Sizes of Brake disc mount BOLTS? ('99 non ABS)

[slparry]

seems to be 8x25mm on here

http://www.realoem.com/bmw/showparts.do ... g=34&fg=11

[slparry]

seems to be 8x25mm on here

http://www.realoem.com/bmw/showparts.do ... g=34&fg=11

Top man! (clever one, as I went wobbly ways)
Thank you!

I'd personally only use the OEM ones or some from a legitmate supplier like Chris Shaw Stainless http://www.shawstainless.co.uk on the brakes ... I'd definately shy away from some of those you listed as suppliers to "the trade and DIY enthusiasts"

Grabbing a handful of brake and having the bolts shear could spoil your day !

[conkerman]

£15 for 10 from motorworks from memory.

Not really worth the bother seeing how mission critical they are. Bobbins are about £4 each also.

[Corvus]

What was found to be the cause of noise, if I could ask?

My mate and I stripped his discs off a while ago, to address a particular problem. We found wave washers under the heads of the bobbins. I assume they are standard fitment?

Also, we came to the conclusion the main purpose of the mounting arrangement is to allow radial expansion. Is that correct?

Yes, the discs can be moved laterally, but the wave washers exert quite a reasonable force.

[conkerman]

The bobbins are a wearing part and worn ones cause the disc to rotate a bit, the wave washers are righly there to allow for a bit of expansion.

Its about £65 for the bolts, bobbins and washers. I need to do mine, the disc is a bit wobbly.

[Corvus]

The bobbins are a wearing part and worn ones cause the disc to rotate a bit, the wave washers are righly there to allow for a bit of expansion.

Its about £65 for the bolts, bobbins and washers. I need to do mine, the disc is a bit wobbly.

Cheers.

Going back to the original post, I'd also change the bobbins and wave washers. Are the wave washers actually there?

Are the discs known to indent?

[slparry]

The bobbins are a wearing part and worn ones cause the disc to rotate a bit, the wave washers are righly there to allow for a bit of expansion.

Its about £65 for the bolts, bobbins and washers. I need to do mine, the disc is a bit wobbly.

Cheers.

Going back to the original post, I'd also change the bobbins and wave washers. Are the wave washers actually there?

Are the discs known to indent?

Should be

[Corvus]

The bobbins are a wearing part and worn ones cause the disc to rotate a bit, the wave washers are righly there to allow for a bit of expansion.

Its about £65 for the bolts, bobbins and washers. I need to do mine, the disc is a bit wobbly.

Cheers.

Going back to the original post, I'd also change the bobbins and wave washers. Are the wave washers actually there?

Are the discs known to indent?

Should be

Cheers.

Sorry my post was confusing. I meant are they there on BMbler's bike? Just thinking that if someone omitted them that may be a cause of noise. The brakes would work mechanically just fine without them I reckon? Not advocating taking them out! Just that it would be possible for them not to be there and it not be known. Much!

[timbox2]

I replaced all the bits on mine once, but also found that you could at a push rotate the bobbins a bit and retighten the bolts, it would sometimes remove most of the rotational play.

[Boxadog 2000]

hmmmm....
Bolts fitted where some DIY stainless (or even mush paste), round off in no time, but held discs in so far, so as it is a prospect of having long day, I already ordered Galvanized HSS bolts on fleaBay for £4.00, could bin them or keep them as spare, dunno!

Galvanised dont be daft.

They will be 60/80 microns oversized and will bind on the way in.

Stainless will be fine where ever you buy it, its all made in china who ever you buy it from.

Remember when you remove the bolt heat it first to release the Loctite

[Corvus]

OK I need to clear few bits as what and how:
only one disc rattling and the other one is having ever so slight movement as "vertically" and quite a bit against the washers- horizontally.

The bad one- I found couple of broken washers and those seemed quite flimsy, then that rattling also did contributed to wear something a bit more etc.

Obviously somebody did DIY job beforehand, as the bolts are stainless and really soft- barely felt anything when rounded of first one.... then other one...

As for how I will go ahead- got to get them HTS Bolts on Wednesday and will have better inspection then, what's worn out, what's really need to be replaced and if new ones are going to be up to the job in a first place. If not- I might need to get all as new set as you suggest, just a a tad dubious as how come it's only one of an pair? also, front discs appear not to be OEM and quite new, as well as calipers and remembered, that previous owner mentioned doing such job.
Thanks for intension to help and I'll post on back on Wed

I like my stainless fasteners, but I have to agree with siparry in that on this application I'd stick with bmw std issue or maybe trust shaw stainless to know the correct grade for the job.

From what I remember (going back a few months) the disc has close fitting radial slots and relies on the precise fit of each slot and bobbin to centre the disc? To my way of thinking the bobbins and wave washers play just as important a part as the screws, as does the accuracy of the slots ie: no wear. Something else which struck me as probably important is that the surface of the turrets should be free from paint. The disc has to slide on this surface if it is to expand radially without distorting itself, plus this metal to metal contact may be an important heat sink path? I made the assumption that the wave washers are there to suppress noise but wondered if they also keep that metal to metal interface intact? At the very least the machined surface of the turrets is a datum to align the disc to caliper. People paint over this surface and, to me, that seems the wrong thing to do.

Good luck with the repair and I for one would be interested in anything you find as you go along.

[Boxadog 2000]

Don't get me started on grades.

There are only 2 A2 & A4 readily available
A2 common or garden
A4 Marine grade

Both have less than 2 thirds the tensile strength of HT steel

Fact

Search my posts of 5 or 6 years back and you will have war and peace on the subject.

Its one of the products that I sell for a living

[nab 301]

, also actual alloy wheel contact point has 0.5mm raised area for the bobbin and recess is for the contact with disc

Are you sure? Sounds like usual wear between the alloy wheel and steel disc . If the wheel is worn it requires (shims to prevent or ) machining and spacers to repair.
Here's mine from a few years back.

[Corvus]

, also actual alloy wheel contact point has 0.5mm raised area for the bobbin and recess is for the contact with disc

Are you sure? Sounds like usual wear between the alloy wheel and steel disc . If the wheel is worn it requires (shims to prevent or ) machining and spacers to repair.
Here's mine from a few years back.

Is the wear caused by constant radial expansion and contraction of disc? Or a dissimilar metals thing? Amazing either way. Although, if you happen to be the owner of said wheel, amazing is probably the last thing on your mind.

It will reduce preload of wave washer and put disc out of line with caliper? Does each turret surface wear evenly?

Thin smear of copaslip or not? In a risky area. What is the mechanic's take?

The bike I worked on a few months ago had the top surface of the turrets intact, but a previous owner had the wheels painted and that included the surface in question.

[nab 301]

]

Is the wear caused by constant radial expansion and contraction of disc? Or a dissimilar metals thing? .

Mostly explained here ..
http://www.boxertrix.com/phpBB2/viewtop ... ting+posts