toplessFC3Sman

Ok, so I have been having this issue for about 8 months now. This is on an '09 Sport, so ABS but no traction control. Basically, when the car is off and residual vacuum is released from the booster, the brakes feel perfectly normal - there is a little bit of travel as I first press on them but it quickly firms up and the pedal does not sink to the floor regardless of how long I hold it, even if I'm pressing with all the force I can. When I first start the car and drive around a bit, it also still feels OK - maybe a little bit squishier than I remember, but the pedal doesn't sink to the floor, it stops nice and straight, the ABS kicks on if I'm on wet roads or gravel and really stand on the brakes etc. However, once I've been driving for a little while, generally including some highway speeds, the pedal feels squishier, like there is more travel necessary to get the same braking force, and the brakes drag more than they should. I haven't measured the exact drag force or which wheel or wheels are causing it yet, but it can be pretty noticeable when coming to a stop gently and letting the car roll forwards or backwards a bit, such as at a traffic light on an incline. The brakes drag much more than those in my other two manual cars (2012 Mazda5 & 1988 Mazda RX-7) on the same incline in the same conditions.

This all seems to have started when one of the banjo bolts for the braided brake hoses (passenger front) loosened on my commute, resulting in a drained brake master cylinder. At the time, I found the problem, tightened it up, refilled the reservoir, confirmed the brake pedal was holding pressure (despite there inevitably being some air in the system), and drove home to bleed the brakes. Since then, I've bled the brakes 8 times that I can count (I may be forgetting one or two in there), using the old 2-person method of manually opening and closing each caliper bleeder, doing the same with speed-bleeders, doing the same with speed bleeders and pulling vacuum at the bleeders, and finally getting one of the Motive pressurized reservoir systems and doing it with that. I have replaced the pads on all 4 corners, replaced the sliding caliper hardware and re-greasing all the pins for all 4 brakes, and even got the ForScan OBD tool to try to actuate the ABS pump (apparently this isn't an option for the ABS-only system). When the ForScan didn't work, I've made a habit of going out onto loose gravel roads nearby and slamming the brakes to actuate the ABS, alternating which side of the car was on looser gravel to try to get all circuits to engage. Each time I've put about a pint or more of fresh fluid through the system, and the first couple of times there was some air that came out, but I haven't seen any bubbles for the past 4-5 times at least.

I was convinced that the problem was still air trapped somewhere in the system, possibly in the ABS pump, but am at a loss for how to get it out. It would make sense that air in some lines in the engine bay would want to expand as the engine bay warmed up, which could apply some force to the calipers and make them stick, but if I'm not pressing the brakes and the master cylinder was at it's resting point, wouldn't any pressure escape back into the reservoir through the holes usually used to draw fluid in to the brake circuits?

The calipers all seem to be sliding well, and I don't notice any pull when braking or large differences with left vs right sides on loose gravel, so both brake circuits seem to be working about equally. Any other failure modes I should try to check out?

Loki

iTrader: (1)

A quick test for brake drag is to feel if one wheel is hotter than the rest after driving. It sounds heat related, you're right,but I'm not sure it's engine bay heat.

toplessFC3Sman

I'll try that again next time I take the car out - I tried to check that before when driving to work, which involves ~50 min of highway driving followed by ~10 min on surface streets, there wasn't a noticable difference when I parked, but the cool-down time on surface streets may have been too much to judge by feel. None of the old pads looked like they were overheated or had unusual wear vs the pads on the other side, and I haven't noticed a difference in brake dust between wheels, but you're right, I should try to test this specifically without cool-down time.

BigCajun

iTrader: (1)

Longshot here, but if you think it's dragging, you could check to see if your rubber brake lines are collapsed.

It acts like a check valve, you apply pressure that will flow through, but when you let up, the pressure stays in the caliper.

