e30 soft brake pedal solved?

#41

you still didn’t answer my question…how are you bleeding the system? pressure bleeder?

#42

[quote=“Ranger” post=71147]Re. harder pedal and MC dia. The objective is to increase the fluid pressure. Pressure = Force / Area, or P=F/A. So if the objective is to achieve 500psi you can use a woman’s high heels or you can use an elephant’s foot. The heavy elephant’s weight is distributed across a large foot print. The woman’s high heal creates the same pressure with much less force.

Turn that into MC’s. It takes more force to get 500psi out of a larger MC, so you have to press the pedal with more force. Since pressing the pedal with more force makes the MC move, a larger MC will create more unintended flex of the braking system.

It’s that unintended flex that I’m working to minimize. Because of the 4:1 pedal ratio the 3-4mm of MC movement means that >12mm of pedal movement does nothing more then bend the firewall or booster. Think about that…the brake pedal moves enough to put the pads in firm contact with the rotors, but then the pedal certainly does not feel rock hard, even tho pressing harder really doesn’t move the pads anymore. When I think about how much my pedal moves at that point, I think in that ballpark of 12mm. Therefore if I can hold the MC still, I think I can significantly reduce that softness.

I’ve raced in 3 SpecE30’s. The brakes on all 3 felt the same. Soft.

The charm of a bigger MC is that it moves more fluid. A small MC can’t handle big slave cylinders because it doesn’t push enough fluid to move the slave pistons far enough in their cylinders.[/quote]

Ranger,

Just to clarify you are submitting that at one point in applying the breaks the input force (from driver) is greater than rigidity of the the mechanical aspect of the breaking system but less then capability of the hydraulic aspect of the system.

I drew a picture to help. (I know work is not measured in #'s but you get the idea)

By decreasing the input force you can shift the hydraulic curve to the left of the mechanical curve and thereby increasing the potential hydraulic work.

As you make changes in the MC to increase its work output to work input ratio you affect the piston travel to peddle travel relationship also. I imagine there is a little adjustment that is possible before the peddle travel becomes too exaggerated; but how much?

Tilton has a nice write up of some of these dynamics and how to choose caliper and MC sizes. Here is a link and page 2.

#43

[quote=“Ranger” post=71147]I’ve raced in 3 SpecE30’s. The brakes on all 3 felt the same.[/quote] Remind me what the problem is again?

What I seek as a driver is consistency and speed. I want my vehicle to give a consistent reaction to my (hopefully) consistent inputs.

I’m still not seeing the issue here.

#44

[quote=“87isMan” post=71145]

The e31 master is a good 50 dollars cheaper than the e30 ate master so that is a decent cost savings. A few years ago I remember the member from down under stating that it was the only ate master they used in their class.

I’m not an engineer so I don’t really understand the harder pedal put less fluid movement argument. It seems to me any firmer pedal will require more human force and you are trying to fix your mushy brake pedal correct? I can’t see the MC moving a bit when you mass the brakes hindering the system, it should still be pushing the same fluid whether it flexes a bit or is stable.

What I’m ultimately saying is your MC flex is not the cause of your squishy brake pedal. How do you bleed your brakes?[/quote]
I read some stuff by an Aussie e30 racer as you described but it didn’t go into detail as to “why”. There’s some subtlties here that get lost in commo confusion, so it can be tricky to talk to someone about. The bigger MC moves more fluid so there’s less pedal slack movement before the pads are pressed against the rotors. Some will say that reduced pedal slack is a firmer brake pedal, but that’s not how I would define a firmer brake pedal.

Consider how a brake pedal would feel in an entirely rigid system. The pedal might move an inch in order to take up slack (move pads to rotors) but then allow no further movement. No matter how hard you pressed, it would be like pressing on granite. The pedal would not move because the hypothetical system was entirely rigid. To me, that’s a firm pedal. It’s not about taking up slack, its about what the pedal feels like once you’ve gotten thru the slack.

