Pedal to the floor after installing larger S3 rear brakes

[jmason]

Yes, 272 mm rears still in place.
I don't have the S3 caliper. I installed the Neuspeed 6-piston caliper.

 

[greekspec2]

Yes, 272 mm rears still in place.
I don't have the S3 caliper. I installed the Neuspeed 6-piston caliper.

fuck sorry getting over cold your the wrong person

 

[greekspec2]

So before my track day last weekend, I went to the shop at the track to throw on some S3 calipers, usp stainless lines,, centric rotors and hawk pads. After installing all of this and bleeding it i noticed the pedal goes practically to the floor. I know it was bled correctly because we went through 2 bottles of rbf-660 trying to get it right. I gave up on them and reinstalled the stock calipers, pads and rotors but left the stainless lines on. With the stainless lines on and stock rear brake components, the pedal still went to the floor. Put the stock rubber lines on going to completely stock rear brakes and it was fine. Im starting to think the lines were the problem but I don't see how new lines could cause this. Also there were no leaks anywhere. Is there a different bleeding procedure I should have done? I did put the rear in "pad lining change mode" through obdeleven. Just wanna hear what you guys think

what model and year do you have?

what brakes did you change out fronts?

you changed all 4 lines to SS?

 

[emichel6888]

I have read with interest your posts. I was particularly interested in the results regarding piston retraction. I measured mine and found results similar to those you achieved through your modifications. In my case, the inside half of the caliper showed about 0.005" retraction, while the outside showed less than 0.001" retraction. On the outside, the pads drag on the rotor when the pedal is not pressed. I don't know why there would be a difference inside to outside.

When the engine is not running, the brake pedal is very firm and has a short travel. All good. However, when I start the engine, the pedal travel is longer, and I can push the pedal to the floorboard with what I think is too little effort. If I pump the brake pedal, the travel shortens (not surprising as this action takes up the piston retraction) and the pedal is firmer. It's the change in the firmness of the pedal I don't understand. As an experiment, I went to a VW dealer, sat in a new GTI and, with the engine running, pushed the brake pedal. I could push the pedal to the floorboard only with a lot of effort.

The remediation to this point has been to follow two VW factory brake bleeding procedures, which I have done twice. The procedures are a gravity bleed (in my case using a Schwaben power bleeder set to 20 psi) and a two person bleed. For both procedures: LF, RF, LR, RR order, outer caliper bleed followed by inner caliper bleed for the fronts. Each procedure is followed by a road test that includes a stop that activates the ABS.

There is no evidence of brake fluid leakage. I have not performed an ABS bleed. To my knowledge, the MC reservoir has never run empty allowing air to enter the system.

I am not sure which caliper you are using, is it a four or six piston? Do you know the piston diameters? What about the master cylinder piston size? It is possible your caliper to MC piston displacement ratio is to large. Is there a larger MC you can install? Perhaps from the S3 or Golf R/GTI PP?

Here is what I believe is happening with my setup, (reference diagram below). There are two factors, one is the amount of piston retraction which affects pedal height, the other is the caliper/MC piston ratio that I represent with the stage 1 and stage 2 lever examples. When you have a larger ratio it is just like having a longer lever which increase pedal travel and makes the pedal feel softer. With a lower ratio (shorter lever) the pedal has less travel and will be higher and feel much firmer.
Even the stock Golf R has the same effect of engine off pedal is high and firm, you start the car and it softens up and drops. What I believe is happening is with the vacuum assist off the MC is in stage 1 (short lever=high firm pedal), however when you start the car the vacuum assist kicks in and causes the MC to move past stage 1 and into stage 2 (by design). So now you have the vacuum assist and the increased leverage of stage 2 which is why the pedal sinks and goes soft when the engine starts. It is as if the lever instantly lengthens and someone else is helping you push all at the same time.

