Backwards brakes?

Here’s a fascinating one and a question I hadn’t given any thought to whatsoever.

In the previous post on this blog I showed a picture of my new wheels:

wheelandrepeaters.jpg

In comments, Edusaab has noted that perhaps my brake rotors are on backwards! This is entirely possible as I didn’t realise they could go one way or the other. I figured they’d be made foolproof so they could only be put on one way. Notice in the photo above that at the top of the rotor, the vent groove is leaning ‘forwards’ toward the front of the car.

Edu’s also included a few URL’s to some Saab-authorised Viggen photos, though having looked at them I’m no clearer on the issue than I was before….

This shot shows the vents in the rotors facing the same way as mine (photo enlarged and extra contrast dialled in to enhance the vents):

viggen6grooveforwardssml.jpg

…..but then this photo, also from Saab stock, shows the vents (looking at the top of the rotor) pointing back towards the rear of the car:

viggen8groovebacksml.jpg

Now, to confound things even more, I had another look at the photos of my own car and as Edusaab’s pointed out, my rotors are pointing two different ways. The rear rotors are pointing rearward and the front rotors are pointing forward!!

I’m so confused.

Edusaab suggests that one direction is more aggressive than the other. Is the setup on my car an example of typical Swedish aggression, with a lot up front but more mild mannered “behind closed doors”? Or is it an example of my mechanic making a slightly embarrassing error?

Any thoughts welcome.

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16 Comments

  1. Swade: They are directional — each pair has a ‘left’ and a ‘right’ rotor. I don’t know which is which, but I assume that the part number stamped on them should be a clue?

    The wheels look great on the car BTW.

    And, as a C900 guy, KEEP THE SAAB-SCANIA LOGOS!!!!

  2. As the wheel turns, shouldn’t the water, dust, etc. be pushed out of the rotor? The last picture seems to do that better than the first. Your current setup will push the debris toward the center of the rotor, IMO.

  3. LOL!

    This reminds me of a time back in 1989, when Ford Australia released the EA Falcon. The Fairmont Ghia version had alloy wheels with laid-back spokes (like these http://i12.ebayimg.com/02/i/08/3c/3a/09_1.JPG ), which pointed towards the rear of the car. That is, they did on the LHS, but pointed forwards when mounted on the RHS. I can recall someone telling me how crappy it looked, and trying to see which way the spokes were pointing on every one of those cars that went wizzing past me in traffic.

    Sound like someone better consult the EPC before you’re driven completely insane!

    Drew B

  4. On Viggen that is perfectly normal. Saab made both rotors identical so on the left side of the car it will look a bit strange but on the right side it will look normal. This is all perfectly ok though.

  5. Swade,
    Want to be even more confused? Read this post:
    http://www.saabnet.com/tsn/bb/NG900/index.html?bID=230705
    I’ll quote it here but search “rortor direction” in the NG900 OG9-3 board and you’ll find lots of stuff.

    Quote:
    I installed EBC grooved and dimpled rotors and greenstuff pads on the front of my 99 9-3 SE this summer, and I’ve noticed that they fade considerably under semi-hard use (not at all during normal use) on the street. It is so noticable that Jak actually mentioned that it was abnormal when he was driving it. Also, at highway speed in rain, they take a noticably long amount of time to dry off before peddle pressure is effective. I started to think that maybe they were installed in reverse so that the grooves were actually trapping gases and forcing the pads away from the rotors when heated up. I began researching, and here’s what I found:

    1. Brembo and Baer recommend that the slots on the rotors attack the pads (outer part of slot contacts the pad first)
    2. Brembo and Baer typically use vanes inside the rotor that are angled to better channel heat away
    3. EBC rotors use straight vanes like OEM that are not angled
    4. Brembo and Baer stress that it is IMPORTANT that slots attack the pad, and OPPOSE the internal vaning
    5. EBC does not give installation instructions on their website, and does not even mention attacking or following anywhere on the website
    6. From people’s installation pictures, and almost equal number of people have them installed each way

    Normally the general rule is, slots should oppose vanes. It is clear that EBC rotors are not similar to Brembo or Baer brakes because EBC uses stright vanes and grooves instead of slots. So standards don’t apply in this case.

    My question is… which way is correct? Could this be causing my problems? I’ve included a picture to simplify things. Mine are currently installed in “B” orientation.