A big MC reduces slack. But what happens next is important. Because the big MC requires more foot force to get the same line pressure (remember high heels vs. elephant), you really have to press on the pedal like you mean it. More foot force, in our case, would mean more distortion of the firewall and booster so the MC would move even more. Lets say it moves 4mm. Because of the 4:1 ratio of the foot pedal arm, 4mm of MC movement is 16mm of pedal movement. Imagine the difference in brake pedal feel between pushing on granite and pushing on something that will happily move 16mm.

My point is that when someone describes their brake pedal as being “firm” or “hard”, it’s not clear what precisely they are describing.

Re. bleeding brakes. I like Speedbleeders because they have a checkvalve that won’t let air into the system, and they make it easy to bleed the brakes w/o a helper. #1 wife does not like to be dragged into the icky garage. I usually put a pressure bleeding on the reservoir, pump it up to 10psi and do a bit of bleeding.

#45

This is becoming way too funny… When Ranger catches a scent there’s no getting him off that tree…:woohoo:

You have some data points comparing Girling systems to ATE…

As one who races with no ABS I can tell you that the pedal pressure your attributing to firewall flex is way out of the normal range. Think about it - we have vacuume assisted braking - the pedal pressure needed to achieve threshold braking is quite low.

I’ll say it again; my 89 with Girling is top notch - pedal travel of about 1.5" from start to finish and hard as a rock…

Because Ranger has made a veiled reference to the credibility of some to judge “good brakes” I’ll throw mine out

1982 Skip Barber Race Series Rookie of the Year (Formula Ford)
SVRA/HSR multi winner - Tilton full race system
2002-2007 Grand Am Cup - E46 ST Class
Past 911 owner - track car

I’ve experienced some of the best and believe me some of the worst braking and am pretty confident in my ability to tell the difference…

#46

[quote=“SeaBird” post=71154]
Ranger,

Just to clarify you are submitting that at one point in applying the breaks the input force (from driver) is greater than rigidity of the the mechanical aspect of the breaking system but less then capability of the hydraulic aspect of the system.

I drew a picture to help. (I know work is not measured in #'s but you get the idea)

By decreasing the input force you can shift the hydraulic curve to the left of the mechanical curve and thereby increasing the potential hydraulic work.

As you make changes in the MC to increase its work output to work input ratio you affect the piston travel to peddle travel relationship also. I imagine there is a little adjustment that is possible before the peddle travel becomes too exaggerated; but how much?

Tilton has a nice write up of some of these dynamics and how to choose caliper and MC sizes. Here is a link and page 2.[/quote]
I follow what you are saying but I kept waiting for a “Therefore…”

“Work” is a hard concept for the non-engineer to really relate to, so we might want to stay clear of it. There’s at least one joke in that sentence so no trying to snatch humor-credit. It’s all mine.

“Pressure”, “Force” and “Deflection” lend themselves better to clear communication because they’re better understood.

Sure, there’s a competing requirement for brake line pressure and the volume of fluid movement. Easy to get one at the expense of the other, but harder to get both. Big calipers require lots of fluid movement so require a big MC. But a big MC requires lots of foot pressure so a powerful booster is needed. The designers play with the variables and work out a solution.

#47

[quote=“Steve D” post=71155][quote=“Ranger” post=71147]I’ve raced in 3 SpecE30’s. The brakes on all 3 felt the same.[/quote] Remind me what the problem is again?

What I seek as a driver is consistency and speed. I want my vehicle to give a consistent reaction to my (hopefully) consistent inputs.

I’m still not seeing the issue here.[/quote]
Fair points.

Mostly I’m just up to my usual highjinks.

I’ve long been irked by the fact that all e30’s I’ve tracked had mushy brakes compared to 911s. One day I decided to see if I couldn’t figure out “why” the brakes seemed mushy. There were lots of Internet references to wimpy calipers, but the only flexing I could spot was the MC. And so it began.

What I’m still waiting to hear from these guys offering data points is whether or not their MC’s are moving.

#48

Ranger,

I think you have missed the compress-ability of the break fluid itself when considering the granite example. Although it approaches the incompressability of water (0%) silicon break fluid has a compress-ability of .3-.7% as a function of temperature.

This does not seem like a lot but it does effect peddle travel. There is a very through write up available here.

