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brake master cylinder upgrade?

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art. just out of curiosity, what size did you find the mits./d-50 trucks to be?  and did you include the monteros or 4x4 trucks.  perhaps some of the guys on a 4x4 forum such as 4x4 wire,  they have a mitsu section and these guys have been helpfull for me in the past. perhaps they might know something good for stopping those big tires.

   also, have you put much thought into swapping the entire booster and master cyl.?  i know were pretty limited in space but just looking for a possible option.

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i looked at most of the mitsu 4x4s. the larger monteros are too different and actaully didn't seem larger.

i count not find the older smaller montero. those might fit

the smaller trucks will fit but have only a 7/8 piston.

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I think thats what the shop is looking into doing, an adapter to UPDATE our OUT-DATED systems. So we'll see what will be more cost effective or have the most BANG for the BUCK Adapter and new master or BORE out OEM master.


We'll see



BTW: thanks for all of the legwork

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I saw on the Montero site and some other one that some of the guys were getting hydraulic brake systems and retrofitting that into the Monteros and completly eliminating the brake booster.  Supposedly it has massive braking power power because it comes off of a cadillac and it ties into the power steering pump.


I would really like to see this just because it would free up some more room for a custom individual throttle body intake manifold with a larger plenum.



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The best option to go with would be to eliminate the booster all together as it isnt necessary. The next thing you need to understand is that your system is closed, therefore volume is mostly fixed! This means that the pistons at the caliper end only moves a maximum of .030 of an inch!!! Larger M/C bore means softer pedal feel with more fluid flow/piston travel. Likewise a smaller M/C bore is firmer feel with less fluid flow/piston travel.

Im not familiar with the kit Oscar supplied however I would be able to tell you what is needed for a master if you can tell me what caliper piston size and number of pistons per caliper you are using. Understand that pedal feel varies by driver comfort and how touchy you like the pedal. Furthermore, if you dont have "steel braid " hoses on the car by now, you have already missed the boat for good feeling brakes!!!

I have designed many race and street rod brake systems and can tell you it is a very sensitive area to experiment with especially on a street driven car due to liability reasons. So please guys, be carefull with what you are doing............... get in a accident with modded brakes and it is automatically your fault!!! Lawyers are wonderfull predators!!!




PS: Dont use a bored or modded master cylinder :o Also, the "hydro-boost" system that ties in with the power steering is not a cost effective system or very well suited to a Quest

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The KIT I provide is simple:

12" rotors with 4 / 1.75" piston Wilwood Superlite calipers. So if you can shine some light into this we welcome it 110% !


But I dont know if I agree with the Bigger to smaller M/C explanation you mentioned.

Our masters were designed for a SINGLE piston caliper use, now we upgraded to 4 piston calipers. Even though the Superlite Wilwood calipers use LESS volume of fluid than any other 4 piston in the market it is still more than the single piston OEM caliper required to work as STANDARD.


Now, if the amount of fluid needed to push 4 pistons calipers is GREATER than the amount needed to push the OEM Single pistons wouldnt this mean that you need more VOLUME of fluid pumped to the calipers to have the same effects ?


So when I asked Prescision Brakes (The original designer of this KIT) about using a smaller Piston Dia Caliper they simply stated its NOT a good idea as we would have too much presure from our masters and little pedal travel and the pedal will be hard as a rock and braking will be greatly affected. They would either recomend a bigger master or a bored out OEM master if none can be found to "Bolt-On". We will possibly end up with an addapter plate to use a bigger master, as the local shop I am dealing with has doughts that they'll find the necessary sized pistons and seals for a Bored out OEM Master.


A local Hot-Rod building shop here in town specializes in Custom Chasis fabrication, set-up and Brakes for Hot Rods and they were MY FIRST choice to make this kit available to us BUT Precision Brakes offered to us at a faster turnaround time. And they ALSO stated that the Cylinder Boring is a popular modification for their Fords and Chevys Rods as they are also using the Wilwood Superlite billet 4 piston calipers and are retaining OEM Masters BUT Bored. This shop have been doing Hot-Rod customs for over 40 years.


Now its VERY TRUE about ANY Brake modification, WELL ANY MODIFICATION done to a street driven car that is NOT intended for street use. The KIT that I sell and even the ORIGINAL KITS were NEVER DOT approved and never will be (Unless someone wants to spend the money for the paperwork and the leg work involved in getting ANY product DOT legalized ). These KIT's are sold as OFF-Road use ONLY.


