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BarryM

Rusted brake caliper

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My front n/side brake started sticking recently but as I had them refurbished only 3 years and 10k miles ago I wasn't expecting to find this when I took it off:

 

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I never jet wash the car and it doesn't get driven all winter so this was a big surprise.

 

I know BMW brakes are known for corroding but that's pretty poor to me, the refurb included painting which is still in pretty good nick so could this be down to a poor piston seal or maybe it  wasn't cleaned up so well when they did the re-furb.

 

How easy is that gonna be to clean up - will a dremel do it and how can I stop it rusting so quickly again, guessing it doesn't have to be 100% smooth as the piston shouldn't actually be touching any of that. Or am I better to just get another caliper?

 

 

 

 

 

 

 

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I'd personally get a refurbed caliper from Brakes International and then paint that to match and refit!

 

Maybe do both so you know they'll wear evenly?

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What did that previous refurbishment include? Looks like it was just a cosmetic outside sandblast and paint job. 

 

Those pictures don't really show what's the condition of the cylinder and piston below the pressure seal.

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1 hour ago, d_a_n1979 said:

I'd personally get a refurbed caliper from Brakes International and then paint that to match and refit!

Maybe do both so you know they'll wear evenly?

 

I might go that route later as I'm also intending to get the rears done but for now want it back on the road.and have a new piston and seals to use.

 

 

1 hour ago, Clavurion said:

What did that previous refurbishment include? Looks like it was just a cosmetic outside sandblast and paint job. 

Those pictures don't really show what's the condition of the cylinder and piston below the pressure seal.

 

The previous re-furb was meant to be everything including shot blasting, painting and new seals but only one new piston (as he said the other piston was fine but if I'd been asked I'd have said replace both pistons).

 

Here are another couple of photos after a bit of a clean:

 

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986023197_2019-04-1318_51_44.jpg.aca617812608f77c9c62658016e8f3d8.jpg

 

Think I'm gonna do a bit more cleaning and fit the new piston and seal I bought as a short term fix.

 

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It's normally the piston that corrodes and creates a rough surface for the square cut seal to get hung up on and so not allow the piston to retract.

 

Looking at your first photo, it looks like there's a slight ring of cruddy rust around the piston. The bore of the caliper and the groove for square cut seal inside the caliper looks OK, though I'm only going on the scant evidence of your photo.

 

Try to get hold of a stainless steel piston (if you can - see below) since this will be more of a long term solution to corroding pistons in an iron caliper. The corrosion on the piston doesn't have to be much for the square cut seal to get hung up. The piston surface needs to be absolutely smooth to allow the square cut seal to do its work properly and retract when you release the brake pedal. The square cut seal sort of rotates slightly against the piston when the brakes pedal is pushed and then resumes its position and shape - and ever so slightly pulls the piston back - when brake pedal is released.

 

Rust can get established quickly on the piston if the dust seal isn't a good fit. Try to get hold of original ATE dust seals since these seem to fit better, more snugly and appear to be made of a better grade of rubber.

 

My 530d has alloy calipers and pistons. I'm on 175k miles and still on the original pistons. Never had them seize. The seals have been changed once. Different story on my M5 with iron calipers and steel pistons. Have yet to find a source for stainless pistons for my M5....though I could get them made at massive expense!

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Try to show some emery cloth or ~2000 grit sandpaper to that piston if it levels. Actually not looking as bad as it could. Though like said in previous post it looks like the dust seal has not been seated correctly after that previous job or the rust between dust and pressure seal was new never removed in the first place.

Edited by Clavurion

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2 hours ago, DepthHoar said:

Try to get hold of a stainless steel piston

Try to get hold of original ATE dust seals since these seem to fit better, more snugly and appear to be made of a better grade of rubber.

My 530d has alloy calipers and pistons. 

 

That's useful info, stainless steel pistons and ATE dust seals will be on my list once I get this back and working then. And the 530 calipers are the same as fitted to my B10 so where did you get ally ones from as that sounds like the best solution? 

 

51 minutes ago, Clavurion said:

Try to show some emery cloth or ~2000 grit sandpaper to that piston if it levels. Though like said in previous post it looks like the dust seal has not been seated correctly after that previous job or the rust between dust and pressure seal was new never removed in the first place.

 

Thanks for the advice but I have a new piston and seals to fit so I'll clean the caliper up best I can and get the car back on the road while I start to think about a longer term solution. I don't particularly need better brakes but this is the second sticking caliper I've had (the first one brought on my re-furb 3 years ago) and I want to be confident I don't need to re-visit this in another couple of years so I'll be doing something with all 4 calipers over the summer - just not sure what yet!

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1 hour ago, DepthHoar said:

Alloy calipers were bog standard OE fitment on my particular 530d (MY 2000, pre-facelift).

