Sigh, I can confirm those piston specifications above are accurate. These piston springs would certainly work, but can't you see it is essentially doing the same thing as the RPV, just one is pushing on the piston with a spring and the other with residual pressure, both have the same net effect. They even advertise the RPV as a way to fix pad knock, again for the same reason it works with these springs. I take it he doesn't have a piston made for those springs with that short a depth?So I was reaching out to Zeckhausen Racing to get the Ferodo DS3.12 for the OEM calipers, and told him that I was switching from Macan back to the OEM, and he asked if it was a race series issue or something else. Dave was super and has tons of information, and knows all things brakes.
He said that the master cylinder should be sufficient:
I told him about the issues that track users faced, such as initial brake pedal issues, and he said
The solution looks like this.
View attachment 200618
He then suggested
So, the pistons that work have the shortest length of 29.5mm, so if that diagram is correct, the stock ones are too short. If someone can confirm the measurements that would be great. Otherwise I will be going back to stock in the upcoming weeks, and will try then to measure. His gut feeling is that they are 30mm, but we would need to get an actual measurement to know.
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If the piston length is shorter than 29.5 and is machined, the springs to use are 8 of these:
This is the first time someone with some braking knowledge even tried to explain these issues. Sounds very interesting and would love to see if it solves the problem. Edit: There is a warning on the page that it can accelerate wear on pads, so that is something else to be aware of. This depends on the spring rate used. Dave said the .4in should not drag the brakes in a daily, and .6in could be used in a track car with severe knockback and should not drag the brakes in either case.
I would reach out to Dave and Zeckhausen racing for any braking needs/information in the future.
Sigh, I can confirm those piston specifications above are accurate. These piston springs would certainly work, but can't you see it is essentially doing the same thing as the RPV, just one is pushing on the piston with a spring and the other with residual pressure, both have the same net effect. They even advertise the RPV as a way to fix pad knock, again for the same reason it works with these springs. I take it he doesn't have a piston made for those springs with that short a depth?
I tried a 4 PSI RPV (which should be roughly equivalent to the 4 lb spring he was suggesting) but it did cause far to much pad drag with these calipers. I will say that when I tested the 4 PSI RPV it measured more like 6-7 PSI so you would definitely have to experiment with different spring tensions. However, the 2 PSI RPV works great with no detectable pad drag so... It is also cheap and very easy to install and remove. Why you folks are so dead set against trying this is completely baffling to me, but suite yourself.
As he also said, the piston displacement is virtually identical between the Macan/Q5 caliper and our stock caliper. I have already demonstrated and proven why these calipers cause a lower softer pedal, it is due to the difference in piston retraction. If you lubricate the seals the piston retraction on this caliper is virtually identical to the stock caliper, and guess what? The pedal height and feel is virtually identical (perhaps a bit better) to the stock caliper as well. Then if you lube the seals and add the 2 PSI RPV's it is vastly superior to the stock caliper, and it provides a degree of knock back prevention, and there is no pad drag with 2 PSI. 4PSi would be even better for pad knock but alas the pad drag was significant.
I also suspect all of the MK7 Golf R's and probably the GTI w PP have the 25.4 mm MC, if someone wants to buy a used ebay MC out of an earlier model R or GTI wpp, we could verify this for sure. Does anyone know what the brake pedal feels like in a Macan? Keep in mind the stock pedal on our cars is artificially assisted, when you turn off those assists (as listed on page one) the pedal engagement does get significantly lower but also firmer with more linear feel. This is because as soon as you touch the brake pedal the ECU starts adding assist based on some algorithm, when you turn that stuff off you find the true engagement point, which is inherently somewhat lower.
Perhaps the Macan has a similar setup and or different pedal linkage or brake booster, so we could have the same MC/caliper displacement and also have different pedal characteristics for a variety of other reasons. So when you turn off the assists and then add these calipers with their increased piston retraction/take up displacement the pedal goes even lower, and as we have seen that can drastically change the servo booster assist, and that drastically changes pedal feel/firmness causing it to be softer and lower. Like I said if you lubricate the seals, pedal height and firmness will be as good (if not better) than the stock caliper. If you then add the RPV's it is drastically improved (almost perfect IMO). I also think (based on my measurements) adding the RPV's to the stock calipers would also have a similar effect.
It works, really, really well, it is low cost, perfectly safe, and very easy to add or remove with no permanent modification to the stock setup. If you are not worried about installing after market SS lines, how anyone could be concerned about adding a small inline metal tube with fittings just seems absurd to me, but again I digress, do it, don't do it... Just please try it before you start telling me I am full of it. I know if you try it that won't happen because it is hard to argue with actual real world results.
