So I'm revisiting this modification, seeing as I couldn't find any definitive answers. We’re talking about fitting a larger master cylinder to match larger calipers.



First of all, let's go over the hydraulics in the stock systems. The R53 front pistons have a diameter of 48 mm (unless you have the rare JCW calipers). R56 cars have a piston diameter of 52 mm, unless you have the gen 2 JCW 4 pot Brembo calipers Anyway, the 52 mm single piston in the floating caliper is roughly equivalent volumetrically to the four 38 mm pistons in the solid mount Brembo caliper. (I explained why & did the calcs in another post; if anyone is interested in that info, I’ll repost here). The brake master cylinder for the R53 car is 22 mm front and rear, but for the R56 cars, It's 23.8 mm for the front and 22 mm for the rear. All the rear systems are the same (hydraulically speaking) so we won't address that any further. This is the whole reason for wanting to upgrade to an R56 master cylinder if you’ve upgraded your calipers, you're basically just duplicating hydraulically what the R56 cars have stock, and that’s what the Mini engineers decided works best with 52mm piston floating calipers; or four 38mm piston fixed mount calipers (and as an engineer, I whole-heartedly agree with them!)




However, R56 master cylinders are made by TRW, and they don't bolt up to the R53 brake booster (the outside diameter is too large). I have found an ATE master cylinder that will fit and is the proper internal diameter (23.8 mm) & does bolt up, but it won’t work; at least, not as is delivered from the factory. In order to make it work, you have to modify the plastic divider between the engine bay and the master cylinder; and also a little bit of the sheet metal. You also need tweak the lines because the master cylinder outputs are in different positions. But most importantly, you will need to do some machine work to modify the master cylinder because it’s about 10mm too short. And I'm not talking about a little work with a die grinder and a hand drill. Nope, if you don't have a mill and a lathe, you're not going to be able to do this. You can't just put a spacer down in the piston because the load bearing surface of the piston is concave, and the push rod is convex. They do this for a reason, it’s self-centering, so the piston wont get cocked in the bore. If you put a flat spacer down there, you risk it flexing and/or cracking, during hard braking, which could prove catastrophic! Because the piston is about 10 mm too short, if you ran it without my mods, the brake booster would have full force long before the pushrod ever contacted the piston, making modulation nigh unto impossible; and the pedal would be almost down to the floor. There was a guy who maintained a website about racing Mini Coopers (trackmini?) who ran into the same problem and eventually shelved the idea. But I’m an engineer, I have a machine shop, and I modified the parts to make it work.



Having said all this, do I think the modification is worth it? Emphatically, yes! The pedal's much firmer, stays high in its travel, modulation is excellent, and the overall braking power is increased because the system has better front/rear balance! I ran with the stock master for about two years before switching over; now I’m wondering why I waited so long (other than having to re-engineer it to make it work). You will need to bleed the brakes with a pressure bleeder and cycle the ABS whilst bleeding. This can be done with Inpa, or with a Snap-on modus.



If you have the 135i 6-pot (or Gen 2 JCW GP) calipers, you will need a master cylinder with an internal front bore of 25.4mm. I also found an Ate master cylinder that meets those specs & does bolt up, but it is PRICEY! It too, needs to be modified as detailed above.





I’ve attached pictures, & as you can see, to the untrained eye it looks completely stock.



Now I know what you're thinking: Thanks a lot, Tom! You told us that it works great, explained why, and then you told us that it can't be done by the average guy. Well, fortuitously for you, I'm thinking about putting together a kit, if there is enough demand for it. If enough people want to do it, I may modify the way I machine the master cylinder, such that modification of the divider wall & sheet metal would not need to be modified.





Let me know what you think.

 

You have found another MC out there that meets the diameter ? Other than the e46 m3?

I would be keen to hear what you’ve come up with

 

IF...you are speaking of a larger diameter "piston"... cylinder ?

Better take a look into a book or two about brake systems !
Small piston, equals more pressure.
Larger piston, equals, more volume, moved.

Unless you install diesel truck brake calipers, the original Mini cylinder will be more than enough to "properly" actuate your calipers larger pistons. Your new piston diameter isn't THAT...large.

Mike

 

Did you even bother to read my entire post? I address what you mention. I am a mechanical engineer with 40 years experience. I've designed more hydraulic systems than you care to imagine. Lastly, if you're close, you can come drive the car & feel it for yourself.

