Brake Booster???
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 =)
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.
B Cast and flat topped!
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.
VH Brake Upgrade
Try this.
Last edited by Lewie; 26-09-2010 at 11:01 PM. Reason: Tried to link a thread - I hope.
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VIP Member
Don't do the VS Booster/Master Cylinder or VS Booster/VT Master combo.
You've put on twin spot VT Calipers? Pair it with what it was designed for - The VT Booster and VT 1" Master
Look through this thread:
VT Brake upgrade - Long and Spongy Pedal
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
This is my vr that I rebuilt ....CLICK HERE to see my vr on Cardomain
......if you want to check it out......Anyway make sure you rubbish a ford daily ....I am a 4DH8RZ Club lifetime member .................new members joining everyday
Banned
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
Banned
Originally Posted by HamaTime
a long and spongy pedal would probaly be the resualt of incorrect bleeding
VIP Member
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.
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.
Banned
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
Banned
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
captain halfajob
wow man, i love your words of wisdom... every post so far has been contradicting someone who has facts...
Banned
look the vt cylinder will give you the optimim brake feel what i said is that a 15/16 cylinder will have slightly more travle but not much
the 15/16 will be better as the proportioning valves will suite the rear brakes so the rears wont be over engauged
im not saying that you cant use the vt cylinder like i said the front brakes work well with it
it's just that i am saying someone with 40 years in brakes has told me that the 15/16 works fine so dont waste your money
is this clearer
Banned
and for the record the booster only helps braking it dosent have any thing to do with the operation of the master cylinder it only is imbetween your foot and the cylinder
you could probaly use a 7/8 master without a booster and have better feel
VIP Member
No the VS one's were not. This is not a question of technical knowledge, this is simple physics. The VT Calipers have two slightly smaller pistons (42mm if memory serves me right) as opposed to one 46mm piston on the VS Calipers. Therefore, there is alot more area (piston) to be pushed out requiring more of a 'push' to get more of the fluid through the lines, and into the calipers to push both pistons out. If you have a VS 15/16 bore Master Cylinder, which is smaller, this is going to be a hindrance? It will restrict flow? Think about it as having a tiny exhaust on a powerful motor, it is hindering performace because it is not large enough to get the increased quantities of gases out of the motor.
Same physics for the Booster. If you are trying to tell me that standard VS equipment is better paired with VT equipment, which it was not designed for, then you are a fool. You are denying simple plain physics.
Well then with all due respect to his 40 years of experience, if he is refusing to accept simple 'FACTS' not myths or opinions, then he does not deserve to be a qualified professional. He is correct there is a loss of pedal, the slight amount he is referring to is wrong, it's in between 1/4 and 1/2 of the entire pedal gone. Not slight braking, just 'NOTHING' - the pedal is ineffective.
I have done this conversion and I have tried all methods, because I wanted to road test the VS booster combo first. It doesn't work effectively. PERIOD
VIP Member
No wrong, the rears under engage and you lose rear braking, because of the greater volume of fluid required to push out the front pistons. Unless you have the appropriate equipment i.e. VT Master. The VT Booster is purely there to maintain pedal feel. The Larger Master cylinder requires a stronger larger Booster to do most of the work for you. The VS Booster being much smaller and only single diaphragm requires a greater 'push' creating this 'brake free threshold' I was referring to in order to push the bore through the M/C.
Once again, simple physics.
WHAT? ARE YOU FROM MARS OR SOMETHING?????
Doesn't have anything to do with braking or the operation of the M/C????
WTF????
Mate when you push the brake pedal it pushes the pushrod through the booster, with the vaccum it pushes the bore through the Master Cylinder pushing the fluid out!
Mate seriously, have you done a brake upgrade before?
Do you really understand how brakes work?
Banned
mate simple physics is
say you have a 1 inch master and just for an example a 2 inch slave you put 100nm on the master the slave will exert 200nm but will only move half the distance
say you have the 1 inch master with a 1/2 inch slave you put 100nm on the master the slave will only exert 50nm but will travle twice the distance of the master
so if you have a one inch master with one inch slave you put 100nm on the master the slave will exert 100nm and will travel the same amount as the master dose
now with all that there is nothing to do with engines and exausts
now to fact i know some one with a 15/16 on there vn it works fine is that good enough for you
and with physics if you increase the size of the master clynider and front brakes but leave the rears the rear pistons would move out further and the rear and front brakes are split
Banned
the booster only helps you push the pedal it dosent have any effect on fluid flow or any other barking componet it only makes it eaiser to push the pedal in
VIP Member
But it's still directly related to braking and is directly related to the Master Cylinder. Without a booster you would have pretty shitty brakes.
No nothing to do with Engine's and exhausts, but the principles of pressure are the same. For larger output, you need less restriction.
Well fine, if you know someone who has a 15/16 Master on a VN then thats fine. I'd be very surprised if it didn't have a spongy/brake free pedal to some extent.
I'm giving up arguing with you, straight facts and in person experience doesn't seem enough to get a simple point across....
captain halfajob
Banned
well ill give up to as we are arguing over how spongy a pedal is with a certain master cylinder pretty stupid
Cheers for all your interest, turned into a pretty big debate, lol. Leaning strongly towards fitting a VT master onto my VS booster, should be all good!
Without a booster the pedal is hard as a rock (what happens when you pump the pedal without the engine running? it goes hard as there is no assistance), so a smaller booster does not give spongy feel, in fact spongy feel is from air in the system full stop. If you do this conversion you should use a VT master as stated many times, because it is a quick fill. For those who dont know it means that the first part of the master cylinder is larger then the rest of it putting it simply, and is like this to push the extra amount of fluid to fill the larger area in the front brakes. Using a N/A master of different spec will result in a long pedal as the piston has to travel further to displace the same amount of fluid as a VT one, giving a long pedal. You do not need a VT booster for these brakes into an early commodore as you dont require as much pedal effort to stop the car as it weighs so much less, using one only requires a bit less pedal pressure to stop, but makes the brakes a little touchy. VT boosters dont actually make the car stop any better, youll just have to press the pedal harder to get the same effect if you use a VS booster.
My VKs VS booster and VT master work perfectly, pedal isn't hard etc, would be a different story in later models as they weigh more.
If you use a 15/16 master youll have a long pedal but once it actually pumps up/ takes up it will be easy to stop the car because of its small displacement. argue all you want with that fact if you do the math its true.
VIP Member
True but pedal feel is important to any braking system wouldn't you say?
Well i wouldnt use anything other then a VT master, but i find i get good feel with my VS booster.
The formula for area of a circle is pi*radius^2, you will get a quarter of the force not half. Travel/volume is limited based on other factors (the caliper pistons can only move so far) so the comparison of travel is only relevant at the pedal end, assuming that both masters are capable of filling the slave cylinder.
A 1 3/16" master (the VT front circuit) has around 60% more area than a 15/16" master. So using the smaller master would require 60% more pedal travel to move enough fluid to engage the brakes when compared to the larger master. You would indeed gain some force advantage due to the master/slave ratio, but that's not particularly relevant because either system is capable of producing more than adequate force (especially when paired with the correct booster).
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