Have any of you guys out there done the swap on a pre-VN Commodore with the front twin pots and stock rear discs? If so, how did it all go in the end? I'm going through the conversion myself at the moment.

I helped out spike to do his. WHT747.... Its quite an easy conversion really. But are you changing boosters or brakes? More information sport.

The lot. Already have caliper/discs bolted up, was going to run the turbo booster/master set up at first until I came across a link on this forum that showed the VS/VT combination. I've since purchased and fitted the VS/VT set up, but as the rest of the car is still months from completion I won't get to test it all just yet. Just wondering if it was worth it I guess mate.

the VS master is same as VLT one... IE 1 inch. If your going to go with the bother of installing a full upgrade with the VT booster. I would do the master as well and make up a larger reinforcement to improve pedal feel! PM me for more details if you like

Wasn't the actual conversion a VT master and a VS booster? Bigger than 1" master with the apparently better feel of the VS plastic booster?

Im fairly sure the VT master wont fit the VS booster. If I was ever going to do it i would grab myself a full VT booster and master. Actually no thats wrong. You need the VT masters pin to be modified(the push rod) so as it will actually fit.

The VS master cylinder is 7/8" or something. VT is 1,1/4" fast fill type. It is also a common conversion to use the VT master with VS plastic booster, You can to buy an adaptor from Race Brakes Sydney to mount the master to it.

Quote: Originally Posted by vhr32 The VS master cylinder is 7/8" or something. VT is 1,1/4" fast fill type. It is also a common conversion to use the VT master with VS plastic booster, You can to buy an adaptor from Race Brakes Sydney to mount the master to it. This is what roy is talking about. There was a link that one of the guys (I forget the name...RB30POWER??) has done....He has a silver VLCT with this booster/master combo but running R32 calipers over VT disks. Has anyone done this with standard VT brakes, and how do they find it I think is the question. Race brakes do this kit, but it's around $600 and if you do it yourself the cost of the parts is quite cheap

Quote: Originally Posted by VLT-025 This is what roy is talking about. There was a link that one of the guys (I forget the name...RB30POWER??) has done....He has a silver VLCT with this booster/master combo but running R32 calipers over VT disks. Has anyone done this with standard VT brakes, and how do they find it I think is the question. Race brakes do this kit, but it's around $600 and if you do it yourself the cost of the parts is quite cheap Yeah I know he was talking about this, I just wrote that in a hurry lol I'm pretty sure it makes the pedal nice with the VT calipers, I dont know from personal experience though. Race Brakes sells the adaptors for this swap ($100??) the VT booster and master kit is $600

I'm using this setup. I have the Nissan 4 pots up front on 330mm discs. With the VLT booster master you get terrible pedal feel. Using the VT 1/1/4 master makes a massive difference. The VS plastic booster makes it all pretty much a bolt up proposition. only 1 tiny mod to be made to the booster. Well worth it. I actually probably rate this mod higher than when i first changed to the 330mm discs and 4 pots. Race brakes sells an adapter for this conversion - not sure what it is actually supposed to do, mine all fitted together perfect. Only adapters are for the brake lines which are about $50 delivered from Cebco. They just allow the single flare VL lines to be used on the VT master that usually accepts double flare lines. Article on the conversion on RB30-POWER's site: www.calaisturbo.co.nr (http://www.calaisturbo.co.nr)

Quote: Originally Posted by 87calais I'm using this setup. I have the Nissan 4 pots up front on 330mm discs. With the VLT booster master you get terrible pedal feel. Using the VT 1/1/4 master makes a massive difference. The VS plastic booster makes it all pretty much a bolt up proposition. only 1 tiny mod to be made to the booster. Well worth it. I actually probably rate this mod higher than when i first changed to the 330mm discs and 4 pots. Race brakes sells an adapter for this conversion - not sure what it is actually supposed to do, mine all fitted together perfect. Only adapters are for the brake lines which are about $50 delivered from Cebco. They just allow the single flare VL lines to be used on the VT master that usually accepts double flare lines. Article on the conversion on RB30-POWER's site: www.calaisturbo.co.nr (http://www.calaisturbo.co.nr) Thanks for this info mate. Ive been waiting to hear from someone with experience to post up about these VT's and bigger conversions and the combo's on boosters. Ive been working on the assumptions because I cant see how a smaller booster could work better/same as a larger one. BUT good to know that someone has actually done it. Couple of questions, did the 1 1/4 booster make the pedal like a rock or did it give you a smooth pedal? How far to the floor do is the pedal when you mash it for full effect?