In the example given, for new pads, the additional peddle travel (calculated) due to the compression of the fluid is .1" or 2.54mm for average worn pads .2" or 5.08mm. Despite the difference in the systems that would put the peddle travel due to fluid properties in the order of magnitude of the mechanical deformation.

(As an engineer I too enjoy the theoretical exercises :wink: )

Regards,

Miguel

#49

[What I’m still waiting to hear from these guys offering data points is whether or not their MC’s are moving.[/quote]

Moving at what pedal pressure??? I’m sure that we all have enough strength to deflect the firewall mounting point but that doesn’t equate to the “real world” threshold braking pressure.

#50

The therefor or but comes due to the nature of the class. The caliper is a constant so when you change MC size you will get a change in peddle pressure as desired BUT at the cost of peddle travel (not due to mechanical deformation). If your okay with a lot of travel then change your MC size. It was my impression that most racers prefer shorter travel not longer travel.

At this point though your talking about objective and not subjective tastes. I think what PDS is saying is consistency over 500 strokes is more important to him than the consistency from top to bottom of a single stroke. He wants to know the peddle is always going to act the same, it does not really matter to him how that is just that it is the same. You just have more refined taste that’s all :wink:

The deformation that your concerned about is plastic so it returns to its original shape after the force is removed. In enough time there could be metal fatigue and the original shape 20 years ago and today might be different but probably not between the start of the race weekend and the end of the race weekend. So one could say that the ultimate feel of the peddle is consistent over the span of a weekend (and probably over the season) and therefor acceptable.

If you are experiencing break fade its unlikely due to your firewall flex but other factors that I am less qualified to talk about.

#51

[quote=“SeaBird” post=71161]Ranger,

I think you have missed the compress-ability of the break fluid itself when considering the granite example. Although it approaches the incompressability of water (0%) silicon break fluid has a compress-ability of .3-.7% as a function of temperature.

This does not seem like a lot but it does effect peddle travel. There is a very through write up available here.

In the example given, for new pads, the additional peddle travel (calculated) due to the compression of the fluid is .1" or 2.54mm for average worn pads .2" or 5.08mm. Despite the difference in the systems that would put the peddle travel due to fluid properties in the order of magnitude of the mechanical deformation.
[/quote]
The granite example was an attempt to illustrate that the idea of a firm brake pedal can mean different things to different people.

We’re not going to ID every deviation from a perfectly rigid system, but it might be interesting if we could mitigate some of the low hanging fruit.

Moving at what pedal pressure??? I’m sure that we all have enough strength to deflect the firewall mounting point but that doesn’t equate to the “real world” threshold braking pressure.[/quote]

I discussed that uncontrolled variable in an earlier post. See reference to uncalibrated wife. Not everything can be figured out rigorously. Sometimes you have to guesstimate.

That doesn’t change the fact that I suggested that folks try the test themselves and see if their MC’s are moving, but what resulted was “my brakes are < >” posts. Not a soul has yet to put someone in their car, press the brake pedal hard, and look for MC movement. Lots of talkers. Few doers.

Re. calibrating brake pedal pressure. This is probably do-able after all. Go fetch your bathroom scale. Turn your car on and press on the brakes a number of times and try to get foot pressure about what it is for anxious threshold braking when your brakes have gotten hot and it’s looking like you made a bad call trying to divebomb someone.

With that same “feel” in your head, put the bathroom scale against the garage wall, sit on the floor or something low, and push on the bathroom scale. Go back and forth between car and scale until the #'s are reasonable consistent. Now grab a helper and have them very carefully observe MC movement at the same pedal pressure that by now should be firmly ingrained. Do enough repetitions of this and I bet you get 10% accuracy on MC movement under heavy braking, and also we start getting absolute #'s as to how hard we’re pushing the pedal.

#52

[quote=“Ranger” post=71164][quote=“SeaBird” post=71161]Ranger,

I think you have missed the compress-ability of the break fluid itself when considering the granite example. Although it approaches the incompressability of water (0%) silicon break fluid has a compress-ability of .3-.7% as a function of temperature.

