Sams Polo 3.0

[Sydneykid]

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

[sambb]

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.

[Sydneykid]

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

[sambb]

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.

[sambb]

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.

[Sydneykid]

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.

Well...................most people wouldn't know where the ABS unit should be, let alone what it looks like, additions are easy to spot, deletions require knowledge of that particular vehicle.

You could leave it in place and just bypass the plumbing. Make it easily removable for the weight saving when required.

Cheers
Gary

[sambb]

I have seen in places (mostly subaru forums) where guys just pull the ABS fuse . The fronts then work through the ABS module as per normal because the module without power is in pass through (you need a good diagram of the module to know that the solenoids would be in and stay in that state though). Similar to what I found when I pulled the ABS fuse their rear biasing went nuts so then run the rear port of the MC rearward via a proportioning valve on a single line before it splits to each rear corner. ABS module stays in place and pipe work stays attached whether its void or not for OEM appearance. A piece of black electrical tape goes over the ABS fault light on the dash ha ha. By killing the ABS/ESP I can then run the Audi S3 hubs that I have with their huge roll centre correction as what looks to be a mechanical plug n play.
I maybe just may have a shot at getting my Dads old car as a daily. If that comes through I'll keep mine as a road registered track car and go engineered 2 seater with half cage and then will definitely do something like this with the brakes. So it'd still need to be stock looking - no pedal boxes etc even at that stage. Whether it stays a daily or goes to registered track duties, either way I need a bigger master cyl.

[Stuwey]

Sam, have you tried bleeding the system at *every* line connection?

I was having troubles with my mini getting a decent pedal and cracked the sads with it and started from the master and eventually every point along the way.

3 months of frustration cleared up in two hours.

I know it shouldn't have needed it, but that's what sorted it in the end.

[sambb]

You mean at the ABS module inputs, then its outputs, then at each brakes corner. No I havent done it at each connection along the way. I have checked each connection for fluid leaks though, but havent had the stomach to go right through it like that. But yeah maybe I should. After a full flush recently I got it half decent/driveable and then paid for a proper pressurised vag.com pulsed ABS module bleed. Then after my first track day on that fluid I gave it a few good ABS stops (which definitely hardens up the pedal for a while) and brought it straight into the garage for another go with my vacuum bleeder at each corner in case some track day air/burnt fluid had accumulated at the calipers. So short of what you suggested, it should be in pretty good shape. I know a lot of stock is put into incorrect bleeding being the source of the problem with these cars but also I've now had 3 polo's since 2014 and they are all the same. They have all had configurations of different pads, fluids, calipers and despite that were/are all fundamentally the same RE the pedal. This car even with master cylinder braces and caliper stiffeners isn't one iota better than all the others. Its got to be something inherent in the design. I just dont know what.
To me the ABS modules are either programmed to behave in that way, like Gary has said are just always bypassing OR the master cylinder is ridiculously underdone.
After trying a different soft coding on the ABS module the other night the module has wigged out. I get ABS and ESP CEL's. The ABS light clears after a bit of driving leaving the ESP symbol on. Says there's a comms error even though the soft coding is back to normal. Despite the errors the ABS is still working?! Who knows maybe whatever state the ABS has defaulted to is better than what its coded for? As long as its not locking the rears which it was when I pulled the ABS fuse, then i'll just keep driving it till I find a solution. I barely even care anymore. I am that close to just stripping it all out and paying someone to come around and plumb the whole car up like its from 1989. Or run sans ABS fuse with a proportioning valve in the rearward line to correct the rear biasing. I mean you put so much effort into getting it to go hard and be reliable and at the end of the day you have a car on the track that you just dont trust in the braking department. Either ESP hammering away at the brakes when you are going 80% or the pedal literally ABS'ing its way to the floor when you have to avoid something on the circuit yet the cars rate of decel is about half of what you could achieve without it. I'm starting to passionately hate all the tech on these things. If I ever get another Polo its going to be pre nanny modules, naturally aspirated on R1 bike carbs with a standalone ignition computer. I want my RS2000 Escort/Celica RA23 GT/Pug 205 gti back!!

[Eddy]

Hoyhoy.

I don't know as to what is going on with the brakes Sam, as the best mod I ever done was the master cylinder brace, to me the difference was fantastic.

