Technical Do I need new brake discs?

[lycopersicum]

I noticed a crack in the rim of one of my front discs (see arrow). Is it a 'don't drive until it's fixed' kind of situation, or can it wait a few hundred kilometers?

Overall the discs show some wear and have 1mm of lip at the front, 1.8mm at the back. Would you replace all four of them now?

 

[The Panda Nut]

The discs look good, but that cracked front one is done as far as Im concerned. Its been hit or dropped at some point or has a manufacturing defect and that small piece could easily be detached adn cause a brake failure. I would say you must bite the bullet urgently even though they otherwise look on great condition

 

[ZaphodB]

but that cracked front one is done as far as Im concerned. Its been hit or dropped at some point or has a manufacturing defect and that small piece could easily be detached adn cause a brake failure. I would say you must bite the bullet urgently even though they otherwise look on great condition

Definitely replace asap (and replace both sides just cos it's on the steering end of the car)

 

[Pugglt Auld Jock]

Definitely replace asap (and replace both sides just cos it's on the steering end of the car)

For starters, it's a very unusual looking failure. Don't think I've ever seem one quite like it before. If just that bit were to detach itself Then it would present a "cutting edge" to the pad which is likely to cut away that outer part of the pad meaning the effective braking area will be reduced so it may pull to one side. I doubt if you'd get a total failure unless other bits start cracking off. However, if it was mine, I'd be very unhappy with it and would be changing it asap. I'd probably risk using it for an emergency if the distance to be covered was short but certainly wouldn't be setting off on one of our Devon sojourns, and, as Panda Nut mentions above, it's a whole different ball game if it's a manufacturing defect as other cracks might manifest themselves. I agree also that both discs should be changed - and pads - to keep the braking performance equal on both sides (I suspect we're teaching you "how to suck eggs" by mentioning that, but others may not be aware.)

 

[lycopersicum]

Thanks for chiming in. So the consensus is replace both front ASAP, leave the rear alone for now.

I don't know how long it's had this crack -- I have no records of a front disc or pad change and I've had the van for 40,000 km out of its 190,000. I've asked mechanics to check the brakes at each service but who knows if they were thorough.

Planning to go with a brembo set. Compared to the small car on which I got my license, the brakes never felt very strong, to the point where I've developed a reflex of downshifting for urgent braking, otherwise it doesn't feel like it's quite going to make it. They did check the braking force for its MOT though and found it sufficient. Wondering if this will improve after changing the discs and pads.

 

[Pugglt Auld Jock]

I'm puzzling over what might have caused the cracked bit on that disc and it's not obvious at all. Assuming it's not a defect? I'm wondering if it's been caused by injudicious use of a hammer? It's quite common practice to remove crusty rust deposits from the outside rim of discs by either scraping with a screwdriver or chisel, or using a hammer to dislodge heavier build up - done it myself often to stop rubbing noises. If the hammer had been used too "enthusiastically" then that might account for this damage?

Although the discs are wearing quite evenly, this is good because it would tend to show there's no problems with callipers seizing or other problems, they do show quite defined wear - look at the edge between the rusty hub area and the polished surface of the disc, there's quite a visible "step". Also quite heavy corrosion of the hub and outside edges of the disc. They're well past their best and, once the new pads have bedded in, I'd expect you to see the new brakes giving you a better experience. Do you have a good "hard" feeling brake pedal when you push down on it? I'm just wondering if the system might benefit from being bled while you're working on it? - Maybe renewing the fluid at the same time?

 

[lycopersicum]

I'm puzzling over what might have caused the cracked bit on that disc and it's not obvious at all. Assuming it's not a defect? I'm wondering if it's been caused by injudicious use of a hammer? It's quite common practice to remove crusty rust deposits from the outside rim of discs by either scraping with a screwdriver or chisel, or using a hammer to dislodge heavier build up - done it myself often to stop rubbing noises. If the hammer had been used too "enthusiastically" then that might account for this damage?

