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How to fix/improve low soft Brake pedal with Residual Pressure Valves and seal lube

GTIfan99

Autocross Champion
Location
FL
I'm pretty happy with just the OBD11 changes, but I think this is a cool idea and should make this a better option for those running STH that can't legally do OBD11 changes.
 

emichel6888

Go Kart Champion
Location
TX
Okay, I found a source for these pistons and some other interesting information. They do have two versions of the same piston, one is part number P42045A and the other is P42045A-B, and the later indicates it is for the Audi Q5 while the former does not specify a particular vehicle:
2020-08-26 22_24_09-Audi Q5 (8R) Front brake caliper piston - For Brembo 4 piston calipers P42...png
2020-08-26 22_25_10-42mm Brake caliper piston for Brembo calipers Aluminium (Option 4 of 4) P4...png



I could not find a piston kit for the 4 pot Macan anywhere, but the Q5 no problem. And when you look at the complete rebuild kit for the Q5 they are all the same dark finish:
2020-08-26 22_12_21-AUDI Q5 2008-2017 FRONT L & R Brake Caliper (4 pot) Seal Kit +Pistons (BRK...jpg

So then I went looking for a good picture showing the pistons on both sides of the Q5 caliper, and sure enough the Q5 version does indeed use the same dark finish pistons on both inner and the outer:
Audi Q5 brake caliper.png

While the picture of the individual pistons is the same, I bet the non B part number is the lighter finish used on the outer caliper of the Macan. I sent a message to the supplier to see if they can confirm this, but they are the same dimensions and indicated material, so what else could it be? This seems to indicate to me that the different finishes are not about temperature, but about tuning displacement through pad retraction. For whatever reason Porsche wanted more displacement retraction on the Macan than Audi did for the Q5. Which is why they only did two of the four, apparently four would have been to much, but splitting the difference was just right?

As I said when I initially tested these RPV's I was only looking at the outer piston retraction assuming both inner and outer would be more or less the same, and that was a mistake. When I installed the 4 PSI valves and looked at the outer piston retraction it looked okay, but when I installed them and went for a test drive I was clearly getting pad drag, which I now realize must have been from the inner pistons which have considerably less retraction.

Regardless, all this tells me there is definitely more pedal height/response left on the table with my current setup. I have ordered a set of these pistons and also plan to do the custom cross over so I can swap the calipers. I will not do that until the pistons show up and this will allow me to do some more precise bench testing at the same time. I have several configurations I want to try and see what yields the best result, and bench testing will make this very easy to do. What I plan to try:

1. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV.
2. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV with piston seal lube applied.
3. All four pistons with the lighter coated pistons with the 2PSI and 4 PSI RPV.
4. Also test seal lube with the lighter coated pistons.

Based on what I have already observed, I am thinking the dark coated pistons with 2 PSI valve will work best. But who knows maybe just one complete set of either coating and some seal lube will do the trick. Or maybe the lighter coated pistons all around with the 4 PSI valves, that would give better track pad knock back resistance so...
 

emichel6888

Go Kart Champion
Location
TX
I'm pretty happy with just the OBD11 changes, but I think this is a cool idea and should make this a better option for those running STH that can't legally do OBD11 changes.
I was meaning to ask you about that, what OBD11 changes are you referring too? Is it just the ones on your OP? Because I have already done those, in fact i did those while I still had the stock calipers on, and definitely like what they did. Are there other changes that I have missed?
 

GTIfan99

Autocross Champion
Location
FL
I was meaning to ask you about that, what OBD11 changes are you referring too? Is it just the ones on your OP? Because I have already done those, in fact i did those while I still had the stock calipers on, and definitely like what they did. Are there other changes that I have missed?

Nope, just what's listed in OP. What fluid and pads are you using? Maybe they make a bigger difference than we think?
 

emichel6888

Go Kart Champion
Location
TX
Nope, just what's listed in OP. What fluid and pads are you using? Maybe they make a bigger difference than we think?

Currently Motul 600 and Ferodo DS2500's. Could just be that I am nit picking here, but when I went from the stock calipers to these Macan's I immediately noticed the pedal was lower and that it would pump up, not a lot but definitely noticeable. Again it is not horrible, and nothing you could not get used too, just not quite what I was hoping for. When I had the RPV's right off the MC the pedal feel and response was so dam good! I just want to get as close to that as I can without spending thousands of dollars.

I also have a BMS throttle pedal tuner, and if you have never experienced that you might think the stock throttle is fine, and it is. But now that I have experienced that improvement, there is no way I could go back to a stock throttle pedal, not now. I know there is an OBD tweak for that too, I have tried it, the pedal tuner is much, much better.
 

emichel6888

Go Kart Champion
Location
TX
Maybe I missed it somewhere but are you only considering half the caliper?
Yes, and that is what you are supposed to do. You have to consider that the single piston is affecting the movement and compression of both pads whereas the fixed caliper each set of pistons only does half of the movement/compression. So when comparing displacement ratio for a single vs a fixed dual you have to compare the single piston displacement against half the pistons on a fixed dual caliper. Make sense?
 

crashracer

New member
Location
Portland OR
Yes, and that is what you are supposed to do. You have to consider that the single piston is affecting the movement and compression of both pads whereas the fixed caliper each set of pistons only does half of the movement/compression. So when comparing displacement ratio for a single vs a fixed dual you have to compare the single piston displacement against half the pistons on a fixed dual caliper. Make sense?
Perfectly clear. Thanks for the ride explanation!
 

