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Odd brake pressure issue non cup 172 ph2



  Clio 172 ph2 / bikes
Hi guys, just want to bounce this off someone.

Clio 172 ph2 non cup with abs.

I’m no stranger to rebuilding bike/car brakes etc, spent more time doing it than I care to think about although I’m less familiar when it comes to abs systems.

So the story,

Brakes were fine prior to this.

few months back when doing a fluid flush with a power bleeder, two callipers already done I ran into a sheared rear nipple, bled It at the rear line till I had a chance to get another caliper, not ideal but works when done right, On the last caliper I ran out of fluid in the pressure bleeder. Took a massive hit of air. So, went and got more fluid and Re bled the entire system

symptom: no matter how much I bled I got soft pedal on first pump much like you’d expect with air in the system, it’s odd as you can feel the pressure build slightly l, move as if proportioning is shifting, then there’s enough pressure to come on properly at 3/4 travel. comes in hard on the 2nd and holds pressure without dropping away.

so, rear caliper is replaced so I can properly bleed. Same symptoms persist after a day of bleeding.

take the car out, activate the abs on gravel, bleed and repeat. Marginally better after day of bleeding.

next I cave in and buy an RSTuner to do an abs bleed. Same symptoms persist after a day of abs bleeding but now the 2nd pump will put you through the windscreen.

So... I’m thinking maybe the master seals are starting to go after all the fully extended presses when bleeding ( bleeding both with and without the power bleeder, as sometimes one method will work better.)even though it’s not acting like a typically failed master.

Replaced the master, spend a day bleeding and chasing the last of the air out and ding ding ding symptoms persist.

the systems holding pressure as the pedals not falling away, there’s no leaks along the lines, the sliders all move fine, are recently cleaned and silicone greased and none of the pistons are binding.

last part of the puzzle has to be the abs pump itself. Must have a valve stuck in an incorrect phase which could also explain that odd pedal feel on the first pump where Its like I can feel transition through different pressures slightly.

Any insight of experience with similar issues would be helpful or interesting. I’m probably 30-40L if fluid down at this point.

also looking for info on matching abs pumps as every post about them is vague or misleading.

so obviously you match the number on the pump with it’s replacement, in my case 8200 270 251 in the top right corner. However, do you also need to match the Bosch ecu number underneath as well? Some say they’re coded, some say it doesn’t matter so long as it’s from the same model of car. Some say ‘match the numbers’... with zero explanation or follow up.

long read, kudos if you made it this far.
 
  Clio 172 ph2 / bikes
Just following this up after sorting but not solving it.

After replacing the abs pump, a rear abs sensor that coincidentally failed and the rear brake over axle line that blew whilst replacing said sensor

It turned out to be the rear right caliper.

figured it out by Pushing a piston in and clamping it in place to block it off from the circuit, seeing if it made a difference to pedal feel, fitting everything and trying the next caliper until the issue showed.

however, prior to this i had measured piston moment and all mechanical lash on every caliper in situ to make sure pistons weren’t over retracting or any other oddities occurring. found all movement to be basically equal and nothing showing out of sorts.

The offending calliper had no real reason to act up. Sliders were all free, handbrake mech worked as it should, piston moved And wound in easily. The caliper also wasn’t showing a pressure restriction.

being Quite methodical in fault finding this is really quite feckin’ annoying to have no real answer as to what the actual issue was.

Nonetheless calliper is replaced and it works as it should again. Lesson learned being with these kind of faults, block each caliper off till the issue highlights itself, that or drop some money on the right pressure gauges for diagnosing.

that’s all folks
 
  Clio 172 ph2 / bikes
Cheers man, that was some journey it led me on. just wish it made some sense. I would’ve deleted the abs system if it didn’t drive the speedo / mot issues.... and still had the same issue.

could’ve been a couple of overlapping coincidental issues but going from taking air when bleeding to it being an unexplainable caliper issue is a bit of a stretch to me.

regarding matching abs pump/module numbers. I matched the numbers on the pump and swapped my old module over to the new pump after deeming it unlikely to be an electrical issue as the issue persisted whilst stationary with the engine off. As for mix and matching modules, I think you can based on speaking to a few people so long as it’s from a car with the same tyre size / abs ring tooth count but I found all sorts contradictIve info online. Ie non cup 172 195/45/16 cars vs 182 205/45/16 Abs modules will hold different info effecting the abs/esp and speed readout marginally. Once again, this is speculative to what I’ve been told. If anyone can validate that, I’d interested to hear.
 

JimF

ClioSport Club Member
  Clio 172
Bit of a bump-from-the-dead for this one, but THANK YOU.
I've been going through a similar issue with mine. Its only a weekend/track toy, so its been a case of, "save up, replace a few parts, try it again, problem still there" repeat. Then you forget about the car for a while, go on holiday, Covid pandemic etc. and then next time you get in, you realise the issue is still there.
I'd bled the brakes maybe 5 times, had the powerbleeder on them, replaced braked lines for braided hoses, new ABS rings on the front and discs & ABS sensors on the rears, and its still there!
So I reckon I'll get the calipers looked at.
I was in the same boat as you, I've spent my lunch break looking at the RS Tuner website and Renault Clip units on eBay. Convinced myself it was the ABS unit itself that was full of air.
So when you changed the caliper, was the pedal back to normal straight away or did it take a bit of driving to sort it all out?
 

Martin_172

ClioSport Club Member
Worth noting too that when I had issues with mine after fitting the abs system into the van (it was drained dry) I must have bled 5 litres thru it with the pressure bleeder and rs tuner abs module before I got a pedal I was happy with
 
  Clio 172 ph2 / bikes
Bit of a bump-from-the-dead for this one, but THANK YOU.
I've been going through a similar issue with mine. Its only a weekend/track toy, so its been a case of, "save up, replace a few parts, try it again, problem still there" repeat. Then you forget about the car for a while, go on holiday, Covid pandemic etc. and then next time you get in, you realise the issue is still there.
I'd bled the brakes maybe 5 times, had the powerbleeder on them, replaced braked lines for braided hoses, new ABS rings on the front and discs & ABS sensors on the rears, and its still there!
So I reckon I'll get the calipers looked at.
I was in the same boat as you, I've spent my lunch break looking at the RS Tuner website and Renault Clip units on eBay. Convinced myself it was the ABS unit itself that was full of air.
So when you changed the caliper, was the pedal back to normal straight away or did it take a bit of driving to sort it all out?

glad my endless hours of bleeding and swearing have helped someone, but yep replaced the caliper, it bled as it should and it was instantly noticeable. The abs bleed on top if that made an unreal difference though, brakes are almost as sensitive as a modern car.

wish I could explain why the caliper failed but there really was nothing measurable wrong with it.
 

Brigsy

ClioSport Club Member
  Kangoo 172cup
At a guess caliper seal must be on its last legs.

Had similar issues with rear cylinders on drum abs setups. Pedal goes long yet firm, traced to a minor weep from the cylinder, not enough to see a drop of fluid on the deck but enough to give a shite pedal.
 


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