Twin Stock Calipers???

[Martiny]

Yogi, lets just check something.

You say you think you had brake fade?

Can you tell us exactly what happened, what were the symptoms, and what did the pedal do.

[yogibear]

Setup that ive got is Grooved Discs, Not sure of the pads, stock clipers and braided brake lines.

The brakes usually work really well but on track you could feel the change in the brake pedal having to push it a bit further after the first few high speed breaking  zones and not biting quite so well. Aprox 140 down to 40-50 through the chicane. Everyone seamed to be braking early . My technique was to break a bit earlyer and not brake quite so hard as the other cars.

Im not gonna be going to modded nationals now so im going to take the calipers off and check them and possibly re build them.

[TonyC]

What you are describing is just over heated pads and fluid. No point over- hauling the callipers unless you\'v got sticking pistons or leaking seals or something.
BY the way, the braking technique you described actually puts more heat into the discs and pads then heavy, short braking.

[yogibear]

Ive got I feeling the pistons maybe sticking a bit as well. I could have left my breaking later but everyone else was driving so slowly id have gone into the back of them.

So is allways better to brake as hard as possible for the shortest period of time?

[TonyC]

Yes, although it\'s more comlicated than that. You aslo need to tape the presure. So you very quickly go from no braking to as much pedla presure as the car will take without locking up (and that will nee dot be modulated through feel as you slow down/surface changes/weight transfers), then as you approach the point where you are goign to turn (prsuming we are only braking in a straight line and not trail-braking), you begin to relax the pedal presure until you are off the brake just at the turn in point. What you should not get when you release the brake pedal is the front of the car lifting up as the weigth trasnfers off the nose - that is why a car will understeer on turn in after hard braking.

You can practice on the roads - same principal, so if coming up to a red light, barke firmly (no need to rush at it - just getting a feel for braking sensitivity) and then ease of the presure so you stop exactly where you want to with no bobing up of the nose.  
if you find you are braking harder and harder as you approach your turn in point on the track, then you need to brake harder in the first place. But don\'t just stamp on the pedal - you still need feel and smoothness.

braking is probably the hardest part of track driving to be good at - it\'s much more complex than appears - you can use the same sensitivity to then brake in corners, etc. or in wet conditions, use the final squeeze of pedal presure whilst in a turn to help the nose bite on the slippy surface.

[Jonathan_F]

Sorry just read the above information...................................

Just seems very odd, ok serious runout would wreck the disc and skimming would ruin the structural integrity of the disc, but then it would be out of tolerance and un-usable anyway. I think there is only about 1mm of wear in a brake disc anyway for these cars.

Sorry if I\'ve mis-informed anyone. I\'m a time served CNC turner and wouldn\'t think anything of it if the runout was minimal, thats all they do when they manufacture the disc.

That would be my own choice and obviously not the clubs and the decision would be only on my own equipment.

Shaun

Agreed Shaun. As long as your within the manufacturers low limit on disc thickness. Skimming is no issue. If you find a company, like extreme, with a hub skimmer, the discs can be skimmed whilst bolted to the car. This trues the discs to the hub and gives the smallest run out possible.

A word of advice if your \'home\' skimming. Make a mandrel to mount the disc to (skim the mounting face prior to mounting the disc) and machine both sides without dismounting the disc. They are very sensitive to run-out.

Regards,

Jonathan

[shaunwil]

I\'ve enjoyed this thread more for the great advice from TonyC on braking techniques.

As for skimming a disc you would at least need a set of soft jaws in the lathe and still need to clock the part up in the jaws with a micron dti on a reference face and diameter to make sure the disc is square in the jaws. Im not completly sure that they could be done off a mandrel, the inside bore of the discs is very short and you would need a hardened mandrel and press. Then the part would need to be turned between centres !

Shaun

Shaun

[Jonathan_F]

The mandrel takes the form of the hub. The disc is bolted to mandrel in the same way as it is on the car. I have used this technique twice before with good results. The key is to face the mandrel off, then bolt the disc to it. Thus reducing runout to a miniumum.
The real trick is machining the back face. To make a tool large enough to reach round and stiff enough to cut true is difficult. I had problems with hard spots pushing the tool off leaving high spots (where the metal of the disc had been hardened during use). I had to take a large cut to remove the surface hardness.

Clive is correct on disc thickness. There is very little stock on Mazda discs. To keep the mass down. Always surprises me when I see people putting huge heavy disc combo\'s on track cars.

[shaunwil]

You can get heavily cranked V style tools that don\'t need much room. Plus we used to used a smaller C style tip that didn\'t need alot of room, plus they made them in wiper inserts.

As said there is only about 1 or 2mm of metal on the disc, theres absolutely no point in touching it if its near the bottom limit.

Shaun

[Brett]

Rebuilding the calipers carries all the same risks as skimming discs.

 I\'d love to know how you reached this conclusion?

[yogibear]

So where would be the best place to get a rebuild kit from?

[Mazdarotaryparts]

So where would be the best place to get a rebuild kit from?

We sell front seal kits for the front calipers for from memory £35 plus vat for a set.

[mullins]

I\'d love to know how you reached this conclusion?

You\'re not going out and buying a new part so you have all the same risks (human error, poor workmanshipm, etc)

What i\'m saying is that any sort of rebuild/modification of parts carries risks and skimming is no different to rebuilding a set of calipers.

[Brett]

True, but you accept a certain amount of risk every time you fit a new or reconditioned part - theres always a chance that a duff part will slip through the net.  Personally if I can repair something then I will - I\'m smart enough not to attempt to use something that doesnt meet or exceed the requirements.
 Not having a go - you\'re first statement was just a little to sweeping for my tastes

[yogibear]

Im exactly the same, if I can repair a part rather than replace it then I will. Also there is the knowledge that if you have done the job your self then it has been done properly.