Pedal feel now is great. Before when using the VLT booster/master the pedal was spongey as hell, and if you stood on it hard you could get it almost all the way to the floor. With this setup the pedal is nice and firm - you will never get it near the floor. The thing that surprised me most was at the track, just how hard you can get on the brakes without locking a wheel. Obviously you can make them lock, but by modulating the pedal you can get some awesome stopping power before they lock. As for the smaller booster working better, I'll bore you with some theory for a bit, but by the end you will understand how it all works. The bigger the master cylinder you use, the lower the hydraulic pressure is that you are feeding the caliper. You get higher FLOW from the bigger master but lower pressure. The early commodore brakes - up to VS - used front floating calipers with a single 54mm piston. The only difference for the turbos/V8's/later models was the caliper body was finned to help with cooling. Formula for working out caliper total piston surface area: Total Piston Surface Area = Pi x R square x No of pistons. (remember a floating caliper has the piston surface area of 2 pistons due to the floating caliper body. VB - VS front caliper. Area=(3.14x(27x27))x2 A= 457.8mm square Not sure how the VT calipers measure up but i'll use my Nissan Calipers as an example. They have 4 x 40.4mm pistons: Area=(3.14x(20.2x20.2))x4 A=512.5mm square. Now if we look at master cylinder pressure: PR = Pedal Ratio (5.2:1 on a VL - VS) FP = Pressure Applied by your Foot (pounds) A = Area of your master cylinder(square inches) OP = Output pressure in PSI Formula: PRxFP/A=OP we will use 100 pounds of applied foot pressure for all these examples. VL NA Master Cylinder (15/16) A=3.14x(15/32x15/32) A=.689square inches 5.2x100/.689 = 755psi VLT/V8 etc (1") A=3.14x(1/2x1/2) A=.785square inches 5.2x100/.785 = 662psi VT (1/1/4) A=3.14x(5/8x5/8) A=1.226 5.2x100/1.226 = 424psi So as you can see, as the master cylinder size increases, the pressure they put out decreases. Keep in mind though that the flow from each master cylinder increases as the bore size increases. In the case of the VL/VLT, They both use calipers that require the same amount of fluid to move a given distance, however the VLT is clamping a larger disc (289mm as opposed to 271mm) and therefore has a greater lever effect. to offset this they have used the 1" master cylinder which puts out a lower pressure, which keeps good pedal feel. If you used the 15/16 master with the larger discs they would clamp with greater force, and with the greater lever effect from the larger disc you would tend to have greatly reduced the amount of modulation you have with your pedal. i.e only a relatively small amount of pressure on the brake pedal would end up resulting in locking up the wheels. I cant comment too much on the VT brakes as i dont know the Piston diameters off the top of my head - If someone can let me know the Piston size we will go through that one. My setup. My Nissan calipers require a larger amount fluid to extend the pistons a given distance than the stock VL brakes do, due to the larger Piston surface area. This is achieved by using the 1/1/4 VT master. Now my calipers are also clamping a 330mm disc as opposed to the 271mm for an NA VL or 289mm for a VLT, hence again requiring less pressure to keep a good amount of modulation available through the pedal. So the VT master is quite well suited with its lower pressure, higher flowrate. With the larger volume Nissan calipers and the VLT master cylinder it took the majority of the pedals stroke just to fill the caliper (extend the pistons and push the pads against the disc), before any pressure could build up. This is why the pedal was so deep and spongy. As far as Boosters are concerned, all they do is provide vacuum assistance. What they are made of - plastic or metal has no effect on how they work (plastic is heaps lighter though). The principal is that you have engine vacuum on one side of the diaphragm and atmospheric pressure on the other side, thus giving "assistance" when you press the brake pedal. I have never pulled a double diaphragm booster apart to see exactly how they work , but i can only assume that they would give double the amount of assistance? Going back to the VLT's case above: I don't have any tech info on the amount of assistance provided by each booster. My best guess is this: bigger disc = less pressure required at the caliper to retain good modulation from the brake pedal. However, with the lower pressure they must have found that too much effort was required on the pedal to pull the car up, hence the use of the double diaphragm booster. As for the VS plastic booster - i have no idea where it fits in with regards to the amount of assistance it provides. It is physically similar in size to the NA VL booster. The VS used a similar brake setup to the VL. all VS models used the 289mm discs and finned calipers. The V8 models used a steel double diaphragm booster identical to the VLT booster (same part number), The V6 models used the plastic booster and a 7/8" master cylinder. In saying that, we can assume that since the master cylinder is putting out a greater pressure than the VL (7/8 would be 865psi if used in the examples above) and using the same size caliper, the plastic booster would be the same, or possibly render slightly less assistance than the NA VL booster. As far as the combo of VT master, VS plastic booster with bigger capacity calipers i.e VT 2 pot, Skyline 4 pot etc, its probably more luck than anything that there is a combination of factory parts that fit with bugger all modification, that work so well together! Anyway, after all that, hopefully that helps with understanding the relationship between some of these parts.