So Mark, if you can help us in this area we WELCOME ANY and ALL help we can get.



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Ha ha ha ha

Guys, I was thinking of using hydroboost from a Lincoln on my car.  I don't have any room for the booster because of the width of my engine, plus the fact it's pushed back about 3" into the firewall.  SOoooooooo, I thought the Hydroboost system would be a great solution.  WRONG!!  It's a crap load of plumbing plus it's a big a** heavy unit.  Another thing I was thinking of was a powermaster unit from a Grand National or Cadillac.  They use an electric vacuum pump to generate the needed power to boost the brakes and there is no booster.  I haven't priced those out but my buddy is a Grand National nut and said they usually go for about $300 per unit or more.  I got that whole pedal setup there for about that.  I have been told the Wilwood setup I posted previously will stop my car like I hit a friggin brick wall.  I hope so.  LOL





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With regards to the calipers, I didnt know they were 4 piston units, therefore you are correct about needing more fluid per pedal stroke. The fact that the hot rod shop that "bores out" the master ??? The factories (Bendix, Raybestos, etc.) use the same cylinder castings for numerous applications, but change the bore size! That hot rod shop you mention is just swapping part numbers based on experience! Like I said, same casting/different bore/different part number.

The car doesnt care what the master looks like or what it  comes from, so lets look at bore size in relation to what we started with. Someone mentioned 15/16, that is available from Mopar perf in the same size with increased travel/fluid displacement. It is also available in 1" and I think 1 1/16" as well. They are a plastic reservoir with a aluminum body. You can also get a similar thing in a For or Chevy iron housing unit.

Keep in mind now that adjustable proportioning valves are not going to change anything but front to rear bias. No matter what route we go here, you are still going to have to form brake lines and re-engineer some things.

Sorry guys, my mind is going faster than the fingers can type!!! I hope I am making sense to someone? Adapter plates to mount a master are the easy part. I havent paid that much attention to the stock firewall as it may have enough "meat" in it to just re-drill the bolt pattern of a new master!! Now we have the push rod dilemma!!!

Can we build a better car than Mitsu- of course! Can we build 500,000 of them......................... NOT!!!


If there are any of you folks that will attend the SO Cal meet on the 25th, I would enjoy discussing this subject and trying to iron out the details. The first version of these type operations are always challenging!!!




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does anyone have access to a 3000GT/EVO brake booster to compare it to ours. the more i look at different setups, the more i begin to think it will be easier to swap the master and the booster together, rather than to adapte one of those masters to our booster. just by looking at it from under the dash, it looks like it has the same bolt pattern.
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i been doin lots of looking around and it seems like our master cylinder is a relatively large size. anything larger than 1" is rare, especially in the aftermarket.


there is this tilton unit that is big and seems to have the same mounting patern as ours.


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The master cyl I mentioned from Mopar is a Mopar Perf part, that means universal application. One would have to change the bolt pattern ( redrill the firewall).

Art, is there a reason for wanting to use a booster for this application? It is definitely not necessary to use one and you will get a much better pedal feel without it. I have not pulled a booster off the firewall of these cars but cant imagine the reinforcement plate beeing too small to re-drill for a master cyl only application. If everyone wants a booster, then make it easy on yourselves and just get a package and mount it in the trunk area!!! No different than under the floor or remote like trucks use.

I really think we are making this more difficult than need be.............. I will do some number crunching on Saturday and come up with a cylinder bore requirement, then its up to you folks which cylinder you like the best.



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I just got off the phone with wilwood support.


here is what  he said:


the 1.75" piston caliper should work just fine with our size master cylinder. they use them all the time for stock replacement applications without upgrading master cylinders. its just a matter of getting used to the pedal feel.


As for the 1.38" pisont caliper, he said those will have plenty of power to stop a 3000lbs car. its just that the 1.75" has more potential if more braking power is needed down the line. So the 1.38s WILL work.


i told them what precision brake had told us and he said that made no sense at all.

our stock caliper has a 2" piston area.

the 1.75" piston caliper has a 3.5" effective piston area.

the 1.38" piston caliper has a  2.75" effective piston area.


so the 1.38" would require slightly less pedal travel than the 1.75" but it would still be a little more than stock. the pedal wouldn't possibly be harder to press.

