Since refitting the alloys I've noticed the rear discs appear to be getting more and more corroded on both sides; beginning to wonder if the callipers are not sticking. Any other 4x4 owner with the Bosch callipers (from WK45/09) experienced this :wonder:

Rear discs; similar both sides.

Front for comparison.

Thanks,

TP

go out for a hard drive and inspect discs then

go out for a hard drive and inspect discs then

Thanks for the advice

however I have done; the above is after a 60 plus miles drive back from Leeds including duel carriageway and associated braking due to slowing traffic ahead.

TP

Iirc there is actually a section in the owners handbook on disc corrosion and how to clear it.

Hi Tim

Mine are still like new and no pitting or corrosion

yours look like they have come off a 5year old car something not right with them, looked at my van as well 03 reg 70k original disc and they are like new as well, hope this helps.

regards

Kevin

Iirc there is actually a section in the owners handbook on disc corrosion and how to clear it.

Many thanks again; read the handbook and I think my journey back today covered its suggestion three or four times over, i.e. firmly apply the brakes form a high speed.

Not that I leave her idle for long periods of time or do short journeys either; 36 miles is my most common run.

TP

Hi Kevin,

thanks and as ours are only two weeks apart re birthdays (and mileage) I would expect them to be similar.

Notice your disc guard is from the same batch as mine WK48/10

TP

Don't doubt that, knowledge is power though. If you do make a complaint about it then saying you have followed the handbook and it's still an issue then they have to take it seriously.

Don't doubt that, knowledge is power though. If you do make a complaint about it then saying you have followed the handbook and it's still an issue then they have to take it seriously.

Good point and much appreciated

Thanks again,

TP

Most disc brake cars are like this, especially in the winter months. Front wheel drive, engine at the front, weight transfer under braking, rear end light - looks about right. The rears will always work less hard than the fronts, especially if you have a light braking foot.

Those rear discs aren't really "rusty", just stained slightly. I'm sure they work just fine on the road. Drum brakes would be fine but ABS systems like a more modern braking system to work with. Drum brakes have a better handbrake action, but only a few cars have combined disc/drum units.

I can't see a dealer seeing anything wrong with them as they are. Sticking caliper sliders normally show different wear patterns side to side, so from your description, not a problem.

Provided you have a lot of empty space to play around in (an airfield is good but a big empty car park is OK), you can try reversing fast and then applying the brakes hard. Repeat a few times. This way, the weight transfer is on to the rear wheels, which circumvents the brake pressure limiter on the rear circuits and lets you work the rear discs harder.

By the way, does anyone know how the Yeti handbrake operates? On the rears, using the main pads, or using its own handbrake pads, or what? I could go and check but I haven't got round to it. I have sometimes cleaned up rear discs using the handbrake.

As others have said, the problem is endemic these days. Three of the cars I have had in the last decade have gone through discs faster than pads. (I live in an unfavourable climate for rust and I am a very light braker - as Ettore Bugatti said, my cars are meant to go, not stop.)

Brake curcuits are split into approx 60% front to 40% rear, this is done by means of a load sensing valve. This valve is adjusted automatically by the amount of weight in the back, the more weight the more pressure applied to the rear.

If you run with no load in the back the valve may become stuck due to muck and corrosion, that way the rear rotors may become corroded due to lack of applied pad pressure, its worth a look and a squirt of WD40.

Another way to check it, is to put a 100 Kg weight in the back of the boot and go for a run using hard braking. If the caliper is siezed or the valve not working, you will see no difference. If you do see a difference then it's just probably light load in the rear thats causing it.

Brake curcuits are split into approx 60% front to 40% rear, this is done by means of a load sensing valve. This valve is adjusted automatically by the amount of weight in the back, the more weight the more pressure applied to the rear.

If you run with no load in the back the valve may become stuck due to muck and corrosion, that way the rear rotors may become corroded due to lack of applied pad pressure, its worth a look and a squirt of WD40.

Another way to check it, is to put a 100 Kg weight in the back of the boot and go for a run using hard braking. If the caliper is siezed or the valve not working, you will see no difference. If you do see a difference then it's just probably light load in the rear thats causing it.

