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Brake Imbalance


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#1 Corinnem34

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Posted 28 October 2013 - 08:00 AM

Hi, could anyone possibly help me overcome an imbalance in the braking system of my 20 year old mondeo? It presents in both the rear and front brakes. I have changed the pads front and rear, and the discs at the front, but this hasn't solved the problem. It keeps failing the MOT on this and any help I will be thankful for!

 

Thanks in advance

 

Corinne



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#2 BOF

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Posted 28 October 2013 - 10:14 AM

Not sure that I can, but...

 

  • did the guy doing the MoT offer any comments, beyond 'its failed'?
  • presumably, he did say that one (or more) were low on retardation; Which ones?
  • (particularly rears) can have a habit of sticking; that can contribute to low retardation and/or sticking on, but can be relatively cheap to cure; in that case, you need to move the mechanics to dislodge the dust that is causing the problem
  • another common problem is corroded slide pins causing sticking; you can 'cure' this temporarily by removing the corrosion and working everything back and forth; if you do this cheap-but-time-consuming process, my guess is that you'll be doing the same thing again in a year's time (or sooner) to get through the next MoT
  • replacing calipers is possible, but costs money; you would only want to do the minimum (probably one axle), rather than all four 'just in case'; to do this, you'd need to know which wheels are problematic

(I've assumed that the problem isn't 'fade'; that would probably be fluid and is a different matter)

 

In any case, at some point the better advice will be to 'get in someone who knows what they are doing', and I'm unclear whether you've reached that point yet.



#3 jamesm182

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Posted 28 October 2013 - 10:33 AM

Welcome to the club Corinne. Could be a calliper sticking?



#4 BigD

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Posted 28 October 2013 - 08:12 PM

A sticking calliper would be my guess too.  It should be quite easy to diagnose - go for a short drive - just ten minutes or so and change down through the gears to do most of your 'braking'.  When you get back, immediately check all four brakes for excess heat.

 

Be VERY careful doing that - if one is binding, it will be extremely hot.

 

I had the problem on my Mk3 which turned out to be a bent guide pin, which was stopping the calliper from returning fully.  I changed the calliper, discs and pads, flexi hoses and a wheel bearing before I got to the bottom of it (the bearing was gone anyway, so I swapped that while I had everything else off).

 

The actual guide pin was a five minute job to replace.



#5 Corinnem34

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Posted 28 October 2013 - 09:10 PM

thanks to all for your help about the brakes, It passed the MOT today (just). Developed a new problem since then however, there is now a high reading of hydrocarbons out of the tailpipe. Obvious props like EGR, thermostat, temp sender are all functioning, and the cat is brand new. Had the same problem last year, and its costing a new cat every year! Again, thanks in advance for any help!



#6 ppeter7

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Posted 28 October 2013 - 09:19 PM

that could be a cheap cat.ive heard that from a garage m8 that they use to use a company that done exhausts and the cats where just falling to bits by the time mot is due.



#7 Corinnem34

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Posted 28 October 2013 - 09:35 PM

apparently, its the only one being sold for my car. tried loads of places and they all gave the same answer. Mind you, parts are becoming harder to get now for it.



#8 wase16ll

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Posted 28 October 2013 - 09:38 PM

high hydrocarbons is excessive unburnt fuel,that wont be down to the cat,that is a tuning problem....such as plugs/leads/compressions...needs proper diagnosing

 

 but high HC will knacker the cat very quicklly

 

though peter is correct in that cheap cats arent worth the bother,you can get quality cats at reasonable prices without having to buy originals.

 

but,like i said,high hc wont be a cat problem,more inclined to believe that cats have been changed without diagnosing/curing the underlying problem thats causing the cats to fail



#9 Corinnem34

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Posted 28 October 2013 - 10:05 PM

i'll hold my hands up to changing it without knowing the underlying cause, but this was on advice of the garage. He couldn't suggest anything else, so i was inclined to believe him.



#10 wase16ll

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Posted 28 October 2013 - 10:25 PM

would be helpfulif you had the full readings of emissions,but high hc isnt good

 

think below 200ppm is mot standered,but ideally you should be looking for under 50ppm on a warmed up engine, closer to zero the better.

anything above 200ppm is very bad,its detecting unburnt petrol going straight into the exhaust,this will coat the catalyst and cause it to overheat and eventually melt/collapse...this in turn will block the exhaust and eventually bring car to a halt

 

there are a number of reasons to give high hc...few eg's

misfire...bad spark plug, ht lead or coil pack

misfire...poor engine compression

flooding...leaking/dirty injector/s

but can also be a sensor problem...such as coolant temp. lambda, air flow, fuel pressure reg...list goes on.

 

so ideally, if you can get a full mot emission printout, let us know the figures for CO. HC and Lambda at both idle speed and 3k revs on a fully warmed engine [if it isnt up to temp then readings will be misleading] then can help to narrow the problem.

also if there is any noticable running problems, such as low on power,hesitations, starting problems.

 

how many times has cat been changed in recent years, plus any history of why....such as was it always down to high HC?



#11 BOF

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Posted 28 October 2013 - 10:26 PM

Had the same problem last year, and its costing a new cat every year! 

 

One per year is excessive. Really excessive.

 

On t'other hand, there is a large number of possible causes

  • poor quality fuel
  • poor quality oil
  • misfires (eg, spark plugs)
  • fuel pump
  • air filter
  • lambda sensor
  • engine wear (cylinder bore, piston rings, valve guides)
  • temperature sensor
  • ECU
  • injectors
  • coil packs
  • spark plugs
  • miscellaneous wires and connectors between the above

and its difficult to comment on which it might be, without further info, and it wouldn't make any sense at all to change everything on the 'battleships principle' (change something and see if it helps, and if it doesn't change something else, because, sooner or later, you'll have a hit).

 

Oh, and there is also some kind of 'magic cat fix' stuff that you can buy from motor spares shops that puts a bit more catalytic material in the fuel and helps you to get through the MoT. This a desperate, last ditch measure, but if you are close to the pass/fail edge, might be worth it.

 

And, I should have asked, the engine was fully warmed up and had had a recent service before it went to see the friendly MoT man, didn't it?



#12 Corinnem34

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Posted 28 October 2013 - 11:07 PM

thanks, yes engine was warmed up, I bear no grudge against MOT guys, i have known them for years. there is a lot more it could fail on, but we wont go into that!  As far i understand the print out, HC is around 145ppm? you can smell it when the car is running!



#13 Corinnem34

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Posted 28 October 2013 - 11:08 PM

oh CO results were within range



#14 wase16ll

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Posted 28 October 2013 - 11:25 PM

with that figure,you have a problem that will lead to another cat failure, especially when you consider that reading will almost double on a cold engine.

appreciate that other figures were within range,but diagnosing can be easier if we get the exact readings....plus not knocking the garage just that something is being overlooked here, they are dealing with a symptom not the cause..this is something i see on a too regular basis.

get to the root of the problem,not only will you save on replacing cats, your fuel economy will improve too..

 

do you have any noticable running/starting issues plus do you find you have to top the oil up on a regular basis?

can you confirm if its had a basic engine service plus whether the correct grade engine oili was used {can make a huge difference to emissions if not and a common mistake made}



#15 Corinnem34

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Posted 28 October 2013 - 11:31 PM

has had a basic service, it doesn't burn oil, but there is aleak from somewhere underneath. 15/30 oil was used. as for running problems, there aren't many. Temp gauge reads bottom end of normal going along, shoots up when idle. engine idles between 900-1200 revs. takes about 25 mins to get to operating temp. other than that, just usual age related stuff



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