This does not seem like a lot but it does effect peddle travel. There is a very through write up available here.

In the example given, for new pads, the additional peddle travel (calculated) due to the compression of the fluid is .1" or 2.54mm for average worn pads .2" or 5.08mm. Despite the difference in the systems that would put the peddle travel due to fluid properties in the order of magnitude of the mechanical deformation.
[/quote]
The granite example was an attempt to illustrate that the idea of a firm brake pedal can mean different things to different people.

We’re not going to ID every deviation from a perfectly rigid system, but it might be interesting if we could mitigate some of the low hanging fruit.

Moving at what pedal pressure??? I’m sure that we all have enough strength to deflect the firewall mounting point but that doesn’t equate to the “real world” threshold braking pressure.[/quote]

I discussed that uncontrolled variable in an earlier post. See reference to uncalibrated wife. Not everything can be figured out rigorously. Sometimes you have to guesstimate.

That doesn’t change the fact that I suggested that folks try the test themselves and see if their MC’s are moving, but what resulted was “my brakes are < >” posts. Not a soul has yet to put someone in their car, press the brake pedal hard, and look for MC movement. Lots of talkers. Few doers.

Re. calibrating brake pedal pressure. This is probably do-able after all. Go fetch your bathroom scale. Turn your car on and press on the brakes a number of times and try to get foot pressure about what it is for anxious threshold braking when your brakes have gotten hot and it’s looking like you made a bad call trying to divebomb someone.

With that same “feel” in your head, put the bathroom scale against the garage wall, sit on the floor or something low, and push on the bathroom scale. Go back and forth between car and scale until the #'s are reasonable consistent. Now grab a helper and have them very carefully observe MC movement at the same pedal pressure that by now should be firmly ingrained. Do enough repetitions of this and I bet you get 10% accuracy on MC movement under heavy braking, and also we start getting absolute #'s as to how hard we’re pushing the pedal.[/quote]

Do you have any idea of how cold it is in my garage right now??? Good God, now were trying to replicate threshold braking with a bathroom scale???

Ranger, don’t interpret my questioning as throwing stones. I always get pleasure and some info from your insuferable quests to learn more about these cars…

But let me riddle you this; My teamates car, all ATE has a terribly long and mushy pedal. We have replaced calipers, m/c, vac booster and all lines to no avail. However, if the engine is not running - no vac boost - the pedal stays high and without any “mushiness(?)”… Hmmmmmmmmm. Would tell me that were are not dealing with flexing at the firewall. Also, you have others stating that their pedal is really good. I’m pretty sure that BMW has not made changes to the firewall through the car’s life cycle. Seems to me that you’re searching a false path/premise.

If I have to eat my words then cool - I’m good with that…

#53

[quote=“SeaBird” post=71163]The therefor or but comes due to the nature of the class. The caliper is a constant so when you change MC size you will get a change in peddle pressure as desired BUT at the cost of peddle travel (not due to mechanical deformation). If your okay with a lot of travel then change your MC size. It was my impression that most racers prefer shorter travel not longer travel.

At this point though your talking about objective and not subjective tastes. I think what PDS is saying is consistency over 500 strokes is more important to him than the consistency from top to bottom of a single stroke. He wants to know the peddle is always going to act the same, it does not really matter to him how that is just that it is the same. You just have more refined taste that’s all :wink:

The deformation that your concerned about is plastic so it returns to its original shape after the force is removed. In enough time there could be metal fatigue and the original shape 20 years ago and today might be different but probably not between the start of the race weekend and the end of the race weekend. So one could say that the ultimate feel of the peddle is consistent over the span of a weekend (and probably over the season) and therefor acceptable.

If you are experiencing break fade its unlikely due to your firewall flex but other factors that I am less qualified to talk about.[/quote]
Fade is a different issue.

You may be mixing plastic and elastic deformation. My bet is that we’re not seeing the results of fatigue. During the normal service life the e30 owner doesn’t push on the brake pedal as hard as we do. The force is spread across a lot of sheetmetal and it’s not deforming more than a couple degrees. That’s not a normal recipe for plastic deformation nor fatigue of mild steel.