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Mark, I am not a big fan of removing power assist stuff on the car even though many race cars dont have them. its makes it nicer to drive on the street.


James, do you still think you have too much pedal travel? do you have braided steel lines in the rear too? what brake fluid are you using?


fyi, I measured the RX7 4 piston calipers. they are 1.3", and they have a smaller master cylinder than us.

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The arp wheel studs are $11.95 from summit for a set of 5.


Also, I did go with the Polymatrix D pads.  They seemed to stop fine autocrossing, pedal feel just didn't feel right.  I plan on getting carbon kevlar pads maybe Porterfields or carbon metallic Hawks.  I'd like to find some with low brake dust.  I do not like the Polymatrix D's at all, they dust like hell.  My wheels get extremely dirty after 2-3 days of street driving.  


phew, why is wilwood turning brake pads into the alphabet soup. they have a zillion versions now. i am just gona go with the porterfield R4-S pads for now and then get the regular R-4 for the track. they are $109 for either version.

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Guest silverngray

Art thanks for the leg work! I have bought the brackets from Oscar just havent bought the rest of it to put on the car. I think I will try the smaller sized calipers if the car ever gets fast enough to need more braking power can always switch to the bigger ones. Since the fastest place the car will ever go is PIR I doubt it will ever need it. Plus the pedal feel will probably be better making them easier to modulate.



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As I look back on the posts of this situation, im thinking the original prob was a an incomplete bleeding of the system. I wasnt aware of the piston size that was beeing used in this situation however it should be functioning with a solid pedal only to change how far it travels or how hard it is to push it (trying to keep it simple here).

As for removal of a booster, I stop my big 1964 Plymouth stationwagon with manual discs with no big effort at all! I can lock them up if I want to!!! Apply pressures can be varied by the brake pedal arm length as well as M/C diameter or caliper piston diameter. Most of the variance that you feel means a significant hydraulic pressure difference. Try playing with air brakes some time!!! Air brake pressure increases as you press harder on the pedal whereas hydraulic is almost the same as you increase apply pressure at the pedal.


I hope I havent confused anyone here, im just trying to make the other folks reading this understand that brake systems are "systems" not just a mix and match program.




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I'm using TEP's ss lines on back.


I've since replaced the master cylinder which helped.  I had planned to autox this past weekend to see if pedal feel has been resolved, but unforunately on the way there I broke an intake valve.   So the car is down again and had to bring out the rx7.  It will be another month or two before I have a chance to test the brakes again.  Maybe sooner if I can find 1 forged piston to replace my damaged piston.

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Actually this is no longer an issue as thins have been ironed out as a possible effect of PERSONAL taste and other parameters from the car's brake system.


Bellow is what I got from the ORIGINAL manufacturer of the first KIT ( MINE )  when I asked him about our little issue.





We like the Wilwood guys and we use a lot of their products, we have a great

relationship with them, but don't necessarily share their philosophy on all

counts... Did anyone ask you about the pedal ratio? Did they ask about the

vacuum booster diameter. Without these two pieces of info it is not possible

to calculate the system pressure. The stock caliper piston diameter is 57mm

(2.249") The area of a 2" caliper piston is 3.1416"sq, the area of a 57mm

piston is 3.955"sq. The difference is 26% just for the piston diameter

error! I don't know where they found those figures.


There are many companies (including Brembo, StopTech, Baer Brakes, Stillen

and Stainless Steel Brakes) who sell brake upgrades which are in fact down

grades from the factory components. There  was an article in one of the

Chevy magazines a few years ago discussing a brake shoot-out in which some

of the companies I listed participated. NOT ONE of the upgrade kits

installed on the cars tested out-performed the factory stock systems on the

same cars. Big rotors and four piston calipers don't mean a (good) thing if

they are not properly matched to the rest of the components in existence on

the chassis.


