the lines but they are very small diameter insided and if you bend them up as soon as you pull them out, you should only loose a miniscule of fluid that wont matter. Definatly bench bleed the m/c first, or when installed put your fingers over the holes and get someone else to pump the pedal to fill it, then quickly put the lines in. Then if you just give it one or 2 gental pumps to force bit of fluid through the air will completely expell into the resovoir as it refils the master, then your on your way.
It should be fine if you do it carfully. I did a whole booster, master swap out in mine withno problems.

[immortality]

pedal has firmed up some today after some more stop/start driving. pedal is firm if used in quick succession but has a little travel if not used for a little while. see how it goes in a couple of days. i'm fairly certain the MC will need changing but i'll cross that bridge when the time arrives.

[hako]

What can happen when you instal new pads on discs that have not been skimmed and have a ridge on both edges of the disc from wear, the new pad being flat rides on the ridges and every time you floor the pedal the new pad has to flex slightly to make contact with the disc surface. After a number of brake applications the ridge will eventually wear itself into the pad so the the shape of the pad mimics the wear contours on the disc.

[Surfwagon]

You can also fit a VT master to a VS by fitting a spacer between the master and the booster.
RaceBrakes in Sydney sell the spacer.
I've removed/replaced Master twice and haven't had to bleed the ABS yet.
This does require 2 people unlike normal bleeding.
When you do the change over have the new master ready full of fluid with the packing plugs still fitted.
Remove the old master and try not to rattle the pipe lines too much to keep as much fuid inside them as possible.
Bolt the new master to the booster then one pipe at a time remove the plug and fit the new line but leave the nut loose.
Do the same with the other pipe.
The next step is quite messy so have plenty of water ready to flush excess brake fluid away.
Now with the pipes still loose have your buddy slowly push the pedal down and this helps push the air out between pipe and the master and then nip up the nuts.
Now bleed the rest of the brakes like normal.
Any tiny air bubles will pass through the ABS with out problem.
The problem with the ABS is when people allow it to drain of fluid.
It's worked on mine both times.

Cheers SW.

[immortality]

as the new brake pads bed in the pedal has returned to where it was before the proble mwith sticking callipers became a issue. there is still more travel then i like (more then my VN) but this i'm told is normal with VS commodores.

giving the pedal a quick pump after intial application firms it up.

[Surfwagon]

You can firm the pedal a bit more by using metal braided hoses to replace all 5 rubber hoses if you haven't already.

[immortality]

You can firm the pedal a bit more by using metal braided hoses to replace all 5 rubber hoses if you haven't already.

it's only the missus daily, not a weekend track car or anything, i guess i'm jsut use to the pedal on the VN which doesn't ahve much travel at all and is very firm.

it cetaily pulls up better then before and looking at the rotors the pads aren't fully bedded in yet so i'll see what it does.

i have read that replacing the bracket that goes from the front of the MC to the strut tower with something much stronger also helps with pedal feel as it helps eliminate any flex in the booster & mounting bracket.

[holdenrocks]

do i need spacer between master and booster on VR-VS for VT abs master cylinder ???

thanks

[VrWagz1]

vr and s are compltetely different setups, be more specific. Vs yes you will, vr dont even attemp it.