Big Brake kit expert thoughts needed

[Tiger]

You are on the right track about needing bigger master cylinder to compensate for brake travel on larger pistons calipers or otherwise the pedal does go to the ground.

I don't know the equation of the fluid dynamic but cracking open a brake handbook should yield the info. I will check my Bosch handbook later tonite to see if they mentioned anything about this.

The smallish piston on multiple pistons caliper means more contact area on pads and thus more force on the greater area of the brake pad and thus better pad perfomance and better braking. As your website said, the balance of the front and rear braking performance is very important.

[Bruno]

As some people know I am working on a BBK for the E28/E24.

I am working on a 635csi but brakes are interchangeable across the board.
I changed my master cylinder to the 750il which should be close to the E34 one.

I installed front wilwood calipers with 1.38" pistons (4) and rear 540i caliper with 40mm (1.57" x1)

Now, the idea is to keep the stock master cylinder and keep the stock pedal height or something similar.

My guess is to achieve it, I need to keep the overal piston surface the same.
Meaning stock setup overal piston surface = 4 pot caliper piston surface.
That should give me the same pedal height.

Am I going through it the right way? I intalled some 1.75" piston calipers (4 pot) are the front and the pedal seems too low.

The idea is to have front and rear 4 piston calipers on the stock master cylinder.

Thanks.

[Bruno]

Here are some information from the UUC kit:
Brake kit options for: E28/E34 5-series/M5 (1982-1988)
E24 6-series/M6/M635CSi (1982-1990)
E32 735i/iL (1987-1991)
E31 8-series (front only)

Stage 2 is a front-only kit using a 4-piston Superlite front caliper with 348mm front 2-piece slotted rotors. Optional black or red caliper color. Maintains correct bias with original rear brakes.

Stage 3 is a 4-wheel kit using a 6-piston Superlite front caliper with 348mm slotted rotors and a 4-piston Dynalite rear caliper with 328mm slotted rotor. Optional black or red caliper color.

It would seem that 6 pot front and 4 pot rear works... But do they keep the stock master cylinder???

I just need to figure out the pistons diameter for a 4 pot front and 4 pot rear setup.

[healtoeit]

But do they keep the stock master cylinder???


It says they do use the stock master in the explination on the UUC web site

[Bruno]

It says they do use the stock master in the explination on the UUC web site

Sooo, to keep a pedal travel that is similar, the caliper piston area has to stay the same...

Meaning the volume of brake fluid displaced has to stay the same so:
Area 4 pot caliper piston x 4 = Area single piston caliper x 1

Right? so comparing with 750i calipers front: 60mm piston= 2.36" Area= 4.37 sqin.
So my 4 caliper piston diam shoul be similar to: 2xSQRT(4.37/(4*PI))= 1.18"

Hummm, seems pretty tiny. And I know that the 1.38" works great for the front.

EXCEPT... if the flotting caliper displace twice as much fluid??? in that case the result would be: 1.67"...???...

[Lee in Ottawa]

i'm still trying to figure out what you just said but i'm definately interested. I've been thinking about TCD's kit because of price and pad availability and options but this seems interesting.

[Bruno]

i'm still trying to figure out what you just said but i'm definately interested. I've been thinking about TCD's kit because of price and pad availability and options but this seems interesting.

Track / race Corvette brake pads aren't cheap... and this setup seems to go through a lot of front pads.

I bought a set of corvette calipers and sold them once I realised how much flex these had. Then I decided to get a cheaper setup (in the $500.00 range) with tons of pads available from $15 to $100.

But they do look cool on the car.

[Lee in Ottawa]

whats the cheaper setup your using? what pads fit the willwood's

[Bruno]

whats the cheaper setup your using? what pads fit the willwood's

Wilwood superlite calipers and pads that go along with them. I am using my car on the track so I am not worried about pad noise but performance.

[Bruno]

I think that the single piston floating caliper displace twice as much fluid as a fixed caliper:

My calculations should be:
Area 4 pot caliper piston x 4 = Area single piston caliper x 2

[Bruno]

The E34 already has a pretty large master cylinder, and I do not want people to start messing with it. So the idea is to keep the same pedal travel as let's say upgraded brakes like 750i front and 540i rear.
If I can keep the numbers the same and determine what size pistons I need then it would be a no brainer for everyone to upgrade if they want.

The equation is (Master Area/Caliper piston Area) x pedal stroke = piston stroke

I think that the Brembo caliper upgrade for the E34 is using around 42mm pistons and the E28 M5 / E24 M6 4 pot calipers were 40 mm pistons.


You are on the right track about needing bigger master cylinder to compensate for brake travel on larger pistons calipers or otherwise the pedal does go to the ground.

