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Thread: Sams Polo 3.0

  1. #191
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    VW Polo 9N3 1.9TDI AXR
    brake system FA: 256mm ATE54 FS-III
    brake system RA: 232mm Lucas C34
    control unit: 6Q0 907 379 AQ
    Component: ESP 8.0 front H04 0002
    Coding: 0002371

    another possibility is that the Polo diesel uses smaller 34mm rear caliper pistons compared to Gti 38mm ones. Thats 20% smaller. If an MC swap for whatever reason proves impossible then perhaps a combination of the stock rear disc with the diesels calipers might produce a better pedal, but at the expense of rear braking power?

  2. #192
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    Keen to hear what the price is on the master cylinder fix ;D

  3. #193
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    Pretty sure its just a Bora V5 23.8mmmasterSams Polo 3.0-bora-v5-2-3-23-81mm-jpg(see here) but needs the spacer so that the reservoir will clear the booster. The spacer is totally DIY'able as well, but its the pin that fits into the master that I'm unsure of. Its obviously got to be longer by the width of the spacer, but I have no idea what the OE part it replaces looks like. It could be that the OE part is a piece of pi55 to modify too. Its also entirely possible that a mallet blow to the booster will clearance the reservoir! I do have a spare booster under the house so i'l have a squiz if thats possible.
    So if its not too expensive from Germany I'd see if a group buy is on the cards. If not I'll make something probably.

  4. #194
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    Rod on the right is OEM, rod on the left is the one I made to suit the commodore master cylinder.

    The rod can easily be made, but like a lot of things, if it already exists its often easier to purchase it.


    Sent from my iPhone using Tapatalk

  5. #195
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    Ok. I was half expecting the OEM rods to be made from a steel/plastic assembly with rods/springs and sockets knowing VAG. If thats all they are then I can do that on the lathe at work no probs. Being the parts guru that you are, you dont happen to have a 23.81mm MC off a Bora V5 do you?
    I know the MC swap didnt solve your issues RE pedal travel, but with fat pads, new bled fluid, braided lines, tyrol caliper stiffeners, MC brace etc there's not much else left to try on my setup.
    Last edited by sambb; 11-07-2021 at 09:25 PM.

  6. #196
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    I doubt very much that the ABS programming will vary based on calliper, rotor and/or piston sizing. It just relies on the wheel's ABS sensor to detect lock up and then bypasses the brake pedal pressure until the wheel starts to rotate again, then pulses the bypassing to achieve the ~20% locked to unlocked ratio. What size the calliper, rotor and/or piston/s are is irrelevant.

    Larger pistons require more brake pedal movement for the same braking force, probably best avoided if you are dealing with a long pedal. Smaller piston area would be better for that.

    There is also what I call the "hydraulic ratio" to be considered, for the same amount of pedal pressure exerted a larger piston will produce less braking effect, due to lower pressure acting on the pad. Another reason to avid larger diameter pistons if you are trying to alleviate a long pedal as you will have to push harder to achieve the same braking effect.

    What is relevant is the leverage ratio of a larger diameter rotor, obviously the larger diameter a rotor is the more braking effect it will have for the same pedal travel and pedal pressure.

    Also worth keeping in mind that a larger pad area increases the friction, hence provides more braking effect given equal pad material. Has no real effect on pedal travel, but may result is less pedal effort for the same braking effect.

    As I have posted previously, the more I read of peoples' experiences the more I am inclined to be suspicious of leakage in the ABS bypass, or at the very least premature bypassing, being the cause of the long pedal. Is it possible that the bypassing can be related to the software programming of the ABSCU, which could be fixed by a few keystrokes in the appropriate places? Master cylinder, rotor and calliper swaps, different pad material, braided brake lines, firewall stiffeners etc etc have had negligible effect. What's left, the ABS unit?