I can tell you that after I substantially reduced the piston retraction using seal lube and the RPV's, my brake pedal stays the same engine off or on it does not move or change feel at all. It is firm and hard all the time, and I love it! What I believe is happening is that I have reduced the MC piston travel to the point that it never gets to stage 2 and remains in stage 1 all the time. See image below, I have essentially reduced the gap between the rotor and pad, and kept the shorter stage 1 leverage, both of these factors together give you a much higher and firmer brake pedal.

Is it okay to use the MC in stage 1 all the time? Well so far it has been fine even with heavy track use, and the Stop tech ST40 calipers actually have 25% smaller piston area compared to the stock caliper, and folks report that setup also has a high and very firm pedal. Which tells me it also stays in stage 1, but mainly due to the smaller piston ratio. So staying in the MC stage 1 area combined with the smaller piston ratio would make for a very firm and high pedal.

Those piston retraction values you mention seem awfully small for a stock caliper, how did you make those measurements? If you read my post the Macan caliper also has different retraction for inner and outer pistons, it has to do with how the piston seal groves are cut. If you read my post carefully I explain it in detail with pics.
Unless you are bench testing as I did, I found it is very difficult to get accurate measurements with the caliper installed on the car. I suspect perhaps your piston retraction is much more than you think? Or perhaps you have a large piston ratio. The Macan calipers actually have a slightly smaller caliper displacement than the stock caliper, so reducing the piston retraction makes a big difference. However, if you are using calipers with a significantly larger displacement and cannot increase the MC to compensate, reducing piston retraction alone may not be enough to fix your low soft pedal.
Hope this all makes sense, I would start with knowing your caliper and MC sizes.

 

[Gvazquez]

what model and year do you have?

what brakes did you change out fronts?

you changed all 4 lines to SS?

I have a 2015 Audi A3 2.0 which has the same master as the S3 im pretty sure.

I changed out front for ttrs brakes and the pedal feels almost the same as stock honestly.

The only thing that changed pedal feel was changing the rears to S3 brakes and SS lines. I should have tried the S3 brakes with stock lines to make sure its definitely an issue with the lines. The front already had SS lines when I installed the ttrs brakes.

 

[greekspec2]

I have a 2015 Audi A3 2.0 which has the same master as the S3 im pretty sure.

I changed out front for ttrs brakes and the pedal feels almost the same as stock honestly.

The only thing that changed pedal feel was changing the rears to S3 brakes and SS lines. I should have tried the S3 brakes with stock lines to make sure its definitely an issue with the lines. The front already had SS lines when I installed the ttrs brakes.

your bleeding outter and inner pistons on the front....I got Brembo GT-S no issues

 

[jmason]

I am not sure which caliper you are using, is it a four or six piston? Do you know the piston diameters? What about the master cylinder piston size? It is possible your caliper to MC piston displacement ratio is to large. Is there a larger MC you can install? Perhaps from the S3 or Golf R/GTI PP?

... remainder deleted for brevity ...

Thank you for your thorough response. Here are some answers to the questions you posed.
1. Neuspeed 6-piston calipers. I don't know the piston diameters.
2. From my research, the GTI, Golf R, and Audi S3 use the same master cylinder. I seem to recall the bore is about 23 mm.
3. The figures I quoted for piston retraction were measured between the pad and the rotor. During the measuring process, an anti-rattle clip was in place. This clip is designed to move the pad away from the rotor when the brake is not applied, which I could verify as I watched the action of the pads and pistons with someone pressing the brake pedal. When making these measurements, I did not see a gap between the piston and the pad backing plate. While perhaps not as precise as your measurements, I think they are representative.
4. My take-away from your research is that your problem was one of "slack" in the brake pedal, meaning that you had to press the brake pedal down a bit before the brakes engaged. You addressed this with the grease and pressure valves. This is not my situation. In my case, brake engagement is near the top of the pedal travel. However, under heavy braking, the pedal travel is longer than I would like and is somewhat soft; not a firm end point of travel. In fact, I can press the pedal to the floorboard. This is not an issue in actual use as I get full braking action well above the floorboard, verified on-track.