I don't know the equation of the fluid dynamic but cracking open a brake handbook should yield the info. I will check my Bosch handbook later tonite to see if they mentioned anything about this.

The smallish piston on multiple pistons caliper means more contact area on pads and thus more force on the greater area of the brake pad and thus better pad perfomance and better braking. As your website said, the balance of the front and rear braking performance is very important.

[Tiger]

F1 wheels are not as small as you think it is.

[healtoeit]

Wilwood superlite calipers and pads that go along with them. I am using my car on the track so I am not worried about pad noise but performance.

On UUC website it says...

Wilwood PolyMatrix
Carbotech
Cobalt Friction
EBC
Hawk
KFP Magnum (formerly Cool Carbon)
Pagid Racing
Performance Friction
Porterfield

sell pads for the kit

[healtoeit]

I think that the Brembo caliper upgrade for the E34 is using around 42mm pistons and the E28 M5 / E24 M6 4 pot calipers were 40 mm pistons.

So that would make the pedel travel greater? You are obviously an engineer...all you equations and what not! hehe! just playing man.

I do think that their si a bigger master cylinder that will fit in the e34. I can't remember which but their is one out there!

[Triton540i]

Why would anybody want larger wheels and larger discs for more rolling mass? Look at F1, small wheels with lots of skin, small, compact braking systems... any huge investment in "Big Brakes" for the streets is a waste of money as I look at it, get some nice cross drilled rotors with a great set of kevlar pads and you're set!

Just my two cents worth on the subject.

-Eric

[Bruno]

Why would anybody want larger wheels and larger discs for more rolling mass? Look at F1, small wheels with lots of skin, small, compact braking systems... any huge investment in "Big Brakes" for the streets is a waste of money as I look at it, get some nice cross drilled rotors with a great set of kevlar pads and you're set!

Just my two cents worth on the subject.

-Eric


Eric... Cross drilled rotors and kevlar pads? Is that what you have on your car?

Big Brake kit is mainly about heat management... and the comparison to F1 is similar to comparing a plane to the space shuttle...

And then you have the talk about fix calipers vs floating calipers, and brake torque... but it is late.

And it does look better under 18" rims hehehe.

[Bruno]

So that would make the pedel travel greater? You are obviously an engineer...all you equations and what not! hehe! just playing man.

I do think that their si a bigger master cylinder that will fit in the e34. I can't remember which but their is one out there!

Bigger pistons mean that you need to push more fluid to make them move... so the pedal goes further down.

Interesting non the less, I will do more testing.

[healtoeit]

And it does look better under 18" rims hehehe.
Ok, here is what i was wondering in my brake thread! What breaks will fit under what wheels? The chart on e34.net only goes up to 345mm rotors fittting under 17in. Wheels. Will the 348mm wilwood kit from uuc fit under 17in. wheels?

[healtoeit]

Bigger pistons mean that you need to push more fluid to make them move... so the pedal goes further down.

So, then how does the UUC Wilwood system allow for you to keep the stock cylinder?

[Bruno]

So, then how does the UUC Wilwood system allow for you to keep the stock cylinder?

Simple calculation to keep the overall piston size the same.

2 AP for single piston floating calipers should be roughly = to 4 AP for 4 pot calipers fixed.

AP = Piston Area.

[Bruno]

Ok, here is what i was wondering in my brake thread! What breaks will fit under what wheels? The chart on e34.net only goes up to 345mm rotors fittting under 17in. Wheels. Will the 348mm wilwood kit from uuc fit under 17in. wheels?

Well not all 17 are made equal, some of them have a smaller diameter inside so you end up as if you had a 16" rim.

[Triton540i]

Oi! I'm running Zimmerman cross drilled rotors with kevlar pads for a street application. I also upgraded to a 2 piece 17" BBS BMW wheel, why? I changed out my wheels because it's difficult to find any type of performance tires for a stock 15" wheel. I could have gone with 18" or larger wheels, but I also felt the car performs much better with a 17" or smaller wheel. I have H&R springs, Koni adjustable shocks and struts, M5 sedan sway bar in the front, M5 Touring sway bar in the rear... I feel I have a great setup for street use, maybe a rare track appearance would be great, but this is a heavy sedan, not a little two seater Porsche.

I think it's funny when I see people spend gobs of money on huge wheels and huge braking systems for cars that will more than likely never see a race track. My stock sized braking system hauls down my heavy 540i without any problems, that's good enough for me. :)

[healtoeit]

Simple calculation to keep the overall piston size the same.

2 AP for single piston floating calipers should be roughly = to 4 AP for 4 pot calipers fixed.

AP = Piston Area.
Gotcha! Thankx a bunch!

[rob101]

I think that the single piston floating caliper displace twice as much fluid as a fixed caliper:

My calculations should be:
Area 4 pot caliper piston x 4 = Area single piston caliper x 2
Actually bruno i am pretty sure that you're first calculations of about 30 mm diameter for each piston in the 4 pot were correct. there is no way that the braking force is multiplied by two for the single floating caliper, in theory it is applied half/half (of the piston force)on each side of the disc. as is the 4 pot (2 pots on each side is 1/2 of the total piston force). might want to look at the pad area as well. If you have a bigger pad you'll get more braking torque per piston force. if you get my drift.
I am not really following when you say "stock pedal height" do you mean the braking feel in general as in pedal position vs. braking force

[attack eagle]

Neverminds I found the diameters for the actual front brake pistons in an article by Pete Read from 99...and pretty much every thing else you need to know... :D


60m x1 front for everything from the e34 and e32 and hte early 850s

e28 m5 used 4x40mm

Look at the dustboot on a later 850 and you can read the piston diameter...
The boot is marked "ATE 11.8102-" and the two digits after that are the piston size.
according to below link best guess is 4x42mm


Aren't you doing this on the 635?

Since you are now running larger rears, you need to go back to the 1.75" (though a 1.65 would be closer to stock ratio front/rear) to keep front/rear proportion ie brake balance, and increase your master's sizing to p/n 34 31 1 156 643 from the E32 750 (25mm +10% increase over stock) to compensate for the increased fluid requirements.

if not, you probably should stay with the smaller fronts and reduce the rears to something like a 525 38mm or go back to the 36mm stock rear brake piston sizing...
otherwise you can expect 14% or more change in (e34m5 or e31 big brakes f& r 540s) pedal travel with your 1.75" pistons and the 40mm rears on the stock master.

M-Register Newsletter:
September 1999, pages 8 - 11
E28, E24, E34 Brake Options
by Pete Read (http://www.nwlink.com/~jrallen/mformation/archive/Pete%20Read/mbrake.pdf)

[Bruno]

Actually bruno i am pretty sure that you're first calculations of about 30 mm diameter for each piston in the 4 pot were correct. there is no way that the braking force is multiplied by two for the single floating caliper, in theory it is applied half/half (of the piston force)on each side of the disc. as is the 4 pot (2 pots on each side is 1/2 of the total piston force). might want to look at the pad area as well. If you have a bigger pad you'll get more braking torque per piston force. if you get my drift.
I am not really following when you say "stock pedal height" do you mean the braking feel in general as in pedal position vs. braking force


I am mainly looking at fluid displacement now, to see if we can keep the same pedal height. Once I can keep a similar pedal height then I will keepd calculating brakine forces.

Right now, I need some rims... So the big rotor can fit under.

[Bruno]

Well I have 1.38 piston fronts and the 540i 40mm single piston rear.
And there is a lot of braking force at the front (But I had some super aggressive pads, I will try some hawk black or HT10 now).... And that doesn't make much sense to me.
I already have the E32 master cylinder also.
Right now the pedal travel is the same as my stock 635csi.
Once I installed the 1.75" pistons calipers, the pedal was very very low... I did bleed and bleed but the pedal was still low... (maybe defective calipers???)
So I will try another set I have 1.62" and 1.75" differential pistons and see how they work and where the pedal travel will be.
I need to calculate pedal travel as I have the formula, it is mainly the ratio of piston diameters between master cylinder and caliper pistons.

[attack eagle]

yeah the 1.75 is probably 1-2 mm per piston bigger than the e31... that is a huge difference in area going from a 1.38 to a 1.75 (x8)...
Area= 'pi' times (radius squared)...

(do calculations in mm for easy comparison to OEM setups and masters.)

1.38= ~36mm (18mm radius)
1.62= just over 41mm (20.5mm radius)
1.75= 44.5mm (22.2mm radius)

The 1.62s would seem to be the perfect size based on piston diameter and fluid requirements.

[rob101]

Once I installed the 1.75" pistons calipers, the pedal was very very low... I did bleed and bleed but the pedal was still low... (maybe defective calipers???)
this sounds very odd, the hydraulics should take up the extra fluid volume in the system. I understand what you mean about brake pedal travel but calipers shouldn't affect brake height at all. otherwise as the pads wore the pedal would get lower and lower. hydraulic disc brakes are self-adjusting.
I am sure i saw a good section about brake feel in a carol smith book also. might see if i can find the section online.

[attack eagle]

They would for the initial bleeding, but to move from not engaged to barely engaged, ie that little dead space at the top of the pedal travel (assuming the distance moved between both is the same) larger pistons take more fluid... and pedal travel would be greater.
I know a multipiston rigid caliper holds the pads closer to the rotors in the unapplied position than a single floater does... so I am only going to compare the two multis.

1.75"
(forgive if I am reading this wrong, I'm assuming there are 8 1.75 diameter (not area) pistons, or 8 1.38" pistons but the ratio is the same anyway.)
1,547 mm2 per piston x8
12,380 mm2 total

1,017 mm2 per piston x8
8,138 mm2 total

So 1.75"s will use 50% more fluid to move from at rest to engaged than the 1.38 because they have 50% greater piston area.

I'm a bit confused like you about whether Bruno is talking about the movement from at rest to initial resistance being larger, or if he really means at rest position is different. at rest is set mechanically AFAIK.

BTW:
in comparison the area of the 60mm
is 2826mm2 or 5652mm2 for both sides.

Obviously there is a LOT more motion for these to still permit use of a 42x4 caliper on the same master, which lends credence to the X2 rule quoted above... and they would then fall right in between the 1.38 and the 1.75 in terms of effective displacement winding up about 1413mm2 (damn near a 42x4 4pot caliper.)

[Bruno]

A floating caliper is like a two piston caliper isn't it?
I think the piston is being pushed against the pad and the body of the caliper is being pushed the opposite side.

So I do think that the fluid displacement on a floating caliper is twice the displacement of a fix caliper piston.

So the area should be multiplied by 2. (or 4 if you take 2 calipers and 8 for the 4 pot calipers.)

If you want to join the Wiki, we can start doing some calculations in there.
http://bmwe34.wetpaint.com/page/Brakes+mods

[Bruno]

this sounds very odd, the hydraulics should take up the extra fluid volume in the system. I understand what you mean about brake pedal travel but calipers shouldn't affect brake height at all. otherwise as the pads wore the pedal would get lower and lower. hydraulic disc brakes are self-adjusting.
I am sure i saw a good section about brake feel in a carol smith book also. might see if i can find the section online.

Sorry I talk about pedal height but it is height when the pedal is depressed.
So it is more of a pedal travel. The pedal height is the same.

I need to get my noise back into the Carol book.

[Bruno]

yeah the 1.75 is probably 1-2 mm per piston bigger than the e31... that is a huge difference in area going from a 1.38 to a 1.75 (x8)...
Area= 'pi' times (radius squared)...

(do calculations in mm for easy comparison to OEM setups and masters.)

1.38= ~36mm (18mm radius)
1.62= just over 41mm (20.5mm radius)
1.75= 44.5mm (22.2mm radius)

The 1.62s would seem to be the perfect size based on piston diameter and fluid requirements.


I would love to know what is the pistons size in the 4 pot front and back setup from UUC... I bought some 1.38 for the back but I think it will be to big now... ARG.

[rob101]

Obviously there is a LOT more motion for these to still permit use of a 42x4 caliper on the same master, which lends credence to the X2 rule quoted above... and they would then fall right in between the 1.38 and the 1.75 in terms of effective displacement winding up about 1413mm2 (damn near a 42x4 4pot caliper.)
Yeah i thought about it last night, and i think i was wrong because the sliding caliper will apply double the force per area of piston because the reaction force of the caliper pressing against the disc will clamp the otherside
http://www.sportcompactcarweb.com/editors/technobabble/0212scc_techno/index.html which is confirmed by this article so there you go....

[rob101]

So I do think that the fluid displacement on a floating caliper is twice the displacement of a fix caliper piston.

So the area should be multiplied by 2. (or 4 if you take 2 calipers and 8 for the 4 pot calipers.)

If you want to join the Wiki, we can start doing some calculations in there.
http://bmwe34.wetpaint.com/page/Brakes+mods
I would join it if i wasn't at work right now LOL, first thing that pops to mind bruno is that for pedal feel you should be thinking about pedal travel vs. clamping force. it sounds like atm your thinking in terms of the displacement of the pads/pistons rather than their clamping force, clamping force is what determines the braking torque on a certain disc not the actual caliper piston travel. if you get my meaning.

[attack eagle]

I would love to know what is the pistons size in the 4 pot front and back setup from UUC... I bought some 1.38 for the back but I think it will be to big now... ARG.

jsut reverse engineer the area needed from what is already fitted.

figure the area now, x2 for sliders, divide by number of pistons, divide by pi, square root. piston radius.

Based on the 40mm rear you have now, i come up with a 28mm 4 pot.
that is a 1.1"... so arg indeed.

[Bruno]

Well, time to sell all my 4 pot callipers and pick up the right ones.
No big deal for the rear anyhow, not a priority anymore.

I need to finishe my A-arms to replace the thrust arm and control arms 1st.