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A question for mechanics/engineers


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Hi all,

First post here but certanly not my last. +++

I changed my discs/pads recently and the bolts that secure the caliper carrier to the hub were extremely hard to undo – conversely when I tightened them back up, I could not get them as tight as they were.

The torque spec for these bolts on my car (e46 M3) is 110nm, for reference the wheel bolts are 120nm. Without a torque wrench I don’t know the exact torque I did them up to but it was nowhere near as tight as a properly torqued wheel bolt, not in the slightest. It was tight enough that its not noticeably loose of course, but using a 16mm spanner and hitting it with a hammer to tighten them can only get them so tight. I also must admit, i fully tightened one bolt and then did the other - which I have now learnt you shouldn't do. :rolleyes:

What would the effect be of under-torqued brake caliper retaining bolts?

I suppose the same applies to the caliper pins that hold the caliper to the carrier, although these are only 7mm allen key sized and don’t require as much torque.

I ask because under heavy braking there is a resonance type sensation that starts around 50mph and goes away once the car slows down to 20mph (similar to a poorly made exhaust that gives you a headache when cruising at motorway speeds – you all know the ones :roflmao:). It doesn’t seem to be disc/pad related as there is no sensation in the wheel or pedal at all, just the whole car resonates like it would from an exhaust. It is also intermittent leading me to think its not a warped disc or pad material transfer.

Could this be something not tightened properly down there?

Cheers for any help

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The caliper bolts are usually glued with thread locking stuff and torqued up. Hence they are a PITA to undo.

However, on all the pads/discs I have replaced (many) I have only used the thread lock stuff once (first time). The next times, I never bothered. The combination of heat expansion and contraction means they get done up very well!

Also, you are supposed to bed brakes in gently over the first few *00 miles, so no heavy braking before then.

Best thing to do, would be to jack the car up, take the wheels off, release the handbrake and rotate the discs - see if they touch the pads anywhere, and have a visual inspection.

Where the pads and discs of a reputable make?

Any loose brake compents will rattle as you drive, so down with the windows and drive about a bit - you'll soon hear them rattle if they were loose.

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