Are rotor sizes interchangeable?
June 20th, 2019, 1:08 PM
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Are rotor sizes interchangeable?
I just got a 2001 Express 3500 van. It appears that there are two rotor sizes, thickness of 32.7 mm and 39.1 mm. It seems from Rockauto that the thicker size was only in 2001 and 2002. Although some vans in those years also used the thinner size. I measured mine, and it is 39.1. However, I'm planning on replacing rotors and calipers, and I would like to switch to the 32.7 if I can, because I can get them for a much better price. So the two questions really are one in terms of fitment, and secondly in terms of braking quality. Although most brands have separate part numbers for rotors and calipers based on the thickness, but I noticed that Centric for example, and one or two others, only had one part number to fit all. That led me to believe that perhaps the parts really are interchangeable. And especially if I also replace the calipers with the 32.7 calipers. I can't imagine that there is a different spindle or something based on a slight difference in rotor thickness. Every other dimension of the two rotors is the same. And there's no RPO code for this, which leads me to believe that it was just a bit random, which ones got put on on the assembly line.
That's in terms of fitment. In terms of braking quality, would I be sacrificing braking quality by opting for the thinner rotor? This isn't something I know that much about. But whether a given van has the thicker rotor or the thinner one, it seems they have the same proportioning valve and master cylinder, so it's not like they're set up to brake differently than each other. And if it's true that it's arbitrary which ones they put on, then you would think it wouldn't really matter. But I would feel stupid "trading down" for inferior rotors just to save money. And technically the size of the smaller rotor is already thinner than even the DISCARD size of the thicker rotor. But I just don't know. Anyone who has insight, please advise...thanks!
That's in terms of fitment. In terms of braking quality, would I be sacrificing braking quality by opting for the thinner rotor? This isn't something I know that much about. But whether a given van has the thicker rotor or the thinner one, it seems they have the same proportioning valve and master cylinder, so it's not like they're set up to brake differently than each other. And if it's true that it's arbitrary which ones they put on, then you would think it wouldn't really matter. But I would feel stupid "trading down" for inferior rotors just to save money. And technically the size of the smaller rotor is already thinner than even the DISCARD size of the thicker rotor. But I just don't know. Anyone who has insight, please advise...thanks!
June 20th, 2019, 8:33 PM
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Not an expert on these things, had the same issue with the rear wheel cylinders on a voyager something like a year ago. Played it safe myself and just replaced with same size. Tried to pull an interchange for your make model and it wants more info (DRW or SRW). Maybe someone will be able to run with that?
June 20th, 2019, 9:13 PM
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Rockauto and every website I saw list both rotor thickness options for front rotors with srw. I did find on Alldata something from GM that seems to indicate that if you have JB8 brakes you get 1.50 inch rotors and if you have JB6 then you get 1.25 inch rotors. It didn't say a year on it, but Alldata put it in the year for my van. I never saw those sizes mentioned online elsewhere, but 1.5 inches is 38.1 mm so it's close. But it's weird that nowhere else online besides that one piece on alldata did I see that the rotors are based on RPO. I'm not sure why there isn't an RPO specifically for rotor size. The bottom line is that my van clearly came with the 39 mm ones and that's what it has now. I'm guessing it's probably fine to switch them but I guess I should just stick with it even though it will probably cost me couple hundred dollars more.....
June 21st, 2019, 10:42 AM
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Well the rotors are close to 100 apiece. I mean they are huge and have the studs built in so it makes sense. I can get the thinner ones for much cheaper. And then the calipers also I can get the other calipers for cheaper. Apparently the calipers that go with the thicker rotors are the same as the calipers that the duallys use in front. And the front rotors for duallys are also 39 mm, although they're a different design than the other ones.
June 21st, 2019, 11:16 AM
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Again, definitely not a pro. Only thing I can think of that rotor thickness would affect in terms of braking would be defection/warping under pressure due to rotational force between the hub and pads. The thinner the rotor, the easier it is to bend to the side. Be careful, ask a local shop if available.
