Wait for brakes light ON to change brake pads, bad idea ? is it too late already if warning lights turns ON ?

[benzw205]

hello,

is it true that if you wait that your brake light turns ON to change your brake pads, it's already too late, and then you will also have to change the brake pads sensors that alerts you when your pads are dead ?

Also, I have been told that you do not always need to change your brake discs, you can "fix" them, kind of renovate to bring them back to "new", do you recommend it ?

Thank you so much for your ideas.

 

[DSM10000]

The brake pad wear sensor is there to give you plenty of warning that you need to replace your brake pads.

Sensors are only about £5 each and my latest set of pads from MB came with a sensor.

You only need to change the discs if they are at or below the minimum thickness which is usually stamped on the disc or would be within a short space of time.

You can clean up wear lips on discs and there are companies that will skim the disc to smooth the surface but again this must not take the disc below the minimum thickness.

If the disc is too thin then it cannot dissipate heat correctly and may cause brake fade. It could also, potentially become weakened.

Brakes are not areas to ignore or try to economise on.

Also, do not rely on on the pad wear indicator to let you know when your brake pads are worn.

This is something you should be aware of from service reports or regular inspections.

 

[benzw205]

The brake pad wear sensor is there to give you plenty of warning that you need to replace your brake pads.

Sensors are only about £5 each and my latest set of pads from MB came with a sensor.

You only need to change the discs if they are at or below the minimum thickness which is usually stamped on the disc or would be within a short space of time.

You can clean up wear lips on discs and there are companies that will skim the disc to smooth the surface but again this must not take the disc below the minimum thickness.

If the disc is too thin then it cannot dissipate heat correctly and may cause brake fade. It could also, potentially become weakened.

Brakes are not areas to ignore or try to economise on.

Also, do not rely on on the pad wear indicator to let you know when your brake pads are worn.

This is something you should be aware of from service reports or regular inspections.

Thank you, this is why I am asking, I do not want to play with brakes, but at the same time, I wanted to know if it's stupid to change them too early.

So I can wait that the brakes warning light turn on, and ten if the disks are not too old, I can only replace the pads ?

thanks again.

 

[tonysmb]

As with everything, there are reasonable assumptions that can be made but the only sure way of knowing is to look/inspect; the reason I think that is that generally there will only be one wear sensor in a set of pads (some cars have rear sensors, some don't). If the calipers are working correctly, in theory each of the pads on an axle would wear at roughly the same rate. However, it is possible, for example if a caliper is sticking, or a pad is sticking in a caliper, for one or more pads to 'wear out' before the better sensor-equipped pad has worn enough to trigger the sensor/light.

However, as a general rule, they're designed such that once the warning light is triggered there is still sufficient pad material for safe braking and enough pad left to allow a reasonable time/mileage to arrange replacement.

As others have said, discs can be skimmed, providing there's enough 'meat' left; my view is for the hassle involved, taking off, getting skimmed etc., I'd simply replace them. A fairly general 'thought' is that discs need replacing with every other pad change; not a firm rule as it depends on how the vehicle has been used, type of pad material etc. etc.. I have seen a badly worn disc (with a sticking caliper IIRC) where the rotor broke away from the 'hub' when the brakes were applied firmly; not ideal and gave the driver bit of a fright.

Just my thoughts, others will have different views/experiences.

 

[DSM10000]

Thank you, this is why I am asking, I do not want to play with brakes, but at the same time, I wanted to know if it's stupid to change them too early.

So I can wait that the brakes warning light turn on, and ten if the disks are not too old, I can only replace the pads ?

thanks again.

No!

I said in my reply that you should not rely on the sensor. Pad wear sensors can fail.

When was the Car last serviced and you get a report on brake condition?

A visual inspection and a report of pad thickness should really be a part of a service at any decent garage.

 

[OneForTheRoad]

hello,

is it true that if you wait that your brake light turns ON to change your brake pads, it's already too late, and then you will also have to change the brake pads sensors that alerts you when your pads are dead ?

Also, I have been told that you do not always need to change your brake discs, you can "fix" them, kind of renovate to bring them back to "new", do you recommend it ?

Thank you so much for your ideas.

Its not unusual to see diyers use an old sensor and just join the 2 wires together to turn off the dash warnings, take heed of whats been said about replying on a sensor telling you. They can be fooled

 

[DSM10000]

Its not unusual to see diyers use an old sensor and just join the 2 wires together to turn off the dash warnings, take heed of whats been said about replying on a sensor telling you. They can be fooled

Wouldn't joining the wires trigger the warning?

I thought that the sensor has the two wires separated in the sensor head but when worn they connect via the disc surface?

 

[tonysmb]

Another thought; unless you've had the car from new AND it's still on the original pads or a reputable garage/person has replaced pads, you can't be 100% sure that a sensor was actually fitted if/when the pads were replaced (you'd hope it had been, but it might not) If not, a light won't ever illuminate as the sensors usually work by starting to wear through and completing the electrical circuit.

