Brake discs below minimum thickness?

Mercedes18

I took my Mercedes for a service today and I was told my front and rear brake discs are below minimum thickness. The minimum thickness for my front brake discs are 26mm and they are currently 25mm so 1mm under minimum thickness. And the rear brake discs are 7.3mm minimum thickness and currently they are 6.5mm so 0.8mm under minimum thickness. 

The brake pads aren’t fully worn yet and have still got life left in them. Is it worth replacing all brake pads and discs now or shall I wait until the pads are worn down?

Also is it dangerous driving with the current brake disks thickness?

thanks 

tacpot12

It will be more dangerous driving with the disks below their minimum thickness. The main issue is that when the pads wear a bit more, the pistons in the calipers will have to move further to apply any stopping force and hydraulic fluid may start to leak past the seals. The likely result is that the first time you need to apply a lot of braking, you'll get none and will hit something hard. You might be ok with the pads as they are, but they might not need to wear that much to cause you problems.

I would suggest that you look to get them changed within the next couple of weeks. You can keep the pads on, but of course they too will need doing at some point. This is one reason why I change my own brake parts - I can replace what ever needs doing for just the cost of the parts. 

[Deleted User]

Last disk change I had all the pads done as well despite material left, one of the disks was quite groovy and all had deep edges, I am guessing other surfaces would have worn the pads to shape or worn the nice new disk oddly or not bedded in (without going down and examine them myself, didn't seem worth the hassle considering what they are there for).

Personally I felt better dealing with new flat pads on the new disk surface. They had the car apart for the disks anyway and it was just a small amount of time billed and the cost of parts. Bedded in quite quick as well.

Only bit they kept was the shoes, they still looked new considering a 2004 car.

Belenus

Is it dangerous driving with the current brake disks thickness?

It may or may not be dangerous but it just isn't worth the risk for the reason that tacpot12 gives above and probably for other reasons too.

Your brakes are there to potentially save your life and the lives of others and the manufacturers specify minimum disk thicknesses for a reason.

Without wishing to appear overly dramatic, if you have an accident that seriously injures or kills someone else, the Police will be all over your car and its service record and will know that you knew about the disk thickness issue. I would not like to be in your shoes defending that in court.

Get new disks asap.

jimjames

How old is the car & the discs? Was the service at a Mercedes main dealer?

I've never seen an MOT refer to the minimum thickness of a brake disc being exceeded yet twice I've seen it mentioned from garages on here. It does make me wonder if there is some level they use that is way beyond what is used for an MOT.

sevenhills

Mercedes18 said:

I took my Mercedes for a service today and I was told my front and rear brake discs are below minimum thickness. The minimum thickness for my front brake discs are 26mm and they are currently 25mm so 1mm under minimum thickness. And the rear brake discs are 7.3mm minimum thickness and currently they are 6.5mm so 0.8mm under minimum thickness.

A quick Google says that the minimum brake disc thickness is 37mm, it could obviously be different for different cars, but "7.3mm minimum thickness" does not look right.

I think the dealer is being over cautious or telling porkies, I would measure them myself.

Mercedes18

jimjames said:

How old is the car & the discs? Was the service at a Mercedes main dealer?

I've never seen an MOT refer to the minimum thickness of a brake disc being exceeded yet twice I've seen it mentioned from garages on here. It does make me wonder if there is some level they use that is way beyond what is used for an MOT.

2015 model - 70,000 miles. Service was done with the main dealer Mercedes

Mercedes18

sevenhills said:

Mercedes18 said:

I took my Mercedes for a service today and I was told my front and rear brake discs are below minimum thickness. The minimum thickness for my front brake discs are 26mm and they are currently 25mm so 1mm under minimum thickness. And the rear brake discs are 7.3mm minimum thickness and currently they are 6.5mm so 0.8mm under minimum thickness.

A quick Google says that the minimum brake disc thickness is 37mm, it could obviously be different for different cars, but "7.3mm minimum thickness" does not look right.

I think the dealer is being over cautious or telling porkies, I would measure them myself.

My rear brake discs from new are 8mm. The front brake discs from new are 26mm. It’s different for each car and if they are front or rear

Mercedes18

Belenus said:

Is it dangerous driving with the current brake disks thickness?

It may or may not be dangerous but it just isn't worth the risk for the reason that tacpot12 gives above and probably for other reasons too.

Your brakes are there to potentially save your life and the lives of others and the manufacturers specify minimum disk thicknesses for a reason.

Without wishing to appear overly dramatic, if you have an accident that seriously injures or kills someone else, the Police will be all over your car and its service record and will know that you knew about the disk thickness issue. I would not like to be in your shoes defending that in court.

Get new disks asap.

I was advised by the lady who done the handover after my service that even though my brake discs are below the minimum thickness it’s okay to wait until the pads have worn down (until brake pad light comes on) and just wait until then to change the discs and pads together.

I asked her is it still safe to drive and she said yes. Hence why I’ve come onto here for a second opinion. 

prowla

I'd replace those disks - the car is under spec and imagine if one fails.

Given that the pads may be worn in line with the outgoing disks, I' change the pads too - a relatively minor job.

Bigwheels1111

I would get a second opinion if I were you.
I used to drive 30,000 to 40,000 miles a year in old 218 or 418 diesel rovers, and changed the disc and pads, timing belt and full Service on day one. Then drove 100,000 miles cabbing it and never changed the discs again.
One of them did 250,000 miles before it got hit from behind and written off, had 100,000 miles when I got it.
So 150,000 on the same set of discs.