Are You Cracking Dba Rotors?

[Roy]

Ok I recently became a victim of the dreaded cracked DBA 4000 rotor club. Wasn’t overly impressed as they were near new. But with the rotors on the bench and inspecting the rotors with DBA it appears as though there could be a fault with the caliper and the use of the rotor…combined with the fact they were used for a hard stop from over 200km/h when cold at an airport run.

So looking at the rotor the outside face (the side that cracked) has obviously run hotter then the inside face. This is evident by the blue hue in the rotor face as well as the paint markings on the outside of the rotor where two of the three thermal paint stripes have been completely burnt off. All whilst the inside face is only on the middle temp paint with all three stripes still being visible and a shiny silver as you would expect.

So, differential expansion as a result of a big temperature gradient hasn’t helped these rotors. Combined with the big hit of heat when cold. The rotors are off for some more testing and inspection. Will post up the feedback when I get it.

But some things we all may want to check. Make sure your pistons are not dragging the pads on the rotor. This is a possibility in my application even though the calipers have been rebuilt. Perhaps where was a bit if run out (doubt it) or the design of thw wheel limits airflow to the outer face (doubt it) Most likely pistons rubbing the pad on the rotor a little, or when I jump on the brakes the outer pad works a lot harder then the inner pistons.

Now finally, especially since its been a buzz topic lately. Be careful if you are going to be running brake ducts. I trialled some ages ago but took them off because I was not happy with them, and decided I would wait and do it properly when i get my new Brembos on. But if you are running DIY ducting ensure that the ducting is directed the centre of the rotor and the air then travels up through the vanes of the rotor. Simply ducting it towards the inner edge could lead to one side of the rotor (inner) running cooler then the outer face. This gives rise to differential expansion which is a known problem for stressing steel components. The main reason I removed my ducts was that I wasn’t satisfied that in the wet they woudlnt be guiding water/mist onto the inner edge causing massive temperature differentials and thermal shock to the rotor. I had not really considered that air itself could have resulted in a 200degC temperature differential across the rotor.

[260DET]

Yeh at the QR sprints very few seem to warm their brakes up at the start of the first lap, gives the transmission a chance to warm up a bit too if you take it easy for the first half lap or so.

[djr81]

I would be curious to see whther anyone has had their DBA4000 rotor crack from anywhere other than the small slots on the outside of the rotor.

[Roy]

I would be curious to see whther anyone has had their DBA4000 rotor crack from anywhere other than the small slots on the outside of the rotor.

Thats exactly what i told the guy when speaking to him . They are introducing a point of failure by running the slot to the outer edge. I dont see Alcon/AP/Brembp/Performance Friction etc etc doing that sort of slot arrangment on their street or competition rotors. My old set of DBA 4000 which lasted an eternity had the old slot design as well, (ie no little slot on outer edge)

[djr81]

Here are a couple I prepared earlier.

I was not running any ducting & the stone guards were in place. Rotors cracked on the outside.

Note the rear failed completely & if you have a look at the front you can see the start of a crack propogating from the small slot.

I don't think you need look any further than those slots to see what kills these rotors. Note that there was minimal wear on all of them, pads were RB74's & they got a bit warm as you can tell by the surface of the rotor.

I have another dead one at home (a front) that is cracked through from the return slot.....If you have the ear of anyone at DBA tell them to bin the return slots.

[Roy]

I will dig up my crack....far, far , far worse then those. And it took no time at all to propogate into the hub.

Makes me wonder why DBA are only doing a limited run of these, curved vane with Alcon style slots.

UAS have some for sale at the moment. If i didnt have the Brembos then i would grab some

[dori34]

how much do are UAS doing a pair of front rotors for atm?

[T04GTR]

yes they are shit. there is to much chrome in the iron. we crack them every 2 race meeting. (v8 utes) they seriously are shit. end of story. they lasted longer with no ducting. no point blowing air on the inside when theres no flow on the outside. this creates unevan expansion and pop. they crack at the slots. usualy all of them. bloody rules...

[T04GTR]

as for the alcon slots? marketing.

[MrStabby]

Environment: DBA4000s, DS2500s, MBF600, backing plates, UAS 324mm kit

Roy, i have the same problem with cooking the outside face of the rotor only. I also assumed it was stuck/dragging pistons and rebuilt the front calipers last weekend. I hope that wasn't a waste of time! Anyway, i'm going to Wakefield on the 8th for some 'testing'.

I also noticed that it was a bit patchy and appeared worse between the 'vanes'. Perhaps the inside face of the rotor is pulling heat across from the outside face, thus cooling the area at the vanes better that the air in the between the vanes does. I should have taken a photo before sanding it off....

or when I jump on the brakes the outer pad works a lot harder then the inner pistons

Its hard to see how this could happen unless the inner pistons are stuck. Force = fluid pressure x area, which is the same on both sides.

[MrStabby]

Makes me wonder why DBA are only doing a limited run of these, curved vane with Alcon style slots.

I would guess the curved vanes provide more surface area and better fluid flow, so better cooling.

Maybe the limited run is a beta test?

as for the alcon slots? marketing.

They're also copying what appears to be a better design - alcon thought well about stress concentration.

[Beer Baron]

I hope they give up on the bloody "wiper slot" and "kangaroo paw" bullshit and keep making those curved vane one with the alcon style slots (or even normal slots).

[Roy]

Its hard to see how this could happen unless the inner pistons are stuck. Force = fluid pressure x area, which is the same on both sides.

yeh i get that but there is that part of me that thinks that because i run teh adpator brackets for the larger rotors that perhaps the caliper is slightly offset a mm or two?!?! So when you jump on the brakes that the rotor is being distorted and compressed against an off centre caliper.

[Lunatikk]

I'm not sure if the calipers being slightly off-set would or should be a prob, as long as they are still running square to the rotor. With all pistons sharing the same fluid circuit per caliper they should "sort themselves out" for want of a better term & simply travel as far as required per side/pad to deliver equal pressure to both sides of the rotor.

Also in regards to pad drag on the rotors, my Brembo 8's actually have springs fitted behind the pistons which acts to both minimise knock-off & provide just enough contact to build & keep enough temp in the pads & rotors that initial bite & thermal shock is never an issue. This allows me to run Hawk HT-10 compound pads with a temp window of 149 C - 871 C as a street pad with no issues or "oh f**k" moments. Literally takes less than 2k's of driving from dead cold to have usable heat with NO application to help it on it's way.

It's obviously a different story if only one side of the caliper is dragging though........

[Primordial]

Would there be any noticeable pad wear from this? Obviously if there is friction to build up heat then it's wearing the pad (even if just slightly, its 100% of the time!). How quickly do you go through pads?

[djr81]

Harden up Roy, & get yourself some single piston callipers with slides.

[Gts-t]

As soon as i grab the adaptor brackets ill be doing this the 324mm conversion only with rda rotors. I have 324mm slotted only fronts and standard size slotted only rears.

Hopefully all goes well

[Lunatikk]

Would there be any noticeable pad wear from this? Obviously if there is friction to build up heat then it's wearing the pad (even if just slightly, its 100% of the time!). How quickly do you go through pads?

Mate to be honest I've only done a few thousand k's on this setup & I haven't had the pads out to take a look but once I do I'll post up the info.

[T04GTR]

thats why "propper" motorsport discs are 500-750 each. cos they can actually take being red hot more than once.

[Abo Bob]

I've cracked 3 of them and always from that slot thingy.

So what's the alternative? DBA5000? Something else? Carbon ones?