Rotor Swap

[jgalt]

In the short time I've had my VX, I've never been happy with its braking power. I've seen some on the board have replaced their rotors with cross-drilled or vented discs but I was considering a slightly different route.

I happen to have two front rotors (knuckles and all) from my '96 Rodeo, which was SASd. The rotors are definitely bigger and was considering swapping them in.

Has anyone ever done this?

I'm going to have to break-out the calipers to make sure the various hub & knuckle sizes are similar but, assuming they are, what other issues should I worry about (I have the calipers from the Rodeo too - should I replace those?)?

Thanks for any input.

[Joe_Black]

I'll have to admit I'm surprised that a '96 rodeo would have larger rotors. The VX's are large enough that you can barely fit a 15" wheel. But if you do the swap you're going to have to fab new caliper brackets to handle the increased diameter. And if the calipers you use can't accept larger pads to cover the additional swept area then you're wasting effort. It's a two-part deal: bigger rotors need bigger pads. Otherwise you'll actually reduce your braking power as the same amount of pad is attempting to stop a rotor further out meaning it has greater force to overcome than if it was gripping nearer the axle. Simple leverage works with braking too. ;)

[ZEUS]

If you have all those parts maybe you can just connect the Rodeo spindle and brake stuff to the VX ball joints?

[jgalt]

If you have all those parts maybe you can just connect the Rodeo spindle and brake stuff to the VX ball joints?

That's exactly what I'm hoping to do.

With larger calipers, however, is there any risk that the brake master cylinder cannot deliver enough fluid to activate? Should I look at replacing this as well (assuming everything else checks out)?

[ZEUS]

Following that route then, I would just check the brakeline fittings on both the VX and Rodeo calipers to make sure they match. If they match, by all means order up some braided brakelines from Independent 4x and keep going! The stainless lines would deliver better brake pedal feel while allowing more pressure to get to the calipers. If they have the same number of pistons in each caliper (prob'ly) and the size of the piston isn't much different between the two, then things should work out nicely with the VX master, I think. If things seem inadequate after it is all put together, you still improved the stock braking by adding the stainless lines and you can either put the stock brakes on again or dig for a Rodeo master. Like Joe says though, it is surprising the Rodeo has bigger discs - I would like to know the difference. Could we get some measurements from you?

[ZEUS]

One more thing... what about the ABS and TOD? Can you transfer the rings from the VX rotor to the Rodeo's? Check into that before anything, I would say.

[BD-VX99]

I'll have to admit I'm surprised that a '96 rodeo would have larger rotors. The VX's are large enough that you can barely fit a 15" wheel. But if you do the swap you're going to have to fab new caliper brackets to handle the increased diameter. And if the calipers you use can't accept larger pads to cover the additional swept area then you're wasting effort. It's a two-part deal: bigger rotors need bigger pads. Otherwise you'll actually reduce your braking power as the same amount of pad is attempting to stop a rotor further out meaning it has greater force to overcome than if it was gripping nearer the axle. Simple leverage works with braking too. ;)

Joe, I think you may have it backwards on that last point. Unless I'm totally looking at this wrong. The brakes apply a force in the opposite direction to which the rotor is spinning, about a lever arm the equal to the radius of the rotor (actually ~2/3 of the way through the pads contact patch). The negative torque applied at the centre of the wheel is equal to the radius times the breaking force (based on the hydraulic squeezing force and the frictional coefficient of the pad/rotor). Increasing the radius, increases the amount of negative torque that can be applied to the wheel using a given caliper/pad. Is there something I'm missing there? I don't think bigger pads change the applied frictional force, as the same hydraulic force is now being applied over a larger surface area. I was under the impression that bigger pads just distributed the negative effects on the heating and wearing surfaces. Anyways I've been wrong before but if I am this time I'd like to understand it better.

[Joe_Black]

It's sorta had to describe in text, at least for me. ;) But imagine a spinning disc in front of you that you want to stop for your hands. Would you place both hands on either side and press, using as much of your hand as possible or just squeeze the outer perimeter with your fingers? Using your entire hand to cover as much area as possible provides more friction and distributes heat over a greater area as well. Using just your fingers on the outside will either burn them or you'll be unable to hold on.

In relation to brakes you want pads that cover the full rotor, which can't happen if the calipers aren't selected or mounted properly for the application.

[jgalt]

One more thing... what about the ABS and TOD? Can you transfer the rings from the VX rotor to the Rodeo's? Check into that before anything, I would say.

I think that's the question. I would think TOD should be fine as that's all internal to the axle housing/differential, etc. The '96 from which these rotors came did have 4-channel ABS so I'm hoping it uses the same sensors - we shall see.

Regards to the "rings" though, I'm not sure what you mean. The '96 Rodeo did come with longer, equal length axle shafts outside of the CV joint so I'm hoping the application (ie diameter of the shaft, bearings, seals and width of the hub) are all the same.

Before I do anything, though, I will check the size. On an "eyeball" basis, the Rodeo rotors appear larger, but that may be due to my bias of looking at a 4,000 lb vehicle vs a 5,500 lb vehicle. Unfortuantely I do not have a caliper that big and my daughter has used every bit of string in the house on summer craft projects so I cannot truly measure the circumference.

I will post back.

Thanks all for your input.