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Defender 90 - uneven braking and sometimes long pedal

 
 
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ianc2051
Just got MTs


Joined: 22 Feb 2009
Odometer: 174
Location: Weare Giffard, N. Devon



PostPosted: Mon May 19, 2014 5:26 pm    Post subject: Defender 90 - uneven braking and sometimes long pedal Reply with quote

I would appreciate some help in which direction to go on my 300 TDi CSW braking system. Firstly on this vehicle all the calipers, discs and pads were replaced together about 1200 miles ago - but the clue maybe that a year has gone by in which to do those miles and things may have partially siezed due to lack of movement. The braking until recently has been excellent but a week or so ago I started to get an intermittent longish brake pedal and at other times a normal pedal - whatever the condition, it never felt like an air in the system problem - always a solid pedal with good braking but at times a longish pedal.

So I replaced the brake master cylinder as there were signs of seal wear (small black bits in the reservoir) and have bled the system twice. The new master cylinder has made a difference in as much that the pedal is more solid than ever but I still get on occasion a longish pedal action. I've noticed also that under heavy braking the vehicle pulls to the nearside.

Can I ask if this could be due to sticking caliper pistons which look okay (no rust or mud deposits) but when observed with someone slowly pressing the brake pedal, do not move exactly together at the same time? I will be bleeding again as one of the pipe unions had a very small weep when the new master cylinder was fitted - this now fixed but it could possibly have drawn in air (but I don't really think so).
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Toseland
Mud Obsessed


Joined: 25 Oct 2011
Odometer: 3209
Location: cardiff


1999 Suzuki Vitara

PostPosted: Mon May 19, 2014 5:56 pm    Post subject: Reply with quote

fluid properties dictate they will always fill the easiest to move first.. until the pressure in that overcomes the next easiest, so on and so forth..

so you will most likely only get 1 moving until the others contact the disk unless you have a special brake master cylinder setup.

i am not 100% knowledgable with the m/c setup on the green oval stuff, but it will (i am 99.9% sure) be a twin piston setup, meaning that the rear brakes will most likely apply first, and even moreso this pressure then applies the fronts.

the difference in timings will however be negligable.



the long pedal seems to me that one of the pistons is being pushed back or retracting a long way, you have to fill it back up more than the others to apply the brakes.

does it have drum brakes on the rear? if so, check the shoes in that, worn shoes or a faulty adjustor can contribute to this (piston having to push pads a long way)

are any of the brake disks warped? even slightly, (look for a slightly different coloured spot on the disk) as this could also push the piston in that particular caliper back further and cause this..

if the pedal stays hard, it may still be air in the system so bleed them, ideally get a pressure bleeder if you can and bleed the system with that to rule out that possibility,

__________________________________
I live by 2 sayings:
1. The beatings will continue until morale improves
2. Pain is just Weakness leaving the body..

The feeling you get when you first smash your shaft out, is one you will never forget.. especially if you do it in front of 10 guys.
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ianc2051
Just got MTs


Joined: 22 Feb 2009
Odometer: 174
Location: Weare Giffard, N. Devon



PostPosted: Mon May 19, 2014 6:27 pm    Post subject: Reply with quote

Thanks Toseland I'll do what you say - just for the record it's disc brakes all round and the front calipers have four pistons per side.
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big_ears
Winch Assistant


Joined: 20 Apr 2004
Odometer: 50
Location: Nuneaton



PostPosted: Tue May 20, 2014 10:50 am    Post subject: Reply with quote

Hi, the problem you describe can be caused by play in the wheel bearings.

If the hub assembly is lose then the disc wobbling around can 'kick' the brake pads back, hence the longer peddle travel.

Hope this helps,

Ian.
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ianc2051
Just got MTs


Joined: 22 Feb 2009
Odometer: 174
Location: Weare Giffard, N. Devon



PostPosted: Tue May 20, 2014 1:56 pm    Post subject: Reply with quote

Thanks guys for all your inputs and help - I now have the right side front hub assembly partially dismantled (stuck for the special socket which fits the caliper securing bolts but my mate will have one) and I can clearly see that the outer bearing has completely disintegrated. I can see that when the securing nuts have been removed to withdraw the hub, the bearing will fall out in pieces!

I've sent off for a 52mm socket so I can undo and later torque up the securing nuts and also the copper grease on the back of the pads has contaminated everything - big clean up required.
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