Technical When to change front brake discs
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Technical When to change front brake discs
it must be replaced when it's got more than 1mm reach on the lip, or if the disc's are shuddering under braking, or if the disc surface is damaged, worn unevenly.
Pads will often have a wear indicator which is a small slot in the middle of the pad. When the slot is worn away you should change your pads. Would have thought that leaving it until 1mm was dangerously low.
(CZ)enda
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Minimum thickness of the front brake discs for all non-turbo Unos is 9 mm.
As the discs tend to wear unevenly, the thickness should be measured at the inner, middle and outer parts of pads trace, diagonally.
Some aftermarket discs have indicators similar to those on the pads, e.g. Brembo discs have two dents with different depth.
If in doubt, I would suggest changing the discs and pads just to be on the safe side - they are not that expensive and it can be done within 20 - 30 minutes per wheel (supposed the discs are not rust-welded to the hubs, in which case a grinder comes handy
).
Hint: Use copper grease on outer sides of the pads to prevent them from screeching.
As the discs tend to wear unevenly, the thickness should be measured at the inner, middle and outer parts of pads trace, diagonally.
Some aftermarket discs have indicators similar to those on the pads, e.g. Brembo discs have two dents with different depth.
If in doubt, I would suggest changing the discs and pads just to be on the safe side - they are not that expensive and it can be done within 20 - 30 minutes per wheel (supposed the discs are not rust-welded to the hubs, in which case a grinder comes handy
).Hint: Use copper grease on outer sides of the pads to prevent them from screeching.
To clear up any confusion: M@nticore was referring (I think) to the unworn ridge at the edge of the brake disc? If this is more than a millimetre deep, it's time to change the discs.
Sometimes the minimum thickness is engraved around the edge of the disc (of course, with salt on the roads that is probably long-gone).
The minimum thickness of 9mm that (CZ)enda quoted is correct, but when new they are 10mm thick - so only 1mm allowed for wear.
In my opinion, the overall condition of the discs is more important than just the thickness. Be careful to look for heavy rust around the narrow part in the centre (where the disc joins the flange - sometimes they can shear!), deep grooves (do they catch a fingernail?), warping (juddering when braking), or overheating (bluish colour). Cracks are less common but still possible if the discs were overheated.
If smooth and shiny I would treat 8mm as a minimum, but then again I saw a FIAT Tipo with the discs down to just 5mm and the brakes were still working OK. It is risky having the discs that thin, as they could warp if they overheat.
When I fit new discs, I treat the centre and the edge to a coat of zinc-rich primer (it was called CRC Cold-Galv or something similar).
As for the pad thickness, at least 2mm is necessary and I like to have about 4mm or so, because with less than this the brakes will overheat and fade very easily. The right choice of pad can make a big difference to the braking performance - please don't just buy the cheapest you can find Go for a name brand like Ferodo or Mintex.
-Alex
Sometimes the minimum thickness is engraved around the edge of the disc (of course, with salt on the roads that is probably long-gone).
The minimum thickness of 9mm that (CZ)enda quoted is correct, but when new they are 10mm thick - so only 1mm allowed for wear.
In my opinion, the overall condition of the discs is more important than just the thickness. Be careful to look for heavy rust around the narrow part in the centre (where the disc joins the flange - sometimes they can shear!), deep grooves (do they catch a fingernail?), warping (juddering when braking), or overheating (bluish colour). Cracks are less common but still possible if the discs were overheated.
If smooth and shiny I would treat 8mm as a minimum, but then again I saw a FIAT Tipo with the discs down to just 5mm and the brakes were still working OK. It is risky having the discs that thin, as they could warp if they overheat.
When I fit new discs, I treat the centre and the edge to a coat of zinc-rich primer (it was called CRC Cold-Galv or something similar).
As for the pad thickness, at least 2mm is necessary and I like to have about 4mm or so, because with less than this the brakes will overheat and fade very easily. The right choice of pad can make a big difference to the braking performance - please don't just buy the cheapest you can find
Go for a name brand like Ferodo or Mintex.-Alex