Just like you're 2 man bleeding, jack up the wheels, have someone press the brake while you try to turn the wheel, then release the brake to see if it turns.
If it doesn't, open the bleeder screw.
If it turns freely now, you have a collapsed line.

toplessFC3Sman

The driver's front side was dragging a bit more than the passenger's side, and after a long trip on the highway they were at 42C and 33C respectively, while the rears were down at 20C or so (it was only about 6C out). Spinning them independently definitely confirmed that they were dragging, and that the front calipers were not releasing all the way. After some more digging and disassembly to check the wheel bearings, I found a lot of rust built up between the rotor and the hub surface which may have also been pushing them out-of-true slightly, causing some pad kick-back. The pistons were also binding in the caliper slightly, so I pumped the brakes a bunch of times with the caliper sitting on top of the rotor (no pads) to extend it, cleaned off the piston circumference underneath the boot (there were some deposits near the end, underneath the groove for retaining the boot), pressed it back in, and repeated this 3X per side until they seemed to be sliding better. I also noticed that the passenger's side front wheel had a bit of a bend to it and wasn't true, and that the wheel bearing on that side was beginning to sound crunchy and was spinning very freely (moreso than the driver's side, which seemed fine), but not showing any play. The brake lines themselves were fine.

I'm in the middle of getting a new wheel & wheel bearing so I haven't gone for a test drive, but hopefully the combination of sticking pistons, rust keeping the rotors from sitting completely flat, and the vibration from the bent wheel was causing the pistons to kick back on the highway, leading to more brake pedal travel when stopping the first time or two, and then the brakes dragging from the sticking pistons was causing the excess resistance. We'll find out soon though

toplessFC3Sman

Well, I'm replacing the wheel bearing but before installing the new assembly i just noticed that the new bearing has a different wheel speed sensor connector, or rather it doesn't have a connector at all, just a hole for a sensor to be bolted on. The new hubs are Mazda part number F189-33-04X, and have that number and the Mazda logo molded into the back face near the threaded insert and hole for the sensor. The old hub has the connector housing molded in to the back face, with most of the NSK past number legible (the NSK part number is 49BWKHS30, but the "49" has disappeared in rust). I was under the impression that the Mazda part number F189-33-04X was common for all S2's and had superceded the 151-33-04X number, but I guess that's not true?

Anyway, I guess I'll have to sort out the difference here and maybe get the other part number, or see if there's a sensor that will work with the ones I have

toplessFC3Sman

Turns out the difference is the 151 part number is for models without traction control and 189 part number is for models with traction control. Anyway, the right part is ordered and the wrong one will be returned. In the mean time, I reassembled with the old bearing since I had to move the car and the old bearing didn't feel loose, just was getting noisy and turned more freely than the new bearings or the one on the other side. Anyway, a quick test drive on the highway and afterwards seemed to show a lot of improvement from the replaced wheel, loosened brake pistons and cleaned surface behind the brake rotor. I haven't driven far enough to conclusively say that the brake feel issue is solved, and I'm planning on replacing the wheel bearing when the right parts arrive, but so far, so good.

TeamRX8

iTrader: (25)

edit: bad information, read posts that follow below:

toplessFC3Sman

By DSC I'm assuming you mean dynamic stability control, AKA traction control? All S2's apparently did not have DSC, since my 2009 (US market, definitely an S2, it has the S2 body, 3rd oil injector per rotor, 2nd OMP etc) does not have DSC, has the non-traction-control ABS unit and non-traction-control wheel speed sensors. It has ABS of course, and I don't know if the S2 non-TC ABS unit is the same as the S1 non-TC ABS, but it does seem different to the S2 with TC ABS unit since I had read that ForScan could trigger those ABS pumps to run to help bleed the brake system, but that's not an option for my car. By experience, it definitely doesn't have DSC since if it did, I would have noticed when it triggered when racing on a frozen lake or snowy autocross course.

Some searching on this site lead me to believe that F189-33-04X was the proper wheel bearing for all S2's (thus why I ordered it originally), probably based on that assumption that all S2's had DSC, but F151-33-04X looks correct in all the images I can find (it has the connector for the wheel speed sensor molded into the back instead of a hole and threaded insert for a separate sensor). Calling a dealer and having them look it up by VIN also gave the F151 part number... sooo... I guess there must have been some non-DSC S2's imported to the US even if they're rare.

TeamRX8

iTrader: (25)

DSC - Dynamic Stability Control i.e. traction control

thank you for informing me on this. I never knew or heard of an S2 without DSC. Otherwise my apology for the error, but appreciation for educating me on it.

So I went back and looked at it further and as you stated, the F189 front wheel hub is the (w/o DSC) part number for the S2.

And the ABS modules are the same part number for both S1 and S2 ABS modules, whether DSC or w/o DSC.