 

Can we hear your solution ?

 

It's in my original post.

 

Yes you have given the dimensions of the proposed cylinder and piston to servo spacer
but no part number ?

 

Because it won't work as supplied out of the box, & it would be dangerous to mount it up stock (I address this in the first post). So I feel it would be irresponsible of me to supply part numbers that won't work without modifications which the average person isn't capable of doing. As I stated in my original post, if there is enough interest, I may make a limited production run.

 

Ok so your going to alter the piston on the master cylinder ?

 

There's a couple of different ways of doing it. Depending on how may inquiries I get, I may do it slightly differently for production. BTW, I posted only an approximate number for distance. To get the exact number, you'll need a coordinate measuring machine.

 

I suppose what we are interested in is what will be different with yours compared to the m3 e46 solution / spacer solution? This is better but doesn’t take out all the travel

I have read over your first post a couple of times and am unclear as the diameters seem to be the same as e46

 

Any further updates on this ?

I wonder if anyone has swapped both the m3 e46 booster and cylinder together?

the r56 booster does not physically fit the r53 as I have now checked this.

however the m3 e46 booster appears to look very similar in size to the r53 booster and shares the same vacuum port

At present I have a very good pedal using the standard mini booster coupled with the m3 e46 master, however there is just that little bit of mushiness remaining

 

Sorry I can't answer your question relating to the M3 booster, but I have been curious about the E46 M3 master cylinder and was hoping that you may further elaborate:

1). Difficulty of install?

2). Was it worth the hassle?

3). Noticeably big improvement or only a minor bettering?

The conversion kit available from Mod-A-Mini would perhaps remove the engineering frustration of installation, but I haven't been convinced enough yet (would love to hear your impressions and opinion related to the E46 M3 master) to proceed and query them if their kit will work on LHD cars...

...the kit they have available was developed by Minipit Racing and seems a good easy-button solution if one wanted to go in this direction.

 

I have returned back to my original 53 bmc. I can also confirm that the e46 m brake servo does not fit the r53 and the firewall would require significant modification.

I believe the solution to this is either a different bmc or a bmc servo combo.

I have also tried two sets of callipers with different sized pistons. The genuine r56 jcw brembos and stop techs 330 kit. Neither produced a good pedal. I substituted different pads before abandoning the bmw genuine pads including red stuff and yellow stuff then mintex. I also swapped out to dot 5 and bled the car with no improvement. I opened up th abs module thinking the issue lay there, however not the case. Bmw dealer in Glasgow again bled the car and confirmed the car had been bled correctly prior to their attempts.

Despite the correct bedding In procedure still no improvement to the overall braking and stability.

At Present my set up is jcw r56 4 pistons with yellow stuff pad and the original cylinder. It is by no means the outcome I was looking for.

I run the stoptechs on my track car with an aftermarket bmc that does not require a vac servo and the bite is excellent.

 

Aye!

Pure dead brilliant.

Many thanks for your quick response, it is greatly appreciated.

Glad also that you emphasized the proper bleeding had been done & confirmed by dealer as well so that can dispel the all-too-often cited response of "you dint bleed em rite" because whenever I've read someone complain of mooshy pedal then comes a chorus of that refrain.

Slightly bummed to hear your experience with the E46 M3 bmc didn't offer the good pedal feel we're all after because if it did the trick would be simple solution.

This modern MINI puts me in the pisser so much because it's such a glitchy b!tch to overcome all the computerized junk, and then even something as seemingly simple like this plain basic mechanical mod for better braking is a fuggin clustermuck as well. LOL

 

I can understand why people will say the pedal feels fine on the original mc with these brake conversations
I suppose it does the job, the car does stop more effectively, but the long travel just doesn’t give that instant bite / feel you want or expect when your running massive brakes on a relatively small car

I step into my 3 series with its garbage one pot tiny calliper lightly tap the brake pedal and it wants to put me through the windshield

For those who say it is air in the system, or worn parts.
I have changed every component in an effort to use the original master or the bigger e46 m3 mc. Including brand new lines, new master cylinders, .4 /.5 fluid new flexible lines and then braided and a new brake servo. I have even changed the vac hoses that run to the servo. All parts from the dealer, this was also checked by the dealership.

