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Brake Booster???

MY_84_VK

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Hey Guys,
I've just fit a VT Twin Piston upgrade onto my VK Commodore and now I'm almost ready to setup the booster, I have a VS Master and Booster but I've heard that the VT master is a much better option. What I would like to know is there really that much of a difference between the VS and VT Master Cylinders?
Any help would be much appreciated =)
 

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VK SL 3800

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VT is need for this conversion as it a quick fill, VS is not. VS booster is more then adequate for an early commodore. People say the VT master bolts straight to the VS booster and they do but even after you wind the adjuster screw in so its level with lower rod (a pic would help explain that) its not far enough in and with the master bolted on it pushes the piston in just a little (just like touching the brake ever so slightly), maybe enough to make the brakes drag i dont know because i put tiny washers behind the two master mounts on the VS booster to bring it out that little bit. But you can fit a VT booster and master but it doesn't bolt straight in, you have to fabricate a mount. Most people use a VS booster with VT master.
Also VT/VX masters are the same, ABS models have a bung in the second front brake port as they only use one line for front and rear.
 

Lewie

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Very thirsty VT & VH project under way! YAY!!
You will need to modify and weld the VT booster bracket before you can fit it to the firewall. VS ones will fit straight on without modification. I did the same upgrade to my VH and found that the VS one (for me) was a much better option. I don't know how to link back to older threads but if you do a search on threads started by me you should find a thread titles"VH Break upgrade"or something along those lines.

Check it out, it might help. It also has a pic of what I did to the adjustment nut inside the booster.

Also I did the VT SS master cylinder and VS booster.

http://forums.justcommodores.com.au/vb-vk-holden-commodore-1978-1985/100012-vh-brake-upgrade.html

Try this.
 
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markovr

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I assume the picture is just to see if everything bolts up ok as you need to put something over the shaft of the shock in the picture to prevent dirt water etc from shortening the life of the shock
 

vr1uz-fe

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just use the vs master cylinder they work fine some are one inch any but the rest are 15/16

a brake mechanic i know has the twin pistons on his vn it has a 15/16 master cylinder he said the pedal moved slightly but the more pedal movement and smaller the master cylinder the more torque you can exsert
 

vr1uz-fe

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HamaTime™

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just use the vs master cylinder they work fine some are one inch any but the rest are 15/16

a brake mechanic i know has the twin pistons on his vn it has a 15/16 master cylinder he said the pedal moved slightly but the more pedal movement and smaller the master cylinder the more torque you can exsert
No, use the VT Master. VB to VS Commodores had a choice of 15/16inch or 1inch bore master cylinders. This is not suitable for the VT twin spot brake calipers. The VT master cylinder is a 1inch bore master cylinder, but is a quick fill. This means that the first section of the master cylinder is actually larger (1 3/1 6inch bore). The quick fill design displaces more brake fluid on the initial application, to help move all 4 (front) pistons and maintain a good pedal feel with minimal travel. Without a VT master cylinder, pedal travel will be increased. In other words, your pedal will go further to the floor before the car stops (some ABS vehicles do not suffer from this problem, but only some!!!).

Therefore running a VS Master/Booster combo which were designed for much smaller brakes/master cylinder will basically eliminate the benefits of the twin piston caliper/greater braking surface.

The VS Booster being single diaphragm doesn't have enough power/push/vaccum to be able to give you the solid pedal feel, you need to push the pedal harder, through the threshold to be able to build up the power to push the volume of brake fluid required to push the pistons out, through the lines.

If your brake mechanic said that, and said that a brake pedal with a 10 - 40% no pedal threshold was fine then he's a bit of a loony. With 40% of your pedal gone - just 'free pushing' what is the point? You might as well have the weaker VS single piston brakes in and just use more force pushing down, at least you have a more responsive pedal where you can actually feel the brakes. Rather than pushing through a 'free push threshold' and either not engaging the brakes at all or locking them up.

As I said, pairing the VT brakes with a VS Booster/Master or even a VT master with a VS Booster is a disgusting combination. It does the larger brakes no justice and IMHO it is a waste of money without the larger more compatible VT Booster/Master.

a long and spongy pedal would probaly be the resualt of incorrect bleeding
The system was bled and re-bled 5 times and re-set up twice. The VS Booster and M/C aren't compatible with VT calipers to the extent of getting a full pedal and responsive prominent progressive braking.
 

vr1uz-fe

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the smaller the master cylinder the less need for a booster hence why you dont get 40% loss

im sure that all the pbr masters from vn on had a quick fill i know that my vr one inch sure dose and it is pbr ill call pbr tech tommorow
 

vr1uz-fe

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oh and this brake mech has like 40 years of experinence lol if you babeled on at him he would just walk away like i said he told me there was a slight loss of pedal not the amount you are claiming
 
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