Upgrading front calipers from VS to VX? What needs to be done???
Hey fellas,
I've just brought a set of VX Commodore twin-piston front calipers off a mate for $100. Apparently they will bolt straight on, but am told I won't get full benefit by running these unless I get larger discs? Is this true? and what size will I need and off which model? Is there anything else I need to get these running effectively?
Will standard VT/VX discs run on the VS without needing any conversion gear i.e. different wheel hub or shimms?
Decided to upgrade the brakes as the pads are about due.
Cheers!
You need the VT conversion rotors, which either have a different centre whole, or use a spacer ring. We've got slotted ones on the shelf for $215 for the pair, or $75 per rotor in standard. Both of which will bolt on.
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Real cars are steel cars.
You need calipers AND rotors. VT calipers alone wont mate up to the VS rotors.
As above, if you can get hold of the VS upgrade rotors you will not need the shim. VS upgrade rotors are VT rotors witha VS centre hole. VS centre hole is 70mm, VT 71.5mm.
You will need to run the VT 1" bore master cylinder as the standard VS 7/8" bore master cylinder won't displace enough fluid when you apply the brakes, causing a low spongy pedal. You will need to do some mods to make the VT master cylinder work correctly on the VS booster.
Try a search as this has been covered many times.....
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Hey mate i just did mine last week, i got a vr commy v6 and my machanic just upgraded my front brakes to VT. My machanic changed the rotors, clipers, discs, master cylinder, lines to VT. Since i got it back its the same as my single piston brakes ,you have to like press more than half way on the brakes peddle in order to pull up. On my mates vs you only have to press it abit and it brakes, but mine like half way, there shit! My machanic then changed the master cylinders 5 times, and pads and bleeded them heaps, and still couldnt get it to work as proper vt brakes..
what do i need to do in order to just press on it abit instead of half way, its 2 loose the peddle..
Or is my brake booster on its way..? i duno need help
Real cars are steel cars.
From memory the VR has a 15/16" master cylinder, this has a large enough bore to cope withthe twin piston calipers.
Sounds like the master is not installed correctly on the booster. A faulty booster usually causes a hard pedal that wont move far.
SEARCH!!!!!!!! This symptom was covered in detail a few weeks ago.........
If I told you I was a compulsive liar, would you believe me?
I just brought the shimms for $40, and brought a brand new set of slotted and drilled vt rotors for $150. I'll get a new set of brake pads and do the install over the weekend, and see how I go.
You wouldn't think that changing from a 15/16th master to a 1" one would make too much difference. If anything, you'd think that there would be more of a difference in the booster i.e. the pushrod that goes to the brake pedal and length? could be wrong, and probably am, but if a lot of people are just changing the master and this is happening, that may be the issue? I've done some reading and some people have just changed the calipers and rotors and it's made one hell of a difference. Others have done the conversion and had no luck at-all, or it's made their braking even worse. Sort of a mixed bag, and i'll have to give it a go myself and report back.
Cheers!
Real cars are steel cars.
Slayer,
You have a VS correct? Your master is 7/8" bore and will need to be upgraded to 1" to prevent a low pedal.
This generally means that the pedal needs to be pushed harder to compensate for the increase in surface area of the master cylinder piston but the larger bore is required to displace the larger volume of fluid required by the twin piston calipers.
I have VS booster with VT master, calipers and rotors and my pedal is high and firm but a little too much pedal effort is now required for my liking. A popular fix is to upgrade the booster to the twin diaphram booster from VT. A twin diaphram booster is used to restore pedal effort when increasing master cylinder bore size. One day I will do this!
The VS booster pushrod is too long for the VT master and the master will require spacing away from the booster to allow correct operation. The the fluid resivour will need to be swapped as the VT one cannot be filled correctly due to the different mounting angle compared to VS.
If I told you I was a compulsive liar, would you believe me?
Cheers RX25SE,
I'll get ahold of a VT master and booster as well, and see how she goes.
Cheers!
I thought there'd be a pushrod difference from the booster to brake pedal on the different models. That would change the ratio and obviously affect the pedal ratio. That makes total sense. Thanks fellas.
I've just Brought a good working VT commodore master and booster for $50. Is there anything would have to modify or change to get this to fit?
RX25SE, you're right about the masters and calipers. I gave the old man a call and he said the biggest difference would most likely be in the reservoir or space inside the calipers. Thinks that this would affect the brake pedal a bit, but now knowing the pushrod length is also a different ratio, that would affect things even more.
It's real nice to know that there's lots of thse brake upgrade kits on ebay kicking around for $500-$700, but they fail to tell you that you've gotta have the VT booster and master to get anything good out of it.
Such is life.....
Cheers Fellas!
