Do I need new brake disks?

londonTiger

I recently drove a zipcar and was shocked at how stiff the brakes on that was compared to my car. It brought to my attention that the brakes needed servicing on mine.

I'm not sure if pad & brake fluid only change would suffice or if I need to change the discs too.

I have taken a picture of the disk. It looks quite badly swirled (or scored?). Pads definately need changing as they are on their last 5mm.

What do you guys think about the disks? acceptable or in need of change?

You can see the original level next to the hub, I think the disk has been worn down about 1mm.



N.b. passed it's MOT about 3k miles ago, MOT tester seemed to be content about the brakes and did not comment on them.

colino

5mm of pads, depending on the vehicle, can be thousands of miles of use. You do have an unswept area of the disc (rusty) that will be matched on the pad, but only a trained eye (OK, the manufacturers spec. if you have access!) will be able to tell I you need to change the discs or a touch of the grinder will make good. Your picture is probably as good if not better than 75% of the cars around you.

Strider590

If they work, they're probably fine..... If you can brake without the car pulling to one side, then you've nothing to worry about with regard to uneven disk or pad wear.

Problem these days is manufacturers are making cars (especially small ones) with EXTREMELY sensitive single pot brake calipers, they're practically on/off braking, but they create the illusion of having really good brakes, because just a little pressure causes the car to stand on it's nose.

This ^^ is NOT a sign of good brakes, good brakes should be very progressive, input should be proportional to braking. Good brakes don't just "snatch" and then rely on ABS to stop them locking.

But unfortunately for as long as stupid people are getting behind the wheel, this marketing tactic will always work.

londonTiger

Strider590 wrote: »

This ^^ is NOT a sign of good brakes, good brakes should be very progressive, input should be proportional to braking. Good brakes don't just "snatch" and then rely on ABS to stop them locking.

I wonder if it's just my driving habit? My pads are worn down to 5mm, if the zipvan had brand new brake pads at 17mm would that make the "break bite point" higher up cause it to break harsh.

Or does the brake caliper compensate for the wear?

With the zipvan I had to feather the break pad at the same sort of depression as you would on the gas pedal to maintain speed on a motorway. Any more pressure than that and the van would break hard - rearender heaven for zipvan I suppose.

londonTiger

n.b. they brake fine and evenly. I think the brake fluid definately needs to be flushed though, but if you guys are saying the disks are fine I'll keep them. Maybe I'll just do a preemptive pad change as well. Because I know that it's a little more convenient to do the fluid and pad change together, than doing the fluid change now and then brake pads 6 months down the line

Strider590

londonTiger wrote: »

I wonder if it's just my driving habit? My pads are worn down to 5mm, if the zipvan had brand new brake pads at 17mm would that make the "break bite point" higher up cause it to break harsh.

Or does the brake caliper compensate for the wear?

With the zipvan I had to feather the break pad at the same sort of depression as you would on the gas pedal to maintain speed on a motorway. Any more pressure than that and the van would break hard - rearender heaven for zipvan I suppose.

Yes, the system compensates for wear.
Also remember that all cars are different, some have assisted brakes and some don't. The thing is that no matter the wear, the brakes will operate as normal until either the pad warning light comes on, or the brake disc snaps through being too thin.

If you drive and brake quite hard, your brake fluid might have boiled, which would make the brakes feel spongy, they'd still work, but would feel somewhat detached.

londonTiger

Thanks, I think that's what it is. Spongy brakes is exactly how I would describe it. I will change the fluid and pads this weekend.

ILW

londonTiger wrote: »

I wonder if it's just my driving habit? My pads are worn down to 5mm, if the zipvan had brand new brake pads at 17mm would that make the "break bite point" higher up cause it to break harsh.

Or does the brake caliper compensate for the wear?

With the zipvan I had to feather the break pad at the same sort of depression as you would on the gas pedal to maintain speed on a motorway. Any more pressure than that and the van would break hard - rearender heaven for zipvan I suppose.

Brakes can be rather sharp in empty vans. They are designed to take heavy loads.

londonTiger

ILW wrote: »

Brakes can be rather sharp in empty vans. They are designed to take heavy loads.

good point. I was just carrying 48kg of load.

Iceweasel

londonTiger wrote: »

Thanks, I think that's what it is. Spongy brakes is exactly how I would describe it. I will change the fluid and pads this weekend.

If you have 5mm of pad left then you are going to waste your hard-earned cash.

Changing the brake fluid is a good idea though. Several manufacturers recommend a change every 2 years.

The manufacturer will also give a minimum thickness for the discs.

These days its fairly common for discs to last only for 2 sets of pads.

At the moment changing your discs and pads will not improve the spongy pedal feel - but a fluid change quite likely will.

Weird_Nev

DO NOT CHANGE PADS with 5mm on them!
They come with less than 10mm in many cases. You're changing your pads less than half way through their useable life!

If your brakes feel a bit spongy and indistinct, then a fluid flush by someone who knows what they are doing is the way forwards.

Those discs look absolutely fine to me. Of course they end up with circular wear marks on them: they are turning as they are clamped by the pads. If in doubt, ask a garage to use calipers to measure them. Manufacturers publish minimum thicknesses. But the thing that really kills disc is pitting and rust from under use. NEver wash a car and then let it sit in it's own juices. Take it for a drive afterwards, to clean and clear the discs of water.

For reference, here are pads I took off of my BMW: Working perfectly, no squeal at all, and passed an MOT a couple of weeks beforehand: