Front disc's fitted backwards!! - The Unofficial BMW M5 Messageboard (m5board.com)

ECM4 · 9th September 2003, 19:35

This sounds daft but its true.....

There I was working my way through an Inspection 2, took the front wheels off, stared at the front disc's (as you do!) then realised they were fitted on the wrong sides.

Theses disc's (at least the larger disc's fitted to the 18", 6sp) are unusual in a number of ways but the cooling fins are 'fluted' in much the same way as the vanes in a centrifugal pump. Mine were facing forwards into the air flow. This is incorrect and would cause the exiting air to stall. I've swapped them over.

Stick you're hand through the top of you're wheel and poke a finger into the slot. The flutes should be facing backwards.

Anybody think different?

Alan Archer · 9th September 2003, 19:44

Never looked closely at the full floaters
however i was thrown when i bought my 3.8 and the
throwing stars were on the wrong way....

I was convinced they were ok ( dont see enough on the road
to compair do you..) until I looked in the handbook.

The solid edge faces fowards, the fluted end towards the rear of
the wheel, hence after much headscratching ive decided they extract the air, not draw it in...

I suspect the same maybe true of the disc rotors...they draw
air through & out through road wheel away from the car.

Hmm, have i opened an engineering can of worms...???!!!

Anyone else comment ???

Alan.

ECM4 · 9th September 2003, 19:51

Alan,

I think it was me that opened the can of worm's...............

The air gets sucked in through the centre (from both sides, very unusual for a road car!) and flung out through the slots.

Imagine dropping a blob of paint onto a spinning disk. It would be thrown outwards but would leave a scroll pattern similar in shape to the fluted fins inside the big disks.

Does that sound convincing?

durt · 13th September 2003, 20:06

alan - my beast has been fitted with 4 number of the same handed throwing star's - i think left - but immaterial i suppose - would i be wrong in saying that bmw "disk" only shows left hand covers ?

M5 powered · 14th September 2003, 01:57

Air on the 345mm is indeed sucked through the centre and out the disk. The disc design is quite unique as you'll notice with the row of spindles allowing optimum flow + allowing the switch to more exotic materials if they became avaliable (I'm sure this was actually stated in the '95 blurb).

As for the orientation of the disks YES they are specific with two seperate part numbers. PLEASE check you are supplied with the correct ones. The rears however can go on either side!

In reality you won't be effected unless you happen to live at the track. Still, worth getting right though!

Regards

M5 Powered

Marek · 16th September 2003, 20:03

It happened to me as well when I was fitting the big brake kit onto my 1991 E34 M5. The air should be sucked in through the centre and exit through the vanes. For the non-believers the disks are marked L & R (left and right in English and German).