I understand the importance of consistency. But it would be interesting to figure out how we might easily make the brakes feel consistently…better.

You seem to be emphasizing the trade-offs associated with MC sizing and I’m emphasizing controlling the MC’s movement. As a result we’re kind of talking past each other.

#54

[quote=“PDS” post=71165]
Do you have any idea of how cold it is in my garage right now??? Good God, now were trying to replicate threshold braking with a bathroom scale???

Ranger, don’t interpret my questioning as throwing stones. I always get pleasure and some info from your insuferable quests to learn more about these cars…

But let me riddle you this; My teamates car, all ATE has a terribly long and mushy pedal. We have replaced calipers, m/c, vac booster and all lines to no avail. However, if the engine is not running - no vac boost - the pedal stays high and without any “mushiness(?)”… Hmmmmmmmmm. Would tell me that were are not dealing with flexing at the firewall. Also, you have others stating that their pedal is really good. I’m pretty sure that BMW has not made changes to the firewall through the car’s life cycle. Seems to me that you’re searching a false path/premise.

If I have to eat my words then cool - I’m good with that…[/quote]
Re. cold garage. Always room in the South for more Yankees. It’s a big help keeping our home values up.

Re. mushy brakes. I dunno. I’d suggest looking at the different parts of the braking system and see if can detect movement or distortion under heavy braking.

Re. bending firewall. Hmm. How to say this diplomatically? One of us has been spending his evenings with his hand stuffed down between the underside of the vac booster and the firewall while grumpy #1 wife pushed on brake pedal, and one of us has not. One of us has been watching the MC move and one of us hasn’t. One of us believes the booster and firewall are distorting and one of us doesn’t. You going to go with the guy that’s been doing this or you going to go with the guy who’s garage is an icebox so conjecture is going to substitute for DIY experiments until the snow clears?

Re. others stating brakes are firm. I hear ya, but it’s tricky to gather info on this because it’s all subjective. There isn’t even agreement on what “firm” means, much less “how firm” is “firm”.

#55

[quote=“Ranger” post=71166]
Fade is a different issue.

You may be mixing plastic and elastic deformation. My bet is that we’re not seeing the results of fatigue. During the normal service life the e30 owner doesn’t push on the brake pedal as hard as we do. The force is spread across a lot of sheetmetal and it’s not deforming more than a couple degrees. That’s not a normal recipe for plastic deformation nor fatigue of mild steel.

I understand the importance of consistency. But it would be interesting to figure out how we might easily make the brakes feel consistently…better.

You seem to be emphasizing the trade-offs associated with MC sizing and I’m emphasizing controlling the MC’s movement. As a result we’re kind of talking past each other.[/quote]

Your right I will correct my previous post, elastic deformation. That’s what happens when you spend to much time in business management and not in engineering :blush:

I also agree that we are talking past each other. That’s why I drew the picture, compare perspectives on consistency, and brought up fade.

The point of the MC was you could decrease the required input force and shift the hydraulic curve away from the mechanical curve. The flexing that is happening is most probably not happening 0-x lbs of applied force but at >x applied force. If you could achieve maximum breaking force a <x applied force then you would never feel the mechanical limitations of the break peddle assembly. What would happen then though is you would also loose “feel”.

I guess I am saying is that it is not as low lying as you might think. I have one of these babies on my Alfa GTV:

And the feel is spectacular. (And that’s not me talking but some Ferrari driving instructor types) It becomes an expensive proposition to correct and it does not seem consistent with the spirit of the class.

#56

[quote=“SeaBird” post=71171]

Your right I will correct my previous post, elastic deformation. That’s what happens when you spend to much time in business management and not in engineering :blush:

I also agree that we are talking past each other. That’s why I drew the picture, compare perspectives on consistency, and brought up fade.

The point of the MC was you could decrease the required input force and shift the hydraulic curve away from the mechanical curve. The flexing that is happening is most probably not happening 0-x lbs of applied force but at >x applied force. If you could achieve maximum breaking force a <x applied force then you would never feel the mechanical limitations of the break peddle assembly. What would happen then though is you would also loose “feel”.

