vibration under braking

[david godfrey]

Driving the tam home tonight (m4 clear for a change) and noticed a slight vibration, a poor attempt to describe it would be "under breaking i can feel a vibration through the steering wheel" - I have checked all the wheel nuts and there still tight - any ideas? Might go get it balanced in the morning

[2 sMoKiN bArReLs]

Wheel balance or warped discs can do this.

[david godfrey]

quick response! ok - will get them balanced and see what its like after that - thanks.

[lasertam]

I get some vibration from my Tam.. when I guestioned this, was told it is a characteristic of drilled disks. Not sure if its the same thing????

[GreenV8S]

Drilled discs often cause a slight whirring noise but not as bad as what you're describing. It may be that the discs have just got contaminated at one point. In theory you can clean this off with carborundum paper, I've had good results just running abrasive GreenStuff pads for a while, or ultimately you have the option of replacing the discs. I'd suggest you stay away from drilled discs in future, they're bad news all round.

[david godfrey]

GreenV8S said:

I'd suggest you stay away from drilled discs in future, they're bad news all round.

Balancing did not help - will get the garage to check this week although it drove fine the last 2 days (typical just when I try and show or explain a fault it seems to fix it's self)
huh - mine are drilled, from what I gather this is the standard on the tam - and the rest of the fleet - why stay away from them? drilled /should/ help reduce rotating weight - and help cooling /ish/ or am I wrong?

[GreenV8S]

Drilling is done for looks, and to degass the discs when they're hot. However, it also aggravates pad wear and noise, and introduces stress raisers which can lead to cracking and potentially catastrophic disc failure if they get hot. Given that you would only need the extra degassing when they are hot, it follows drilled discs are a waste of time if you don't get them hot, and potentially lethal if you do. They look pretty, but they're just bad news all round.

Grooved discs are just as effective at degassing the pads and don't tend to suffer from the cracking problems that plague drilled discs. If you need extra ventilation, fit grooved rather than drilled. However, even grooved discs are a waste of time unless you are getting the pads hot enough to suffer spongey brakes. Plain ordinary discs are quieter, produce less pad wear and give better braking (due to increased contact area) when they are cold. Stick with them unless you *need* to go to grooved discs.