Help, strange high speed braking vibration !

[youngsyp]

Guys,
I have been experiencing a strange vibration when braking from high speed. The brakes are absolutely perfect in normal use but, when braking from high speed, 90 mph +, they vibrate very badly, violently even. Basically, it shakes the whole car and gets worse the more they are used. There is no loss of stopping power though and once they are not used for a while, after they cool down ?, they are fine again !
The kit I have fitted is a Godspeed 308mm grooved disc conversion with separate disc and bells and Pagid fast road pads and goodridge hoses.
It feels almost as if the discs are rubbing on something. I have checked the calipers and carriers. They were a bit tight so, I ground some off. I also noticed that the rust on the outside of the discs (not braking face) seems to be smooth ish on the inner disc but, normal rust like on the outer disc ?! I haven't used them hard yet since grinding them so, not sure if this has cured it. Also, I noticed a very small gash in the nsf caliper piston dust seal. Could this cause such simptoms if brake fluid got on the linings ?
Lastly, not all of the pad comes into contact with the disc surface when braking. There is a very small, 2mm, part on the leading edge of the pad that just hangs over the edge. This was the best fit I could get with decent clearance between disc and carrier.
Now, if the discs were warped, they would vibrate all the time, no matter what speed so, I don't think it is that. I have rose jointed track rod ends, recently replaced, and full polly bushes at the front. The balljoints were also replaced in March.

Anyone got any ideas ?

Cheers

Paul

 

[Brett G]

I had exactly the same but my standard disks were old and they were warped! So it sounds like that is not the answer for you as yours are new :?
The symptoms were hardly noticable till after 60 ish mph. at what point (in mph) do you notice the vibrations stop? Do they stop gradually or suddenly? At the same sort of speed each time?

Brett

 

[youngsyp]

If I stay on the peddle all the way from 90mph ish to a stop, they will vibrate all the way to probably 20 mph. In normal driving, I can use the brakes at 80 mph and they are as normal, no vibration but, if they are used very hard, they will vibrate from around 90 mph upward. If I dab them at high speed, they are fine but, I guess that's because they aren't getting hot ?!

Cheers

Paul

 

[Brett G]

Mine would vibrate till about 20mph too but symptoms would be there at anything over 40 ish just much worse at high speeds :shock:
I'm clueless :roll: :? :?:
I don't know much about the abs system but maybe its releasing one side then re-aplying causing it to judder or something? Probably way off the mark there but just an idea

Brett

 

[youngsyp]

Brett,
I don't have ABS so, none of those worries :lol:
I have tracked down what it is though, I hope. From my symptoms, it seems I am experiencing 'hot judder'. This could have been caused by inproper pad and disc 'bedding in' or a number of other things. But, it can be rectified fairly easily. I need to get my disc's 'Blanchard grinded' or skimmed and this should remove the offending deposits and or 'cemetites' from the disc face. I shall then do 10 fairly hard stops from 60-10mph to bed the new discs in. Apparently, the key is to get a uniform layer of pad material on the disc surface for the best results.

Hopefully, that should sort it !

Cheers

Paul

 

[Brett G]

Yeah thats just what I was gonna say!!! :lol: haha Glad you found the prob Sorry I couldn't be a bit more helpful.

Brett