Our ABS equipped cars don't have load sensing valves, not required when ABS is fitted.

Provided you have a lot of empty space to play around in (an airfield is good but a big empty car park is OK), you can try reversing fast and then applying the brakes hard. Repeat a few times. This way, the weight transfer is on to the rear wheels, which circumvents the brake pressure limiter on the rear circuits and lets you work the rear discs harder.

By the way, does anyone know how the Yeti handbrake operates? On the rears, using the main pads, or using its own handbrake pads, or what? I could go and check but I haven't got round to it. I have sometimes cleaned up rear discs using the handbrake.

As others have said, the problem is endemic these days. Three of the cars I have had in the last decade have gone through discs faster than pads. (I live in an unfavourable climate for rust and I am a very light braker - as Ettore Bugatti said, my cars are meant to go, not stop.)

The handbrake works off the same caliper as the foot brake.

Our ABS equipped cars don't have load sensing valves, not required when ABS is fitted.

I didn't know Skoda did not fit them, must use ABS load bias instead or by EBD, but, still weighting the boot will require additional force to be applied to the rears.

Edited 5 April, 201214 yr by Tech-Yeti

On my car (which is not a yeti and doesn't have Bosch calipers!) I had a problem with corrosion caused by muck building up on the pad and the shims which sit between the pad and the caliper which seemed to stop the pad moving evenly. So the pad twisted rather than slid (albeit only very slightly, the pad looks OK) and so only made contact on the inner part of the disc. That lead to corrsion rather like what your seeing.

I stripped the brakes down and cleaned everything and it has been fine since (though the disc on one side is heavily corroded).

This is a common problem in my experience, which I cured by removing the pads, cleaning the sliding part of the caliper and applying a smear of copperslip to the surface which stops the cast iron of the caliper corroding. Usually also put a smear on the rear of the pads and any shims that are present--that stops the brakes squealing

Just do a few 30mph stops using only the handbrake (with no one following).

Just to update my thread;

decided against taking it to one of the local dealers, as the quality of their workmanship in the past has been left wanting. Therefore I asked a mate of mine who teaches motor vehicle to have a look, which he had chance to do this morning.

Found that there was little movement from either sets of pads due to a build-up of hard crud in the stainless steel clips, which both hold/support and allow the movement of the pads against the disc. Neither was there any sign of any lubricating medium to help retain this movement.

Cleaned everything up added a bit of copper slip and put it all back together. Of note however was the level of surface corrosion on the calliper castings (she's only a year old), some of which had to be ‘brushed’ off to get the clips seated correctly back into the castings. Also the calliper piston acts directly on the outer face of the inner pad, the witness makes to this suggest that neither piston is acting square in the middle of said pads but slightly offset, again reducing the effectiveness of the pad acting against the discs with an even pressure :S

Of further concern was the condition of the discs which are in a generally poor state. There’s a noticeable ‘step’ between the clean inner disc face and the corroded and grooved outer section. Hope with use this might improve, as the 20 mile drive back only managed to clean off the high points in the corroded area, despite re-facing the pads to remove the corresponding grooves. Otherwise it’s new discs and pads after only a year

Interestingly since picking up on this issue with mine, I’ve noticed a handful of Mk VI Golf’s have the same problem with their Bosch rear callipers; i.e. corroded outer discs :wonder:

TP

I would expect the pad to wear and match the disk, so that over time it should sort itself out, but it depends on how much extra the pad had worn on the inside edge.

This is a very widespread "problem" in this damp and salt laden winter isle. As aired above, corrosion of the caliper pad holders holding the pads tight in the carriers can push the shim and restrict the pad movement, especially on the rears. A sort of fix is to file/grind a little metal off the contact areas of the pad backing metal so as to enable the pad the "rattle" about in the carrier. That's part of the problem, there are other reasons for it. The rears more so than the fronts because of weight transference etc, and the fact that brakes are not normally used hard in the UK - a few runs down the Stelvio would soon get them mirror shiney

The only "cure" is more routine maintenance, something which is not popular or widely carried out. Despite the many improvents in technology, a bit of housekeeping can alleviate many seeming annoying "problems". Maintenance free is a good phrase, it works for a while and then you have to bin the kit and fit new.

