Which master cylinder is best?

[jay castriotta]

I have always considered the 19 mm master cylinder as th gold standard in terms of upgrades, but I recently saw someone suggest a 23 mm master cylinder (would this result in longer travel, but a lighter pedal?). Why? Would this work with non power assist. I'd still like to see someone do a power assist on a 914. By the way, my questions are more geared towards systems with 911 type brakes.

[yoh!!!]

There is no one best masterbrake cylinder, it all depends on the combination caliper/MBC.
With out any other changes to your brake system increaseing the piston diameter of the MBC will result in less pedal travel and higher pressure on your right foot. Think in terms of amount of brake fluid that the MBC needs to move in order to cause the same effect on the calliper side...
I read also postings of people who use 23mm MBC. I think those are neccessary when the guys use the big Volvo 240 four piston callipers in the front in combination with some bigger stuff in the rear. 19mm MBC seem to be a good solution for BMW 230i conversion in the front and sock or mild upgrade in the rear.

Patrick Koch

[Dave at Pelican Parts]

A good article discussing the pros and cons:
http://www.pelicanparts.com/techarticles/914_BMW_calipers/brake_calc2.htm

--DD

[jay castriotta]

Interesting article. I am using turbo (black) calipers and rotors, so it sounds like the 23 mm would be an interesting choice except it will require more effort; hence, my question regarding power assist. Naturally I would not want to do this at the expense of not being able to modulate the brakes. I look forward to more in put.

[scotty914]

jay you have it wrong the 23 mm will give you less travel with more force needed

thats why the 914 has the 17 mm stock ... more pedal travel less force needed to generate the nessesary force at the caliber

when you up grade the cailbers to larger piston you can run out of pedal travel before max pressure is reached so therefore the larger master to give more fluid volume

[jay castriotta]

Righto- the article set me straight on that. So- back to the question at hand- which works better/best with the 911 set up. Anyone done a booster on a 914??

[scotty914]

do the bmw 320 up grade it is wonderful i just did mine and i am in love with it

justa make sure you do the pedal cluster rebuild too

but use a 19 mm master

[jay castriotta]

the car already has the turbo calipers and rotors front and rear- with the hotted up 2.7 it needs them. They work okay, but do not give you the 'hand of God' stopping power they should (based on my experience with other cars with similar set ups). The master cylinder (I think) needs to replaced; hence, my question since the time is at hand to do something

[toman]

sheesh, somebody give this guy a straight answer!

[John Rogers]

Here is what I found with brake upgrades on my race car. Stock calipers and 17mm m/c were fine. 320i calipers on the front and a 19mm m/c is needed to reduce the pedal travel and get a solid pedal. 320i calipers front and rear and a 23mm m/c was needed to reduce pedal travel to about that of stock and a very solid pedal feel. I removed the prop valve immediately when I bought the car so it was never a factor. I use Good year 23x9x15 slicks and this brake setup is now limited by the tires as they can slide if I am not careful braking in a race. Any bigger calipers will require a change of rotors to vented custom hats and then larger tires which means one of the aftermarket large fender kits and I want to continue vintage racing so I'll keep the setup I have. To go to the 23mm m/c you need the alloy steering rack support to replace the steel tube stock support and there is definately not enought room for a power booster under there. I learned to drive before ABS or even power brakes and our 1987 930 has equal brakes front and rear and I have gotten used to that feel and like it on the race 914. I will be at the CA Speedway this month for the vintage festival so anyone is welcome to check out the brakes. Good luck.

[jay castriotta]

Very interesting. I've got the alloy rack and- from what your saying- I gather that pedal force is not objectionable with the 23 mm master cylinder (again the turbo set up may behave a little differently- maybe). Hmm, sounds interesting. By the way, do you happen to know what size MC your 930 uses- and does it have power assist?? Thanks to everybody for the input so far.

[chibone_914]

Hi Jay,

I'm using the 19mm brake master cylinder with the Volvo Girling 4 pot calipers, stock 914 rear calipers and no brake proportioning valve. Braking power is amazing.

To answer your question on power assist.....Where do you propose on putting the booster?? There is absolutely no room underneath there to put one in.

[Dave at Pelican Parts]

Toman, we can't "just answer his question". There is no one answer!