Although the discs are wearing quite evenly, this is good because it would tend to show there's no problems with callipers seizing or other problems, they do show quite defined wear - look at the edge between the rusty hub area and the polished surface of the disc, there's quite a visible "step". Also quite heavy corrosion of the hub and outside edges of the disc. They're well past their best and, once the new pads have bedded in, I'd expect you to see the new brakes giving you a better experience. Do you have a good "hard" feeling brake pedal when you push down on it? I'm just wondering if the system might benefit from being bled while you're working on it? - Maybe renewing the fluid at the same time?

The pedal is very easy to push at the start and then gets increasingly harder. The braking itself is very progressive with no bite whatsoever. I cannot jerk the van with the brakes. It feels precise, and I'm super comfortable with it for light to medium braking, but beyond medium braking it feels like extra pressure on the pedal gives less and less extra braking.

Mind you, I'm a long time cyclist and that comes with a strong reluctance to smash that pedal -- my body remembers

I've not tried to do an emergency stop out of consideration for the habitation at the rear but maybe this would be good to try with the new discs. I've only ever felt the ABS activate at low speed on wet leaves.

I have no idea what the plumber who used to own the van could have done to the poor discs so everything is possible.

As for changing the brake fluid, my mechanic was of the opinion that it doesn't go bad. Maybe I'll insist a bit more next time.

 

[ZaphodB]

As for changing the brake fluid, my mechanic was of the opinion that it doesn't go bad. Maybe I'll insist a bit more next time.

Doesn't go bad ?????? - he's talking out of his ****
It picks up moisture , it's hygroscopic , that's why it needs replacing/flushing every 2-3 years or so, even in a sealed system on a car.

 

[Pugglt Auld Jock]

As for changing the brake fluid, my mechanic was of the opinion that it doesn't go bad. Maybe I'll insist a bit more next time.

Doesn't go bad ?????? - he's talking out of his ****
It picks up moisture , it's hygroscopic , that's why it needs replacing/flushing every 2-3 years or so, even in a sealed system on a car.

If you've got someone working on your car who honestly believes brake fluid "doesn't go bad" you need to stop him/her right now and look for someone else. Anyone who earns their living repairing vehicles should know that the manufacturers all recommend changing brake fluid every two to three years and, because it absorbs water and that water might boil under extreme braking events - thus turning into a COMPRESSIBLE gas - it's potentially very dangerous to ignore regular fluid changes. The problem is that it's only likely to happen under the most severe braking situations so many people might never experience it in their lifetime of driving however, do you want to be sitting on a potential "time bomb" by ignoring it? - I definitely don't! If he/she doesn't know this then I'd be asking "What else doesn't he/she know and what dangerous other practice might they consider acceptable?

 

[ZaphodB]

, my mechanic was of the opinion that it doesn't go bad. Maybe I'll insist a bit more next time.

He's doing a complete disservice to the title of mechanic

 

[lycopersicum]

Sounds like a change of brake fluid is in order then.

Mechanics in my area certainly push the "don't fix it if it ain't broken" attitude to extremes. Mine apologises profusely about the extra cost whenever he needs to order a new part.

Any reason why I shouldn't attempt to do it all myself? I'm generally very competent mechanically, though kind of new to car mechanics.

Does the gravity bleed method work well on Ducatos?

 

[ZaphodB]

I'd recommend some pressure bleed kit.

Google Search

 

[Pugglt Auld Jock]

I'd recommend some pressure bleed kit.

Google Search

"Proper", professional quality pressure bleeders are a great asset and highly recommended. Cheaper DIY quality kit can be a bit of a mixed blessing - I speak from personal experience. I've reverted to bleeding by pumping the pedal and working the bleed nipples in the time honoured way. You do need two people to do this effectively but what else are wives for?

There's one thing to be aware of if doing it this way which, as many of us will already know, is that you must restrict the stroke of the master cylinder piston so the seals don't run down into the part of the master cylinder which they normally don't reach - Think about that for a minute. The pedal doesn't usually go more than half way down the cylinder bore under normal operating conditions so the "bottom" half of the cylinder walls accumulate deposits and even may corrode slightly. If the seals then get forced over this rubbish there's a good chance they will be damaged. It's very easy to control this as all you need is a block of wood, or other suitable obstruction, which you place on the floor under the pedal so it can't go more than half way down.