 

Well that's got me interested but after searching, the only reference I get to alloy calipers on the 530d are my old thread from 2016 when I mentioned my first sticking caliper (you can also see how good they looked after being refurbed)!

 

 

After searching on RealOEM though I see that PN. 34111163385 from 1995 weighs 2.107KG and the later calipers PN. 34116773131 weigh 4.578KG so you could be right! 

 

The PNs don't cross reference in Real OEM from the earlier model to facelift but most other references seem to think they are all the same fitment so I wonder if they do fit. I guess the other point is that 20yo alloy calipers could have been badly corroded by salt. Anything else you can add would be useful  :)

 

 

 

 

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Re. Alloy calipers and salt.

 

My 530d has spent most of its life plying its trade on Britain's most heavily salted roads up here in the Scottish Highlands. There was some pitting on the end of the piston (almost certainly salt related) where it's exposed and in contact with the brake pad but they were more or less unmarked everywhere else. Apart from the exposed contact area just mentioned, the rest of the piston behind the dust seal looked unmarked and as smooth as a baby's bum. Properly fitted and undamaged dust seals do a lot to protect the piston from corrosion due to the ingress of road crud and salt. Replacement of those dust seals really ought to be part of a maintenance schedule on most vehicles. I bet most only get replaced when they're shredded due to age and have already let a whole load of salt/crap creep past them and ruin the piston.

 

I'd actually bought new steel pistons from Bigg Red when preparing for the refurb but decided to reuse the old ones. Didn't realise the calipers were alloy until I actually took them apart. Had assumed they would be iron with steel pistons so, when planning the refurb, I bought new standard replacement steel pistons. Looking back, not an entirely good idea putting steel pistons inside an alloy caliper due to the potential for galvanic corrosion, though in reality that may be a minor issue in the grand scheme of things.

 

Brakes International are up to speed with the different caliper types for the E39 530d (Bigg Red, take note!) and list factory re-manufactured calipers for the 530d in both alloy and cast iron (depending on model/age) as well as selling alloy pistons. Interestingly, the alloy calipers are a fractionally cheaper than the cast iron ones.

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1 hour ago, DepthHoar said:

Brakes International are up to speed with the different caliper types for the E39 530d and list factory re-manufactured calipers for the 530d in both alloy and cast iron (depending on model/age) as well as selling alloy pistons. Interestingly, the alloy calipers are a fractionally cheaper than the cast iron ones.

 

That's very useful info, looking at their webpage it seems the alloy calipers up to  MY2000 have 296x22 discs and MY2000 onwards have 324x30 discs the same as mine with cast iron calipers :(

 

I wonder if that's just down to different carriers for the slightly larger discs, I've def seen E39 people upgrading from the smaller to larger discs but not sure if the calipers are different or not - guess I'll just have to either read up some more or order an alloy caliper and see if it fits.....I guess I haven't actually asked if you know if the earlier calipers will fit the facelift?

 

Just done a bit more reading and 99% sure the fronts aren't interchangeable so back to the drawing board!

 

Interestingly, I think the rear calipers on mine are alloy (I bought some s/hand ones last year) and have just compared them for weight and feel to the fronts so know that is the case.

 

 

Edited by BarryM
Update

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Caliper cleaned up some more, new piston, piston seal and dust seal fitted and brake working as expected.

 

 

I'm gonna look at getting 2 new front calipers and send them off with my 2 rear spares and get them painted but not get new pistons and seals fitted by the painter so I can see exactly what's been done next time! Then I can fit the new pistons and seals myself knowing the full condition - I'll look out for stainless or ally pistons as suggested by DepthHoar.

 

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One thing to consider is a healthy dose of tannic acid in the seal seats. This will stabilise any corrosion if moisture gets in there, which it will.

There is very little point in stainless pistons, as they are just too soft and gall with the friction against the caliper body, then damage seals regardless of corrosion. Hardened chrome plate pistons, like the ones you have, are much better suited this purpose. For reference, hardened chrome plate steel is typically around 8 times harder than any stainless.


I made a set of Ti (6Al4V) pistons for the corrosion resistance and heat transfer. They work beautifully, but they are not as hard as chrome, so I have to rebuild the calipers and  polish pistons every couple of years. These are twice as hard as stainless!

 

If you want minimal servicing - go for the hardest pistons you can get and take precautions with corrosion treatment.        

Edited by sinner

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3 hours ago, Sir Anthony Regents-Park said:

Also, replace brake pads when they get down to 4/5mm. The further the pistons are out due to worn pads, the more they'll rust. I've had to replace both calipers on an E46 because the pads were down to 3mm. Pistons as rusty as an old horseshoe. 

 

Piston protrusion should not matter as long as the dust seat still does its job properly.

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