Rip

Has anyone messed with converting over to manual brakes? I've been searching and really havn't found much.

I've found a few pics here and there

http://tnoms.thenyceone.com:9999/john/101-0113_IMG.JPG

https://www.rx7club.com/forum/attach...chmentid=55377

but not much more than that.

I'm looking for a web site that shows the extent of work involved, and hopfully the parts they used. If not that can someone help narrow my searches? What keywords should I use? And is there a person here that has done this so I can search thier old posts?

thanks
Rip

tims

my second gen car has manual brakes. Wilwood dual pedal, a custom bracket welded to the firewall, and some new brake lines. Not a big job but it does take some upside down welding. best brake mod I ever made. check my website gallery for some photos.

tinner

iTrader: (2)

I converted my fc using stck components. It does involve some fabrication though. I made an adapter plate out of .25" aluminun that mounts the stock master cylinder directly to the firewall in a location about .625" higher than stock. That and drilling a new hole in the brake pedal for the pushrod is required for a new pedal pivot raio. Power brakes us about a 3 to 1 ratio whereas manual brakes use around 6 to 1. This is for more leverage which IS needed. I can take some pics if you think this is a route you would like to go.

Rip

well I will be using the stock 2nd or 3rd gen four pot calipers. And want to use aftermarket pedals, wilwood or tilton. And figured the best master cylinder to use would be the stock master cylinder or at least one similar in size.

Is the stock master cylinder 22mm? if so what size master cylinder should I use? 3/4? 1inch?

Also what pedal ratio did you guys use? I beleive 6:1 is normal right?

but what would be the result if I used a larger MC like a 1 inch then used a 5:1 pedal ratio? to much or too little pedal travel?




Basically I'm hoping to find out what you guys have done and see what would be best for me. thanks for any help.

Rip

IanS

iTrader: (4)

This is an intersting topic to me. What does manual brakes mean exactly? Does it simply mean to not have them assisted with the booster? It seems that way in the pic above. What type of gains would be expected from this? Would it give a better braking feel? Would this be a way to remove ABS (I have first gen so I obviously do not have it)? Basically just give me a run down of what this is used for. Thanks and sorry to jack this thread a bit.

Rip

manual brakes just mean that you have no assistance, like the vacumn or power booster. You use only the leverage at the pedals to create braking force. For some people this is okay.

If you have ever driven a old car like a old ford with out power brakes you have to press harder to stop than an equally heavy modern SUV. don't get me wrong it's not bad; like you reallly really have to push, but I'd be lying if I didn't say that there wasn't a definate difference.

The main reason people went to power brakes was the ease of effort and to get more room in the driver seat. Because you now have a vaccum helping out you don't need the longer pedal to create the braking force.

But, along with that you don't feel the responsivness as you once did with manual brakes. You can feel the brake push back. And I beleive you have a little bit more control. Such as the breaking point in which your tire brake free, and you slide. With a power booster its harder to tell the amount of force you're putting in; where as with manual brakes you have to press harder to stop quicker. To me the power assitance somtimes feels like a on off switch. You can still judge the force but more so with the distance at which you've moved the pedal. Manual brakes it's more of the force you're exerting. Get it?

Now the biggest problem with moving to manual brakes is getting the bore of the master cylinder correctly matched not only to the calipers but also to the pedal ratio.

See you need to get a master cylinder that's volume will activate the calipers, give you a good amount of press, and then get them to lock up. But, not to big inwhich you really have to push hard to get them to work.

And you need a pedal ratio big enough to not get your leg tired, and not swing soo far that you bottom out the master cylinder or hit the firewall.

Anyone want to add? Or change some of this let me know cause I'm not exactly experienced when it comes to this. But, I think this is the jest of it.

Rip

speedturn

iTrader: (1)

I converted my 1st gen to manual brakes, with Tilton dual master cylinders and a Tilton swinging pedal assembly (this gives you adjustability to balance the brakes F/R.) I use 3/4" dia master cyl for front brakes and 1" dia master cyl for rear brakes; this gets the F/R balance pretty close, and then the balance bar lets you fine tune it. I should add that these master cylinder diameters work with my matching 4 piston Wilwood calipers at all 4 corners.

