Front Caliper Distortion Problem?

[boxer]

I've replaced the 4 cap heads that hold the two halves of the front calipers together with stainless bolts.

Now the pads bind slightly on the discs, not that badly, but more than before when the wheel rotated very freely.

It was difficult to judge how tight the originals were in due to corrosion and/or loctite. By trail and error I found that the wheel rotated OK with the 4 bolts at about 16nm torque. This didn't seem much so I loctited the bolts in.

Now both caliper are on, the pads appear to drag on the disc presumably because the caliper are distorted.

Does anyone have any idea what the 4 bolts should be torqued up to? Do they need tightening in a specific order? This was supposed to be easy.

Thanks.

Russ.

 

[cookie]

figures i have for similar R100R caliper are:

outer connecting screws 10 +5 Nm

inner connecting screws 30 +5 Nm

ps. things like this are normally torqued up inner bolts first, then outer, often in stages like cylinder heads. no such insructions in BM manual though.

pps. just noticed it specs loctite 273 on the threads.

 

[Greg Masters]

Why do people do this?

Sorry Russ, but all you've done is bolted in a problem.

Stainless might look a bit blingish, but it's just not the same as the OE material. If you've got a problem when it's static, what's going to happen when it all gets a bit warm. Do you know the relative expansion rates of the bolts you've taken out and those you've put in? What about their brittleness? But then it's only the brakes!

As my old Grandad used to say, "If it isn't broken, don't fix it!"



Greg

 

[boxer]

Thanks for the replies.

The nearside, inside upper piston was sticking. I removed the nearest upper bolt and re-torqued to 16nm and everything spins just fine.

Of course Greg and his Grandad are dead right and I knew it before I started - which doesn't help. I didn't want shiny bolts just something that didn't look corroded. I've ended up with two front calipers I absolutely no confidence in.

I got what I deserved.

 

[Alte Wolf]

Why do people do this?

Sorry Russ, but all you've done is bolted in a problem.

Stainless might look a bit blingish, but it's just not the same as the OE material. If you've got a problem when it's static, what's going to happen when it all gets a bit warm. Do you know the relative expansion rates of the bolts you've taken out and those you've put in? What about their brittleness? But then it's only the brakes!

As my old Grandad used to say, "If it isn't broken, don't fix it!"



Greg

Was seriously considering a S/S kit for whole bike advertised on here, where does that leave it then

 

[the civil one]

Greg,s right.

Its just not as strong.
I was removing the rear foot peg holder on my bike which i had fitted some stainless fastners to and i managed to break off the head on the fastener, i,ve never managed to do that with steel fasteners.
Another thing i wonder about is the Quality of these fasteners
some of the stainless is of good quality ,some of it down right bad,, question is ? How do you know the differance.

 

[cookie]

i guess if it's A2 quality it's to that spec. whatever that spec is.

i know A4 is marine, but probably refers more to corrosion resistance.

stainless is quite capable of holding calipers together in my experience.

edit: i'd be wary of s/s wheel spindles, though plenty of ppl use them with no prob.

 

[boxer]

, where does that leave it then

BMW clearly state that the two halves of the caliper should not be split. Because of this they do not [least non that I could find] give torque values or any sort of tightening sequence for the bolts. This should have been warning enough.

A lot of people have done this mod to their satisfaction. I have not.

I'm left wondering:-

1. If the bolts are tight enough
2. If the bores the pistons move in are round. Are the seals seated.
3. Will the seal fail
4. Will the next corner kill me
5. After 45yrs on the plant why do I still do stupid things.

At the start I decided not to replace any of the suspension bolts because of the unknown mechanical properties of stainless. I did not expect this problem with the calipers.

 

[Greg Masters]

5. After 45yrs on the plant .....

You're smoking too much!



Greg

 

[Steptoe]

Was seriously considering a S/S kit for whole bike advertised on here, where does that leave it then

with my kits i don't supply the bolts that hold the calipers together, i've seen people have trouble in the past doing brake caliper bolts, ( never had trouble doing my own ) , due to corrosion, and taking them all out at once, instead of doing one bolt at a time - I've never encountered a problem on my own bikes in 20 years of using stainless -

the brake caliper bolts i refer to when your ordering a stainless kit, are the caliper mounting bolts - i.e. the bolts that hold the caliper to the the fork legs