410mm RB Racing discs - Vibration when braking

[RMC83]

Hi All,

I've been meaning to ask this Q for a while, but just didn't get round to asking.

Anyway, I'm running a stage 3 C6 and upgraded the brakes with 410mm RB Racing discs at the front, with DS2500 pads, ATE superblue fluid & braided hoses all round.

When the discs and pads were brand new, i did the bedding in process of x amount of braking from high speeds etc, but noticed when braking at 70mph+ there was quite a noticeable vibration. I did ask the garage that installed them & they mentioned that putting bigger / non std discs and pads can cause this. During my cars last service (different garage), they also noticed the vibration and said it would likely be warped discs, as from their knowledge, if the discs fit, then they will be secured & there will be no vibrations. As the discs were brand new when i first noticed the vibration, i'm almost certain they would not be warped coming out the factory, so not really sure what the true issue is likely to be.

Anyway, the Q is, for anyone running the same set up, as i know there are a few, anyone else have this or faced the same problem & what was the solution?

If i recall Ian has a similar set up & been to many trackdays, so if your reafing this Ian, any similar stories with your brakes?

Thanks in advance
Roy

[pcorpe]

Hi, I'm running 410s on the front also, and near identical setup, and have a strong vibration the faster i am when starting to brake. a strong though brake seems to result in less vibration. the garage thought it was warped discs also, however the were 3k or so in, didn't feel like it was warped, but needing a solution swapped out for new discs.

second set now doing the same (I also purchased a spare set to avoid future delay in delivery)

I've done a few high speed stops on the current ones and think the vibration is less as a result, would expect that if the discs were warped.


Conclusion...
I think I'm not breaking hard enough, I think I'm building up a high spot over time, and the discs are not warped. I suspect if I did a really long run (few hundred miles) with a good amount of breaking the problem would reduce or disappear.

I've no clue on what to do on my above assumption. could be an excuse for a day of driving sometime. could take them and see if I can get skimmed, though I'm a little wary of the process, and finding somewhere to go (Hants) or leave as is and try to be harsher on the breaking here on in.

hope this helps a little. try a few high speed aggressive stops, see if you think it improves

[IanH755]

Hi Roy,

As this happened when the discs were still brand new I'd suggest one of two things is potentially the issue -

A - they may have arrived "warped" or, to be more accurate "not trued or has bad run-out" despite being new i.e. could have been a simple mistake during manufacture. Or

B - the wheel hub that the brake disc bell fits onto may have had some small non-squashable bits of "dirt" like rust etc still on it (not cleaned first) when the disc was fitted which has prevented the disc being fitted true.

To fix/test for this you can take the discs off and check the surfaces for crap on the hub or bell. If there's nothing then you could get the discs skimmed back to being flat/true and, if needed, you can even do this with the discs still fitted on the car nowadays, rather than having to remove them. As part of the skimming a decent garage would check for how true the disc is before they start.

The garage's excuse of "you get that with aftermarket brakes" is utter rubbish TBH. I've had two types of AP Racing 410mm Disc (the "old" style direct bolt-on to the bell and "new" style using a floating bobbin to attach them to the bell) and neither of these setups had any vibration.

However, as pcorpe mentioned regarding vibration, once you do get a few thousand miles on any of these style discs, what you can get is a high spot or two caused by "pad transfer" onto the discs (keeping your foot on the brake pedal when the car isn't moving - autobox issue - when you've got hot brakes), which gives a vibration on braking but can quite easily be removed if you just re-bed the discs, which removes those pad build-up high spots.

[RMC83]

Thanks for the info & maybe it now makes sense....

My car is my daily & most days driving in/around town, therefore not doing heavy braking, which i guess adds up to the point being that high spots can develop with these discs. I'll try & re-bed the discs again & see how that goes. If the vibration still occurs, i'll get all the surfaces checked & if required, get the discs skimmed as a last resort.

Thanks for the info & interesting that pcorpe has had the same issue with maybe the same problem, ie not doing enough hard braking to avoid the build up / high spots. Looks like I need to go & find a quiet road for some aggresive braking...haha.

Cheers
Roy

[drybeer]

I seem to remember this also happening with worn rubber bushings allowing the wheel carrier assembly to oscillate under braking, and being not noticeable under acceleration.

Might be worth checking all bushings?

[ATinOf]

This could also be a result of partial piston seizure in the calipers, one or more pistons not moving freely, hence the pad is not being applied squarely, normally a result of a bad dust boot. Difficult to diagnose without taking the caliper off and checking each piston movement; especially the rear facing pistons. I had this problem; so much so I couldnt shift one of them no matter what I tried, even high pressure air behind the piston; and had to change the caliper. Worth adding a 'free piston movement check' to your pad change procedure.