Discs running out of true, how to find the source of the problem?

[Brett James-McCall]

As the title says, in case you didn't see the update to my build log. It looks like the disc is running out of true, it is visible to the eye when I stand over it and turn the disc.

However, how do I find out if it is the disc the bell or even a problem with the hub. Any suggestions?

I am running a set of Ray Christopher uprated GTD front upright and hub. Thanks in advance

 

[Paul Thompson 'Hooligan']

Hi Brett -

Where did you source the discs/bells? I've seen some 'std GTD fit' bells that do not fit, without a slight chamfer to edge of hub facing flange, or s slight cut to the bell.

Got any pics as that always helps.

 

[Dave P]

Brett :

A magnetic base with an dial indicator mounted on the spindle touching face of the adaptor where the drive pins are first and then the bell and then the disc face

 

[Dave Bilyk]

Brett, I dont know if you mean out of true radially (concentricity), or out of true on the side (swash), but;

Make a mark at the high point on the disc with a felt tip pen or chalk or something,

then remove the disc, rotate it 180degrees and replace.

then look at where the high point is now.

If the high point is still at the mark on the disc, the disc is the problem.

If the high point is now opposite, the bell or hub is the problem.

If it is the bell or hub, you can put the disc to one side, and repeat the exercise with the bell to determine whether it is bell or hub.

You might ultimately need a dial indicator (clock) to do it.

Also look carefully to make sure that this is not caused by a rag, swarf or other trapped between the surfaces.

My guess is it is unlikely to be the disc, more likely to be the bell depending on who machined and drilled it.

Dave

 

[Brett James-McCall]

Hi Brett -

Where did you source the discs/bells? I've seen some 'std GTD fit' bells that do not fit, without a slight chamfer to edge of hub facing flange, or s slight cut to the bell.

Got any pics as that always helps.

Paul,
Discs were source from Dave Morton as a NOS item.

Upright and then the making of the bells and the hardware for the caliper were done by Roy all those years ago when I got the first GTD chassis made by him. Its only now that I've got round to paying any attention to the brakes area. I've just had them sitting on the chassis up till now.

I'll tryand take a few pics to try and explain later.

Brett

 

[David Morton]

Brett,
I have a magnetic base dial guage if you want to use it.
Is this problem on both brakes or just one?
Dave.

 

[Chris Duncan]

a little bit of runout isn't that bad, it helps knock the pads back so they don't rub the rotor when the brakes aren't applied. A visible amount is probably too much, like .010" approx max.