DIY E46 320 to 330 Rear Disk Brake Conversion Process

I have started a 330 rear brake conversion. After a lot of research, I came to the conclusion that the only limitation for a direct bolt on upgrade, is the inner diameter of the 330 rotor, which is larger, requiring the e-brake assembly from a 330 to be transplanted to the lower model cars in order to work properly.

There are 3 solutions available for this retrofit.

1. Find the entire rear e-brake/hub assembly of a 330 and transplant it, which is expensive and not worth it imo.

2. Fabricate a spacer and press it/weld it inside the 330 rotor to create a smaller drum diameter so that the original e-brake can work. Not good because it will add more weight to the already heavy rotor, it will throw rotor off balance, and each time a rotor will need replacing, a new spacer must be manufactured. Also, difference in materials used will probably create a problem with heat expansion.

3. Fabricate custom brake shoes, with the mounting base of a 320/23/25/28 and the proper length to reach the standard 330 rotor drum diameter. I chose to follow this method for the following reasons:

a. I have access to laser cutting / waterjet equipment, and I will be able to manufacture the brake shoes with the proper dimensions.
b. I have access to brake shoe manufacturer therefore I will have no problem making the design I want.
c. Once the original design works, I will be able to fabricate virtually any kind of brake shoe, enabling anybody with a 320/25/28 to upgrade to rear 330 brake setup with the lowest cost.

The advantage of this method is that, reversing to OEM will be as easy as just putting oem rotors back with oem brake shoes. To save on the expense of buying 330 rotors and begging mechanics, I'd like to know these dimensions, exactly please, if somebody happens to have them.



Also high quality pictures of the rear hub, assembly would be great After the correct CAD design is done, it will be a matter of just mass producing these things. Anyway, waiting for measurements etc

Oh please oh please sign me up for this!

I can't help you with the dimensions but I'd love to see this succeed and buy a set of pads off of you

Hopefully it will work. Materials are very cheap too so it will be a nice project. Luckily the waterjet machine can virtually accept any drawing format, so I decided to use Autocad for the design of the brake shoe. It will take time though but hey, better late than never

Nobody? Can't imagine no-one has a rear 330 disc lying around

apparently so
I'll have to go to a couple of shops here with the hope they will have a rotor to give me.

This would be a very interesting thing. The only real thing holding me back for a 330 brake upgrade were the costs of the e-brake upgrade.

But i don't have any dimensions on 330 e-brake/brake assembly.

I'll be going to the dealership tomorrow for maintenance shopping, I'll ask them nicely if I can measure up the inside of a 330i rotor.

I will want this for an M3 rear brake, btw, but I can ask my aftermarket parts supplier, when he gets his M3 back, to do the same.

I'm PM'ing multiple forum members for input on the M3 rear brake retrofit they did in the past, but am not yet getting conclusive answers. Everyone seems to say on the forum that it's a "big problem", but I haven't yet found out if that's simply because of the parking brake, or something. If the caliper & disc bolt up fine, we might as well do this whole thing for an M3 brake.

Thank you in advance! Over here the dealer for some reason doesn't want to give me 1 used rotor. Like I will copy it or something. I haven't thought about the M3 rear brakes, but essentially the only thing that we can do is just measure the distances to see if the M3 caliper will bolt on fine. Today I received my rear 330 brake calipers, used, but seem in very good condition along with a set of hardly used pads! During the weekend I will take them apart and start the reconditioning process.

7 1/4 exactly....which seems strange but I triple checked. This was with a tape measure as my calipers aren't big enough. I'll see if I can get a calipers and double check but even if I'm off a tiny bit the adjustment in the ebrake should compensate.

Tim

Doesn't the parking brake pads mount to the dust shield, so all you need is the 330 dust shields to make this work?

Originally Posted by tim330i

7 1/4 exactly....which seems strange but I triple checked. This was with a tape measure as my calipers aren't big enough. I'll see if I can get a calipers and double check but even if I'm off a tiny bit the adjustment in the ebrake should compensate.

Tim

Excellent!! Thank you!

Originally Posted by nite-stalker

Doesn't the parking brake pads mount to the dust shield, so all you need is the 330 dust shields to make this work?

No, you need the entire hub assembly

Originally Posted by tim330i

7 1/4 exactly....which seems strange but I triple checked. This was with a tape measure as my calipers aren't big enough. I'll see if I can get a calipers and double check but even if I'm off a tiny bit the adjustment in the ebrake should compensate.

Tim

Great, thanks! Saves me the humiliation because I was almost on my way to the dealership... and intended to bring calipers that also would have come up short

Thread revival...

Ordered a set of rear 330 brake shoes. A friend of mine will transfer them in Autocad along with a 330, 320 inner rotor design and 320 shoes and we will fabricate a prototype bracket on which an actual shoe will be welded on. Stay tuned Once the final CAD is ready.. well ... it can be produced I guess more easily

Keep us posted

I dont think all this trouble is worth it. What performance are you going to get out of this?.

Cheaper then replacing the rear Trailing Arm for Drum E-brake...

Originally Posted by gewse

Keep us posted

Will do for sure!

Originally Posted by n2Bimmer

I dont think all this trouble is worth it. What performance are you going to get out of this?.

less brake fade. I know you will say rear brakes don't count as much but hey, I got the rears to become blue after some spirited driving rendering them useless. So, bigger is better. Plus, rear calipers go for peanuts. I already started taking the calipers apart to paint them.

Originally Posted by TrippinBimmer

Cheaper then replacing the rear Trailing Arm for Drum E-brake...

true plus it's a fun project to work. And plenty of time as my brakes don't need changing.

well good luck hope it pays off.

This is the current 320 rear e-brake setup. The inner diameter is 160mm
According to the measurement Tim took, the inner 330 diameter is 184mm. 184-160=24mm (About an inch). So each brake shoe must increase by only 12mm to compensate for the rotor diameter increase. That's not too bad. Till the 330 shoes arrive (hopefully) I will have found a used 330 rear rotor - a bit difficult considering there are 30-40 330 E46 across the country.

keep us posted!