LBmk7r

New member
Location
BC
Okay, I found a source for these pistons and some other interesting information. They do have two versions of the same piston, one is part number P42045A and the other is P42045A-B, and the later indicates it is for the Audi Q5 while the former does not specify a particular vehicle:
View attachment 184259View attachment 184260


I could not find a piston kit for the 4 pot Macan anywhere, but the Q5 no problem. And when you look at the complete rebuild kit for the Q5 they are all the same dark finish:
View attachment 184261
So then I went looking for a good picture showing the pistons on both sides of the Q5 caliper, and sure enough the Q5 version does indeed use the same dark finish pistons on both inner and the outer:
View attachment 184262
While the picture of the individual pistons is the same, I bet the non B part number is the lighter finish used on the outer caliper of the Macan. I sent a message to the supplier to see if they can confirm this, but they are the same dimensions and indicated material, so what else could it be? This seems to indicate to me that the different finishes are not about temperature, but about tuning displacement through pad retraction. For whatever reason Porsche wanted more displacement retraction on the Macan than Audi did for the Q5. Which is why they only did two of the four, apparently four would have been to much, but splitting the difference was just right?

As I said when I initially tested these RPV's I was only looking at the outer piston retraction assuming both inner and outer would be more or less the same, and that was a mistake. When I installed the 4 PSI valves and looked at the outer piston retraction it looked okay, but when I installed them and went for a test drive I was clearly getting pad drag, which I now realize must have been from the inner pistons which have considerably less retraction.

Regardless, all this tells me there is definitely more pedal height/response left on the table with my current setup. I have ordered a set of these pistons and also plan to do the custom cross over so I can swap the calipers. I will not do that until the pistons show up and this will allow me to do some more precise bench testing at the same time. I have several configurations I want to try and see what yields the best result, and bench testing will make this very easy to do. What I plan to try:

1. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV.
2. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV with piston seal lube applied.
3. All four pistons with the lighter coated pistons with the 2PSI and 4 PSI RPV.
4. Also test seal lube with the lighter coated pistons.

Based on what I have already observed, I am thinking the dark coated pistons with 2 PSI valve will work best. But who knows maybe just one complete set of either coating and some seal lube will do the trick. Or maybe the lighter coated pistons all around with the 4 PSI valves, that would give better track pad knock back resistance so...
Just spitballing ideas here, but could you put 1 of each piston on each side? or would this cause uneven pad wear? the first point of contact would be different, but the pressure applied should be even?
 

emichel6888

Go Kart Champion
Location
TX
Just spitballing ideas here, but could you put 1 of each piston on each side? or would this cause uneven pad wear? the first point of contact would be different, but the pressure applied should be even?
I suppose but why would you want to do that? The idea is I want to reduce piston retraction as much as possible without getting pad drag. That will give the highest, firmest, and most responsive brake pedal. So the idea is to find the combination that does this best, which I am thinking will be to use the same piston type all around. Either the dark finish with the 2 PSI RPV, or maybe the lighter pistons with a 4 PSI RPV, or possibly some combination with lubricated seals.
When the pistons arrive I will bench test all of these options to see which works best. I am curious to see the effect of lubing the seals, if that works well I may lube the rear pistons as well. I am already happy with the improvement from the RPV's but there is room for additional improvement. I am optimistic this can be done, possibly just lubing the seals is all it will take, we will see.
 

emichel6888

Go Kart Champion
Location
TX
One other note, after testing the retractions you can see why the 4 PSI RPV did not work and caused pad drag. When I only looked at the outer it seemed okay because at the time I did not realize the inner and outer were different. But another benefit of lubing the seals is that it makes the pad knock reduction more effective, but the 4 (/7 PSI) would be even better.
I did not test this but I am thinking if I rub off the finish on the inner pistons with some 2000 grit so bare metal, and only lube the outer piston seals, the 4 PSI RPV might work well? I have those other pistons so... maybe next time I service the brakes I will give that a try. However for now I am good with the brakes.
 

emichel6888

Go Kart Champion
Location
TX
Oh and i also did the cross over conversion so the calipers are facing the right direction for more even friction/wear:
Cross over pics.jpg


As you can see besides the custom cross over tube you need to make a small extension for the brake line, but not hard to do. Other than pad wear there is no objective data to say how much this helps, but theoretically it should, and subjectively it feels better.

This is the tubing and fittings I used:
https://www.amazon.com/gp/product/B01KNGVV0S/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B07C8NK65K/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
The M10 female-female adapter I just bought from Auto Zone.
 
Last edited:

LBmk7r

New member
Location
BC
Thanks for your super thorough testing and time spend on this; it was very informative!
Would you say the grease on the piston affects the retraction by reducing the effectiveness of the seal to retract on the piston?
 

emichel6888

Go Kart Champion
Location
TX
YW, I did it for myself, but it is always makes it more worthwhile when you can share and maybe help out others. I would not of even known about this option if these other folks had not taken the time to post about it so...
Yes that is the idea, less friction equals less distortion of the rubber seal, which equals less piston retraction. If you look at my test data, even the factory calipers use grease to control this effect.
 
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