The system was bled using the correct procedure using bmw software to cycle the abs.
This was repeated many many times, countless litres of fluid, I even reverse bled the mc and the callipers at the calliper nipple to push air back up and out of the mc reservoir.
As mentioned the bmw dealership confirmed all air had been removed with no improvement on pedal travel. This is a 2007 gen 1 car.

I will be glad when someone figures it out and would welcome any thoughts or ideas. I would be quite happy to throw money at it to reach achieve a better solution.

 

[QUOTE=cut7;4660256]So I'm revisiting this modification, seeing as I couldn't find any definitive answers. We’re talking about fitting a larger master cylinder to match larger calipers.



First of all, let's go over the hydraulics in the stock systems. The R53 front pistons have a diameter of 48 mm (unless you have the rare JCW calipers). R56 cars have a piston diameter of 52 mm, unless you have the gen 2 JCW 4 pot Brembo calipers Anyway, the 52 mm single piston in the floating caliper is roughly equivalent volumetrically to the four 38 mm pistons in the solid mount Brembo caliper. (I explained why & did the calcs in another post; if anyone is interested in that info, I’ll repost here). The brake master cylinder for the R53 car is 22 mm front and rear, but for the R56 cars, It's 23.8 mm for the front and 22 mm for the rear. All the rear systems are the same (hydraulically speaking) so we won't address that any further. This is the whole reason for wanting to upgrade to an R56 master cylinder if you’ve upgraded your calipers, you're basically just duplicating hydraulically what the R56 cars have stock, and that’s what the Mini engineers decided works best with 52mm piston floating calipers; or four 38mm piston fixed mount calipers (and as an engineer, I whole-heartedly agree with them!)




However, R56 master cylinders are made by TRW, and they don't bolt up to the R53 brake booster (the outside diameter is too large). I have found an ATE master cylinder that will fit and is the proper internal diameter (23.8 mm) & does bolt up, but it won’t work; at least, not as is delivered from the factory. In order to make it work, you have to modify the plastic divider between the engine bay and the master cylinder; and also a little bit of the sheet metal. You also need tweak the lines because the master cylinder outputs are in different positions. But most importantly, you will need to do some machine work to modify the master cylinder because it’s about 10mm too short. And I'm not talking about a little work with a die grinder and a hand drill. Nope, if you don't have a mill and a lathe, you're not going to be able to do this. You can't just put a spacer down in the piston because the load bearing surface of the piston is concave, and the push rod is convex. They do this for a reason, it’s self-centering, so the piston wont get cocked in the bore. If you put a flat spacer down there, you risk it flexing and/or cracking, during hard braking, which could prove catastrophic! Because the piston is about 10 mm too short, if you ran it without my mods, the brake booster would have full force long before the pushrod ever contacted the piston, making modulation nigh unto impossible; and the pedal would be almost down to the floor. There was a guy who maintained a website about racing Mini Coopers (trackmini?) who ran into the same problem and eventually shelved the idea. But I’m an engineer, I have a machine shop, and I modified the parts to make it work.



Having said all this, do I think the modification is worth it? Emphatically, yes! The pedal's much firmer, stays high in its travel, modulation is excellent, and the overall braking power is increased because the system has better front/rear balance! I ran with the stock master for about two years before switching over; now I’m wondering why I waited so long (other than having to re-engineer it to make it work). You will need to bleed the brakes with a pressure bleeder and cycle the ABS whilst bleeding. This can be done with Inpa, or with a Snap-on modus.



If you have the 135i 6-pot (or Gen 2 JCW GP) calipers, you will need a master cylinder with an internal front bore of 25.4mm. I also found an Ate master cylinder that meets those specs & does bolt up, but it is PRICEY! It too, needs to be modified as detailed above.





I’ve attached pictures, & as you can see, to the untrained eye it looks completely stock.



Now I know what you're thinking: Thanks a lot, Tom! You told us that it works great, explained why, and then you told us that it can't be done by the average guy. Well, fortuitously for you, I'm thinking about putting together a kit, if there is enough demand for it. If enough people want to do it, I may modify the way I machine the master cylinder, such that modification of the divider wall & sheet metal would not need to be modified.





Let me know what you think.





Hi there,

What is the part number for the 24.5 mm cylinder? Thanks