I really agree with Rip that you get better feel and feedback with the manual brakes.

Putting a proportioning valve in the rear brake hydraulic line to adjust rear brake pressure is a half assed way to balance race car brakes. The only real way to do it is two master cylinders with the pedal mounted on a balance bar in between the masters.

Rip

Really? you used a larger MC for the rear brakes. I figured that the front calipers, having a larger bore, would require more fluid and the bigger MC. Can you explain why you went the way you did?

thanks for the reply
rip

Howard Coleman

iTrader: (6)

if i ever get the time i will convert my fd to manual brakes...

just for laughs i disconnected the vacuum assist this summer and took a drive. it was a very short drive as it was almost impossible to stop the car.

there are numerous ways to get it done but the best is to install a wilwood or tilton dual master cylinder assmbly w an adj balance bar for front to rear proportioning.

the key will be proper master cylinder sizing.

as to why the rear needs a larger bore master... larger bore equals less force which of course you need in the rear.

a worthwhile project.

howard coleman

Tofuball

(Posting here so I can find this excelent thread later)

Anyone have any good links on how I would size the cylenders?

Travis R

I have an Excel spreadsheet that I used to calculate the MC sizes. So that means this is all theoretical since I haven't done the brakes yet. But this same spreadsheet has been used by other people with success.
Using the stock FC brakes (4pot fr. 2pot rr.), and the Wilwood dual master cylinder pedal setup (5.11 ratio) and balance bar... I came up with .75" for the front and .625" for the rear.
tims I'd like to hear what size you have in your car.

M's

yes, he would go with a larger master cyclinder to help solve the force amplification problems often associated with rear brakes. Additionally with dual master cylinders you can actually "proportion" your brakes. Duals is a nice way to go.

Rip

Can I get that spread sheet?

Also I suppose if you wanted you could just get a 3/4 and 5/8 MC's then just hook them up and if you want swap them. A odd way to do it but it will get it done.

thanks
rip

speedturn

iTrader: (1)

Rip,

Like I said in my post, I use the same identical calipers and rotors on all 4 corners, so it works out that 3/4" front master and 1" rear master puts the right amount of hydraulic pressure at each end of the car.

Rip

Cool I get it. Because the front will take most of the load when braking, you could either have

-went equal MC in which case you would have had to use the balance bar to change the bias and feel

or

-went with a larger rear MC and the balance bar isn't needed as much.

I don't know what happened when I replied.
thanks
Rip

tims

To All,
The one thing about the after market pedal assemblies is that for about $60 you can totally change the way the brakes feel. feel is the main reason for converting to manual brakes. you can feel the tires lock up and you can also taylor how far the pedal moves and how firm the pedal will be. My setup is kind of backward because I am a big guy and I tend to generate more pedal force than the brakes normally need(with the vac booster I constantly flatspotted tires). I run Wilwood Billet Superlite 6 calipers on the front and the stock FC calipers on the rear. I use a 1" front M/C and a 3/4" rear M/C. This gives me a pedal that only moves a 1/2" at best, but it takes alot of force to operate. For a set of stock calipers I would start with 3/4" front and rear. The larger bore diameter will give you a firmer pedal with less travel. A smaller diameter bore will give you a softer pedal but will increase the travel. So start with the 3/4" M/C's and try to fine tune it with the balance bar and if the travel is to long go to a 7/8" or 1" on the rear. there is no setup that will be perfect for everybody. so you may have to adjust the sizes to get what you feel is the best.

macdaddy

OK, Howard, I don't get it. "as to why the rear needs a larger bore master... larger bore equals less force which of course you need in the rear"

I'm not an engineer, and my high school and college physics classes were a long time ago, but...

Assuming:
-brake fluid is non-compressible
-balance bar is set in the middle so that each master cylinder piston moves the same distance when you press on the pedal

Then:
-a larger diameter master cylinder for the rear means that more fluid is moved in the rear system than the front

Unless the rear brake cylinders are larger or the pistons have to move farther than the fronts,

Then:
-more fluid moved should = greater pressure.

Is there a hole in my logic here?