[sambb]

No it’s not on you Eddy. Like I said it’s not this car alone. It could be that something has degraded a bit since you last tracked it in anger but I doubt it. All my polos have been like this RE long pedals, vague feel and premature ABS intervention. I think I got used to it over time plus also mostly did hillclimbs initially so it didn’t really show up that drastically. A mate drove my last polo pretty hard through a national park and then pulled over certain he’d stuffed the brakes. It’s was the ABS pulsing and sinking the pedal down at speeds that wouldn’t even have his Clio troubled. He was saying that he couldn’t believe I drive the car flat out like that. I hadn’t really even thought about it much before then. After doing more circuit stuff it’s now getting disconcerting. My gut says it’s the master cyl but also It could be the ABS unit but I don’t want to stump for the latter to no avail, and even if it did improve the pedal at the end of the day im still stuck with the ABS. If I’m going to spend that kind of coin that’s where I’m thinking I’d rather just go with a reworked non ABS system that I can build upon. Going to look into the cost of doing that and if it’s even possible with the engine still in the car! The car has enough grunt it’s just tyres and brakes that are top of the list now. I’ll have time on my hands I suppose. This Sydney lockdown is getting pretty heavy now.

[Sydneykid]

My suggestions, go for the larger master cylinder, I think it needs it anyway and there is a power booster so it will increase the pedal effort which is not a bad thing, but not make it too heavy.

Bypassing the ABS unit is easy (well it has been on the cars that I have done), there are fundamentally 2 fluid inputs from the master cylinder and 4 fluid outputs to the wheels. I use as much of the standard pipework as possible, basically just bypassing the ABS unit itself. I use braided lines, with appropriate fittings, sparingly to complete the linking, as it can get expensive. That and a couple of generic 3 way blocks to do the joining.

When we get out of this lock down more that happy to catch up at the race workshop and we will have a look at it and make some suggestions. You can have a look over the Honda if you like, it has all the good tricks that you can pinch ideas from. Justin is also really good at motorsport fluid connections, so he will have plenty of options to suggest.

Cheers
Gary

[sambb]

Yeah that'd be good Gary. From what I can gather to run a street approved type setup, each master cylinder port would run to a tee that would tie diagonal fronts and rears together. For the life of me I cant figure out how you proportion that though. Having one master cylinder port for the fronts and one for the rears with the rear proportioned before it split to each corner seems like the most workable though.
I'm only hesitant at what kind of wobbly the ABS/ESP will throw. It'd definitely need to stay plugged in (no weight saving) as without the wheel speed sensors I'd loose dash info. But I'd love to go to the S3/TT front hubs that use different sensors so there's an issue there. Wonder if the 4 wheel speed sensor inputs to the module could just be parralleled off say one of the wheel speed sensors, so that the module doesnt know any different.

[sambb]

On a good note, the new oil cooler setup - different to previous in that it now runs a T-stat sandwich plate and the cooler core is blanked off on the street - is running the oil temps right in the good 90-100 window now. Oil temps now run higher than water temps in normal driving. As a result the catch can is for the first time catching plenty of water. To my mind that means the oil is getting to a temp to evaporate out any water contamination and the crankcase water content is coming out as a gas and being caught/condensed in the can. Better out than in. If I run the catch can system with the PCV connected you dont see as much water in the can as it most likely just gets drawn into the inlet manifold under vacuum as a gas. But if the PCV valve is blocked off and the catch can is only TIP connected, then you see plenty of water caught. Yes there's always going to be more water caught in the cold weather but either way it wasnt even
doing this when the oil temps were so low before.

[Sydneykid]

Yeah that'd be good Gary. From what I can gather to run a street approved type setup, each master cylinder port would run to a tee that would tie diagonal fronts and rears together. For the life of me I cant figure out how you proportion that though. Having one master cylinder port for the fronts and one for the rears with the rear proportioned before it split to each corner seems like the most workable though.

For the diagonal split you could run 2 proportioning valves, one each between the front and rear wheels. Obviously only one required when the split is front / rear.

We use the Tilton ones, they have 7 settings, so it would be easy to keep them the same setting, the infinite adjustment screw type would be much harder.

I'm only hesitant at what kind of wobbly the ABS/ESP will throw. It'd definitely need to stay plugged in (no weight saving) as without the wheel speed sensors I'd loose dash info. But I'd love to go to the S3/TT front hubs that use different sensors so there's an issue there. Wonder if the 4 wheel speed sensor inputs to the module could just be parralleled off say one of the wheel speed sensors, so that the module doesnt know any different.

Welcome to the world of Production Car Racing, it's brain ache on the BM's when the windscreen wipers won't work if you disable the traction control. They talk to each other via the Can Bus and the traction control + torque split settings depend on how fast the wipers are wiping.

Cheers
Gary