Good to know!
.

toplessFC3Sman

Well, after a bit of time driving it, including a few ~1 hr trips on the highway, I think that finally solved the braking problem. The combination of a bent wheel, sticking brake pistons, sticking slide-pins, and possibly rust build-up between the rotor and hub all contributed to at least one of the front brakes consistently knocking back the piston at higher speeds and dragging the pads, causing the odd feel and extra travel. The new wheel bearing without DSC (F151-33-04X, same as S1 without DSC) was the correct part with the built-in wheel speed sensor and also has been installed now.

Oddly, there is still a bit of a front-end clunk every once in a while when transitioning from a right to left turn at higher cornering forces, but all the front end bushings, ball joints, tie rod ends etc feel very tight. Still trying to track this one down without just throwing parts at it.

TeamRX8

iTrader: (25)

what lug nut torque are you using?

There was a TSB that raised the torque value to 108 ft-lbs and cleaning of the mating surfaces for correcting an otherwise undetectable clunking/snapping sound

https://drive.google.com/file/d/1ZXr...N8KUfXJwX/view
.

toplessFC3Sman

I've been going to 80 lb-ft, driving around the block, then re-torquing to 85 lb-ft, just to double-check nothing tightened up improperly because of taking the wheels off. After all the cleaning and rust removal I'm certain there's no deposits and build-up between the rotor face, but I'll go and re-torque to 108 - I hadn't heard of that TSB

TeamRX8

iTrader: (25)

I only TQ to 90 lb-ft due to using antisieze on the threads

dry threads need the higher setting.

toplessFC3Sman

It looks like the problem was some combination of a slightly loose passenger's side engine mount bolt, which I must have missed when re-installing the engine 2 years ago, and a slightly loose passenger's side lower control arm front nut, which would have been last loosened when I took the car in for an alignment a few months back to address steering vibrations (before discovering the bent wheel). Neither was very loose, but weren't as tight as I would normally go given the size of the fastener. I checked just about every other bolt or nut I could get a wrench on but those were the only ones that were off. Anyway, after a few test drives including around a couple traffic circles where the right-left transition would reliably cause the thunk, it seems to be gone. Time to put some more miles on her now

toplessFC3Sman

Well, as the weather has been getting dryer here & I've been driving Vera more, the initial brake feel issue has come back - a "softer" pedal after highway driving and sticking brakes, especially in stop-and-go traffic after highway speeds (where it's most notice-able). On the way to work today, it was 2C out, but immediately after pulling off the highway the driver's front rotor was at 43C, pass front at 36C, driver's rear at 26C and pass rear at 38C. My guess is that the wet weather and occasional snow has masked the problem by keeping the brakes cooler and wet so there was more pad-rotor lubrication, making things feel normal.

Unfortunately that also means I'm not really sure where to look next - All the issues identified above were probably contributing, and I found a wheel bearing that was probably on its way out, a bent wheel, and fixed a clunk, so it was not for nothing. Anyway, I'll probably start by re-checking all the previous work, especially the caliper slide pins, pad binding in the calipers, caliper piston corrosion and binding, generally looking for and cleaning off corrosion, and that the parking brake is releasing fully. Here we go again...

toplessFC3Sman

Well... sometimes its the small things that cause the most frustration. My driveway where I've been doing all the work is on a slope, and I almost always pull in forwards, which would put the nose maybe 12" higher than the tail of the car. I think the only times I've pulled in backwards have been when I was intending on working on just the back brakes to re-bleed, clean etc. When jacking up the whole car, I would try to use larger jack stands extended further in the back to get closer to level, but it may not have been enough. Anyway, the other night I was flushing the brake system again to make sure its all fresh, new fluid from just-opened containers instead of ones that were opened from previous work over the past year (I was using Motul RBF-600, which is suggested to be flushed every year) and it finally clicked that the front bleed screws are basically horizontal, so any rearward tilt to the car at all could trap air in the front brake calipers. The thread sealant on the driver's side front speed-bleeder was no longer sealing either.

Anyway, jumping to the conclusion, I turned the car around with the nose down and kept it in a decidedly nose-down position when re-bleeding the fronts (and removing the driver's front speed bleeder to clean it and re-apply sealant), and seemed to get a small bubble out of both front calipers. Driving to work today, and the brakes felt about as normal as I remember, there was no dragging even after spending ~40 min on the highway, and immediately after getting off the highway the rotor temperatures were much lower at 26C for both front rotors and 18C for both rear rotors (it was just about 0C out).

So, fingers crossed that this is finally solved, and the lesson is to pay attention to the details and keep the nose pointed slightly downwards when bleeding, especially if you suspect there's air trapped somewhere!