The simplest answer is to use the master cylinder from the 911 that your brakes came off of. However, it is very likely that any actual 911 Turbo had power-assisted brakes. (BTW, there were several different 930 brake setups. Do you have the "A" calipers? 3.5" mounting bolt spacing, and a magnet will stick to the caliper.)

The 19mm M/C should be fine if you have A-caliper front brakes and stock 914 rear brakes. The 23mm M/C has almost half-again the volume of the 19mm one, so it's a pretty large step... You'll only have to push the pedal down 2/3 as far, but you'll have to push 3/2 as hard to get the same clamping force as if you were using the 19mm M/C.

From John's experience, the 23mm one might be a better choice if you have larger calipers on the rear. You may need to move that extra fluid.

To go back to step 1, is your pedal travel about 1/3 longer than you want? Can you live with having to push the pedal 1/3 harder to get the same braking force? If so then go up to the 23mm M/C. If not, stay with 19mm.

--DD

[SummerSledSix]

Here's a little more mud for this puddle... I put the 23mm MBC in my teener to go with the Carrera (A) calipers (all 4) and vented hats, to balance the 3.2 motor. Prop valve is still there. That 23mm JUST fits behind the alloy crossmember. Actually, I had to cuss it into place, but no need for metal alterations. Also had to re-plumb the reservoir lines slightly, using at least one 90 deg fitting, because the forward reservoir port is directly under the steering rack. Again, things are pretty cozy, but everything fits.

Was a little worried that I overkilled, having read the aforementioned tech article AFTER I bought the MBC, but am quite happy with the pedal travel and firmness. One of my DE instructors, was also quite impressed with the stopping power of the car, and I'm only running 205's.

[John Rogers]

Hey, that looks just like the install I did, so it saves me from taking a picture. I loosened the bolts and moved the rack support so I would have more room to work with and then bolted it back down when finished. For those that race or DE, you can set the adjustment of the brakelight switch so they come on as soon as the pedal is pushed, but no pressure has been builtup in the brake system and you'll gain 25 feet on the driver behind you in every corner! Good luck.

[SummerSledSix]

John, I like your style! Are you referring to the brake light switch on the pedal cluster, or one of those pressure thingies on the MBC? My brake light comes on a little too late, and I'm not sure who winds up more surprised, the guy behind me, or me watching him in my mirror!

[jay castriotta]

This is great stuff!! I can't wait. By the way Dave, I've got the big black alloy calipers. The pads are the larger tubo pads vs the carrera size on my SC.

[Zeke]

Both Johns, help me out here please. I had been planning to use a 19mm m/c with S cals in front and Ms in back. Sounds like I could use the 23mm m/c, but a 19mm is what operated this set up when it was on a 911, right?

Maybe for racing I need a little firmer pedal. This is the first Iv'e heard of the alloy rack support. In the pic it looks sorta like an I-beam. What cars did this come on? And what car did the 23mm m/c come from? I read on another thread that is was a Mercedes.

Shoot, I just finished bead blasting and painting my steel tube support. Live and learn

[SummerSledSix]

Milt, just think of the bead blasting as preparing the crossmember for sale! The alloy crossmember is what comes stock on 911's, at least the 84 Carrera I cannibalized for my conversion. It doesn't just hold up the steering rack, it holds up the tail end of the control arms, etc, and is a major component of the front suspension. I had to replace mine because the parts car had been t-boned and the xmember was bent(!), PartsHeaven was the source.

I personally can't help you with the caliper combo you mentioned except to say the 19mm was stock for 911's, and the 23 is indeed from a Mercedes. If you've got a 19 laying around, try it with your combo and see if it feels OK.


The basic tradeoff with MBC bores is that the smaller bores will give you more pedal travel, but exert more force on the brake pads for a given amount of muscle exertion. Another way to say this is that for a given set of calipers, the larger the MBC bore you use, the stronger your leg will need to be for a given amount of brake pressure. The 23 feels fine to me *in my application*, and I'm no weight lifter. So it's kind of a personal taste thing. Don't confuse pedal travel with a "mushy" pedal, which is due to tired brake fluid/air in the lines/tired flexible lines. Tighten that stuff up first before you start swapping MBC's.

All of these MBC's are actually made by ATE, a German company that makes calipers, MBC's, etc for most Teutonic vehicles.

[Zeke]

Excellent info, thanks. Does anyone have a photo of the 911 alloy crossmember?