Very few kits sold in this market are upgrades. We don't design anything which

is not an upgrade. Wilwood, for example, sells a big brake upgrade for the

Honda Civic. It fits 88-2000 or so. In fact, Honda Civic's use two different

calipers (and rotors) for those years, with 54mm and 57mm pistons. They have

one kit that covers both. Their kit has a 12.19" rotor and a 4 piston

Dynalite with 1.38" pistons. The area of this small Dynalite is 2.99"sq. the

area of the small Civic caliper piston (54mm) is 3.55"sq. The Wilwood

caliper upgrade is in fact a 17% down grade. That means that the clamping

pressure at the rotor is reduced by 17% over stock. The rotor is 12.19" as

compared to the factory 9.5" unit and so the overall effect is a meager 8%

upgrade. The factory caliper used with this 12.19" rotor would have

delivered an upgrade in excess of 28% with no change whatsoever in pedal



That whole scenario isn't so terrible. The Civic with the 57mm stock caliper

and the 10.3" stock rotor sees an overall down grade of 10.5% using the same

parts. Just the 12.19" rotor change on this car would yield an upgrade of

18.3%. Too bad. As you can see, 4 piston calipers are not automatically



So here is the scoop from our side on the Starion/Conquest system we developed for you:


The kit we designed to fit within the parameters of the factory Starion/Conquest

wheel. This limits rotor diameter. The kit shows an overall upgrade of 33%

over the factory system. If we change to the SL caliper with the 1.38"

pistons the overall upgrade will be -17.3%. A 17.3% DOWNGRADE!! Why spend

the money?


The balance between master cylinder and caliper is a delicate one. We don't

take the matter lightly and we don't design down grades. The factory master

cylinder diameter is 15/16" if you move up to a 1.0" master cylinder your

brake effect goes down to a 17% increase over stock or about a 12.1%

decrease from where you are now. This is still pretty good but not as good.

Before changing the master cylinder I would be inclined to check a few other

things. How much pedal travel do you have before the master cylinder

actually starts to move? Most vehicles have quite a lot of pedal movement

prior to brake actuation and this can frequently be adjusted out at the

booster. After removing the master cylinder from the booster, see if the

booster pushrod (the part which pushes on the master cylinder) is

adjustable. If so, adjust it out to take up the amount of pedal travel prior

to brake actuation, or at least some of it until the pedal travel is more to

your liking. Too much adjustment can create a situation where the master

cylinder piston does not retract far enough to release the brakes, so care

must be taken when adjusting and testing. "Slop" in the linkage and pedal

can also increase travel and attention to detail there can alleviate

unwanted travel.


One mustn't overlook the possibility of pedal travel increasing as the

system becomes hot either. Using brake fluid with a lower boiling point than

the system will develop leads to premature failure. Also, any trace of

moisture in the system will create similar problems. As soon as the fluid

heats up past the water boiling point, you suddenly have steam in the

system. It has the same effect as air. Mild performance street driven

vehicles do not require as frequent attention, but competition driven cars

typically have their brake fluid changed after very event. Use 600 degree

fluid and make sure it is hygroscopic, that is glycol based, not silicone



I hope this is of some use to you Oscar. Please let me know what you find.


And that my friends is STRAIGHT from the horses mouth.

Hope that helps all of you.



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  • 4 weeks later...

OK guys...

I may just have the answer to out problem here.

I just got an e-mail from the master itself and he recomended that we tried the "Residual Presure Valve" Check out the info bellow:






These in-line pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in both disc and drum brake systems.


The two pound valve is used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers and fluid drain back occurs from gravity and vibration, thereby causing excessive caliper piston retraction and a longer brake pedal stroke. The minimal two pound residual pressure prevents fluid from flowing back without causing the brakes to drag. With drum brakes, a ten pound valve is used to compensate for return spring tension in the drums. Residual Pressure Valves are made from billet aluminum and color coded for easy identification. Ideal for drag racing, street rod and many off road applications.


I'll be installing these in a week or so as soon as I figure our ALL tyhe adapters needed to properly install these into the OEm system. These will be INSTALLED IN-LINE as close to the master as possible and I'll try to do with ONE for both front wheels BUT we may need two depending on dificulty of installation due to the Hardlines we have to attach these to.


I'll keep you guys posted of ANY progress.


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  • 3 weeks later...
I used ARP studs for a late model corvette and F-bodies.  About $12 from summit.  I just ground done the knurl area to fit the hub and squared off the head of the stud a little like the stock studs.  The heads are a smaller then the stock heads, so there may be a concern it rounding off in the future, but I've taken my wheels off several times with an impact and haven't had any problems yet.  You could just put a tack weld too.
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