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Punto brake disc

Discussion in 'Technical' started by ashtek, Jul 12, 2012.

  1. ashtek

    ashtek Amatore

    Messages:
    60
    Bangalore
    Bangalore
    Grande Punto 1.3
    All,

    My Punto MJD is now 9 months old and i have done around 9k kms. Recently when I went for a long drive, I noticed steering vibration at speeds above 90-100kmph. The vibration was so much that after experiencing it couple of times, I stopped going at speeds above 90kmph.
    Upon return, I took the car to service center and asked them to check brake pad & disc and wheel alignments (info gathered from teamfiat discussions). They did wheel balancing & wheel alignment and said the problem is resolved and brake pad & disc were fine. Steering vibration at high speeds stopped, however when I applied brakes gently at speeds above 60kmph, there was still vibration (this was always there but increased off late). Went there again and asked SA if it could be due to issues in brake pads/discs. This time SA said he'll clean the brake pads and after cleaning we went for test drive but the issue was still there. Then he said this must be due to faulty brake discs. As I have done only 9K and it is 9months old, they said they'll replace it under warranty. They have told me that they'll get the new ones next week and will call me.

    Q1 - is the diagnosis correct? The steering "sometimes" vibrates even when I "do not apply" brakes (and "always" vibrates on gentle braking at speeds above 60kmph). Does it mean issue is not with brake disc?
    Q2 - I saw them removing the wheel while cleaning the brake pad - does this undo wheel alignment? Should I ask them to do it again?

    Thanks,
    Ashish
  2. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    It looks like brake judder. Probably it looks like hot judder, which is the result of sinusoidal hotspots on disc resulting uneven distribution on disc surface.When brake pads come in contact the discs these unevenness results in vibrations. Typically observe between 120-60 kmph. Cold judder is not due to hot spots but due to uneven disc surface that can be due to misalignment, rough usage or even wrongly fitted(over tight) disc. In both cases it is the disc problem and disc need to be replaced. Remember it is not a problem with the manufacturer of the car. It can happen with any car. May be for punto being heavy every time the contact force between the brake pad and disc will be more than a light vehicle. So I think the diagnosis is correct. I am not sure whether he under stood the problem correctly as in India the troubleshooting skills of workers are very poor. Any problem with brakes they do routine things like cleaning the brake pads, changing the disc etc. In most cases this solve the problem. Another problem is resonance. Ie a small vibration that otherwise negligible can be amplified and transferred to the vehicle. What I described is the some possible causes and since the car is in warranty there is no need to worry. One thing that you need to take care if the pads have changed is not to apply hard brakes for first few kms~300kms). Rough use of brake pads are one reason for non uniform disc surfaces.

    Here I am attaching a portion of clutch disc to illustrate the hot spot. I couldn't get a picture of brake discs.
    hotspot.jpg
  3. ashtek

    ashtek Amatore

    Messages:
    60
    Bangalore
    Bangalore
    Grande Punto 1.3
    Thanks Sungoa. Hope that disc replacement solves the problem.
    I am not a rash driver, dont remember applying brakes suddenly at high speeds. In fact, the first time I touched 100kmph was when I went for the long trip after crossing 8.5K km!!! as I dont get a chance to go at high speeds here.
    Did you mean 60-120kmph or 120-160kmph?
  4. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    I mean a hard braking at speed of 120 to bring it down to 60 kmph.
  5. ashtek

    ashtek Amatore

    Messages:
    60
    Bangalore
    Bangalore
    Grande Punto 1.3
    When they replace brake disc, should I ask them to do wheel alignment again?
    Last edited: Jul 16, 2012
  6. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    Wheel alignment is not needed. I am not an expert in that area please wait for some expert opinion.
  7. gurjinder

    gurjinder Staff Member Janitor

    Messages:
    3,989
    Punjab
    If replacing the brake discs, replace the pads as well. New discs are always accompanied by new pads.

    Cheers.
  8. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    Ask the TASS people to tight the disc with the prescribed torque, otherwise there is a chance of pads and disc getting problem later.
  9. ashtek

    ashtek Amatore

    Messages:
    60
    Bangalore
    Bangalore
    Grande Punto 1.3
    Thanks, I'll ask them to replace pads as well. Because discs come with pads, I assume they should not charge me for pads seprately considering that discs are being replaced under warranty (btw I have no clue about the cost of these parts...)
  10. gurjinder

    gurjinder Staff Member Janitor

    Messages:
    3,989
    Punjab
    I assume you've misunderstood my post. New discs do not come with new pads. They are separate.

    But it is a good practice to install new pads whenever we install new discs. Kindly check with the service people if the brake pads will also be included in warranty.

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