Real cars are steel cars.
Push rod won't change the ratio. (Unless you mean hydraulic ratio, the different bore sizes in the master and calipers?)
The pedal ratio is the distance from the footpad to the pushrod pin compared to the distance from the pushrod pin to the pivot.
Somewhere in VR model run there was a ratio change of the brake pedal to improve feel and decrease pedal effort a bit. From memory it was someting like 6.00:1 to 6.25:1.
If I told you I was a compulsive liar, would you believe me?
So, is the VT/VX master and booster unit a direct fit into the VS without any major modifications?
Real cars are steel cars.
Can't answer that one, I haven't done it yet!
If I told you I was a compulsive liar, would you believe me?
No, the VT M/C is not a straight bolt up but there are adaptor blocks around. Maybe read below before you get into that though.
Putting standard VT calipers onto a VN-VS is fundamentally flawed as it alters the brake balance towards the front of the car resulting in reduced braking capability. I've posted it before, quite recently, but here's why:
StopTech : Balanced Brake Upgrades
Some maths:
VN-VS calipers have a single piston of 54mm in diameter and, for the heavy duty brakes, a disc diameter of 289 or 290mm. The effective pad width, = radial dimension of the swept area, is ~45mm.
VT-VZ have two pistons of 42mm in diameter and a disc diameter of 296mm. The pad width is also 45mm.
Brake torque is the force on the pad x the distance from the centre of the pad (~; actually the distance to the centroid of the swept area defined by the pad but that => calculus) to the axle centre x the coefficent of friction between the pad and the disc x 2 disc/pad surfaces.
The force on the pad is proportional to the area(s) of the piston(s) => proportional to the piston diameter(s) squared.
Ignoring the factors that cancel out, the ratio with VT-VZ front brake components to VN-VS front brake components is:
[{(296/2)-(45/2)} x 2(42^2)] / [{(289/2)-(45/2)} x (54^2)] = 1.24
i.e. + 24% = bad!
If you can find a PBR twin piston caliper with pistons of 38mm in diameter you will have something that should work, without altering brake balance, without affecting the ABS and without increasing pedal travel. I believe that there is a member or two on here who have used twin piston calipers (HSV?) with 40mm diameter pistons which is a step in the right direction.
Yes, the low pedal is caused by the increased volume required to move the larger piston area into contact with the discs.
VS use a fast fill M/C which reduces the (perception of) pedal travel.
VT-VZ brake hoses are required with the calipers.
Real cars are steel cars.
What about changing the spring in the proportioning valve (in the VT m/cyl) to a higher "crack off" pressure to increase the line pressure to the rears?
Falcon wagon use basically the same m/cyl but with a different spring.
If I told you I was a compulsive liar, would you believe me?
Thanks Cheap6 and RX25SE. There's more to this upgrade than I thought!
So, with a VS booster/master and a VT booster/master there's gotta be a way around it all, i'm assuming?
So what if I just use and modify the VT master cylinder "space it up?" and use the vs fluid filler and bolt that to the vs booster?
But is the VT booster the same as a vs one??
Real cars are steel cars.
No.
The VT from memory is a double diaphram which provides a geater force on the master cylinder, VS is single diaphram and made from plastic.
As before, I am running a VS booster and VT master setup.
Brakes are worse when cold, better when they get heat into them. This would mostly be pad compound, but they seem to suffer less from fade regardless of pad choice.
If I told you I was a compulsive liar, would you believe me?
DO you think it'd be easier for me to replace the whole unit - booster and master with the VT one I have. I've heard that the pushrod just needs the connecting hole to be drilled closer in a little and cut down slightly and it should all fit?
Real cars are steel cars.
If it were me I'd do that.
Just remember this whole job is a modification to the braking system and may need to be certified by the registration authorites.
If I told you I was a compulsive liar, would you believe me?
I reckon that's what i'll do. I've been told that the VT booster unit is a dual diaphragm type, and will get better assist with the braking of the car by using it.
Cheers Fellas!
Possibly. Altering the rear line pressure is discussed in the Stop Tech article accessed via the link above. You might find a proportioning valve that backs off rear line pressure less at higher pressures and still maintains adequate rear pressure at lower M/C pressures but you will have to be careful to avoid unintended consequences. Stop Tech. again:Originally Posted by RX25SE
StopTech : Balanced Brake Upgrades
It still doesn't address the behaviour of ABS, if applicable, though.
Real cars are steel cars.
Mmmmmmm............probably should read the article.
Cheers.
If I told you I was a compulsive liar, would you believe me?
Articles. While the links appear to be the same on here they are for two different locations. Actually, if you chase the links back there is a lot of really good info. around brakes on the Stop Tech site.
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