This has been a real puzzle to me... It seems NOBODY has upgraded their 308 master cylinder, to better accomodate larger displacement calipers. I would like to upgrade mine, because I installed 4 large Wilwood calipers, and large rotors. This system was designed by Concours Ferrari for track use. The brakes are awesome, but I now have a long pedal. Still functional, but I'd sure like to get back to the original factory pedal feel. (Please refrain from telling me to put back the stock brakes!!! ) They don't compare to the new ones--twice as large and powerful, half the weight! In other threads here on F-Chat, some have mentioned that MAYBE a BMW or Mercedes MC would fit. DOES ANYBODY HAVE A REAL-WORLD EXAMPLE OF THIS ACTUALLY BEING DONE? Can anybody provide an actual part/model number? Otherwise I'm going to have to go to a parts counter and compare a million MCs with my 308 one to verify mount compatibility--not to mention I'll be guessing if it matches my new brakes... I'd prefer to NOT have to change my booster or pedal assembly. Can my OEM master cylinder be bored out/upgraded to provide matching displacement to my calipers? Would a Testarossa MC match-fit, and provide more displacement than a 308 MC? Can anybody provide specs/photos of a TR MC? I've contacted Wilwood and they don't have anything close to the square-mount bracket on the 308 MC. Plus, their line threads are standard, not metric. Any advice would be appreciated........please.... Greg
there is someone on here who changed their master cylinder, I think it was only a few weeks ago, do a search and you should find it, if I remember they had problems getting the balance between front & rear
Here's what I have on the TR MC/BB: Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Steve, Thanks so much. Your MC looks very similar to my 308 one. Looks to be the same square 4-hole mount. Also, the reservoir mounts looks similar, as do the line outputs. Overall size is very similar. The mount holes on my 308 MC are 1 11/16" apart, perfectly square. The mount bracket itself is 2 1/2 inches square. Reservoir mount holes are 3.5" apart, center-to-center. Steve, is there any way you can measure your mount/reservoir dimensions against mine? The $64,000 question is: Does the TR MC have more displacement than the 308 MC? My guess is: yes. The TR MUST have more OE caliper piston area than the 308, so the factory MUST have fitted a larger MC. Do you, or anybody else out there, know what the MC displacement specs are for both 308 and TR MCs? Thanks again for the pix, Steve. Very helpful. Greg
Well, I was hoping there would be something obvious that would clearly indicate "no way" I don't have any other information, but I'll check the TR WSM to see if it gives anything at all (like maybe the MC piston diameter -- but you'll need the pedal geometries too to make an overall system comparison). Try comparing some of the MC/BB figures in the 308GT4 WSM to that TR MC/BB figure too. You also might ask the originator of this thread: http://ferrarichat.com/forum/showthread.php?t=113211 if he can make a few measurements for you. (Unfortunately, my TR is at FoDenver now getting the seat belt recall done so I can't make any measurements myself until probably mid-late next week).
Greg -- Here's the tabular data given on page G6 of the TR WSM for the MC/BB (and the item descriptions for that earlier cross-section figure): Image Unavailable, Please Login
see this thread: http://www.ferrarichat.com/forum/showthread.php?t=106237 POST by: velocityengineer If you can find a 25mm master cylinder with the right stroke and imilar in/outputs, it will make a big difference. maybe get friendly with a parts guy who can do some cross reference. or build a small adapter to put a Tilton or other 25mm MC on the OE location. Another way is to shorten your brake pedal (not so easy or ergonomic) to reduce the pedal ratio. Around 3:1 puts you back to OE feel. (4.5:1 OE) The brake booster could be played with. There may be a limiting valve or vacuum regulator you can apply to limit full vacuum to the unit and lower its boost amount. unplug the booster and drive around a bit -CAREFULLY- you probably wont have enough brake pedal to stop, but you can feel how much effect the booster has on your system.
Most master cylinder's have a number cast in the housing. The 308 probably has a number 17 or 19. Try to find at least a 23mm MC for your caliper upgrade. I changed my 911SC calipers to 930 calipers and had the same pedal problem. Porsche 930 turbos use a 23mm MC, but it is only a 2 bolt. Please pass the info if you find a larger capacity MC. Charles
The last 3 posts are awesome!! I think I see a "19" on the backside of my 308 MC. What about re-sleeving my OEM MC to a larger size? Is that possible? Is anybody aware of a BMW/Benz MC substitute? Somebody on here mentioned that once.... Thanks so much. Very useful info..... Greg
Steven, If the TR Mc has the same mounting points, that is a good start for a trial fit. The stock 308 mc has a 22 mm diameter, the tr has a 25 mm diameter. Doing the math this amounts to a 29% increase in piston area, or I would think a 29% decrease in the pedal travel, (assuming that the caliper piston area were the same). Limiting the vacuum only reduces the assist, hence increasing the pedal pressure required to stop. The pedal travel will still be the same -long. Similarly, shortening the pedal arm only reduces your mechanical leverage, rising the effort, but the travel is still - long I am not sure, but the stock total car caliper volume was calculated to be 9.2 and with the Brembo kit is was figured to be 22.5 With the mechanical leverage being the same this might suggest that we need a mc 22.5/9.2 or more than twice as large, (this can't be right). I am sure that i am slipping a digit or using the wrong points of comparison - could someone help me with the physics? befuddled, but very interested, chris
There is an outfit, I believe is called, Stainless Steel Brake, or something similar and they resleeve master cylinders with stainless. I do not know if the casting is large enough to do this. They may have a policy not to do bigger than stock, for liability reasons. Many, not all lawyers, are looking for deep pockets and brakes are a touchy subject. hth, chris
Chris, Good to see you on the thread.. Agreed, altering the pedal travel or boost assist doesn't seem to be the solution--would just result in less leverage/boost assist. Can anybody check out a TR's mount plate measurements? I need to compare to my 308 MC... Looks like a TR MC may be the answer to my needs, if it'll mount up OK.. Wonder if the interface w/ the booster is the same on TR/308.. Thanks, GG
GG, yes indeed, please let us know how it goes with the TR unit. Please take pic and deatils of install. Agree i DO NOT want to shorten the pedal or play with the booster.
