Grinding down disc rotors?

[Aust162]

After further searching for replacement jdm st185 gtfour disc's with not much luck, i was told that it's possible to grind disc's down to size.

The aussie delivered gtfour front disc's are 278mm diameter. Do you think grinding them down to 258mm (20mm) is fine?Dodgey? a safety issue?

I want to get DBA slotted rotors, if anyone is familiar with the DBA (disc brakes aust) "kangaroo paw" technology design, would this effect the grinding down idea?

Thanks people

[TurboRA28]

I've grounded down my peugot vented rotors and never had a problem with it. I dont think it is dodgy at all.

But in regards to the kangaroo paw design, im not sure if that might change the way the pattern works for cooling.

[Aust162]

Thanks for that info joel.
With regards to the kangaroo paw design, i was more concerned about the grinding affecting the strength of the disc.

I'd image the grinded disc would cool just the same as a disc originally made that size.

[MWP]

I've grounded down my peugot vented rotors and never had a problem with it. I dont think it is dodgy at all.

But that wasnt 20mm.
Ive heard some brake shops wont mill down past the start of the cooling fins.

Personally, i wouldnt do it.
20mm is a lot, and it could effect the strength of the join between the two halves of the disc.

Maybe try calling DBA... ask them if its safe?

[Aust162]

20mm diameter, not the width. there 25mm wide from new, but the width isnt an issue.

I plan to call DBA regardless, i was just after a few unbias opinions.

[gianttomato]

The aussie delivered gtfour front disc's are 278mm diameter. Do you think grinding them down to 258mm (20mm) is fine?Dodgey? a safety issue?

That's quite a bit to machine down. Probably OK but, geez, you'd hate to find out it's not the wrong way.....

Have you checked the dimensions of your rotors? I strongly recommend doing this if you reckon you have something oddball.

Are you sure there are no ther discs that are even close? Have you looked through the DBA catalogue? Looked like DBA 739 was 258mm in diameter, 22mm thick and 47.5mm total height and come slotted - are these not right for you? My suspicion is that they are what you need but you will need to measure your rotors up.

The ST185 discs (DBA743) are 3mm thicker (so if you get this bit wrong, they won't fit with your current calipers), 20mm greater diameter and have 1.5mm less total height - seems like an imbroglio to me.

[Aust162]

Thanks for that GT.

If been reading though the catalog
Well i have the gt4 twin piston calipers on the front. So i didnt want to use the standard celica dba739's.
At the moment i have disc's on it that Toyospares gave me.(from a half cut) I've been told they are jdm GT4 ones.
They measure 255mm x 23mm (min thickness)
Now thinner rotors will be a downgrade from them (heating up etc) and being used with the gt4 twin spots calipers, the pistons will come out further and may risk staying non captive...maybe :?

So i thought the best way to go would be to get the dba743's and get them ground down to 258mm (standard dba739 size,3mm bigger than what i'm using now). thats if its completely safe ofcourse. i dont feel like buying brand new dba slotted rotors and grinding them down/stuffing them up..

[Thomas]

If you have a look on the DBA catalogue, most rotors have an initial thickness of x but then go on to state that the minimal thickness is y, y usually being no more than 5mm less than the initial thickness. 20mm seems a bit of a stretch to me.

[takai]

But that is thickness, not diameter.

I think you will be pretty safe. The "Superstrut" conversion for the Corollas involves machining a ST185 GT4 disc down to 260mm (from memory, cant be much more than that). Many people are running this conversion, including my own car, and havnt had any issues whatsoever. I did mine on normal DBA slotteds, and im not entirely sure on how the Kangaroo paw design would hold up, but all i can see it doing is reducing the surface area mildly, but also by the same token reducing the amount of heat able to be held.

Here is the brake upgrade article on Twincam.org (http://www.twincam.org/forums/index....&hl=superstrut)
Hope that helps.

[TooF]

thomas: he is grinding the diameter not the thickness.



as far as grinidng the diameter i would suggest not to use slotted discs for this.. as DBA dont slot all the way to the edge.. this prevents cracking at the edge where the slot it.. however if you take 20mm off this you will have the slots all the way to the edge which will promote cracking at this point.

consider DBA750 I can confirm these work a treat with the JDM twin piston calipers you will only need to get them redrilled to 5x100 from the 4x100 they come in.

[Thomas]

My mistake

[StuC]

i have a set of the twin pistons on with the standard st162 fronts discs. not ideal but no problems as yet. i'll be upgrading to the larger Aus Spec single piston/rotor combination in the near future. i suggest you do the same. then you'll hvae no problems with finding a slotted/drilled rotor.

[Aust162]

Thanks for the input guys

I will have to find out about grinding the kangaroo paw disc from the DBA guys, but its good to see grinding them down should be ok..

With regards to the slotting, i suppose i could get the standard disc, then grind them. I also know someone who can properly slot the rotors afterwards, so i wont have the issue with the slots going right to the edge

Stuc: I doubt the larger single piston and disc's will clear my wheels. they only just clear with the twinspots atm. The wheels are 14's and i dont want to change them.
Thanks for the info though

[TooF]

no the single piston items will not fit under 14" wheels.. the twins will *just* fit in.

my suspiscion will be that dba will give a resounding no in terms of grinding the kangaroo paw, reason being is that it is designed to have the "toe" of the paw on the outer edge providing strength.. cutting into this will comprimise the strength moreso then a standard straight or curved vane disc.

[Youngy]

Not sure if the slotting to the edge is an issue. On the home page - http://www.dba.com.au/default.asp - they show the 4000 series using the "wiper slot" pattern with a slot very much going right to the edge.