e32 & e34 rear rotors- what is the difference?

[genphreak]

The e32 and e34 have essentially the same calipers, carriers, shocks, springs (w a different rate) & even wheels, so can someone (for dummies like me) please shed some light on why the rear rotors are a different part between the 5 and 7 series? Bruno says on his site that e32 rotors do not fit e34 but for I can'r see why they wouldn't as all the parts around them, (excepting the output flange/hub/bearing) are the same.

So why the rotor difference? If you used e32 hubs also, you would be able to fit e32 rotors. Would this widen the car's track perhaps? (just guessing this might be the reason the parts are different)

EDIT: The online ETK lists the rear hub assemblies (or more specifically the 'side shaft' #33411134877) as specific to the 5 or 7 series. The trailing arms that these mount into are common, so there is definately nothing to stop you swapping the side shaft, bearing and output flange (if necessary as these are common on some models) and then using e32 rotors.

btw; if anyone has an e32 rear rotor hanging around that they can measure and compare this would be a great help.
The overall dimensions of a standard e34 520/525/530/535 rear rotor is;
11 25/32 inch diameter 2 25/32inch overall height

[Bellicose Right Winger]

According to my ETK carriers and calipers are not the same on 9/89 build E32's & E34's. Likely due to different rotor dimensions, E32 rotor is 300mm x12mm thk, E34 is 300mm x 10mm thk.

Paul Shovestul

The e32 and e34 have essentially the same calipers, carriers, shocks, springs (w a different rate) & even the wheels, so can someone (for dummies like me) please shed some light on why the rear rotors are a different part between the 5 and 7 series and why the e32 rotors do not fit e34 (as described on www.bmwe34.net's bigger brakes page)?

It seems to me that everything else is the same-except perhaps the hub and bearing, so why the rotor difference? If you added e32 hubs also, would you then be able to fit e32 rotors and widen the car's track perhaps? (just guessing this might be the reason the parts are different)

EDIT: The online ETK lists the rear hub assemblies (or more specifically the 'side shaft' #33411134877) as specific to the 5 or 7 series. The trailing arms that these mount into are common, so there is definately nothing to stop you swapping the side shaft, bearing and output flange (if necessary as these are common on some models) and then using e32 rotors.

btw; if anyone has an e32 rear rotor hanging around that they can measure and compare this would be a great help.
The overall dimensions of a standard e34 520/525/530/535 rear rotor is;
11 25/32 inch diameter 2 25/32inch overall height

[genphreak]

According to my ETK carriers and calipers are not the same on 9/89 build E32's & E34's. Likely due to different rotor dimensions, E32 rotor is 300mm x12mm thk, E34 is 300mm x 10mm thk. Paul Shovestul

Thanks Paul, you just uncovered the same thing I mailed Bruno about- see my previous post. The 12mm is used on all 735i and 735il but no e34 as you say. But that doesn't mean it won't fit- it just depends on the actual differences in the rotors and the hub assemblies. Evidently BMW vary the size of these along with the thickness of the carriers in order to align the braking components in just the right place, however on e32 they seem to have modified the rotor (...somehow) too.

It is quite possible, that along with e38/39 components, that there are as yet undiscovered combinations that would work, hence my posts trying to pool our collective knowledge on the subject. Nick

I sure wish we had a breaking yard w access to a few vehicles so we could work this stuff out...

[angrypancake]

there is/has been a set of e38 4pot calipers on ebay for a while, saying "with a small bit of drilling can be made to fit an e34." i'll email the seller

[genphreak]

there is/has been a set of e38 4pot calipers on ebay for a while, saying "with a small bit of drilling can be made to fit an e34." i'll email the seller

Thanks ap, I know the one, but I think he needs some niggling to reveal the secret. He was claiming that one needed to fabricate a bracket. I'm glad I'm not the only one to want to know exactly what kind one needs to make... somehow I doubt he'll go so far as to include a diagram for his customers... or even specify exactly what rotor and carrier combo one needs.

[Johntee540]

is that the guy in Malaysia? I think I have seen those - JT

[Kalevera]

Nick -- just a thought, here. Around '91, there was a change to symmetrical hub flanges (at least on the fronts)...That is, symmetrical WRT the location of the rotor retaining bolt. Cars previously used an asymmetrical pattern. Ergo the rotors and rotor part numbers changed. I was looking at this a few weeks ago on an E31 -- from what I remember, the flange changed with the 4pot introduction. Seemed to happen at different times with different cars -- E34s were around '91, as previously mentioned. Don't know when the E32s changed, if at all. And despite the fact that I had the wheels off of an earlier E32 today, I can't remember the specifics. Have a 735 in the parking lot, though, if it comes down to that.

best, whit

[genphreak]

is that the guy in Malaysia? I think I have seen those - JT

Yep, he's the eager beaver with the gold-plated black calipers...

[genphreak]

Hi Whit, yes interesting that- I expect that the hub sizes are tweaked on some cars fit a particular rotor and carrier and caliper combo. I haven't looked into the front much, but I can just smell other options... perhaps the manuals will tell us something as they might be adjusting the track of the cars with the bigger brake setups. Its funny, but those 750is do look super -phat for some reason I can never quite put my finger on...

So it might be important to note that e32 rotors might not fit e34 because BMW are adjusting the hub to position the wheel further out to suit the wider body of the 7er.

Essentially I think what all this is proving that the front and rear hub components are mostly compatible on these era BMWs- all one has to really do is change the rotor, caliper and carrier in most cases but the hubs assemblies in others- its just the testing of this that is hard without having parts to compare or cars to try it out on.

A few mm further in or out may actually be OK for e34 too, or even advantagous depending on the wheel setup, but it will most likely cause too big a difference. One simply doesn't know until one tries (or measures up) an e32 rotor and hub assembly or actually try fitting them on an e34.

Anything that comes with a V12 is a candidate for a check of the brake setup. I expect for rotors larger than 302mm dia. they would have used different caliper and disc combos. I'm sure it'd be hard for you to find the time to check this out on the cars you mentioned, but I'd sure love to know if you do! Also, Erich might be able to tell us something more when he gets back, Cheers, Nick