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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 was thinking that they'd work better between the hard and soft lines at the front when you posted originally. Easier too.
 

emichel6888

Go Kart Champion
Location
TX
I was thinking that they'd work better between the hard and soft lines at the front when you posted originally. Easier too.
I think it is going to work really well too, perhaps not quite as high and tight as my original setup, but I am hoping near enough as to make no difference, and it is definitely a LOT easier to do. Regardless, it will definitely be a big improvement, of that I have no doubt. We will know soon, USPS sent my order back because they claim the address wasn't exactly right:mad:. The entire address was correct, but the town name was listed twice, that apparently confused someone at the post office.🙄
Anyway, I had to reorder but should have what I need by the weekend. Trying to find a 1/8-27 NPT male to M10 x 1.0 DIN bubble flare male fitting was not easy, only found this one place in NV that carries them.

Out of curiosity I also ordered a set of the 4 PSI RPV's. It will probably be to much and not allow enough clearance, but they are cheap and easy to swap out so I just have to try it. If the piston retraction is not linear to the RPV pressure (and it might not be), so the going from 2 PSI to 4 PSI only causes a minor difference say from .004" to .003" that would be even better for multiple reasons. Figured it was worth a few bucks and 20 minutes to find out.
 

GTIfan99

Autocross Champion
Location
FL
Awesome, once you've figured it out, please post the ordering info and I'll add the info to the first post in the Macan thread.
 

emichel6888

Go Kart Champion
Location
TX
I'd be wary of actually worsening the braking distances though by changing my front/rear brake bias with this mod if not careful though so just be sure to be careful here, even small changes in F/R brake bias can have big impacts on max braking distances.

Hey Bill, I was just thinking, doesn't the much smaller piston area of the ST40 (2160 vs stock 2827) already cause a significant change in this car's brake bias? One of the main factors of braking force is the MC to caliper piston area ratio no? And these calipers are changing that by almost 25%, which is not a small change.
I get why these calipers would have a firmer pedal, but did you notice a difference in trail brake turn in? Knowing how the factory always seems to run on the conservative safe side promoting under steer, a bit more rear brake bias might actually be better.
However, this seems like it is quite a bit more, so I am wondering if this is noticeable on track handling or perhaps even just increased rear pad wear?
 

Mini7

Autocross Champion
Location
Charlotte, NC
Car(s)
2017 GTi Sport PP
Did UPS make it to your house......?
 

emichel6888

Go Kart Champion
Location
TX
Did UPS make it to your house......?
Yes! The M10 x1.0 bubble to 1/8 NPT fitting was to short on the M10 side, :( it's always something). However, I contacted the supplier and they found another option (but it involved using two fitting instead of one, oh well), and that actually got here today and looks like it will just fit. So I am getting ready to install it later today and should have some updates by later today or tomorrow.

20200815_135422.jpg
 

GTIfan99

Autocross Champion
Location
FL
I'm here for the party too. Let's see them.
 

Mini7

Autocross Champion
Location
Charlotte, NC
Car(s)
2017 GTi Sport PP
🍿🍿🍿🍿
We are patiently waiting for this movie to start again........onto my 4th bag of popcorn.....
 

emichel6888

Go Kart Champion
Location
TX
Okay so I updated the original post with all the latest info/pics of the new version modification. I even changed the title because as far as I can tell this is just for the this caliper. Anyway, you can read the OP but essentially it does work well, is it the awesome pedal I had with the RPV's at the MC? Sadly no, it is a much more subtle improvement. It essentially brings the pedal back to where it was with the stock calipers, the pump up is gone, and the pedal is firmer and more consistent. So it is good, but I am spoiled with the initial mod now so...
The pedal always stays well above the throttle pedal, it is better in every regard, it feels like more but by my measurements it raises up just 1/4 inch. It is also a fairly easy modification for even an intermediate DIY person, if you installed these calipers yourself and have a drill and a vise, you could do it.

I did try the 4 PSI RPV's but they did cause pad drag so those are a no go. I tested these RPV's on the bench, the 2 PSI valves are spot on, but the 4 PSI valves are more like 7 PSI so... Even so i took more careful piston retraction measurements of each piston this time and found at least one inside piston was retracting less than the outside pistons. No drag but most pistons were .004 -.005 and one was around .002. I pumped i tout and pushed it back in a few times and it seemed to improve so...
Do I need new seals already? Regardless the 2 PSI works with no drag, but you can't do much more than that it would seem.
 

GTIfan99

Autocross Champion
Location
FL
Why can't you just install between the hard and soft lines?
 

emichel6888

Go Kart Champion
Location
TX
Why can't you just install between the hard and soft lines?
What do you mean, that is exactly what I did. Do you mean why the need for the bracket? Well the stock clip attaches to the soft line and I was not comfortable bending the hard line that much. You can bend them to a degree, but go to far and the line kinks, then your screwed. So you need some way to fixate the soft line/hard line connection point and this just seemed like a simple easy way to do it.
What else would you do? I suppose you could rig up some tie wraps or something, but this was super easy for me to make and has stock reliability/function. I never even considered doing it any other way, but there are other ways to do it. You could just order the fittings and the valves and try something else.
Take pictures and let me know how it goes.
 

Mini7

Autocross Champion
Location
Charlotte, NC
Car(s)
2017 GTi Sport PP
Thank you for the detailed write up. This makes it easy to source the parts and get them fitted.
 
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