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

nono0044

Drag Racing Champion
Location
Toronto
I thought so too, but I was wrong. There isn't enough pressure/bias to move all the pistons. The bottom 2 pistons in each caliper were not being fully pushed out.

see my findings here: https://golfmk7.com/forums/index.ph...de-thread-read-first-post.371028/post-7519084

bottom line: i'm going back to the stock calipers
1603217052436.png

Source:
https://www.essexparts.com/news-blo...QcqbJj5BGG81C086B-jC3v_vT4eDzO3x8_qnkmL3kVtZQ

Additional reading:
https://www.buybrakes.com/help/raci...oePJKrH0NTPKPMsqb6iprLqlgKpwvkHt_noeXuuBXw3zw

the pics of your pads didn't even look that bad. They don't look "toasted" in terms of bad thickness left, and the taper isn't that bad.

You're still going to get pad taper on the stock calipers. I had it on mine, my friend has it on his.
 

scrapin240

Drag Racing Champion
Location
IzzaGolf
Car(s)
Golf
View attachment 189366
Source:
https://www.essexparts.com/news-blo...QcqbJj5BGG81C086B-jC3v_vT4eDzO3x8_qnkmL3kVtZQ

Additional reading:
https://www.buybrakes.com/help/raci...oePJKrH0NTPKPMsqb6iprLqlgKpwvkHt_noeXuuBXw3zw

the pics of your pads didn't even look that bad. They don't look "toasted" in terms of bad thickness left, and the taper isn't that bad.

You're still going to get pad taper on the stock calipers. I had it on mine, my friend has it on his.
Good to know, but going down the straight at 138 and having to brake for T1 with no pedal for the first third of the travel over enough laps was enough for me.

It wasn't the first track day or course it's happened to me with these calipers or pads. I've tried 3 sets of different types of pads (StopTech Sport, Ferodo DS2500 and Ferodo DS1.11) and pretty much the same results with lack of stopping in the first part of the pedal travel.

It goes from nothing to something to almost lockup and that 1st 3rd of brake travel with nothing happening gets unnerving and doesn't lead to smooth transitions. My GTI with PP did a much better job on track with feel and better stopping distances.

For the street they may be fine for most users, but stopping on track felt more like an adventure.
 

GTIfan99

Autocross Champion
Location
FL
Good to know, but going down the straight at 138 and having to brake for T1 with no pedal for the first half of the travel over enough laps was enough for me. It wasn't the first track day or course it's happened to me with these calipers or pads. I've tried 3 sets of different types pads and pretty much the same results.

It goes from nothing to something to almost lockup and that 1st 3rd of brake travel with nothing happening gets unnerving and doesn't lead to smooth transitions. My GTI with PP did a much better job on track with feel and better stopping distances.

For the street they may be fine for most users, but stopping on track felt more like an adventure.

Sorry it didn't work out for you. I'm not having that much dead space at the top of the pedal, thankfully, and hope to resolve the issue completely with different pistons and grease. Maybe at some point we'll get this setup sorted. It's always a little bit of an adventure when you do something like this. Thanks for your contribution to the project. Keep us posted on your tracking and setup in the future.
 

burgerkong

Drag Racing Champion
Location
Ontario, Canadeh
Good to know, but going down the straight at 138 and having to brake for T1 with no pedal for the first third of the travel over enough laps was enough for me.

It wasn't the first track day or course it's happened to me with these calipers or pads. I've tried 3 sets of different types of pads (StopTech Sport, Ferodo DS2500 and Ferodo DS1.11) and pretty much the same results with lack of stopping in the first part of the pedal travel.

It goes from nothing to something to almost lockup and that 1st 3rd of brake travel with nothing happening gets unnerving and doesn't lead to smooth transitions. My GTI with PP did a much better job on track with feel and better stopping distances.

For the street they may be fine for most users, but stopping on track felt more like an adventure.

What pads are you using?
 

emichel6888

Go Kart Champion
Location
TX
Looks like I missed a few posts here, so no one else has tried this yet? Good grief, am I casting pearls here? All you really have to do is lube the piston seals and add these inline RPV's, that is it. The custom cross overs help as well, but not absolutely necessary IMO (but recommended).
Perhaps, I was I not clear in my review? This is way, way, better than the initial upgrade, or the stock calipers, the pedal is now high, firm, consistent, with great modulation. If you think it is already good, you will be amazed how much better it can be, and if you are not entirely happy with it, this will fix it. Yes a better pad also helps, it is like suspension and tires, you need both for a great setup. However, a better pad will not fix the low soft inconsistent pedal, this does.
IMO the Ferodos are like a set of MPS4 tires, good overall but certainly not like a dedicated race tire/brake pad. The torque is not as high as I would like, and you have to manage heat, so you can't go all out for very long, but they are good enough to have some fun with, and much better than the stock pads.