If you have any doubts and aren't confident doing it yourself, have a reputable garage give it a quick check. I'm not trying to paint a scare story but it's not a good idea to rely entirely on a warning light; in my view it should only act as a 'back up'.

There's no real advantage in changing them early but you can only make that decision once you know their true condition.

As DSM has said, what sort of service history, any paperwork to show previous brake checks and measurements of pad wear?


Eta- just seen other post above, which wasn't there when I started - must type more quickly,

 

[OneForTheRoad]

Wouldn't joining the wires trigger the warning?

I thought that the sensor has the two wires separated in the sensor head but when worn they connect via the disc surface?

No, the warning comes on when the circuits broken .

 

[DSM10000]

No, the warning comes on when the circuits broken .

I am sure that isn't the case for all.

I have a memory of unplugging a sensor once, essentially breaking the circuit but not triggering a warning.

 

[OneForTheRoad]

I am sure that isn't the case for all.

I have a memory of unplugging a sensor once, essentially breaking the circuit but not triggering a warning.

Mercs work the opposite. I've done it myself joining the wires to rid the warning message

 

[benzw205]

Thanks to all.

Can you tell me more about discs skimming / reconditioning ? is it something very usual and 100% safe ?

 

[DSM10000]

Thanks to all.

Can you tell me more about discs skimming / reconditioning ? is it something very usual and 100% safe ?

I have never had it done on any car and I have never been offered it so I would say it is not usual to skim discs

A brake disc has a finite life expectancy.

Normally you change discs after every other pad change. Modern brake pads are quite abrasive due to their construction and consequently discs may wear out more quickly.

A braking system in good condition will wear out pads and discs evenly. There should be no need for skimming, just routine replacement as required.

 

[Petrol Pete]

benz205 , depending where you are in the world removing the discs and putting them on a lathe or having them skimmed while on the car with a disc lathe is rarely worth the effort/cost as new discs are relatively cheap.

On a modern car getting the disc lathe in place often means removing the brake calliper with the car up on a 2 post lift, by this stage fitting a new disc is just one holding screw away so running the lathe is hardly worth the time and effort (here in the UK) Disc lathes are often used on the front of old 4x4's where removing the front disc is a hub off job in which case the workshop time saved is worth it.

Buy new discs .

 

[markjay]

The pad wear sensor will provide early warning. If you ignore it, then eventually you'll hear some mild grinding noise when braking, this is your second warning - the last layer of the pad material, closet to the metal backing plate, is intentionally rough, so that you can hear it when it makes contact with the disc and be warned that the pads are now really wearing thin. At this point the brakes will still work fine, but If you ignore the second warning as well, then eventually you'll hear a pretty loud metal-to-metal grinding noise - that's when the pad is almost all gone, and the metal backing plate is now eating into the disc surface, at which point the braking effect will also be both reduced and uneven.

 

[markjay]

benz205 , depending where you are in the world removing the discs and putting them on a lathe or having them skimmed while on the car with a disc lathe is rarely worth the effort/cost as new discs are relatively cheap.

On a modern car getting the disc lathe in place often means removing the brake calliper with the car up on a 2 post lift, by this stage fitting a new disc is just one holding screw away so running the lathe is hardly worth the time and effort (here in the UK) Disc lathes are often used on the front of old 4x4's where removing the front disc is a hub off job in which case the workshop time saved is worth it.

Buy new discs .

When I was a young lad, discs were always skimmed until they got nearer to their minimal thickness. You'd typically get 2 to 3 sets of pads on a disc.

That said, I have not been offered this on any car I owenrd in the past 30 years or so... and I suspect most garages no longer have the equipment or skills to do that anyway.

And yes, given the cost of new pattern discs, it's difficult to justify skimming.

 

[markjay]

No!

I said in my reply that you should not rely on the sensor. Pad wear sensors can fail.

When was the Car last serviced and you get a report on brake condition?

A visual inspection and a report of pad thickness should really be a part of a service at any decent garage.

Agreed, the sensor is a failsafe system and not a replacement for regular servicing, including checking the condition and thickness of the pads and discs.

Just as you should check the actual engine oil level, coolant level, brake fluid level, and tyre pressures, and not just rely on the relevant sensors to alter you.

 

[markjay]

As for pad wear sensors... they are always replaced as a matter of course when new pads are fitted... I've never heard of pad wear sensors being reused. I suppose you could do that if you really wanted to (assuming you manage to get the old one out without damaging it), but I really can't see why anyone would want to do that.

 

[Deleted member 126251]

No!

I said in my reply that you should not rely on the sensor. Pad wear sensors can fail.

When was the Car last serviced and you get a report on brake condition?

A visual inspection and a report of pad thickness should really be a part of a service at any decent garage.

Don’t they check it at MOT time?

 

[DSM10000]

Don’t they check it at MOT time?

It is checked but I think it is only commented on as an advisory if the pads are worn.

There must be a minimum of 1.5mm of friction material remaining to pass.