 

[Gvazquez]

your bleeding outter and inner pistons on the front....I got Brembo GT-S no issues

View attachment 193074View attachment 193075

Yeah I bled both bleeders up front. Im not sure why I'm having this issue. I should be able to eliminate the front as the problem cause I was running those brakes for awhile with no problem

On a separate note, your setup is really legit. Im not sure the springrates on kw v3s but I know they're a good damper and the brake kit is gorgeous

 

[greekspec2]

Yeah I bled both bleeders up front. Im not sure why I'm having this issue. I should be able to eliminate the front as the problem cause I was running those brakes for awhile with no problem

On a separate note, your setup is really legit. Im not sure the springrates on kw v3s but I know they're a good damper and the brake kit is gorgeous

Thanks....these are Clubsports 2way not V3's they run the same spring rates as the Golf TCR racecar setup for the Nurburgring.
571f
456r
The Clubsports use there motorsport valving very different valve system than the street coilovers every bump/rebound click change is noticed and ride way better than my Damptronics previously had.

 

[jmason]

By poking around the VCDS dialog boxes and menus, I did some translation of Bleeding with ABS Hydraulic Unit -N55-Pump into VCDS. I haven't tried this yet, so I can't vouch for its accuracy.

• Connect VCDS
• Switch the ignition on
• Select Control Modules, 03 – ABS Brakes. Security code is 40168 (don't know when or if this is required)
• Select Basic Settings, Bleed Brakes
• Select one of the following:
  • First Flushing Cycle
  • Bleed Rear
  • Bleed Front
  • Second Flushing Cycle
• Select Go!
• Bleed brakes

I don't know what the flushing cycles are, if the order is important (it's the order presented in VCDS), or if those four steps all need to be performed. By "Bleed brakes", I assume you just open the caliper bleed valves like doing a gravity bleed.

I tried to perform the Bleed Front procedure. The security code did not work, nor would the selection activate without a code. Back to the drawing boards.

 

[emichel6888]

Thank you for your thorough response. Here are some answers to the questions you posed.
1. Neuspeed 6-piston calipers. I don't know the piston diameters.
2. From my research, the GTI, Golf R, and Audi S3 use the same master cylinder. I seem to recall the bore is about 23 mm.
3. The figures I quoted for piston retraction were measured between the pad and the rotor. During the measuring process, an anti-rattle clip was in place. This clip is designed to move the pad away from the rotor when the brake is not applied, which I could verify as I watched the action of the pads and pistons with someone pressing the brake pedal. When making these measurements, I did not see a gap between the piston and the pad backing plate. While perhaps not as precise as your measurements, I think they are representative.
4. My take-away from your research is that your problem was one of "slack" in the brake pedal, meaning that you had to press the brake pedal down a bit before the brakes engaged. You addressed this with the grease and pressure valves. This is not my situation. In my case, brake engagement is near the top of the pedal travel. However, under heavy braking, the pedal travel is longer than I would like and is somewhat soft; not a firm end point of travel. In fact, I can press the pedal to the floorboard. This is not an issue in actual use as I get full braking action well above the floorboard, verified on-track.

Sounds like maybe you have air in your system, when you were installing these parts how did you keep the brake fluid from draining out of the system? Did the reservoir ever run low?
If you get air in the MC and or the ABS unit, it can be very difficult to remove. The only procedure I have seen that works is to use a pressure bleeder, crank it up to 30 PSI and bleed both front calipers at the same time for several minutes (use a large quantity of cheap fluid in the pressure bleeder). This is the only method that has ever worked well for me. (read about this method in the VW shop manual)
It would also be a good idea to know what the piston displacement of your calipers is, and you can't really measure piston retraction with any real accuracy with pads installed. Your issue might be air trapped in the system but high caliper/MC displacement ratio and or large piston retraction may also be contributing to the problem. Sometimes it is not one thing but several small issues that add up.
If my work on these brakes has taught me anything, it is that all caliper piston seals should be lubricated. Even if they don't necessarily need lubrication, it will always help. Then you can decide if RPV's are a good idea or not. But yes, in your case it does sound like you may still have significant amount of air in your system.
Good luck!