I am absolutely thrilled with my current brake setup and want to thank you guys for turning me on to this setup. I am just trying to return the favor, your so close to having a great setup, it just needs a little bit more.
Oh, I thought you said you weren't sure what car that MC came out of, what year GTI and did it have the PP brakes? Yes I would like to know as well. There are several on EBAY for around $50-$80 and they specify the donor car and even provide a VIN#. I would rather spend the money then all the time and effort to pull it out of the car. Maybe one from a 2016-2017 Golf R and GTI.I just told you I bought a GTI M/C and it measured 23.81mm (you saw my measurements)...my P/N starts with 5Q1xxxxxxxREP. Sometime in 2018/19 VAG swapped to a 5QMxxxxxx P/N. Waiting on confirmation if the new part signified a departure from 23.81mm to 25.4mm. Let's not jump to conclusions again.
Well, I believe I have figured out a way to answer this question without anyone having to order more parts. As I mentioned EBAY has MC’s for sale out of the cars in question. I tried to see if they would take measurements for me but none would do it. However, most of them did take decent pictures, and while not very precise, I figured it might be close enough to determine if the piston size was 23.8 or 25.4 just by carefully examining the photos. It turned out to work even better than I had hoped.I just told you I bought a GTI M/C and it measured 23.81mm (you saw my measurements)...my P/N starts with 5Q1xxxxxxxREP. Sometime in 2018/19 VAG swapped to a 5QMxxxxxx P/N. Waiting on confirmation if the new part signified a departure from 23.81mm to 25.4mm. Let's not jump to conclusions again.
Well, I believe I have figured out a way to answer this question without anyone having to order more parts. As I mentioned EBAY has MC’s for sale out of the cars in question. I tried to see if they would take measurements for me but none would do it. However, most of them did take decent pictures, and while not very precise, I figured it might be close enough to determine if the piston size was 23.8 or 25.4 just by carefully examining the photos. It turned out to work even better than I had hoped.
I started by taking pics of the 2019 Golf R MC I acquired from a friend and examined it for reference:
View attachment 201067
The outer raised lip is 46 mm, so that is the reference point. What I found is regardless of the camera angle, if I sized the image so that the lip measures 46 mm, and then measured the piston shaft with the same angle, it was very close to 25.4 mm. Therefore, with that established, I grabbed images and details for several master cylinders and examined them in the same manner, and here is what I found:
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As you can see I did find some MC’s with a 23.8 mm piston, those seem to be found on SOME versions of the non GTI Golf’s and SOME versions of the Audi A3.
View attachment 201075
In the image above all MK7 GTI’s and Golf R's 2015-2019 can and apparently do use the same MC, and all have a 25.4 mm MC piston diameter. This same MC is also used in the S3, RS3, TTRS, and many other models.
As for the difference between the 5Q1-614-019-X-XXX vs the 5QM614019F, I did find an MC out of a wrecked 2019 Tiguan which is supposed to have the 5QM… MC (see below) and it also seems to have a 25.4 mm piston, and when I compared the images of it to the 5Q… part number they look identical.
View attachment 201076
The fitment guide does say it is compatible with the 2019 GTI? And it really does look to be the same part only a lot cheaper. Unfortunately they did not have a picture of the bottom of the MC where the manufacturer information is stamped and cast. So I don’t know for certain, but it is possible this new version is essentially identical, only maybe from a different lower cost supplier? I know that in my business different vendors of identical parts get new/different part numbers, so it seems likely the only tangible difference between the 5QM-614-019-F and the 5Q1-614-019-X-XXX is the cost.
With this plainly visible data and the fact that VW IS telling us the same MC is compatible with the 2015-2019 Golf R and all GTI’s, I think it is safe to say that we all already have a 25.4 mm MC (even those with a non PP MK7 GTI). Also the fact that folks with the 2019 R report experiencing the same softer/lower pedal with this caliper, now we know why.
I don't understand, we can literally see it is the same size piston, at least for the 2015-2019 Golf R and the GTI's, which is really what we wanted to know yes? At this point I have no doubt that the piston size in my 2017 Golf R is 25.4 mm, so there is no reason to swap it with the 2019 MC I happen to have. That is all I really wanted to know.The issue is why the dealer as well as why the VW parts site lists out everything from say a 1.4L to the R as using the same caliper when the vendors on ebay say otherwise. I'd think a piston change is significant in the way the brakes and pedal performs. So really again, it's to buy a 5Q1 part for a Golf R and the same 5QM part, both direct from dealer, and conclude.
I think that will give us the surefire response, I doubt VW will tell us why there's a variance.