I guess I am saying is that it is not as low lying as you might think. I have one of these babies on my Alfa GTV:

And the feel is spectacular. (And that’s not me talking but some Ferrari driving instructor types) It becomes an expensive proposition to correct and it does not seem consistent with the spirit of the class.[/quote]

Re. “The point of the MC was you could…” Understood. That’s why I explored the idea of a smaller MC, only to find that apparently I already have the smallest MC. Altho there are other models of MC’s that are smaller, 1)We could easily find that smaller was too small because too much travel, and 2)I’ve a pretty good sense of what I can win a rule change on and what I can’t. I think that a non-e30 OEM solution would clearly require a rule change and I don’t think I’d get it. That makes that solution a lot less interesting to me to poke around.

I don’t buy that we’d necessarily lose “feel” tho. I’m not exactly sure what “feel” is in this context, but there’s no way that >12mm of MC movement contributes to it.

Re. aftermarket pedals, or to go one better, aftermarket brake upgrades like the booster delete kit. Another rule change necessary an I’ve no argument strong enough to win the day.

You brought up “fade” because we were talking past each other? Have you been discussing debate techniques with my wife?

#57

First feel is about a subjective as it comes. Second let me state that I have no fidelity and I understand little of what I feel and how its correlated to what is happening at the rotors. With these two premises out of the way I will venture into this death trap of a thread :wink:

Feel has two parts; a)the drivers ability to experience the feedback at the peddle (fidelity) and b) the ability for what is happening at the peddles to be communicated through the car’s systems (feedback).

With regards to fidelity you have what you have, get use to it.

With regards to feedback mechanical/hydraulic advantage used to assist the driver in applying breaking force works both ways. It makes it easier for the driver to apply pressure to the pads but it makes it more difficult for the pads to apply pressure to the peddle.

Think of a gear box and the difference between the input and output speeds and the input torque and the output torque. Same thing is happening in with the hydraulic system.

The more advantage you build into the system the less feedback is available at the input side. This then requires a higher fidelity on the part of the driver. Its easier to increase physical strength than to increase fidelity so generally speaking heavier break peddles is the norm in performance driving.

On street cars the feedback is less important to the driver than easy of breaking so manufactures design their systems accordingly. Hence the breaking systems we have in the e30s.

I remember the first time I drove a gt-40 I drove home after the test drive thinking how much more I liked the breaks on my Vette. As my experience with different breaking systems expanded the Vette’s breaks have lost favor. I tell people that it is my 430 hp sofa. Mind you it will certainly out break everything in my stable. I just have no idea what its doing.

#58

[quote=“Ranger” post=71173]
You brought up “fade” because we were talking past each other? Have you been discussing debate techniques with my wife?[/quote]

No I was just pinging to see just how far apart we all were in our conversations. Much like someone earlier question if you were actually bleeding your breaks well. :wink:

And if that’s what your wife is doing too, smart woman!

Wow I should actually try and do some work today…

#59

Re. bending firewall. Hmm. How to say this diplomatically? One of us has been spending his evenings with his hand stuffed down between the underside of the vac booster and the firewall while grumpy #1 wife pushed on brake pedal, and one of us has not. One of us has been watching the MC move and one of us hasn’t. One of us believes the booster and firewall are distorting and one of us doesn’t. You going to go with the guy that’s been doing this or you going to go with the guy who’s garage is an icebox so conjecture is going to substitute for DIY experiments until the snow clears?

Nahh, I’ll go with the guy who isn’t having a problem with his brakesB)

I’ll continue to watch you go down that rabbit hole :slight_smile: Like I said, my garage is too damn cold. Plus, my parents taught me at a young age to be careful where I’m trying to stuff my hands… From the sounds of it you could be risking blindness

C-Ya!

#60

This thread isn’t going anywhere. We’ve said the same thing about the physics at least 5x, and we’ve not added anything useful to the thread in 2 pages. I’ve learned what I wanted to learn. I started the thread, as usual, in case others found the discussion useful. The first couple pages, anyhow.

I’m throwing smoke and breaking contact. Indirect fires will cover the withdrawal. Charlie Mike.