I am absolutely loving the brake feel/response with these very cheap and simple modifications. In fact just lubing the seals should help a lot, with slightly lower displacement and less piston retraction (with lubed seals), that alone will be a big improvement. However, the RPV's combined with seal lube just takes it to a whole other level, I love that now I get in the car, fire it up, and the brake pedal does not go soft under my foot. I recall how disappointing that was, I am trying to think of a good analogy here, let's just say this is the little blue pill this cars' brake system needs :).

2020-10-21 23_39_45-2020-09-13 15_20_43-Presentation1 - PowerPoint.jpg


Yes it was a lot of work to figure all this out, but now you know so... Anyway, it has been working great for me, I am loving this brake setup now.
I think I am pretty much done with modifications on this car, the brakes was the last missing piece for me, now it is just maintenance and enjoying it. Good luck with your project, I hope this information is eventually useful to someone.
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
I want to do this but I don't have the vice needed to beat the aluminum into the correct angle... so close but so far!
 

emichel6888

Go Kart Champion
Location
TX
I want to do this but I don't have the vice needed to beat the aluminum into the correct angle... so close but so far!
The way I did it was just one option. After doing mine I think you could use the stock bracket and just bend the stock hard line up enough to make it work. Or just get a small L bracket from a hardware store and hose clamp the RPV to it. It wouldn't be as clean but should work fine, at least just to try it out for a while, and if you like it (and I know you will), then you could always fine a small fabrication shop to make a bracket for you.

Something like this:
wheel well line RPV install.jpg
 
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emichel6888

Go Kart Champion
Location
TX
BTW, for those that aren't following some of the other BBK threads on here, we have found that the MC is actually not a stepped/QTMC after all. So my theory on why this works was incorrect however, I did more digging and discovered the real reason this works so well. Rather than reposting it all again
you can see my explanation in my post on this other thread: Why it works
This also explains why it does not affect the adaptive cruise/emergency braking function. If anything it just improves response by a small margin.
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
I'm about to order this stuff and was wondering why you're using thread sealant? I thought you're not supposed to use thread sealant on brake line fittings, and that the brake line fittings (NPT thread) is tapered and flared anyways so you don't need sealant.
 

emichel6888

Go Kart Champion
Location
TX
I'm about to order this stuff and was wondering why you're using thread sealant? I thought you're not supposed to use thread sealant on brake line fittings, and that the brake line fittings (NPT thread) is tapered and flared anyways so you don't need sealant.
Correct, it is not for the compression fittings however, you absolutely do want to use it on the NPT fittings. Just google "Do I need to use sealant on NPT fittings?".

"NPT, National Pipe Taper (American) and BSPT (British standard Pipe Taper) are tapered pipe thread standards. Male and female tapered pipe threads wedge themselves together but need a sealant for a completely leak-free connection. Sealants fill any voids between the threads that could travel along the thread spiral."

Perhaps in theory NPT does not need sealant, but there are an awful lot of pipe thread sealants used on pipe threads, and for good reason. Also you may notice that one M10 M10X1 M10X1.0 Male Flat to Flare (the only option I could find) is actually NPS not NPT so...
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
Correct, it is not for the compression fittings however, you absolutely do want to use it on the NPT fittings. Just google "Do I need to use sealant on NPT fittings?".

"NPT, National Pipe Taper (American) and BSPT (British standard Pipe Taper) are tapered pipe thread standards. Male and female tapered pipe threads wedge themselves together but need a sealant for a completely leak-free connection. Sealants fill any voids between the threads that could travel along the thread spiral."

Perhaps in theory NPT does not need sealant, but there are an awful lot of pipe thread sealants used on pipe threads, and for good reason. Also you may notice that one M10 M10X1 M10X1.0 Male Flat to Flare (the only option I could find) is actually NPS not NPT so...

This is in no way a criticism of your post/thread, but I think the thing that keeps giving me pause on trying this is the amount of adapters and new points of leaks/failure it introduces. I would think using something like this:

https://empius.com/products/2-psi-residual-pressure-valve-sae/

would introduce the least amount of new connections, and also uses an SAE flare fitting instead of NPT + thread sealant (I've always been told not to use thread sealant on brakes in case of contamination). Only issue would be having to cut the hard lines to install that fitting on the front circuit of the master cylinder.

