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E28 ('86 524td) brake upgrade to M3 calipers? M5??

Posted: Mar 31, 2021 1:52 PM
by 524td-primary
Will M3 or even M5 calipers (and rotors and pads) fit on my E28? If so, what year or make/model calipers would you recommend? I would be very grateful for as much detail as you'd care to give here, even including part numbers and vendor/store names where they're available if you happen to have them at hand.

I was told a few years ago that I could easily upgrade my front brakes to M3 calipers, etc. So,---and here comes the rip-off story--I paid a kid (he's in his 30's; to me, that's a kid) to buy me new M3 calipers, rotors and pads and install them. At that point I figured out that I'd need larger wheels to accommodate the larger calipers, so I went ahead and took the hit on the $$$ and bought some used 1991-ish BMW 17" wheels (and tires) and they fit just fine with H&R's biggest spacers; they actually look great. Cut ahead to 2 weeks ago; I went to another shop to ask them to change out my rotors. It took them all day, along with them taking 2 trips to separate parts stores trying to figure out the mystery that baffled them, only for them to finally figure out that the kid I mentioned had installed calipers made for a Mercedes and that the threads on one of the calipers' pins was irreparably stripped and probably was in that condition when the kid installed them (probably pulled by him out of a junk Mercedes he'd been working on). Live and learn.

Anyway, I want to get new, bigger calipers on my front brakes like I tried to do 2 years ago, but this time I want to buy the parts myself and do it right! ...without that kid's wonderful help. Please tell me what calipers I can put on my car.

By the way, I know there are many brake postings on this blogg, but I used this site's search engine and started getting buried in responses. For instance, I typed "brake upgrade," which gave me nothing. Then I typed "M3 brakes," which gave me 14996 matches. So, please be patient with me as I'm not a computer guy and I easily get lost trying to do what I would have thought were some very basic topic searches. ...and PLEASE don't be one of those guys who replies with generalized/non-specific (and useless) advice or a comment that says "hey pal, there are tons of articles already posted on this blogg that answer your query" (unless you can kindly email me the web link to those postings).

Re: E28 ('86 524td) brake upgrade to M3 calipers? M5??

Posted: Mar 31, 2021 2:03 PM
by austin8753
e34 540i (1994/1995 540i) calipers/rotors/pads are a direct, bolt on solution and will be (likely) the most cost effective option for you.

Re: E28 ('86 524td) brake upgrade to M3 calipers? M5??

Posted: Apr 02, 2021 2:21 AM
by RobertRO
Based on my experience with upgrading brakes on an E28 535i and an E32 730i, I have a slightly different suggestion.

Yes, you can go with the front and rear brakes of an E34 540i, and you will end up with a very capable brake system. You need all the brake components, downstream of the caliper brake hose (and preferably swap new hoses, too): caliper brackets, calipers, rotors, brake pads, clips, wear sensors.

However, I believe that the brakes of an E34 520i, 525i or 535i are a better choice, in your particular case.
They provide (about) the same braking power as the 540i brakes, considering that the rotors are the same diameter (302mm front, 300mm rear), and the caliper brackets and brake pads are identical.
The pistons of the front calipers have the same diameter for all E34 models: 60mm.
The pistons of the rear brake calipers are different: 38mm for 520i/525i/535i, but 40mm for 540i. It means that the front/rear brake bias is slighly different on 540i. However, if you go for the rear brakes of an E34 Touring (= not sedan), their rear calipers also come with 40mm pistons, thus the same braking power as of a 540i.
The main difference comes from the rotor thickness. The 540i comes with 302x28 mm vented rotors front and 300x20 mm vented rotors rear. All the other E34s come with 302x22 mm vented rotors front and 300x10 solid rotors rear.
You get superior brake fading endurance on 540i. But it is very unlikely that you will need that extra endurance on an E28 524td, considering the weight of the car, the power of the engine, and its top speed. I assume you don't track your car in a hard way, do you?

But the beauty of the E34 520i/525i/535i brakes comes from their weight. They are lighter. You save about 0.7 Kg per side in the front, and 0.8 Kg per side in the rear. It does not sound much, but it's unsrpung and rotational mass. Coupled with not such a powerful engine, your car will accelerate better with the lighter brakes, while having the same stopping power as with the 540i ones.
Thus my recommendation to go with E34 520i/525i/535i brakes.

Note: I see that you already added quite a lot of rotational mass by installing 17" rims. You really do not want to further increase it.

Re: E28 ('86 524td) brake upgrade to M3 calipers? M5??

Posted: Apr 02, 2021 11:22 AM
by 524td-primary
Thank you, Austin and Robert. Excellent input, and very helpful. I have an upgraded/newer diesel engine that's much more powerful than the stock engine was, but it's got some big bugs that I haven't been able to work out since the newer engine was dropped in. Even with those bugs, though, the car is much more powerful and about 60% of the time it accelerates in a way that gives me great joy (or at least a modest surge of adrenaline). What I'm getting to is that I ride that car very hard, and it's my primary wheels (thus, my blogg name "524td-primary"). The e28 handles so excellently that it's hard not to take advantage of it. That's why I didn't think twice when it was suggested that I put larger brakes on the front. But when I added the larger wheels and very thick H&R spacers a couple of years ago, no one ever mentioned to me that I'd be adding weight to my wheels that could affect performance or other factors. Wow. I had no clue. Thanks for the education on that. One more thing: the person who advised that I could/should put larger brakes on the car said that it's quite common to only upgrade/enlarge the front end e28 brakes, which is what I did since most of the braking happens up front, I believe. So, when I go ahead and do this latest upgrade, is there a compelling reason I should also put the larger calipers, etc, on the rear as well?
Thanks again.

Re: E28 ('86 524td) brake upgrade to M3 calipers? M5??

Posted: Apr 05, 2021 2:37 AM
by RobertRO
Upgrading only the front brakes it's not such a good idea. You will unbalance the front/rear brake bias of the car, meaning that the front brakes will be too strong compared to the rear ones.
Here's some data. Your E28 has 57mm brake pistons in the front and 33mm in the rear, with 284mm brake rotors front and rear. The E34 comes with 60mm brake pistons in front and 38mm/40mm in the rear (depending on the model), and 302mm brake rotors front / 300mm brake rotors rear.
Ideally, you should also swap the brake master cylinder, but a lot of E28 cars had their brake system successfully upgraded while still using the stock master cylinder.