Mmmm, choices.

ps: on my MG TF, the discs rust like mad, which annoys the hell out of me as they are expensive. The problem is open spoked alloys, not used avery day, and stored outside open to the element.

This is a very widespread "problem" in this damp and salt laden winter isle. As aired above, corrosion of the caliper pad holders holding the pads tight in the carriers can push the shim and restrict the pad movement, especially on the rears. A sort of fix is to file/grind a little metal off the contact areas of the pad backing metal so as to enable the pad the "rattle" about in the carrier. That's part of the problem, there are other reasons for it. The rears more so than the fronts because of weight transference etc, and the fact that brakes are not normally used hard in the UK - a few runs down the Stelvio would soon get them mirror shiney

The only "cure" is more routine maintenance, something which is not popular or widely carried out. Despite the many improvents in technology, a bit of housekeeping can alleviate many seeming annoying "problems". Maintenance free is a good phrase, it works for a while and then you have to bin the kit and fit new.

Mmmm, choices.

What sort of maintenance do you recommend Yety?

Chris

This is a very widespread "problem" in this damp and salt laden winter isle. As aired above, corrosion of the caliper pad holders holding the pads tight in the carriers can push the shim and restrict the pad movement, especially on the rears. A sort of fix is to file/grind a little metal off the contact areas of the pad backing metal so as to enable the pad the "rattle" about in the carrier.

My "last of the line" Escort, a 1996 RS2000, has rear disks & the rear pads are just as you describe... slightly loose in the calipers. They do indeed move slightly, keeping the disks clean as they seat in a slightly different position forwards/reverse. So I've never had corrosion issues with the rear disks. The downside is that there's a loud clunk the first time you brake going backwards, then another loud clunk the first time you then apply the brakes again going forwards. Very unnerving until you get used to it and the subject of so many complaints to dealers at the time the cars were new that Ford issued a bulletin to RS dealers to make them aware that there was nothing wrong.

The rear disks are the shape of a "Top Hat" with the foot-brake working on the "brim" and the handbrake working on the inside of the "hat" using separate conventional looking shoes. There is a downside though, you need to occasionally apply the handbrake briefly whilst moving in order to clean off the rust or they stick, especially after heavy rain/washing the car unless the disks are warm. . So no system is perfect!

Edited 22 April, 201214 yr by speedsport

What sort of maintenance do you recommend Yety?

Chris

Hi Chris,

from this experience I think by maintenance an annual removal/clean of the rear pads seems in order. Although I will be interested to see how we go on now I've had them out and greased them up a bit.

Also I don't think it effects all cars the same, looking at wakev's photos the level of caliper corrosion appears much less and the disc's are worn nice and even.

Why my disc's corroded in this way can only down to how tight a fit the pads are in the clips and or lack of factory lubrication, plus a poor design that allows a build up of crud in the moving surfaces.

Whereas with the calipers then maybe dissimilar metal corrosion, the harsher climate up here (and subsequently more winter road salt) or a combination of both (suppose salt laden road spray makes a good electrolyte) :wonder:

However the previous Monster did not have these problems and interestingly that had the Lucas rear calipers, which the Bosch set-up superseded :wonder: :wonder:

TP

We got our Yeti the first week of January, and the discs still look like new - only because they are not used hard in urban traffic and only the odd motorway journey.

In mid summer? I'll have the wheels off and fettle the backing plates of the pads to enable an audible movement in the carriers, coppaslip the contact surfaces and the wheel studs etc.

When the wheels are off I'll cast my eye over anything visible - I don't expect any problems but it's reassurance more than anything.

My other car, Suzuki SJ413 on the other hand, has it's pads off after every trip when in motorsport mode to remove encased mud/twigs/etc. Sometimes the discs rotate in liquid mud and appear rusty when parked up. The discs front and rear are scored with trapped grit and stones, but my MoT man is happy as the car is always presented clean. The brake test figures are good and there is no requirement in the MoT test to fail visually marred disc braking surfaces. Obviously cracks, severe wear likely to be structural, are fails.

So long as the brake test is good, and there are no obvious defects, I wouldn't worry about a little surface rust which might well disappear if we have a dry summer.