myc43amg

I went to purchase a DRIVER SIDE rotor at the dealer.
The new rotor has the L marked on the side which mb part guys says its for the driver side,great.

I install it and the rotor VENTS are pointing BACK AND UP. On my old rotor the vents point forward and down which seems right so as to cool the rotor as it spins FORWARD,right??

And get this, on my OLD rotor there is a R stamped on the side where the NEW rotor has L on it????

Whats going on?

I took it back and the part guys said they sold me the right rotor for the LEFT driver side. BUT, when I install that rotor it spins and rubs the break back plate. My old rotor does not rub at all.

This is weird, any suggestions as to what may have happened?

BTW, I was having problems with my rotor as it was causing my steering wheel to shake above 40 mph. It also was making some loud noise after driving the car alot. I thought that the rotor was warped.

BUT, after taking the whole thing apart (including the hub which holds the wheel bearings) and putting it all back together again the issues I had are GONE!.

I drove it hard and alot yesterday and even took it to the highway at 50-70 and no shakes. Got off the express way and no noises at all. Before, 2 minutes on the express way the rotor would make all kinds of noises as if the rotor was warped and rubbed against the brake pads.

So I'm really glad I took the whole thing apart. But soon I will be needing to replace the rotors and want to know whats going on with the above?

svt ricco

this won't help but i just wanted to know how much you got the rotor? thanks

m a x i m u s

these are the part numbers: 210 421 18 12(left) and 210 421 19 12(right). how do these correspond with what you have?

i just bought a set of rotors myself, i can verify the venting pattern, etc. later tonight when i get back home ...

myc43amg

$232.00 plus tax. But I returned it.

myc43amg

210 421 18 12(left) is what they sold me but the vents where facing backwards compared to my old rotor. Its like they stamped the wrong numbers on the rotor. That can happen right?

Please do check the direction of the vent and let me know.

Thanks!

svt ricco

thanks for the info! hope you get the right one next time

m a x i m u s

myc43amg... the rotors i have are also marked "backwards", meaning the "L" looks like it should be R and vice versa. i havent had a chance to look at the rotors i already have mounted, but what did yours say? was your old drivers side rotor stamped "R"? what was the part # stamped on it?

ultimately i know that it doesnt matter, bc i have one of each, and ill just mount them to match the old ones i have on there now, but i am just as confused and curious as you are!

Ausmbtech

Your original rotors have been installed incorrectly.
The new rotor has the correct oriantation.

You'd be better of not changing the rotors back to the proper direction until you replace them as they look pretty worn on the pic, best not change the rotating direction so late in their life.

Just to confirm, the picture is of the left hand side when you are sitting in the car. (i'm used to RHD, just making sure)

myc43amg

The driver side OLD rotor thats on the left side of the picture is marked R. I believe it SUPPOSE to be L for driver side. That is what the NEW rotor from the dealer had stamped on it L NOT R like the old rotor. The new dealer rotor I believe had the part # 210 421 18 12,again with the R stamped on it.

myc43amg

Get this, when I installed the NEW rotor with the R stamped on it, the rotor would rub the brake shield. I spinned it slowly and it ruend with no rub and than when I kept on it got to the end of the spin and would rub the metal. It was as if the rotor was crooked since only a part of the rotor would rub. The old one will spin staright and no rubs at all.

Also, according to what you state "Your original rotors have been installed incorrectly." I think not unless the vents are suppose to spin where they will NOT catch the air as it spins forward. That is what the old rotors are doing, they catch the air as they spin forward. The NEW rotor once installed will catch the air when the tires spins BACKWARDS.

You wrote "Just to confirm, the picture is of the left hand side when you are sitting in the car." Yes, when sitting in the car its the left side. I always just tell the sales guys DRIVER SIDE or pass side, so nothing gets confused.

This is really weird, I wish someone would take a peak and see which way the vents face to catch the air. That will answer my questions and solve the problem. I believe the rotor I bought was stamped wrong, was suppose to be for the passenger side and not the drive side.

But until someone confirms the vent position I will not know. I'm going to check the passenger side to see whih way the vents are pointing.

m a x i m u s

im sure ill find out this sunday when i actually take my wheels off and replace the rotors, but it makes sense to me that the cooling fins would be facing towards the back of the car, like how slotted rotors are.

myc43amg

Just checked my passenger side rotor and the "fins" are facing forward so as to catch the air as the wheel spins forward. Why you would think it has to face back of the car is hard to understand? Think about it, the holes on the vents have to be "open" so air can go to the middle of the rotor and cool it off. If the vents or fins face backward it will not catch the air. Unless Im wrong but I dont think so. You can check which way the vents point without taking the tire off. Just look through your wheel (unless you do not have the orignal rims.

Ausmbtech

The don't "catch" the air from the outer side, they actually "release" the hot air through the outer side. The air is drawn in through from the inner side. The flow of air is aided by centrifugal flow which is why a "normal" rotor with straight vanes can still cool itself.

steve s

that is odd indeed (altho the mb software indicates my c36 via vin number is supposed to have the 4-pot pistons but instead has the single sliding ate crap)... anyway...

the rotors from brembo rotors on my wagon's bbk have the internal veins swept backwards, inside to out. how ur old rotor looked

StapleGun

There's nothing wrong with the shape of your rotors' innards, it's shaped in such fashion to provide a suction (negative pressure) effect - if any of you guys have seen the old Kirby Vacuum impellers (I guess I'm showing my age on that note) you'll remember the impeller 'fan' having this shape. The shape provides a vacuum effect caused by a high flow rate of a fluid, such as air or water (venturi effect) traveling over a foil shaped mass or object - akin to why a foil shape (wing) causes negative pressure above and subsequent lift (read Bernoulli principle).

'Ausmbtech' - I like that 'catch and release' analogy

m a x i m u s

thanks staple and ausmbtech for the explanations. makes total sense. im such a noob

myc43amg

Glad you understood.

So guys let me ask this as simple as I can.
Do the holes in the middle of the rotor point down like my old rotor on the left (see picture above). Or are the holes suppose to point up like the new rotor on the right? OR are you saying with your explanations that it does not matter which way they point??
This is for the driver side.

This is all I need to know, why cant someone just confirm this by taking a quick look at their rotor. You DONT need to take the wheel off. Just slip your hand and feel which way the holes are pointing (when car is cold of course).

Thanks.

myc43amg

IF you are talking to me steve, just take a look at the picture above. Left rotor (dirty one) is the old.

TENNAc43

So I just checked my Rotors and they are infact installed incorrectly. The vanes are facing forward "catching" the air instead of releasing the air. They have been like this for probably 3,000 miles. Do I need to swap them around or is it too late? Would this lead to further problems?

myc43amg

I think they are installed the right way.

TENNAc43

They are installed the same way as your old rotors in the picture. I think that is the wrong way.

myc43amg

I think you're right, look here:
http://m3forum.net/m3forum/showthread.php?p=2873279

TENNAc43

Thats dropin science like Galileo droped the orange!

Thanks bro,

steve s

i must've had a brain freeze or something.

the veins are supposed to be swept back. here is a pic of my brembo rotors. it is for the right side. u'll notice the veins are swept back, but the slots are actually swept forward, just as those described in the stoptech on the bmw forum link above.



if u'r old rotors were going the opposite way, then they were incorrectly installed.

Ausmbtech

Only 3000mi, they should be ok to swap around. If you don't do any particularly hard driving or track days then they'd be ok the leave the way they are. They still get plenty of cooling, it's just not optimal.