Greg, This morning after a cup of coffee, instead of a couple of beers, i come up with the following numbers, (using Pi x r squared x 1mm, to get vol): Stock 308 ft vol. (48 mm pistonx4) 7.24 cc r vol (38mm piston x4) 4.53 cc stock vol at 1mm travel 11.77 cc Brembo Ft & stock rear ft vol (40mmx4 + 36mmx4) 9.09 cc stock rear (38mm x4) 4.53 cc "Brembo" car vol. 13.62 cc comparison: Brembo Front caliper/stock: 9.09/7.24 = 126 % = 26% volume over stock. Brembo+stock rear/ Stock f&r 13.62 / 11.77 = 116 % = 16% more volume. Let's say that the stock pedal travel to make pad contact is two inches. The stock pedal ratio is 4.5 to one, that is if the pedal is pushed we will get 4.5 times the force delivered to the brakes, (disregarding the booster). The flip side of this leverage business is that we only get 2/4.5 in master cylinder travel. ( in this case we are assuming two inches pedal travel divided by the leverage ratio gives 2/4.5 = .444 or about one half inch. So, if the master cylinder ust move about 16% more, we multiply this by the leverage ratio of 4.5 to find the distance and we get: Ratio 4.5 x .16 = .72 If my reasoning and numbers are correct, this means that we will have a 72% greater pedal travel with the Brembo kit, so if the pedal travel was 2 inches before, it now is 2 inches times the 172 percent and we get pedal travel of 3.44 inches. Does this seem like what you guys with the brembo kit are experiencing?? more coffee, chris
Steven, I'll be happy to share any info re: the TR MC, but I need somebody to step up and provide some TR MC info, before I rush out and buy one..!! If anybody has a TR MC laying around, I'd really appreciate some measurements: Overall dimensions w/ and w/out reservoir, and mount plate size and hole spacing. Chris, Wow, all the numbers are making me dizzy! One difference regarding my car--I have large brakes @ all 4 corners. My rear Wilwoods are huge. I need to measure the piston area, but the caliper itself is probably 2x stock, and .5 the weight! So, my pedal travel is probably a bit longer than all you Brembo-on-front-only guys.. Here's the thing: I just drove my 308 this morning to the gym and back. Really enjoyable..!! After living w/ this situation for a bit, I guess I could live w/out upgrading my master cylinder. HOWEVER, I would feel MUCH safer with a more stock-feeling pedal. My braking style now must include an early "deeper" push of the pedal to get down to the bite. Obviously, the tradeoff is "modulatability" (is that a word?) Thanks Chris, Greg
Well, it's really not that much. Perhaps I've overstated the problem. Yes, the brake pedal on my car feels deeper, but if I were to actually measure it, it may only be an inch or so more at the beginning of pedal depression. Liveable, but not preferable. Greg
Took me a while to do it, but that was my own lack of experience. Now i can do it but yeah, your heel is 'up there' versus, say, just rolling your foot.
Chris, it has been so long since stock, or using a car in stock form, io could not say for sure but the pedal IS longer. If need be, could measure it. What i DO LIKE about the uprated condition/pads is that the feel when grabbing provides excellent feedback. My hopes for a shorter pedal is to aid in heel/toe so that my heel does not need to be 'way up there.' Have been spending lots of time practicing heel-toe in the past few months and it is paying off. Lime Rock is easy enough and will see how things go at Watkins Glen in eary September as there is MUCH MORE downshifting at WG than at LR.
Wil, Hey, yes I did receive the MC last week, thank you very much. It's been helpful in determining several measurements. The endcap also shows that it's a 23mm MC. I think I may have found a solution to my problem--Brian @ T Rutlands tells me they are now stocking 25mm 308 MCs. Price is $500!!! I wonder if that's enough of a MC volume increase to handle my large Wilwoods..... Not sure if I want to spend $500 on this problem, though... What do you think, guys? Greg
According to Eric Dahl at Girodisc 25mm is the way for us uprated brake guys and Eric is THE GUY who originally designed the brakes for the 308. He worked for Brembo at the time and now does speciality brake stuff for racers, etc. Guess what i am saying is, if Eric says 25mm is the way to go i have FULL confidence. $500? i'll call them shortly buy one. So how hard will it be to install it? What other parts will be needed (gaskets, etc)? How long should it to to RR the MC?
OK, so 25mm will suffice. Good to know.. Do you think $500 is reasonable though? I've always found T Rutlands to be a bit "gougey" with their prices... As far as R & R, seems to me it would be rather simple. Just drain the old reservoir with a turkey baster, remove all lines, unbolt the old MC, bolt in the new MC, re-attach lines, refill, bleed all 4 corners, and away you go. Maybe bleeding wouldn't be necessary, if fluid remains in the lines. You're just removing the "top" fluid in the system..??? Brake experts, is this correct? Greg
