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My partner just had her 45,000 mile SAAB 9-3 serviced. The manager said that everything was fine but the mechanic said that she needed new braks discs and pads, front only presumably. I could believe pads at that mileage but don\'t plan to inspect them myself. However the front discs have worn about one 16th of an inch, measured by feel. The ridge on the outer edge of the disc is about the same as that on the edge of my spectacles, if you run your finger nail across the lens and up to the frame ie not very much! These are ventilated discs but the amount of wear I can detect does not look like a replacement job to me. They are not warped or scored -just worn by an amount commensurate with the mileage. May I have comments from Back Roomers on this please?
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sounds about right to me nowadays discs are seen as throwaway items have known garages replace them at less miles than that and i didn't think there was anything wrong with them however my mate who is a mechanic had a look at the old discs and assured me that they should be replaced . not like the old days when discs seemed to last forever
cheers...keo...ex-mechanic.
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Is the car automatic? Auto's do get through pads/discs at a much higher rate than manuals.
Saab's manual will specify how much wear is acceptable however IMHO 1/16 does not justify disc replacement - we are talking less than 1.6mm which seems to be well within any reasonable wear limits.
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The minimum thickness is usually stamped on the disk. If not it's in the manual. Measure it.
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I've just changed the front discs on my Subaru Legacy at 85k. The old ones had wear ridges of about 1.5mm on each side. The disc was stamped with the min thickness which was 22mm, the new ones were about 25mm thick so it looks like wear of about 1.5mm is about the maximum. This could well be different for different cars though.
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Thanks for the comments so far. The car is manual gearbox. I am suprised that one can only have wear of 1.5mm on something 25mm thick. Just as well it doesn't work that way on tyres, we'd be changing them every few weeks!
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AS
Brake disc wear is much greater than it used to be with the use of non-asbestos pads, so replacement at 45k isn't unusual.
If the disc is 25mm thick new, it's almost certainly internally vented, and not solid. The actual wearing surfaces are therefore much thinner than the overall dimension suggests.
regards
John S
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>> looks like wear of about 1.5mm is about the maximum. This could well be different for different cars though.
The Haynes manuals give the max. wear for:
Rover Metro as 1.96mm
Nissan Micra as 2mm
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Sometimes the lip cuts into the pad wear sensor and gives a premature REPLACE BRAKE PAD warning, I think that's one reason,
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>>Sometimes the lip cuts into the pad wear sensor and gives
a premature REPLACE BRAKE PAD warning, I think that's one reason>>
Spot on that man!
--
groups.msn.com/honestjohn - Pictures say a thousand words.....
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>> >> looks like wear of about 1.5mm is about the maximum. This >> could well be different for different cars though. >> The Haynes manuals give the max. wear for: Rover Metro as 1.96mm Nissan Micra as 2mm
The figure I quoted (1.5mm)is the ridge each side giving approx 3mm wear overall. Sorry if that was misleading. And yes, the discs are ventilated.
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Similar max wear figures from Haynes:
Vx Corsa (vented) 3mm
Rover 800 (vented) 2mm
i would ask the garage what the measured thickness is and how this compares to the specified minimum. If they are 75% or more worn and new pads are needed, then do the discs at the same time.
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I had to replace my 93 pads at 45k. Although the discs were scored my (independent) dealer said their was no need for replacements discs. Shortly afterwards, I detected a rumbling from the the offisde rear under hard braking. The disc apparently has a 'minor high spot' and again the advice was to live with it until the new pads took the shape. 20k later, they have and all seems well. Apparantly rear discs are pretty expensive, I'm not sure about the front. It's also worth looking at driving habits. Discs are now wearable items since asbestos came out of the pads. Heat is a major cause of damage so after coming to a halt (particulary from speed), aim to get the footbrake off quickly and use the handbrake to hold. The longer the extremely hot pads and disc remain in contact, the greater the wear.
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Keeping the brakes on after stopping will not wear pads or discs. Some people say it can lead to the discs warping but in driving well over 200,000mls in heavy Merc autos I have never encountered this problem as I always leave my foot on the brake after stopping.
On saying the above though, my W211 E320 CDI has just had new pads all round after only covering 22,000mls. I do brake quite heavily, but the main cause is the new SBC braking system as it is continually applying the brakes slightly for safety reasons, to remove moisture etc. This is according to the garage.
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