OZ ATV :: The Australian ATV Forum

[surfin]

I have an intermittent problem with losing pressure in my front brake on my LTR.

With my quad sitting there I have full front brake. Go for a ride its mostly still ok at the start, do a few jumps etc and then most of the lever pressure is gone. Come back and let it sit and its all good again till the next ride.

It just started out of the blue one day...no prior crashes etc.

I have bled all the old fluid out of them, but still the problem is there when its ridden

I just put a master cylinder seal kit through it and bled it up...still the same problem.

There is no visible oil loss anywhere. Front pads look to be ok

Any clues as to what to check next?
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[bullet]

Sounds like the pistons are being pushed back.
Excessive disc run out (bent or distorted) or buggered wheel bearings can cause this.

When you ride and the wheel is turning, the pads get knocked further apart that they should and the pistons are pusshed back.
The next time you grab the lever, the first half of the travel is wasted just pushing the pads out to the disc thickness.
So it feels like you've only got half a handfull of bakes.

let us know.
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Can-Am X Team
Bullet #Y12. MrsB #Y18.

[surfin]

bullet wrote:

or buggered wheel bearings can cause this.

How buggered a wheel bearing will do this?

I do know I have play in 1 of the front bearings...and I'm waiting for new ones to turn up
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[bullet]

With normal disc run out your pads only get pushed back a couple of thou.
The piston O-ring desidn also helps determinr this small 'back off' distance.
It is so small that if you jack the wheel up and spin it you will still not that the pads are slightly scraping.
So if you wheel bearing allowed the pads to be pushed back half a millimetre... that might be more than 10 times the ideal 'back off'.

Easy to check, jack the front wheels up and spin and wobble the wheels in all directions.
This will simulate the normal movement when riding.
Then in one hit, pull the brake lever in, and note how far it goes.
let the lever go for a few seconds and pull it in again.
If there is a noticably much larger grab the second time...
you are dealing with excessive piston push back from some sort of increased disc run out.

If not, it's probably something else ???
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Can-Am X Team
Bullet #Y12. MrsB #Y18.

[surfin]

Thanks for the info Bullet.

This is my outer wheel bearing. With the wheel attached the top of the wheel would have been moving 5-10mm I reckon. Need the new bearing first to see if its fixed the problem now


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Team Ironpot 701 Just Doin It

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[noodles]

I think you can pretty safely gaurantee you found the problem
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say NO! to ball sports

[surfin]

Yeah Bullet you nailed this one on the head. New wheel bearings have fixed this problem.

Cheers to Bullet
_________________
Team Ironpot 701 Just Doin It

2011/2012 National Vets Champion 35-45
2012 SA Vets Champion
2012 VIC Vets Champion

Thanks to:

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ATV PRO/PEPS
Coastal 4x4 Hervey Bay
Colac Motorcycles
and my credit card

[bullet]

Cool, i'm glad you didn't start replacing brake components first
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Can-Am X Team
Bullet #Y12. MrsB #Y18.