What are the benefits of a E12 brake master cylinder?

[Grass Hopper]

My Question:
What are the benefits of using a E12 brake master cylinder instead of a E21 master cylinder.

Reason:
Because the brakes on my car suck, and I think my master cylinder might be leaking. I dont have an extra E21 master cylinder, but I do have a E12 master cylinder laying around.

Background:
I just upgraded my front brakes to vented last week. I'm pretty sure my rear drums are not working (Need adjustment). I'm not going to bother with adjusting them, in about a month I am putting on some 323 rear disks (Already have them, waiting for the school semester to end). While I have everything apart I'm going to change out the brake lines and rubbers, and basically anything on my brake system that needs replacement. So my brakes will perform like new. While doing this, should I change out the master cylinder to the E12 one, or just rebuild/change my E21 one? What are some gains/disadvantages I'll get?

Alittle extra info:
Currently my brakes barely work. The brake pedal has to hit the floor in order for the car to slow down, and it still takes a while and will not lock up. The old non-vented brakes easily locked up, so the new ones are better. But the stopping distance hasn't changed much. I did not rebuild the vented calipers, but when I change out the rears I'm going to rebuild them (Waiting so I can powder coat them/rebuild them at the same time, plus I need to focus more time on school atm)

[mdschurtz]

it almost sounds like you have air in the brake lines. maybe try rebleeding all the brakes

[edennelson]

X2 bleed the system if you have not already.

Sent from my iPhone using BF.com

[Tom D]

you definitely have either air in the lines or a leaking master so here's a piece of advice;

Stop Driving The Car! at best you'll get away with it (faulty brakes), at worse you'll kill somebody!

[Layne]

The E12 one has a bigger piston, so you'll have less pedal travel but require more force to do the same work. It's exacly like lifting a rock with a lever, the E12 lever is shorter than the E21 one. There's no harm in using it.

If you can't lock the wheels you should not be driving the car. Vented brakes don't change anything except the cooling ability. They should feel and behave exactly the same, because they ARE exactly the same (up to the point that the non-vented ones would start overheating).

[Grass Hopper]

I should probably mention that I'm not driving the car lol. Its just a project, the car is sitting in my garage and wont be driving till atleast another month and after I change the rear brakes. I dont want to drive it because of the brakes. Also re bleeding can work, but I'm not driving the car anyways

My daily driver is my E36 in my sig lol, so dont worry everyone, I'm not driving the E21.

[Grass Hopper]

The E12 one has a bigger piston, so you'll have less pedal travel but require more force to do the same work. It's exacly like lifting a rock with a lever, the E12 lever is shorter than the E21 one. There's no harm in using it.

Thank you, this is the answer I was looking for. It makes sense.

So is it worth doing the volvo conversion? And if I do it, it'd probably be better to use the E21 cylinder

I really like having big powerful brakes. Even did M3 brakes on my 4 cylinder E36. I wouldn't drive a car that doesn't have adequate brakes. Also was a big difference driving my E21 around, then my E36 afterwards...

[Layne]

So is it worth doing the volvo conversion?

Going from vented stock to volvo? Not worth it in my opinion. The point of the volvo conversion is that vented stock calipers used to be really expensive. But the volvo has more piston area, so it has the opposite effect of the E12 master cylinder, which is why they usually go together.

[epmedia]

Loose rear brakes will make the brake pedal mushy too.

[Grass Hopper]

Going from vented stock to volvo? Not worth it in my opinion. The point of the volvo conversion is that vented stock calipers used to be really expensive. But the volvo has more piston area, so it has the opposite effect of the E12 master cylinder, which is why they usually go together.

So if I did the Volvo conversion then the E12 master cylinder would be good to use?

But if it's about the same then I should just keep the E21 cylinder, and stock vented rotors with rear disks

[Layne]

Yep. But if your master cylinder is leaking, I would use the e12 one over buying a new one. It's not that different, 23mm vs. 21mm I think. Also, the E21 one has a check valve that is needed for rear drum brakes, but has to be removed when going to disc. The e12 MC won't have this check valve.

[gsumzzz]

a properly set oem disc/drum setup will handle just about any street situation. hawk disc pads and ferodo drum pads set up correctly are very good brakes. new rotors and drums help as well. i drive pretty hard on the back roads and never felt like my brakes were thinking of leaving me (read brake pedal feel never changes). my rotors are not vented. if you track the car i can see a benefit to all discs. drums are so easy to work on.

[sonomaGTLN2]

Layne, how is the check valve mounted in the E21 MC? I wasn't aware there was one and this is relevant because I'm doing a 323i rear CA swap soon. There's the residual pressure valve in line with the rear circuit on the lower firewall, but I didn't think there was actually something IN the master cylinder.

[Layne]

Well I might be wrong since I haven't done it myself, but I seem to recall that the check valve (residual pressure valve) is a brass fitting in the rear circuit output of the master cylinder. I believe that the input and output threads are different which means you have to gut the valve as you cannot just remove it. The one on the firewall is the pressure limiter for the rear that keeps them from locking up before the fronts do, same as a bias valve but not adjustable.

[sonomaGTLN2]

Alright, when I get to removing it I'll get back to this thread and my build thread. In addition I'll be installing an adjustable bias valve for the rears.

[Tom D]

I'm with gary on this one, with hawk pads and ferodo shoes my stock vented rotors and drums can easily overpower my 205 HP tires. the only way I can improve my braking system is with better tires.