Also, when you initially installed the RPVs on the master cylinder, and then went to the wheel well setup, did you end up replacing the hard lines?
 

emichel6888

Go Kart Champion
Location
TX
This is in no way a criticism of your post/thread, but I think the thing that keeps giving me pause on trying this is the amount of adapters and new points of leaks/failure it introduces. I would think using something like this:

https://empius.com/products/2-psi-residual-pressure-valve-sae/

would introduce the least amount of new connections, and also uses an SAE flare fitting instead of NPT + thread sealant (I've always been told not to use thread sealant on brakes in case of contamination). Only issue would be having to cut the hard lines to install that fitting on the front circuit of the master cylinder.

Also, when you initially installed the RPVs on the master cylinder, and then went to the wheel well setup, did you end up replacing the hard lines?

No worries I don't mind questions or new ideas, and you are not the first person to bring this up. I guess it is because I have done so many projects like this (in some cases practically building an entire brake system from scratch), that this seems like a relatively minor low risk modification to me. NPT fittings with sealant like this are frequently used in custom/aftermarket brake systems, which is why they are available for purchase all over the place. These NPT fittings with this sealant create a seal that will withstand chemical exposure and pressures far beyond what it will ever see in this brake system, and it is literally made for this type of application.
There is no reason to be concerned about using them, sure it may not look as clean, and if you were to get significant quantities of this sealant into the system that could be a problem, but if you apply it as directed (see pics), that cannot happen. You are supposed to apply it a couple of threads down and then let it harden before assembling the parts. If done that way it will not cause any contamination issues and will provide a very safe reliable connection.

"Permatex high-temperature thread sealant is an OEM-specified product designed to lock and seal threaded fittings on a range of applications. It prevents leakage from vibration, temperature cycling, and extreme pressures—and it won't shred or tear like PTFE tape. This high-temperature thread sealant is exclusively formulated to withstand up to 10,000 psi for fast, responsive curing on metal, tapered pipe thread fittings. The PTFE offers good antifriction properties and high resistance to chemicals and harsh environments."

"Suggested Applications: Head bolts into through holes, oil PSI sending units and sensors, oil and coolant lines, fuel fittings, rear axle fill plug, brake, and power steering fittings"

So unless there is corrosion, or you severely over tighten a fitting so that it starts to gall or crack, these fittings are as strong and reliable (if not more so) than any other part in the stock system. In fact the sealant acts as a lubricant while assembling, so it provides a great seal without having to excessively tighten the fittings. It also acts like a mild glue making the possibility of the fitting loosening up or develop a leak over time due to vibration extremely unlikely, perhaps even less so than the stock compression fittings.

Some even say that bubble fair fittings are supposed to be one time use fitting, which is absurd IMO as they are frequently reused multiple times by virtually everyone. However, if you over tighten them they can get distorted and cause leaks. But if you are careful and check for leaks there no need for concern.

In my experience brake lines/fittings do not spontaneously develop leaks unless they were not tightened properly, or there is severe corrosion, or damage from severely over tightening (which the sealant makes less likely), or some other damage like a rock hitting a line. The weakest link within any brake system is always the flexible lines, so if you are not worried about those, why would you worry over a couple of added fittings? As with everything, if you install them properly there really is no need for concern with these RPV's or the fittings.
I just use moderate torque, bleed the system, clean everything up, then start the engine and stand on the brake pedal to check for leaks. If you find one give it 1/8 incremental turns until it stops. When there are no more leaks you are good to go. It really is no less concerning than any other brake work/modifications, as long as you know what you are doing, and if not, find someone that does to help you.

Second question: I did not cut or replace any hard lines. When I was doing this I had no idea if it would work, so I made custom lines that let me install the RPV's without modifying the stock hard lines (see pic on page one). The brake system in our cars use what is called a "dual diagonal brake circuit" meaning each line off the MC feeds one front and the opposite side rear caliper. So if you want to install these RPV's under the hood for just the fronts, you would have to insert them in the lines coming off of the ABS unit, and there is not a lot of room to work with up there so... Putting them in the wheel wells is a much easier proposition.
My flare tool is the type designed to work in a vice, I don't have one of those nice portable flare tools, so flaring a line on a car is not something I am setup to do. However, now that I know it works, and if I had one of those nice portable flair tools would I consider cutting the line and inserting the RPV inline further up. Sure why not, but I think most folks here are already intimidated by a couple of fittings, so probably not a good option for most folks . However, now that I already have it installed with the fittings, I don't see any reason to switch it up now. It will look a lot cleaner when I look at it with the wheel off, and I know that kind of thing is important to some folks on here.
I certainly would not fault anyone that wants to go that route. Maybe in Europe you can find a 2 PSI RPV that has the flare fitting built in, that would be a really clean install. There are a lot of different ways to get this done and I encourage anyone to install them in whatever way works best for them. Good luck!
 
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