  6. Swade, the best way is to ask to AbbottRacing. They are especialist in the 9-3, 9000 and 900 and they made the Viggen rescue kit.

    AS I said I purchased from them the Groove discs for my 9-3ss and my dealer fitted the discs in the other way as Abbott recomended.

    I say aggressive in terms of stopping power, but also it makes more noise and is less comfortable.

    also check, garaget.org there are plenty of Viggen pics, as this….

    http://www.garaget.org/show_ext.php?car=903&image=26649

    One friend of the Club Saab crashed its 9-3viggen few days ago, the car is in the dealer(totally crashed), if you would like something, as some wheels…..

    Its important that some units hasn’t the groove discs. Saab changed those discs from others that are normal as a replacement part. If you change your discs with an OEM discs in Saab, the new ones won’t be grooved.

    greetings

  7. Doesn’t it depend on which side of the car your are facing?

    I mean, they couldn’t be “handed” rotors could they – manufactured differntly for each side- nah not from GM!

    (irony folks, irony…)

    Nice wheels now.

  8. After checking many pics of Viggen in garaget.org, it seems there is only 1 type of discs and there is no diferentiation for every side. For this reason if you look the right side of the car you will see the grooves pointing backwards, but in the left side points forward.

    In my 9-3ss in both side points backwards(like the right side of the viggen). Usually must be this.

    http://img174.imageshack.us/my.php?image=imagen002ij2.jpg

    The front of the car is in the left.

    greetings

  9. Swade,

    If you ship the Viggen to the Northern Hemisphere (specifically Vancouver), I’m sure all the brakes will work properly as intended …..

  10. I’d love to Ken, but as it happens my wife and I had another “moving back to Canada” discussion last night and whilst I’m keen to do so, she wants to stay.

    Looks like we’re stuck here in Tassie. Not such a bad thing, but I wouldn’t mind if someone developed one of those Star Trek transporters in the next 2 or 3 years.

  11. I don’t think it would have any effect except on aesthetics.

    The problem the slots are trying to solve is superheated air sitting between the pad and disc. This air reduces the friction between the pad and disc, and the slots (or holes or vents ) are simply a space for the hot air to expand into and bleed away. Given the tiny amount of air involved it doesn’t matter whether the font edge is toward the inside or outside – it’s not like the tread pattern on a directional tyre flinging water to the outside. The superheated air is under such high pressure it’ll expand into any gap provided, whether it’s travelling with or against the centrifugal forces.

    The key thing is how much of the brake pad area the slots sweep, not the exact pattern of the slots/holes. Like tyre tread patterns, the exact geometry of the slots is mostly for marketing purposes, to make the brakes look more impressive. That’s why HSVs have really agressive slots, FPVs have those wavy cross cut slots. It’s the rough equivalent of whether your calipers are red, yellow or brake-dust coloured 🙂

  12. …except…

    I just realised why “handedness” would really matter, and it’s not to do with the slotting direction. The central vanes that ventilate the disc and keep it cool are designed to run in a set direction. They generally slant backwards when looking from above, so that the venturi effect pulls the air through the centre of the disc and out towards the edges when it is spinning. Reversing the direction of travel of the disc would try to force air into the slot, against the natural inclination of the airflow.

    So a quick check would be to pull the wheels off and check the internal vanes to see if they have a bias one way or another. If the vanes are straight between the disc surfaces you have a genuine ambidextrous brake rotor. If it slants either forward or backwards you will know which direction the discs should point.

    The internal vanes are much more important that the slot direction.

  13. I suggest you go to John at Elkparts and get all the bits as shown in Abbott’s rescue kit from him. With your budget, Elkeparts will certainly be most economic and effective. I also suggest strongly the BSR kit as opposed to Maptune (nothing wrong with them but you pay a premium). You can always take it off if you sell this vehicle and upgrade your BSR kit to another one which you can’t with Maptune. Look at the performance curves and you’ll see that BSR’s performance is even better. As for your suspension, check the 30mm lower springs kit at Elke and the more rigid sway bar. That is a must.

  14. Joe,

    Unfortunately the rescue kit stuff from Elkparts isn’t RHD compatible. It’s the Taliafero GenuineSaab unit with is for LHD cars only (the steering rack brace is at least).

    I’ll consider the other stuff though, but down the track when finances allow.

    That said, the service my mate received with his 9-5 Maptun upgrade was pretty darn good and the price he saw was the price he got, freight included.

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