Thanks for input mate, it's always good to hear from someone with some real life practical experience and not just what someone else read in a bloody magazine somewhere. I'll post up some pics of the whole conversion soon and hopefully not long after that I can describe how they feel on the road. Thanks again champ.

awesome post, how do you know all that??

Experimentation, reading, asking, qualifications, employment - probably some (or all) of those I'd say!

Quote: Originally Posted by 5spdvl Experimentation, reading, asking, qualifications, employment - probably some )or all) of those I'd say! All of the above lol. I give Credit to RB30-POWER though for doing the experimenting and working out which parts fitted together. Anyone know the piston size in the VT twin spot calipers? Scott.

VT = 2x 42mm C4 = 2x 38mm C5 = 2x 40mm Nissan = 4x 40.45mm VB-VS = 1x 56mm VE = 2x 43.2mm

The spacer needed to adapt the VT master to the VS plastic booster is $55 and this is alloy. The VT booster modified to mount to the earlier firewalls has a adjustable rod on both the master cylinder and brake pedal ends for easy adjustment and the VT master cylinder with the three adaptors to make the brake lines fit is also supplied from us at Race Brakes Sydney for $590 and was tested on a VK down at Phillip Island last month with fantastic feedback.The only problem with this conversion is the support bracket that bolts to the end of the master to the strut tower does not fit as the master sits in a different position.

Quote: Originally Posted by LAZYASS The only problem with this conversion is the support bracket that bolts to the end of the master to the strut tower does not fit as the master sits in a different position. I don't see this as a problem, Commodores should have a beefier custom bracket anyway!!

Quote: Originally Posted by LAZYASS The spacer needed to adapt the VT master to the VS plastic booster is $55 and this is alloy. The VT booster modified to mount to the earlier firewalls has a adjustable rod on both the master cylinder and brake pedal ends for easy adjustment and the VT master cylinder with the three adapters to make the brake lines fit is also supplied from us at Race Brakes Sydney for $590 and was tested on a VK down at Phillip Island last month with fantastic feedback.The only problem with this conversion is the support bracket that bolts to the end of the master to the strut tower does not fit as the master sits in a different position. Do you have a pic of the adapter you guys use to fit the VT master to the VS booster?. The only place i can possibly think it would be required is to space the master cylinder out off the booster so you don't need to modify the pushrod?. Also agree the standard support bracket should be ditched in favor of a stronger item.