MAJOR brake issue - But ONLY when they on the BIKE?

[Wabby]

Hi guys,

Just been on the blower to the garage fixing front brakes on my ZXR400.

I have the following issue with the brakes:

Can pull them back to the bar before they bite (even then they are shite)
No air in them at all
Discs are not warped (apparantly)
Wheel bearings are set right
Calipers are free and in good working condition

If you take them off the bike, and put a spanner between the pads - It brakes as soon as you touch the lever - And they are AWESOME. As soon as you put them on the bike, they just push the disc at one side.

Anybody ANY ideas?

Garage says he has been told from other garages that have come across it before that it was the discs - But he is struggling to see how?

ANY help is GREATLY appreciated - And beer will be bought if we ever meet! lol
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What restriction?

[Tim..]

Are all the pistons moving freely?
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[Wabby]

[Fisty]

Are you running the standard lines or braided? Id try another master cylinder on it to rule that out.

When the brakes on my zxr400 went tits up it was a worn out master cylinder.
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Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Stalk]

Is it possible that you have reused the old brake pads and mixed them up?
This woild mean that the pads would have to re-bed on the disk face giving a spongey feel. (Old pad reuse not reccomend)
OR
Have you fitted new pads on worn disks? this woild also give a spongey feel. Had the same problem with a BMW. What I did in the end was to carefuly ride the bike whilst applying the front brake in order to assist the pads to bed in a bit quicker, don't overdo this as it is possible to overheat the brakes.
The bit to pay special attention to is the word carefully.

Hope this helps
Cheers
Stalk

[Wabby]

Braided lines.

Master Cylinder rebuilt before taking to garage - They have confirmed that is fine and rebuilt correctly with no issues.
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What restriction?

[Wabby]

[finpos]

it is a bit hard to see how it would be caused by the disks. I'd suggest there is actually still some air in there. When they are tested off the bike, are they being held in the same orientation as when it's all bolted up?

Also, I'm assuming it's not a sliding caliper, as what you describe is exactly what happens when your slide pins are seized - but I'd expect a mechanic to know that!

f.

[Stalk]

[Kickstart]

Hi

Only way I can see the disks causing a problem is if they are bent such that they are dished. Pulling the brakes flattens them out, but releasing the brakes they go back to being dished and push the pistons back further.

However how are you checking with a spanner? One caliper at a time, and if so what are you doing with the other caliper? Are both calipers behaving in the same way?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Wabby]

[Wabby]

Anybody know if their is a difference between L3 (1993) and L9 (2000) calipers on a ZXR?

I replaced my faulty ones with ones from a 2000 as part of installing the braided lines. Starting to think they might be different in some way - As they are still pushing the disc
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What restriction?

[Kickstart]

Hi

Doubt they are different to be honest, and can't see why any difference would cause the problem you are having.

I have put ZXR400 calipers on a ZZR600 when trying to find a brake problem (ZZR600 brake pistons are far bigger) without any issues

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Fisty]

calipers are identical through the L models
____________________
Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Wabby]

[Fisty]

Daft question but you havnt used H model discs have you? They are smaller than L models
____________________
Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Vincent]

Is the spanner the same thickness as the disc

[Wabby]

[Fisty]

If the discs and pads are fine you are left with 4 options.

Dodgy lines
Buggerd master cylinder
Buggered calipers
Air in the system

It cant be anything else.
____________________
Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Wabby]

[Pete.]

If they are wedging a spanner in between the pads and the gap is tight i.e. they don't have to pump the pads out to meet the spanner and the lever is then solid, then I think the problem is that when fitted on the bike they are pumping the pistons out to meet the disks and the seals are grabbing the piston and deforming, causing the pistons to be pulled back from the discs slightly. You then need the extra lever travel to pump the pads up to the disks before they grip.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Wabby]

That makes sense, Geri. Thanks.

I will remove the discs later, and try wedging them between the pads when the calipers are off the bike.

If I have a good brake then, I don't know what to fucking do! lol
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What restriction?

[steven_191]

try holding the caliper on the disc but not actually bolting it to the fork. that way it will have complete free movement. see if it bites properly then, to me it sound like not all the pistons are moving evenly. when you put a spanner in there it can move anyway, when you got a disc bolted up and a caliper bolted up your relying on the free movement in the pistons.

you need to have a close look as you slowly pump the brake and see if you can see every piston moving evenly. if not then its either pistons or seals. cant see what else. maybe the path of the fluid between either side of the caliper could be blocked and stopping one side working??

[Wabby]

Inside pistons on both calipers are MUCH slower than the outside pistons - Outside pistons are almost fully out before they try to come out.

I take it this means its the calipers that are at fault here?
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What restriction?

[Kickstart]

Hi

Sounds like the pistons are not freed off. Maybe the seals were nipped when they were put back together. Strip the calipers again, take the seals out and clean up thoroughly behind the seals. Lube everything with brake fluid and reassemble.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing