Brake setup questions.

[billgatese30]

Hi Guys, I am thinking about changing the brakes on the track car. I am currently running 310mm Wilwoods with standard rears and thinking what I can do different.

I have thought about dropping rotor size so that I can run 15's again and also upgrading the rears at the same time.

I have also started looking into making a pedal box to run dual master cylinders with no servo, no ABS and no linkages to reduce pedal feel.

Pedal box shouldn't be a problem but when it comes to ABS delete and servo deletion I am in the dark.

Is there anything in particular that I need to do when removing the ABS or is it just a case of removing the unit and re piping the system?

As for servo deleting, is it just a case of removing it and upping the pedal ratio and m/c sizes?

Also, one thing that has always confused me. When you have a bias bar, and it adjusted off centre, won't it result in not having a good alignment with the centre line of the m/c's anymore?

[Rav335uk]

Not sure of the ABS and servo stuff, but if you're thinking of getting rid of the 310mm setup, what would you be looking for???

[billgatese30]

Not sure. £600 new but there is a spare set of rotors there too (£120)

[Rav335uk]

So £720???????

[billgatese30]

Less than that obviously as they're used, but I'm not sure how much cheaper, I've never really given it any thought yet, plus I may end up keeping part of the front setup yet, depending on how much performance I would lose by dropping the rotor size

[Rav335uk]

Ok, just a query as i'm looking at set ups for the M30, the little ones are not up to the job

[billgatese30]

No probs, I'll let you have first dibs on anything that does become surplus to requirement if you haven't sorted anything by then.

[Rav335uk]

[jmc330i]

As for servo deleting, is it just a case of removing it and upping the pedal ratio and m/c sizes?

Just going to subscribe to this one as I was going to be asking this exact question in a few weeks.


How come you want different front brakes? For the rears, I think there a few 290mm (ish) conversions that are possible.

[billgatese30]

I already have a set of Z1 discs waiting to go on. I was looking at getting my hands on some e36 compact rear calipers to see how easy they were to fit, but haven't come across any (was going to get some free to try it out without he hasn't sent them yet) but I am also looking at e46 vented rear's too.

for the fronts I am just trying to think out of the box a little plus using one piece discs which aren't the £60 a pop that the wilwood rotors are, and if I can go back down to 15" without losing any real performance then so much the better.

[UweM3]

have you seen compbrakes pedal box? Maybe no need to make one yourself.
If you delete the servo you want SMALLER M/C's to generate the pressure required and change the pedal ratio.
ABS delete is straight forward, just repipe from M/C's. but why do you want to delete it? I wish I would have kept mine for this "oh shit" moments

[billgatese30]

The ABS delete was really just for ease of piping and bleeding really. Are the compbrake pedal boxes a bolt in fit?


edit:
just had a look at them online.

I was going to do the clutch cylinder too (as it is stupidly heavy after the S50 swap) but I could do that as a separate or even add it on the side of the compbrake box

[GeoffBob]

Hi Guys, I am thinking about changing the brakes on the track car. I am currently running 310mm Wilwoods with standard rears and thinking what I can do different.

I have thought about dropping rotor size so that I can run 15's again and also upgrading the rears at the same time.

I have also started looking into making a pedal box to run dual master cylinders with no servo, no ABS and no linkages to reduce pedal feel.

Bill, have a read this PDF here that I put together while helping Theo325 with exactly the same task.

Dropping your rotor size will not effect your braking performance so long as you can still exert the same braking torque at the wheel, which simply means the calliper will have to bite slightly harder into the smaller disc, which (assuming you use callipers with similar pistons) will simply require a higher hydraulic pressure. However, as I have said many times on this forum, the braking ability of a set of brakes (braking deceleration and hence stopping distance) has more to do with your tyre traction and the cars mass distribution than anything else. The only advantage to larger discs and callipers is reduced fade and wear (due to improved heat distribution/dissipation over a larger working surface).

The sad truth of the matter is that many brake upgrades/changes result in a substantially decreased stopping distance. Take the ever popular example of fitting larger/multiple piston front callipers and larger diameter front discs, without any attention paid to the dual E30 master cylinder. The result is that the stronger front brakes now lock-up the front wheels much sooner, well in advance of the rears in fact, which have themselves barely begun to take. The car now understeers wildly. Under these circumstances you have two choices: a) don’t press the pedal as hard in order not to lock up the front brakes (while all the time marvelling at how your rear pads and discs never wear out ”“ simply because they never get used) or press the pedal even harder after the fronts have locked up in order to get the rears to take. Neither offers optimal braking and both situations are vastly inferior to the stock brakes!

Not wanting to put anyone off the idea of upgrading their brakes, the point I am trying to make here is to emphasis the concept of tyre traction and braking balance, and to point out that any change to a disc or calliper that results in either increased or decreased hydraulic pressure in order to lock a wheel MUST be tempered by a change in the M/C sizes in order to ensure that both ends of the car reach their limits of braking traction simultaneously ”“ or else you could wind up spinning madly and regretting the day you ever considered bigger brakes better.

Pedal box shouldn't be a problem but when it comes to ABS delete and servo deletion I am in the dark.

Is there anything in particular that I need to do when removing the ABS or is it just a case of removing the unit and re piping the system?

You can simply delete the ABS and servo units. The front M/C then simply connects to the front callipers, and the rear M/C to the rear callipers. Technically, there is however no reason to have to remove the ABS. In my case I actually installed a Bosch-5 ABS unit after the two M/C’s. The front and rear hydraulic circuits are separate so there was no reason for me not to do this. FYI, the whole reason for increasing the surface area of the calliper pistons, resizing the M/C’s and increasing the pedal ratio is to return some of the mechanical advantage lost when the servo is removed. The big advantage to removing the servo is vastly more linear braking response.

As for servo deleting, is it just a case of removing it and upping the pedal ratio and m/c sizes?

No, unfortunately it is not simply matter of upping the pedal ratio and changing the M/C sizes. Have a look at Theo325’s thread here with regard to pedal boxes, M/C’s and brake proportioning valves (see the graphs that I posted around page 4)

The M/C’s have to be chosen according to the hydraulic pressure to bring both the front and rear brakes to the limit of threshold (termed threshold braking) simultaneously. This pressure is calculated as a function of the size of the callipers and discs respectively, as well as the cars weight distribution while braking (don’t forget that while braking the cars weight distribution shifts forward. The emphasis is at all times upon having the front and rear brakes contributing equally (per unit mass over each wheel) to the deceleration of the car in order to maintain stability. If the front wheels lock before the rears, or vice verse then there is a problem.

Also, one thing that has always confused me. When you have a bias bar, and it adjusted off centre, won't it result in not having a good alignment with the centre line of the m/c's anymore?

The M/C’s should be chosen to achieve identical braking deceleration (per unit axle mass) between the front and rear, with the bias-bar adjusted 50/50. Adjusting the bias bar may be used to compensate for tyre wear, draining fuel load from the rear, and track conditions; but should not be used to compensate for an incorrectly sized M/C. Shifting the bias bar left or right does indeed adjust the alignment of the pedal with the two M/C’s, which, following Newton’s laws, is precisely how the pedal force is divided between the two M/C’s. If the bias-bar is adjusted 50/50, and you apply 30lbs of force to a 6:1 ratio pedal, then you are effectively applying 90lbs of force to each M/C. The hydraulic pressure that this results in at each brake cylinder is thus a function of the size of the M/C’s.

[billgatese30]

Cheers Geoff, I'll re-read Theo's thread tonight, I can remember it the first time around but never paid too much attention to it as I just flitted in and out as it progressed, rather than getting as heavily involved as Theo and others did, I can remember the lengths that the data, explanations of theory etc were excellent though, so I'll give it a re-read again to save you from regurgitating what you have already typed.

I'm going to put the kettle on and turn the radio up whilst I read that pdf.

I do realise that there is alot of theory work needed for calcs etc before anyone can say its going to go one way or another. Hence why I knew that I would probably be able to get away with smaller discs than I have (and be able to go to 15" bbs) as I know that larger caliper pistons, and mechanical/hydraulic advantage plus, just the fact that it will be a nice balanced system will allow me to brake better than ever before.

[GeoffBob]

[billgatese30]

Let me know if you’d like for me to do some calculations for you, as I did for Theo, once you have some idea as to what brake components you plan to use on your car. I can then set about helping you choose your two M/C’s. Given the position and weight of your engine I suspect that we will see your brakes slightly more forward biased than either mine or Theo’s.

I might just hold you to that Geoff. Thanks

I would have thought that my engine is alot heavier than your's and theo's being an iron 6 cylinder lump, although the rest of my car is both heavier and more softly sprung than your cars too. And whilst a suspension upgrade would be nice, I can't afford to do it and the brakes at the same time

[BadDave]

Let me know if you’d like for me to do some calculations for you, as I did for Theo, once you have some idea as to what brake components you plan to use on your car. I can then set about helping you choose your two M/C’s. Given the position and weight of your engine I suspect that we will see your brakes slightly more forward biased than either mine or Theo’s.

I may well be in touch in the next few weeks Geoff,IF you'd be willing to do a little maths work on my setup?

[GeoffBob]

I would have thought that my engine is alot heavier than your's and theo's being an iron 6 cylinder lump, although the rest of my car is both heavier and more softly sprung than your cars too. And whilst a suspension upgrade would be nice, I can't afford to do it and the brakes at the same time

Indeed, quite a bit heavier I would expect, which is why you will find a lot more weight over your front axle than over your rear while attempting a high G braking manoeuvre. Hence, you will have to rely a lot more upon your front brakes, which is why I say that your brakes will be more front-biased. Any attempt to bite down harder upon your rear rotors (thus shifting the bias aftwards) could result in your rear wheels locking up with so little weight acting down upon them.

Interestingly, your suspension has absolutely no effect upon your cars dynamic weight distribution. A softer sprung car will pitch forward to a greater degree than an identical car with harder springs, while both execute an identical braking manoeuvre. The softer sprung car, however, pitches forward more because that is, quite simply, how softer springs respond. It isn’t, by any means, an indication that the softer sprung car is experiencing a greater shift in weight

The only way to keep as much weight as possible over the rear axle while braking hard, is to lengthen the cars wheel-base, lower the centre-of-gravity, or start with as much weight in the back to begin with. This is why rear and mid engined cars have such a distinct braking advantage over front engined cars. Short of moving your engine to the boot, one of the best ways to allow you to shift your brake bias aftwards (without locking the rear wheels) is to replace as much of the glass in your car with polycarbonate as possible, thus substantially lowering the height of the cars COG.

[GeoffBob]

I may well be in touch in the next few weeks Geoff,IF you'd be willing to do a little maths work on my setup?

Always a pleasure to help where I can

[billgatese30]

Interestingly, your suspension has absolutely no effect upon your cars dynamic weight distribution.

Interestingly, that makes me very happy and yet very stupid at the same time as it means that I have less to worry about later on for future upgrades, but also stupid as I'm sure I have read that in a book somewhere as well as reading it in a post or two on here (possibly even penned by yourself)

[GeoffBob]

Interestingly, that makes me very happy ...

Which is entirely why I mentioned it

So long as you never pitch or yaw to the point where you run out of suspension travel and pick up a wheel, you have nothing to worry about. Well, at least not from a braking perspective at least. Stiffening up the suspension has other effects and purposes, but we'll leave that for another day.

[billgatese30]

Already know of the downsides of soft springs and stiffer roll bars

http://www.e30zone.net/modules.php?name ... c&t=147711

[BadDave]

I may well be in touch in the next few weeks Geoff,IF you'd be willing to do a little maths work on my setup?

Always a pleasure to help where I can

OK here goes.

The front calipers are these here.
http://www.wilwood.com/CaliperList.aspx?subname=Grand National

With 335x32mm disks


The rears are 4 pot Wilwood Superlites with 1.75" (45mm) pistons clamping 310x32mm disks

The adj pedal box is from Compbrake
http://www.compbrake.co.uk/PEDALBOXES/PEDALBOXES9.html

The pedal box fits where the servo normally would,so a servo delete is required. I intend retaining the ABS
With regards to the boat anchor up front. It's an M20B25 at the moment.
Re your earlier comments, It's coilovers all round with 550Lb/in springs and 4Lb/in helpers up front.

If theres anymore info needed, just ask.

Cheers

Oh,

I'm hoping that a 0.75"/0.625" M/C's will suffice.

[billgatese30]

Dave,

does that compbrake "pedal box" still use the link that the standard setup uses?

[BadDave]

Dave,

does that compbrake "pedal box" still use the link that the standard setup uses?

Fraid so Chris.

If you fancy making something up directly above the pedals and running the M/c's under the battery tray, PM e21Jason as Brookers old rally M3 which he happened to purchase had that type of setup fitted.
Hence why i have the Compbrake pedal box which Brooker removed.

HTH

[keri-WMS]

Well if you're after a big increase in piston area under the 15" BBS there's always the 1.62"/1.75" staggered-piston version of the WMS T20, in case it helps! Here are some numbers:

E30 OEM 1.89" piston (x"2") caliper = 5.61 square inches effective area
WMS 1.25"/12.5" caliper = 4.91 square inches (87.5% of OEM)
WMS 1.38"/1.38" caliper = 5.98 square inches (106.6% of OEM)
WMS 1.62"/1.75"caliper = 8.93 squaare inches (159.2% of OEM!!!!)

Hope that helps, more numbers for the GeoffBob mill!

[GeoffBob]

The rears are 4 pot Wilwood Superlites with 1.75" (45mm) pistons clamping 310x32mm disks.

Goodness, those are huge Dave!! You’ll need a huge rear M/C compared to your front M/C (to keep the rear fluid pressure down) to stop those rears from locking up. Is there any way that you could put back a smaller (2-piston?) calliper at the rear? Pulling a 1G braking manoeuvre in a 1300kg (est.) road car with an M20B25 in the front will probably see you with close to 900kg of dynamic weight over the front axle, and only 400kg left behind over the rear. You therefore require a softly-softly approach to those big rear callipers to stop your rear end from swinging like-a-pendulum-do! At present I can’t see your car as being anything else other than tail-happy. Even with the stock E30 pressure regulating valve in the rear I am sure that your rear fluid pressure is high enough to exert a substantial brake torque on those rear discs via those big callipers. This must make trail-braking a nightmare for you at present. Sorry ”“ I don’t mean to come over nasty at all, I just speak it like I see it. If you want to keep your rear hardware we will need to look at a way to get your rear hydraulic pressure way down compared to the front.

If theres anymore info needed, just ask.

I need to know your cars current static weight distribution, so you’ll need to get her to a set of scales and weigh her up. I also need your tyre info - sizes, tread and compound.

Sorry, but I don’t really know your cars application. Is she track only? If so is the glass removed or intact. Roll-cage or not? This all affects the height of the cars COG.

And remember gents, the only way to take advantage of all this brake hardware is to have tyres that enable you to transmit these brake forces to the ground. Your bestest brake upgrade ever is a set of sticky track tyres.

[GeoffBob]

Dave,

does that compbrake "pedal box" still use the link that the standard setup uses?

Chris, try steer clear of anything that retains the stock linkage. I realise that space is tight and that the exhaust precludes fitting forward facing M/C's to the firewall, but there are other options (such as fitting a Jap motor with the exhaust on the left - just kidding )

I think page 1 of Theo's brake thread includes some pictures of MartinPallot's work (with the M/C's on the inside of the firewall above the pedals). You might also consider Tiltons overhung pedal assemblies here. Keep your pedal ratio around 6:1 to 7:1 if you can.

[BadDave]

The rears are 4 pot Wilwood Superlites with 1.75" (45mm) pistons clamping 310x32mm disks.

Goodness, those are huge Dave!! You’ll need a huge rear M/C compared to your front M/C (to keep the rear fluid pressure down) to stop those rears from locking up. Is there any way that you could put back a smaller (2-piston?) calliper at the rear? Pulling a 1G braking manoeuvre in a 1300kg (est.) road car with an M20B25 in the front will probably see you with close to 900kg of dynamic weight over the front axle, and only 400kg left behind over the rear. You therefore require a softly-softly approach to those big rear callipers to stop your rear end from swinging like-a-pendulum-do! At present I can’t see your car as being anything else other than tail-happy. Even with the stock E30 pressure regulating valve in the rear I am sure that your rear fluid pressure is high enough to exert a substantial brake torque on those rear discs via those big callipers. This must make trail-braking a nightmare for you at present. Sorry ”“ I don’t mean to come over nasty at all, I just speak it like I see it. If you want to keep your rear hardware we will need to look at a way to get your rear hydraulic pressure way down compared to the front.

If theres anymore info needed, just ask.

I need to know your cars current static weight distribution, so you’ll need to get her to a set of scales and weigh her up. I also need your tyre info - sizes, tread and compound.

Sorry, but I don’t really know your cars application. Is she track only? If so is the glass removed or intact. Roll-cage or not? This all affects the height of the cars COG.

And remember gents, the only way to take advantage of all this brake hardware is to have tyres that enable you to transmit these brake forces to the ground. Your bestest brake upgrade ever is a set of sticky track tyres.

Geoff, I only have the front setup fitted at the moment with the stock servo and an E30 M3 Master cylinder.
The rears are almost ready fit.
Trying to find a 2 pot caliper thats ready to bolt on would be quite difficult
I do "happen to have" another set of Superlites with 1.38"(35mm) pistons available for experiment purposes which could be pressed into service

I'd guess the car weight to be roughly 1400KG with the additional items in the rear loadspace and nearer 49/51 distribution biased towards the rear.
The car is road based with 215/35/18 and 215/40/18 road tyres. Full set of OE glass, and all interior still in place( no cage)

Acquiring and fitting an adjustable proportioning valve is an option if needed


HTH

[billgatese30]

Dave,

does that compbrake "pedal box" still use the link that the standard setup uses?

Chris, try steer clear of anything that retains the stock linkage. I realise that space is tight and that the exhaust precludes fitting forward facing M/C's to the firewall, but there are other options (such as fitting a Jap motor with the exhaust on the left - just kidding )

I think page 1 of Theo's brake thread includes some pictures of MartinPallot's work (with the M/C's on the inside of the firewall above the pedals). You might also consider Tiltons overhung pedal assemblies here. Keep your pedal ratio around 6:1 to 7:1 if you can.

That was half of the reason for deleting the servo, to remove the linkage, and whilst doing that, it just made sense move to a proper dual master cylinder setup.


Keri, I may have a word with you later about the larger Calipers.

[keri-WMS]

Keri, I may have a word with you later about the larger Calipers.

Cool, only one pair of them left just so's you're aware..

[gareth]

Dave, you'd need a lot of extra clutter in your car to take it up to 1400kg, unless you're including yourself in that?

mine weighs in at 1400kg with a M30 and the LPG setup

[GeoffBob]

That was half of the reason for deleting the servo, to remove the linkage, and whilst doing that, it just made sense move to a proper dual master cylinder setup.

Excellent idea! One of my favourite things about dual M/C's is that you get to choose the M/C's to match the calliper setup. You can have six-pot Willwood callipers on the front and stock E30 single piston sliding callipers on the rear, but still find a a pair of M/C's and a proportioning valve that enable the front and rear to function in balanced harmony with each other. Might not be the worlds best setup, but it works correctly until such time as you have the money to buy a nice pair of two-pots for the rear, and then just by swopping one M/C all works correctly once again.

Tandem M/C's just don't provide quite the same opportunity for fiddling, and brake servo's simply annoy me.

[GeoffBob]

BadDave, I have noted the info you have provided and will respond as soon as I have answer for you. 'Fraid I have to agree with Gareth over the 1400kg though, are you sure? And with 51% of the static weight biased to the rear - Are you sure? Oh wait a minute - we're talking about a tourer here aren't we? Sorry, I must have missed that bit. Hmmmm, but with that big old engine at the front is it still as much as 51% to the rear? Any help anyone please. Always best to answer this by putting the car on a set of scales.

[gareth]

bodies in the boot again dave?