Early (2003) Rear Calipers

[Ratcatcher]

As part of the ongoing refurb, i was thinking of swapping out the rear calipers with some exchange units but i noticed the websites state a difference between vented or unvented discs. My rear discs are currently vented but i suspect a previous owner fitted these so im now unsure whether these are standard ie were they unvented previously Or, were the vented ones standard on a 2003 2.5i?

The obvious answer here is that the current calipers wouldnt have fitted vented discs if unvented were original, but i just wanted to make sure before i purchase.

As usual, any info is much appreciated.

[BumpyZ4]

According to RealOEM the 2.5 came with non-vented discs. I check up to 11/2005 build date.

[Ratcatcher]

According to RealOEM the 2.5 came with non-vented discs. I check up to 11/2005 build date.

Good plan, and yes youre right, the non vented discs are for the 2.0/2.2/2.5 and vented for the later 2.5si/3.0 models. So i have the 'wrong' discs on the back. Question is, do i have the matching calipers........

[patriot66]

According to RealOEM the 2.5 came with non-vented discs. I check up to 11/2005 build date.

Good plan, and yes youre right, the non vented discs are for the 2.0/2.2/2.5 and vented for the later 2.5si/3.0 models. So i have the 'wrong' discs on the back. Question is, do i have the matching calipers........

The answer to that question is yes. The calipers that fit over an unvented 2.5i rear disc are physically 'narrower' than the 3.0i calipers that fit over the physically thicker vented disc.
I have just recently completed a 3.0i brake transplant onto my 2.5i using a mixture of new and old refurbed parts. Just for your information the front calipers are common to 2.2i, 2.5i and 3.0i. It is the disc size (300mm dia) on the 3.0i that is bigger and the actual caliper carrier is 'larger' placing the caliper further out on the larger diameter disc.
Photo of rear 2.5i unvented disc

20210311_170625.jpg (186.92 KiB) Viewed 488 times

Photo of rear 3.0i vented disc and 'wider' calipers

20210403_164051.jpg (211.15 KiB) Viewed 488 times

Have a look on https://www.realoem.com/bmw/enUS/select
for all the parts numbers

[Ratcatcher]

Cheers! Yeah, i looked at new discs last night and the unvented are 10mm thick whereas the vented are 20mm. Im coming to the conclusion that the unvented calipers wouldnt physically fit over the vented discs and looking at your photos, theres a definite difference in the throat profile of those calipers. I shall check later which ones i have.

[Ratcatcher]

Well, something didnt look quite right to me so after a chat with my local BMW garage, the parts guy volunteered to order the caliper and mount in for me to look at. Top Man! It seems that it is possible to fit the wrong caliper on the vented discs but i suspect they will only work with full pads. Anybody have a pair of 3.0l rear calipers they dont need????

PXL_20210514_130805831.jpg (106 KiB) Viewed 404 times

PXL_20210514_130753006.jpg (145.83 KiB) Viewed 404 times

[patriot66]

Well, something didnt look quite right to me so after a chat with my local BMW garage, the parts guy volunteered to order the caliper and mount in for me to look at. Top Man! It seems that it is possible to fit the wrong caliper on the vented discs but i suspect they will only work with full pads. Anybody have a pair of 3.0l rear calipers they dont need???? PXL_20210514_130805831.jpgPXL_20210514_130753006.jpg

I agree, theoretically possible to fit the 'wrong' 2.5i calipers over a 3.0i 20mm thick vented disc. However, there wouldn't be much room for full pads, if any at all....they would have to be down to the backing plates !
Have a look at the these two photos:
1) 2.5i caliper and carrier, 10mm unvented disc, almost new with almost new pads

20210311_170632.jpg (145.6 KiB) Viewed 390 times

2) 3.0i caliper and carrier, 20mm vented disc, almost new with brand new pads

20210403_164022.jpg (126.83 KiB) Viewed 390 times

As you can see you definitely couldn't squeeze a 2.5i carrier over a 3.0i disc !

[Ratcatcher]

I hear you, but thats whats been fitted to my car. ie smaller carrier and caliper on a vented disc! I did think that it might have been larger carrier and smaller caliper that had been used hence the check with both stock items.

If i get chance ill remount the brakes later to take a photo but tbh, its all bit worrying how this was done.

[Ratcatcher]

I agree, theoretically possible to fit the 'wrong' 2.5i calipers over a 3.0i 20mm thick vented disc. However, there wouldn't be much room for full pads, if any at all....they would have to be down to the backing plates !

What diam are your rear discs, i wondering if a smaller disc has been fitted to allow the clearance...

[patriot66]

Have a read through this post from quite a few years ago. All brake sizes and combinations described in detail
viewtopic.php?t=8399

[Liam22]

Photo of rear 3.0i vented disc and 'wider' calipers

What are you painting those discs with? Does it last?

[patriot66]

Photo of rear 3.0i vented disc and 'wider' calipers

What are you painting those discs with? Does it last?

Black and Blue Hammerite Smooth. It loses its shine slightly over time but it never flakes, chips or rusts through. Looks much better than red rust

[Liam22]

Black and Blue Hammerite Smooth

Nice. Thanks.