VR ABS Master Cylinder

[muttley383]

Hi all,
Is it possible to fit a 1" master cylinder from an earlier model to a VR V8 with ABS.

At the moment I have the standard 15/16" master cylinder and I was wondering if I could fit the 1" unit to give a higher pedal.

I run AP 4 spot calipers on each corner and did not want to go to the trouble of trying to convert the VT booster and cylinder. I have read that some have fitted the earlier model 1" master cylinder and block one of the front ports as the VR has only 2 lines from the master cylinder to the ABS unit.

[VrWagz1]

will be fine, no commodore atleast i know of has a different master because of abs they are all the same in their repective models abs or no abs.

[muttley383]

The difference is in the number of output ports/lines from each master cylinder, the abs unit has only 2 with the standard non-abs having 3 or 4.
I don't know if they are the same internally with just extra ports.

[VrWagz1]

no extra ports, they just whack a bung in one of the rear outputs as you only need one line going to the abs unit

[Cheap6]

For VP and VR, they are different internally between ABS and not but I can't recall exactly how. I think that it is because the ABS unit has to be able to pump fluid back into the reservoir when dumping pressure from a wheel cylinder and there is a valve in the MC cyl. somewhere (on the firewall end of the secondary piston?) to allow that. You could run an ABS MC without ABS but not the other way around, at least not without affecting the ABS operation and you would never know until the ABS is active.

[stocky]

if youve upgraded your brakes to those specs, why be lazy about the master cylinder? go get a VS booster, a VT master cylinder and they will bolt straight up. youll have it installed in a couple of hours

[VrWagz1]

For VP and VR, they are different internally between ABS and not but I can't recall exactly how. I think that it is because the ABS unit has to be able to pump fluid back into the reservoir when dumping pressure from a wheel cylinder and there is a valve in the MC cyl. somewhere (on the firewall end of the secondary piston?) to allow that. You could run an ABS MC without ABS but not the other way around, at least not without affecting the ABS operation and you would never know until the ABS is active.

Looks like i was wrong, but how does the abs re-pressurise the caliper if it dumps the fluid. I was of the understanding it just released a piston in the abs unit to de-pressurie a line and then the piston would re-apply to lock the wheel again.

[holdenrocks]

yea, i have same problem... hows could i find the 1 inch bore master cylinder for VR ABS. as i wanna to upgrade my brake.. need get properly master cylinder for VR ABS ?? how much cost will get these ??
thanks

[VrWagz1]

according to previous posts you cant use the Vn/p 1" master, so therefor there is no 1" master available for vr with abs.

[Cheap6]

Looks like i was wrong, but how does the abs re-pressurise the caliper if it dumps the fluid. I was of the understanding it just released a piston in the abs unit to de-pressurie a line and then the piston would re-apply to lock the wheel again.

I had a quick dig around in my tech. stuff and my memory can't be as bad as I thought as there is indeed a valve on the firewall/booster end of the secondary piston to allow fluid pressure to be returned to the M/C.

There are two modes of operation with the ABS.

There is a 'hold' mode that just isolates a line (i.e. a front wheel cylinder or both rear wheel cyl. - VP/VR ABS is three channel) from the master cyl. This just stops the pressure in that line from increasing, regardless of any further increase in M/C pressure.

If the (a) wheel speed doesn't recover the second mode is activated. This is a 'dump' mode that opens the line to the inlet of a pump that pushes the fluid back against the pressure in the master cyl., dropping the pressure in the line until the ABS valve for that line shuts again. If a non-ABS M/C was to be used it is this mode that wouldn't work.

The pressure in the master cylinder is always maintained at that generated by the force on the brake pedal.

As a matter of interest, you can see the electric motor for the pump as part of the ABS module under the bonnet, under the dress cover, and hear it run during each self test.

[Adza75]

I have just converted my front VR brakes to VT 2 piston, and I replaced the booster and master to the VT 1" one. I believe the VT master will go straight onto the VR booster, but I opted to use the VT booster anyway.

There is no return line from my ABS unit. The VT only had the 2 holes as well, just needed to bend a pipe to use it.

I believe the older 1" ones will also work, as long as you bung the hole as they were made pre-ABS models so have 3 outlets instead of 2.

But my bet would be just chuck a 1" VT cylinder onto your current booster.

[VrWagz1]

I had a quick dig around in my tech. stuff and my memory can't be as bad as I thought as there is indeed a valve on the firewall/booster end of the secondary piston to allow fluid pressure to be returned to the M/C.

There are two modes of operation with the ABS.

There is a 'hold' mode that just isolates a line (i.e. a front wheel cylinder or both rear wheel cyl. - VP/VR ABS is three channel) from the master cyl. This just stops the pressure in that line from increasing, regardless of any further increase in M/C pressure.

If the (a) wheel speed doesn't recover the second mode is activated. This is a 'dump' mode that opens the line to the inlet of a pump that pushes the fluid back against the pressure in the master cyl., dropping the pressure in the line until the ABS valve for that line shuts again. If a non-ABS M/C was to be used it is this mode that wouldn't work.

The pressure in the master cylinder is always maintained at that generated by the force on the brake pedal.

As a matter of interest, you can see the electric motor for the pump as part of the ABS module under the bonnet, under the dress cover, and hear it run during each self test.

Thanks, that was an interesting read, alwasy wondered if abs had a way of generating its own pressure to force fluid around.

I have just converted my front VR brakes to VT 2 piston, and I replaced the booster and master to the VT 1" one. I believe the VT master will go straight onto the VR booster, but I opted to use the VT booster anyway.

There is no return line from my ABS unit. The VT only had the 2 holes as well, just needed to bend a pipe to use it.

I believe the older 1" ones will also work, as long as you bung the hole as they were made pre-ABS models so have 3 outlets instead of 2.

But my bet would be just chuck a 1" VT cylinder onto your current booster.

1" vt wont go on vr booster, what you did is the best option. Its so much better than the vr setup.

[stocky]

and VT master is bigger than 1 inch as well

[muttley383]

I think the VT master also has 3 ports, not 2. Since the VR with ABS only has 2 lines I will have to block the extra port on the VT master cylinder.

[stocky]

VT has 2 ports