Front brakes-- again!!!

[wessexrfc]

So I have now picked up my car for Urban Racing, now sporting a lovely new set of front grooved discs after the old ones were reground and didn't cure the vibration fault. But, alas, after being told all was sorted, I found that under heavy braking from around 100 the vibration came back!!!. It seems once there is heat into the disc and possibly the bells, this causes vibration but through the brake pedal. Has anyone had this fault??? Do I need to replace the bells (more expensive than the discs!!!) or could it be the rears? How do I check then this only happens when the discs are hot. One last question, am I going to do any damage to my new discs???

[hollowpockets]

Braking from big speeds i get a slight vibration, the previous owner said it was something to do with the rears, have never bothered my arse to sort it, only notice it on track which isn't often enough to justify fixing at this point.

[TuxMan]

not good to get too much heat in the straight away !!! try not too drag the speed off by constantly pushing the brake pedal it creates heat try a solid stab then lift off at the right speed (hope that makes sense) AP give good instuction about bedding in pads . have a read .

[Adrian W]

chances are the uprights were machined to take the bearings out of line, clock the disc or hub run-out, any more than 2thou ish on the edge of the disc or 0.5 thou on the hub is unacceptable, you can make the best of a bad job by getting the discs trued on the car.

[Mike Tuckwood]

Are there any other symptoms for this at all?
Greater brake pedal travel once warm, slight vagueness when changin direction at speed?


Mike.

[BobE]

I have a similar problem on my car which happens at lower speeds... As others have said the most likely cause is disc run out (wobble). It could be that the discs are warped if you didn`t bed them in properly and heated them too much too soon etc. The build manual gives a maximum `out of parallel` for both sides of a disc as 0.006"/0.15mm and a `run out` maximum of the same. You can check the former by using a micrometer to measure the disc thickness in various places around the area swept by the pads and the readings shouldn`t differ by more than the figure quoted. To measure the runout you need a dial gauge securely mounted and in contact with the disc surface at 90 degrees - then slowly rotate the disc and see the maximum variation in the reading having `zeroed` it at a start position. This is fairly easy with drilled discs as you can set it up to miss the holes - it will be more tricky with grooved discs....
On my car all the discs are within 0.002"/0.05mm for parallelism and the runout on the four discs are 0.0018"/0.045mm, 0.0031"/0.08mm, 0.0031"/0.08mm, and 0.0043"/0.11mm. So in theory they are all in spec but I still get vibration, the discs are almost new and there seems to be nothing else wrong anywhere...So, I`m going to get my discs machined/skimmed on the car so I`m absolutely sure there are no runout concerns and hopefully this will sort the problem. (Find an experienced outfit to do the machining).

[Mike Tuckwood]

Also give a very close look at track rod ends, suspension ball joints and in particular, wheel bearings.
It isn't always just the discs.


Mike.

[wessexrfc]

Dave drove the car down from Manchester to Worcester and then I onto Exeter so the discs and pads were nicely bedded in. The problem is once they are hot I get vibration, How do I test under these conditions ??? The dynamics of the system are simple, its just trying to locate the component that is causing the problem, very fustrating

[Mike Tuckwood]

wessexrfc said:

Dave drove the car down from Manchester to Worcester and then I onto Exeter so the discs and pads were nicely bedded in. The problem is once they are hot I get vibration, How do I test under these conditions ??? The dynamics of the system are simple, its just trying to locate the component that is causing the problem, very fustrating

What Torque settings were used when the new discs were installed and were new bolts/nuts used?


Mike.

[wessexrfc]

No idea Mike, What should they be?? Going to take to friends workshop tomorrow so could test the torque and inspect the bolts

Cheers

Paul

[F.C.]

I had this pulsing through the brake pedal when I first drove my M400 turned out to be one bell causing the problem.
F.C.

[Mike Tuckwood]

wessexrfc said:

No idea Mike, What should they be?? Going to take to friends workshop tomorrow so could test the torque and inspect the bolts

Cheers

Paul

Bugger, now ya got me, it's a REALLY low figure though, far lower than you'd imagine. I'll try and log into my work PC in the morning, see if I can find it and let ya know.

Mike.

[Mike Tuckwood]

F.C. said:

I had this pulsing through the brake pedal when I first drove my M400 turned out to be one bell causing the problem.
F.C.

We see it a lot, it's also important when fitting new kit to make sure that the mating surfaces of the bell to hub are thoroughly clear of corrosion and dirt. Any slight error or issue here is disproportinately compounded over distance, (disc diameter).

Mike.

[wessexrfc]

F.C. said:

I had this pulsing through the brake pedal when I first drove my M400 turned out to be one bell causing the problem.
F.C.

How did you come to this conclusion F.C?? can't belive the bells are more expensive than the discs!!!

[wessexrfc]

Mike Tuckwood said:

wessexrfc said:

No idea Mike, What should they be?? Going to take to friends workshop tomorrow so could test the torque and inspect the bolts

Cheers

Paul

Bugger, now ya got me, it's a REALLY low figure though, far lower than you'd imagine. I'll try and log into my work PC in the morning, see if I can find it and let ya know.

Mike.

[Mike Tuckwood]

wessexrfc said:

14Nm.


Mike.

[wessexrfc]

Mike Tuckwood said:

wessexrfc said:

14Nm.


Mike.

Will check tomorrow...thanks!

[F.C.]

wessexrfc said:

F.C. said:

I had this pulsing through the brake pedal when I first drove my M400 turned out to be one bell causing the problem.
F.C.

How did you come to this conclusion F.C?? can't belive the bells are more expensive than the discs!!!

I bought the car via North London Noble (TVR Centre) when I test drove it I mentioned the problem but they had already diagnosed the problem and ordered the replacement part along with the two top ball joint plinths.
They sorted it before I eventually picked it up.

Edited by F.C. on Sunday 23 August 01:03