Howard Coleman

iTrader: (6)

as i understand it this is how it works........


equal pressure input.

large master
small master

large master you move more fluid so more work is required leaving less power available for pressure.

small master, less fluid moved so more power available for pressure.

the other consideration is fluid volume needed to move the pads... generally a larger # of pistons need more volume however the net between multipiston and single is often less than you'd think.

tilton, wilwood have all the formulas in their literature to help you dial in the proper master cylinder size.

howard coleman

DamonB

From our Suspension and Handling Links sticky:

Everything about Brakes by Grassroots Motorsports

Page two covers master cylinder bore sizes...

speedturn

iTrader: (1)

macdaddy:

Don't think volume - think pressure (pounds force per square inch of area)

For a master cylinder, psi output = force applied / piston area

So a smaller diameter master makes more psi than a big dia master.

On the other end of the system, at the wheel brake calilper pistons, if you want more clamping force by the caliper, then you put in larger diameter caliper pistons.

Brake balancing is all about pressure, not volume of fluid moved.

macdaddy

Howard: I still don't get it - "large master you move more fluid so more work is required leaving less power available for pressure. small master, less fluid moved so more power available for pressure."

speedturn: that helps - think about transferring force, rather than mechanical translation of the piston. Same amount of force to each master cylinder/area = lower psi for larger piston.

Rip

Off the article

In order to calculate the amount of clamping force generated in the caliper, the incoming pressure is multiplied by the area of the caliper piston. In our example, the 558 psi that had been generated at the master cylinder has traveled through the brake pipes and lines and is pushing against two 1.5-inch pistons per caliper. Therefore, the effective area of the caliper will be equal to two times the area of a single 1.5-inch piston. Working the numbers reveals that 558 psi will generate 2068 pounds of clamp load [558 psi x (1.84 in. x 1.84 in.) x 2].

I don't get something here particularly

Therefore, the effective area of the caliper will be equal to two times the area of a single 1.5-inch piston. Working the numbers reveals that 558 psi will generate 2068 pounds of clamp load

the area of a piston = pi x radius ^2
the radius of the piston = diameter/2 = 1.5/2 = .75

thus

the area of a piston = 3.14 x .75^2 = 1.76625
now two times that is = 2 x 1.76625 = 3.5325

3.5325 in^2 is the area two pistons cover now 558 psi should generate about 1971 pounds of force, where did they get 2068 pounds?

558 psi = 558 pounds / in^2

so 558 pounds / in^2 x 3.5325 in^2 = 1971 pounds

that's correct, right?
Frankly I don't even understand where the 1.84 values come from.

tims

clamping force is all well and good and all the math looks fine. problem is if you apply the same amount of force to the front and the rear brakes the rear brakes will lockup and tires will skid. as the brakes are applied weight will shift forward and less force will be needed to the rear and more to the front, since there will be improved traction with the weight shift. so by using a larger m/c on the rear you will increase the force needed to lock the brakes/tires, allowing you to add more force to the front without locking the rears. I over analysed the brakes with all the formulas and suggestions in these and other books and found after trying several combinations what worked for me(my initial calculations didn't fit my driving style). all the combinations will work. I have a racing friend with a 3rd gen that uses a 5/8" front m/c and stock calipers with a 3/4" rear m/c and stock calipers. the pedal has alot of travel compared to my setup but he likes the softer easier to push pedal(he's also 100# lighter than I am, so it works for him). there is a point where you will not be able to push the pedal or the pedal goes to the floor and doesn't stop the car, but you will be safe starting with the 3/4" front and rear m/c's with nearly any caliper oem or aftermarket(this is by far and away the most popular size for the manual setup).

Tofuball

Ok, I have decided that I am going to go ahead and do this.

I'm wondering if anyone can post the part numbers for the parts they used (I have stock 4pot FC brakes). I'd rather use a tried and true method then try constructing my own :p

rexrcr_eNz0

This is a must read:

BRAKE HANDBOOK
Fred Phun
"Something the street machiner who's building a technical library will defeniely need" - Popular Cars
Facts about everything from the earliest drum brakes to advanced carbon/composites brakes. Practical techniques and formulas tell how to design, improve, test and maintain complete brake systems.
ISBN: 0-89586-232-8
UCP: 0 75478-62328 0
Size 8 1/2" x 10 7/8"
HP328 176 pp