    Cheers
    Gary
    Polo GTi 2017, Golf Mk7 110TSI Highline, Golf Mk7.5 R, Skyline R32GTST, Stagea RS4,

  7. #197
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    yep the bigger 41mm rear piston was only something I was going to consider if a bigger master cyl was in place because yep the pedal absolutely cant get lower than it already is.
    I might look at the lucas C34 rear (34mm rear piston) as that would have a positive effect on the pedal but I'm unsure at this stage what pad size it carries. Its crazy to me that with the hugeness of the TT rear brake hardware that it still carries the same pad as the solid disc stock Polo Gti. If the diesel C34 caliper carries the same pad again, then that'd be a win. I wouldnt do it if the pad was smaller agin though.
    RE bypassing, thats why I was looking into the bosch 8.0 coding. It just struck me that different brake configs seemed to carry codes that related to their hardware. I initially thought it would be a brake balance thing but I guess it could be more about ABS thresholds depending on the 'sportiness' of the car, its weight bias etc?
    I might just put the code in that was for the Cupra with 312mm fronts 232mm rears from the factory. Thats obviously a 'sportier' setup and may run the ABS module differently. If I feel a proper change then yeah the abs module could be the source of it all.
    But like Simon was saying in his brake woes thread, the abs module doesnt really explain why at pedestrian speeds I can brake and its like nothing is happening until you are 1/2 way into the stroke and then its like you are standing on a sponge. I could go out there now and my foot would nearly go 2/3 of the way to the floor with a steady hard push. Thats what makes me think the master just isnt moving any volume. Dunno its a tough one but it becoming one of those things where you wonder how far you can actually take the car lng term if you cant sort the brake issues.

  8. #198
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    Personally I'd remove the ABS unit from the system (as I have in the Skyline), they are heavy suckers and with their road biased programming and relatively "slow" hardware can be an issue on the circuit, particularly in a gravel trap event or 2 wheels on the grass.

    There is no "magic" in braking systems, all of the factors are measurable and formula based solutions are well known. For example on a number of race cars (FWD, 4WD and RWD) I have run a 1/2" front master cylinder and a 5/8" rear master cylinder, with a 5.5 to 1 pedal ratio, 4spot/6spot front callipers, with 315 to 355 mm front rotors, plus 2spot/4spot rear calipers with solid and vented rear rotors from 290 mm to 325 mm. If there is a bit too much travel I move the 5/8" master cylinder to the front and use a 3/4" for the rear. The brake bias adjustment and/or rear pressure limiter enables balancing of the braking force. As a result my spares kit only has the 3 master cylinder sizes, no matter what car I am working on.

    I don't think overall weight or weight balance would have any effect on the ABS programming, "sportiness" or maybe "track worthiness" would be more likely. For example the road Porsche GT3 has very different ABS programming to the more track oriented Cup car.

    The low speed brake response sounds to me like excessive ABS bypassing, whether that's a programming issue or a hardware issue is the question. The harder you push their more they bypass. Early ABS systems tried to avoid the very intrusive pulsing brake pedal problem by running a higher level of bypass at low speeds, at higher speeds the pulsing is much faster, therefore not as noticeable. My 2018 Polo GTi, pulses at higher speeds when the ABS is activated, but not at all at really low speeds. Keeping in mind that the ABS pulsing (bypassing) frequency is totally linear with the frequency (rotation) of the road wheels, slow rotation = slow (longer) pulsing.

    There could also be a brake pad temp question if it only happens when they are cold.

    Cheers
    Gary
    Polo GTi 2017, Golf Mk7 110TSI Highline, Golf Mk7.5 R, Skyline R32GTST, Stagea RS4,

  9. #199
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    Oh believe me despite being still a road car I have toyed with the idea of scrapping the ABS system. I dont think it'd be a good look if I was ever caught that way though.

  10. #200
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    Well I tried to set the soft coding to what the SEAT Ibiza Cupra ran (a few posts back) in the hope that i'd get myself some keystroke brake performance. It had different component coding so I didnt expect it to work but I winged it anyway. The code took, but then I had all sorts of ABS errors that persisted even after I set the coding back to the Polo's one. I got it all to clear eventually (heart rate settled again as I thought I'd flashed the unit or something). So I think unless you have the same control unit and component coding then coding changes are a bit iffy. I'll keep digging.

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