Bosch Discs OK?

[trickywoo]

Just wondered if anyone has any thoughts on Bosch brake discs? I got a pair before winter and they haven't rusted at all but have developed a vibration (no abuse by me, sitting on the pedal etc) after 3k miles.

A good BMW specialist is saying I need BMW branded discs to fix the issue despite the runout on the Bosch ones being in tolerance and all suspension bushes OK.

I suspect I may not have bedded the pads properly but its really hard finding somewhere you can do 10 consecutive stops from 60mph to 10mph.

[GreenV8S]

Are they just ordinary cast iron disks? No reason to pay over the odds for those - the main difference between budget and expensive is the box they come in.

[trickywoo]

Yes just cast iron, not drilled or groved.

I know you can't tell just by looking but the casting on the Bosch discs looked good. If I had the cheapest Chinese stuff maybe but I really can't see why just because the Bosch aren't OEM that has caused my issue. The overall difference in price is £300 v £600.

[battered]

Bosch are good. Whoever makes for them won't be fools. Its prob friction material on the discs. Buy some garnet paper and a block, scrub them clean. Try a green scourer alternatively. If you can get a green pad on a power tool, so much the better.

[trickywoo]

Thanks guys. I'll provide an update for anyone else with the similar issues when I've had a go.

[Martin350]

trickywoo said:

I suspect I may not have bedded the pads properly but its really hard finding somewhere you can do 10 consecutive stops from 60mph to 10mph.

Ferodo DS2500 pads, by any chance?

If so, I've had problems following the bed-in method they suggest and, as mentioned above, have had pad material transfer to brand new discs.

[trickywoo]

Martin350 said:

Ferodo DS2500 pads, by any chance?

No. Matched Bosch pads.

Its pretty frustrating as for 3k miles they were great.

I'll give scrubbing them a go but think I'll end up needing a skim, which hopefully I'll get done via one of the on car machines so if I do have any hub issues it'll fix that too.

[trickywoo]

Just thought I'd do a quick update for anyone thats interested.

I had the car into a garage with a pro-cut lathe. Having run the skimming they took the car out for a road test and the issue was still there.

Skimmed again and it still has a shimmy / shiver through the steering wheel when you first get on the brakes at 50mph +. Its much better than it was but obviously frustrating as they are a professional outfit and took their time over the job. The runout is fine and its reasonable to assume any disc thickness variation has been resolved. It felt better after I found a piece of road to bed the pads in and hopefully will improve.

I've had a clean bill of health on the front suspension from a couple of garages now and the tyres, wheels and tracking are OK. Nothing happened that I recall leading to the vibration (pothole, curb, hard braking etc). If its still the same after a few more miles I'm looking at new discs again.

Am I right in thinking it can't be a hub issue if the runout is OK? I don't know why the hub would be an issue but its a confusing situation now. Also can I rule out a wheel issue? There is no obvious damage and no vibration unless braking in certain circumstances.

[battered]

If the runout is ok then there is nothing with the hub. Check also that it is concentric. It will be, but check. It could be a warped wheel, unlikely to give this symptom but worth checking. Also wheel balance, again unlikely but it may contribute when decelerating. You will of course detect this undernnormal deceleration without touching the brake. You can also get odd effects from worn CV joints in FWD cars, though more usually it's vibration under acceleration, not braking. It's odd that the skim has not resolved it.

[trickywoo]

battered said:

If the runout is ok then there is nothing with the hub. Check also that it is concentric. It will be, but check. It could be a warped wheel, unlikely to give this symptom but worth checking. Also wheel balance, again unlikely but it may contribute when decelerating. You will of course detect this undernnormal deceleration without touching the brake. You can also get odd effects from worn CV joints in FWD cars, though more usually it's vibration under acceleration, not braking. It's odd that the skim has not resolved it.

Thanks. Helpful stuff.

The garage doing the skimming seemed equally disappointed.

Just as an aside the pro-cut lathe is a really nice bit of kit. I have a bit of a machinery fetish and apart from being electric and not petrol that ticked a lot of boxes.

[battered]

I bet it's tasty. It takes a serious bit of kit to do something as big as a disc, then clear the edge and do the other side without removing the tool. Obviously you can remove the tool and flip the workpiece but you then lose accuracy, as you'll know.

[The Wookie]

GreenV8S said:

Are they just ordinary cast iron disks? No reason to pay over the odds for those - the main difference between budget and expensive is the box they come in.

You'd be surprised, although I'd hesitate to trust the boxes on quite a few that seem to be knocking about

[The Wookie]

OP bushes and bearings can be worn enough to exacerbate judder without being obviously knackered but clearly if the car hasn't done loads of miles then it's unlikely.

One other thing to check is the centre bore diameter, if it's undersized it can cause some 'interesting' side effects when running.

BMW have been known to use a different, softer grade of iron than is typical too, so it could be that the stuff you've bought is more conventional and it's had some obscure side effect.

[Dogma1978]

battered said:

Bosch are good. Whoever makes for them won't be fools. Its prob friction material on the discs. Buy some garnet paper and a block, scrub them clean. Try a green scourer alternatively. If you can get a green pad on a power tool, so much the better.

Bosch were used by fords at one point during production. There good discs

[battered]

Dogma1978 said:

battered said:

Bosch are good. Whoever makes for them won't be fools. Its prob friction material on the discs. Buy some garnet paper and a block, scrub them clean. Try a green scourer alternatively. If you can get a green pad on a power tool, so much the better.

Bosch were used by fords at one point during production. There good discs

The thing you have to watch out for is that Bosch don't actually make all their stuff, they have subcontractors doing it to a specification. I know that in the 80s Ford were getting their driveshafts made by Martins Engineering of Alford, Lincs. It sounds unlikely because it's only a small light engineering outfit in a sleepy town, but there you go. A mate of mine worked there, they clearly knocked out what Ford wanted, packed them in Ford boxes and off they went to Dagenham or wherever the Escorts and Fiestas were being assembled.

[Unhinged]

trickywoo said:

No. Matched Bosch pads.

Its pretty frustrating as for 3k miles they were great.

I'll give scrubbing them a go but think I'll end up needing a skim, which hopefully I'll get done via one of the on car machines so if I do have any hub issues it'll fix that too.

It sounds to me like the pads are overheating in operation and depositing unevenly on the disc causing DTV (disc thickness variation). You are right that if the disc runout is correct then you shouldn't have an issue. The brake pad bed in you are referring to sounds like it would kill a lot of road pads and sounds more akin to a race pad. Is it a heavy powerful car? Many cars are just under specced in the braking department. You could try a pad with better high temperature performance.

[Petrolhead_Rich]

binding caliper? just a thought?