bmwe21.net forums

Hey Guys
I did a big brake conversion on my 81 323i, 300mm front rotors with vt commodore calipers on the front and standard discs on the back with e30 calipers, all pretty standard for Australia. However now i have found the master cylinder isn't up to the job. So my question is who has put what on a rhd e21 (with the booster up near the rh head light)? Im happy to do a booster and master swap if need be, but the booster cant be to big because im fitting an m50 in a month once im on holidays. So go nuts guys let me know what is possible?
Oh and i can post pics of what i have done so far if anyone wants to see how to do the commodore rotor and caliper swap and FYI for people that are, the rotors are factory vt commodore rotors and you can buy blanks off DBA Australia and they can drill them to suit. I didn't Because i purchased a set of a guy that had them drilled and then never used them.
Cheers Callan

you can in theory use a 4 port master (which are a little more rare and expensive) or just get a two port master which are cheap and common, then use a T piece to make the lines go to each front brake.

what I did was fit a brake bias pedal box, but im not sure if your allowed to do that on a road car in oz? If you go that way then I highly recommend a floor mount setup, it will be way easier then the hanging pedal bias box that I did.

my bias box works really well. but I had to weld in a lot of bracing to stop it flexing.

What 4 port or 2 master cylinders (MC) fit up to the factory booster? its so hard to find accurate info on the spec's of various MC's!
Im not sure if adjustable bias setup's are road legal or not, id have to look into it. But i wanted to keep it quite cheap so it might be a bit too costly for me.
Oh cost is also my reason for not using the e12 MC.
I was told by e21-mark that 944 MC's fit but my concern is the step in the 944 cylinder from 23mm to 19mm bore diameter, which would give the rear brakes 1mm less bore diameter than it currently already has. Im not sure if this is or isn't a problem though, has anyone done this or know of it being done.
I found that early 928 MC's have the same 23mm bore except they are not stepped, also they look remarkably similar to 944 MC"s, has anyone fitted or know if they can be fitted?

My advice is to go to a brake supplies type of shop or look at an online catalogue.

I don't know what other masters work but the mounting is fairly standard size from what I see. The push rod might be your biggest problem.

Lemonayd is possibly the man to answer the 944 question? I'm pretty sure he runs a 944 m/cyl that was the same more size as the e12 535 item, but with 2 outlets that were blanked off.

I may have dreamed this though but it seemed remarkably real. Hopefully Ayd will be along shortly to confirm or deny.

I have been in my local parts suppler but your right i might have to go to ABS (Australian brake specialist) and see if they have more detailed info.
Cheers mark i appreciate all your help.

Do you have any dimensions on the rear of the MC where it fits into the servo? Just curious to compare with the few MC's off VW's and such that I have kicking around,

Could the e32 25mm master cylinder fit? This is a common mod on e30s. The shaft diameter might be different (12mm vs 10mm?) but you could lathe down the e21 shaft & rethread if this is the case like the e30 guys do when using the e21 booster for M50 swaps.

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A bigger master doesn't always mean better brakes. You need to match the master to your caliper pistons.

What's the exact problem? Too much travel?

What's the Commodore 64 use for a master? That's the size you probably need.

Isn't a commodore 64 a crappy computer from the 80's?

Haha yep thats a game console
A VT commodore is a large sedan that is sold mainly in Australia its similar in size to a 5 series.

nas80 wrote: What's the exact problem? Too much travel?

What's the Commodore 64 use for a master? That's the size you probably need.

The bore size of a commodore MC is Bore Size: 25.40/31.75mm and yea the issue is pedal travel, the reason why im doing it is because i want to match the master better to the brakes as you said.

luke wrote:Could the e32 25mm master cylinder fit?

No idea luke i was wondering about this too if anyone has a definitive answer please chime in. I think that e30 MC only has the 2 outlets if i'm right? which means id have to put a t piece in which isnt a huge problem but i have no idea on the input specifications.

polov8 wrote:Do you have any dimensions on the rear of the MC where it fits into the servo?

I have a spare e21 MC in my storage shed ill go over and measure it. The biggest issue is that i cant find any info on various MC specifications other than bore diameter which is so bloody annoying

Measured a few MC's I had kicking around, all ATE, a 20mm one from a late 90's polo, a 25mm one from similar era Mondeo, and a 22mm one off a golf, all with the following dimensions.



Be interested to learn how the E21 cylinder compares

nice contribution polo v8

Agreed, great work Polo v8.
Im going to get my e21 MC today so ill whack some vernier calipers on it and let everyone know the specs.
All this support is awesome, cheers guys!

Ok hear are the measurements of my e21 323 MC i stole Luke v8 pic to make it easier to understand the various measures.

Also i measured a e30 master cylinder and it was the same so i ordered a e32 25mm MC and fingers crossed its the same as well! i figure since e30 guys use e21 boosters and e32 MC's there is no reason it wont, ill keep everyone updated.