2001 E39 530i, chanigng brakes - follow on

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Many thanks for you all for helping me (I've decided to go for it after getting hold of the Haynes manual (#4151)).
There are a couple of questions at the bottom, but FYI.
-- In fact my car went for an oil service today (190) and as well as pads, discs being knacked (service manager said discs that do 50k miles had done a good job - is he right or just BWM dealer/rip-off speak?) the front caliper is 'sticky' and needs replacement. The only good thing about the service was the courtesy car, a Z4 conv 2.0 litre. Fun for a day but wouldn't switch for my 5 series + the Z4 new is, gulp, 24k (or $40k), staggering!!
Had a good on-line look about replacing the caliper seals but generally seals to be a bad idea, so new caliper it is at 50-60 - Haynes manual says it's pretty easy and actually explains how to refurb it, I don't have enough confidence in my DIY skills to attempt a refurb. But for the record has anyone done, found it easy and worked? -- So, off to GSF tomorrow for my parts and of course a new tool (mandatory); a piston retraction tool. -- Questions
I did notice that GSF have stacks of varieties of discs (vented, solid, brands) - Does anyone know the OE make of the DISCS?
When changing the caliper, I have to clip the hose to stop brake oil leaking, when I reconnect do I have to bleed the air out?
Thanks again
Matt
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No idea what the OE discs are. I would go for a better/harder wearing brand anyway. I use ATE power discs on my 325 and they have been very good.

Yes. As the callipers will be empty and full of air that needs to be got out. The clamp just stops all the fluid leaking out from the resevoir and the ABS system.

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THANKS.
So using a brake bleed kit (one man type), I should be able to get all the air out? No need for BMW to inspect?

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Yup. As long as the fluid hasn't completely drained out you should be good to go after bleeding the brakes with your one man kit.
--
Cheers

Rick

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I've not done a BMW, but recently did my other car which has four pot calipers so rather more work. On it, the pistons - which are chrome plated - required replacement due to corrosion. Otherwise a straightforward task, but obviously you do need to clean and examine the parts for corrosion or damage before fitting new seals. And I'd do both calipers on that axle - the seal kit will probably be for two anyway.
I've got one of those battery operated tyre compressors and used this to force out the piston. But you *must* use a secure strong clamp to stop it flying out as it might need considerable pressure to move it. The other (messy) way is to pump it out while still on the car.
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Take the Haynes back and get a Bentley instead. You won't be sorry, unless you elect to muddle through service with that Haynes.
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Normally the thickness lower limit is engraved on the edge of the disk. Remove the wheel, turn the hub until the mark appears, Measure it with a calliper.

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Difficult to do since you won't get the calliper off due to the ridge at the edge. If you don't have a micrometer use the callipers with a known sized HSS twist trill as a spacer. Say about 3mm.
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wrote:

Say what!!!
It's an easy task to spread the caliper in order to remove it, and its no trouble at all to turn the hub around to locate the specification stamped on it, even without taking the rotor off. And, it's possiblle to measure the rotor without taking the caliper off.
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Perhaps it's a language thing. Measuring vernier callipers have usually parallel jaws. So can't get get past the rust rim unless you use some form of spacer. Same with 'normal' callipers where they are curved and could measure the thickness, but have to be removed to do this.
A micrometer is the easy answer.
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wrote:

Why would anybody use a tool with such an obvious flaw in a particular application? The only tool that can be used to measure a rotor is a micrometer or calipers that haven't got parallel jaws. And the micrometer is the first choice when making the measurement on the car with the brake calipers still in place because a micrometer can get into the tight spot to make the measurement. Having said that, I can't imagine why one would want to measure a rotor and NOT consider replacing the pads. I'd be in there with the intent to replace the pads, and measure the rotors while the calipers were out of the way to see if I needed more parts than I was on my way to get.
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Indeed. But calipers have to be removed from the work piece to measure their gap - unless they are vernier types, and common ones have parallel jaws. If you're saying there are reasonably priced vernier calipers with curved jaws then ok - but I've never seen such a beast.

That's what I use, but not everyone has a micrometer, or knows how to read one. But parallel jaw digital readout calipers are now pretty cheap and one of those may be used with a couple of twist drills as spacers and some simple arithmetic.

You're confusing me now. ;-)
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wrote:

No, the brake calipers do not have to be removed, there is plenty of room to measure the rotors with the calipers in place.

While it is certainly possible to measure the rotors with the brake calipers in place, why bother? The brake calipers are off to replace the pads anyway, measure the rotors then.
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I'm talking about measuring calipers - not the brake calipers.
But I think I'm pissing into snow.
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I'm talking about measuring brake rotors with the appropriate tool(s).
It is not a requirement to remove the brake calipers to measure the brake rotors -- but as a practical matter I don't see any particular advantage of measuring the rotors while the brake calipers are still mounted. Of course, there are those among us that have to drive the car they are servicing when they go for parts, and they would want to get as many of the probable parts as possible in the first trip to the store. I have several cars, and I can disassemble one, and get into another for the Parts Run, and this tends to color my repair technique.
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Describe the calipers you use to measure disc (rotor) thickness.
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I don't use calipers to measure thickness, I use a micrometer. I use calipers to hold the brake pads, and I don't bother to measure these calipers or the pads. I visually inspect the pads, and replace as needed, and I open the calipers as far as possible before dismounting them so that I can mount them again when the new pads are fitted.
You introduced vernier calipers to the discussion, and said that they require the use of a twist drill or other to create a surface that is wider than the lip of the brake rotor, then subtract the size of the twist drill or other to arrive at the thickness of the brake rotor.
There is no need to use a twist drill or other to effectively shim the rotor to measure around the lip, then subtract the shims to arrive at the thickness of the rotor. With a micrometer, one can measure the thickness of the brake rotors, and it's even possible to do this while the brake calipers are still mounted.
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Ah. But that's not what you seemed to say.

Calipers - not brake calipers - are an engineer's tool for one way of measuring thickness They can be internal or external, parallel jawed or even odd leg. You set them to the thickness then remove them and measure that thickness on a rule.
[snip]

Yes. It's a way for those that don't possess a suitable micrometer.

If you possess a micrometer. And know how to use it.
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wrote:

Or, with the digital variety, you close them, set them to Zero, then open them to fit over the item to be measured and close them again, and extract the measurement from the digital readout.
YOU introduced vernier calipers to the discussion, and said that the use of this tool would require some manner of shim to measure around the lip of the brake rotor being measured. A vernier caliper would most certainly require this sort of adjustment to the proper use because they are not well suited for this application. There are calipers with curved jaws that can reach around the lip on a brake rotor, and a micrometer is an even better tool to use. (actually, I use a micrometer because I have one, but it might not be the superior tool to use, it's just the one I have. It's hands down better than a vernier caliper though.)

When a suitable mic can be found for $20 (USD), there is very little justification for not having one. When the make or break measurement of of the brake rotor is a matter of thousandths of an inch, shimming the wrong tool with a twist drill, then subracting the shim amount from the measurement just seems silly to me.

Well, if one possesses a mic and doesn't know how to use it, I can't help much. That guy should take the rotors off and take them to the shop to see if they are still serviceable.
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I'm well aware of how these work. Now perhaps you'd say how you'd use then to measure the thickness of a worn disc?

They are perfectly suitable *if* you use known thickness spacers to get round the lip of unworn steel and rust at the edge of every other than new disc.

[Sigh] [Again] And just how do you remove the curved jaw caliper to measure its gap?
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