RRC Brakes 'problem' - never known anything like it before..

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TwoSheds
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RRC Brakes 'problem' - never known anything like it before..

Postby TwoSheds » Fri Jul 15, 2011 10:59 am

On the first application of the brakes in the morning the pedal goes down further than normal. It still works well in every way, it's just that it goes possibly a centimetre or two further down before it gets firm. It is not spongy - there is just nothing at the top of the travel.
Subsequently the brakes are fine in every way. They do not need pumping or anything and are not spongy.
It may also happen a little bit after being parked up at work all day, but if it does then it is so slight that I can't be sure.
It is not leaking or using brake fluid.
It happens whether the first application is in reverse or while going forward.

It feels like after you have had the pads out and the first application is taking up the slack..

Any ideas please?

Roger

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davew
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Postby davew » Fri Jul 15, 2011 11:40 am

The first thing I'd do, although it doesn't really fit that well with your description, is check all the wheel bearings. It may be that one of your wheels (and it's connected brake disk) are leaning over slightly when it's parked, pushing the pads back. The more usual symptom for this is spongy brakes after a motorway run or other journey where you've not touched the brakes in a while.

Second choice would be the servo although again the symptoms don't fit exactly. I take it the engine is running when the pedal is longer ? Test the servo is operating properly by operating the brake pedal a few times with the engine off until it goes hard (ooh err matron !). With your foot still on the brake pedal start the engine and the pedal should go further down.

How long ago did you last change the brake fluid ?

Do you still have rubber flexi hoses or have you changed to braided ? If you're still using rubber then it may be that one or more of them is getting tired and ballooning, overnight they may then be slowly shrinking back to their correct size, pushing the brake fluid back.

That's all I can think of for now :)

TwoSheds
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Postby TwoSheds » Sat Jul 16, 2011 5:06 am

Thanks for the thoughts Dave:

Wheel bearings, disks and pads are all ok (checked last week before and during MoT).
Servo - interesting thought, but behaves exactly as it should in the 'start up' test.
Brake fluid is two years (but only about 10,000 miles) old and came from a brand new container so I think that's ok.
All rubber hoses were replaced with braided three years ago.

The only other things I can think of are:
1. For some reason the pistons are not fully withdrawing in normal use and that overnight they slowly creep back fully, in which case what I currently consider to be a normal pedal would actually be too 'high'?
2, Same as number 1, but master cylinder. The master cylinder is the only part of the brake system which isn't new(ish) and might even be original, so currently I suspect that.

For the moment it feels perfectly safe so I am happy to keep driving and monitoring the situation - especially since a master cylinder would be £250 and even a master cylinder repair kit (genuine) is nearly 50 quid for four bits of rubber and a circlip!

:o :shock: :x

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Bo
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Postby Bo » Sat Jul 16, 2011 8:30 am

Rog, I had a similar problem last week on the morning of the MOT (isn't it always the case).
The week before I had changed all of the pads and whilst doing that, worked the pistons fully in and out a couple of times to check them and clean them. Having put it all back together, I had a fine nice firm pedal and was good to go, or so I thought. I was away all week so the Disco didn't move until I set off for the MOT, I then noticed an inconsistent pedal. Thinking it was the new pads that needed bedding in on to the old discs, I drove a couple of miles left foot braking but still no joy. Called in at Rod's, bled the brakes, solid pedal was back, jobs a gud'n and MOT passed. I have not changed any major brake parts for a couple of years so I assume that winding the pistons in and out has moved some air in the system.
5/4 of people admit that they’re bad with fractions.

TwoSheds
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Postby TwoSheds » Sat Jul 16, 2011 9:29 am

Got to be worth a try! I'll bleed them next time i'ts dry and see if it helps. (although in my case the pedal does go solid, it just moves too far before it gets there...)

Like you - before the MoT I had the brakes apart (although didn't need to replace anything) and cleaned and moved the pistons, so maybe... :)

Roger


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