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Weird brake problem

Brett_jjj

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Yesterday I replaced the front and back brake pads,I removed the calipers to clean up and grease the slide pins, and to generally make sure the caliper seals etc were all ok...I completely drained the old brake fluid and bled the system.The pedal feel was nice and firm like it should be,I drove the car to bed the new pads in,and they bedded in perfectly...Then last night whilst driving into town,the brake fail dashligh came on, and the brake pedal was just about going to the floor when the pedal was pressed.I thought I must have left a bleeder screw a bit loose and she'd sucked in a bit of air,so I thought Id just check them and rebleed it this morning.Now this morning the brakes are back to normal again,they are exactly like they should be with new pads and a bled system.I checked the bleeder screws and brake hose connections, everything is sealed tight and not leaking at all.Ive never seen this happen before in all the years Ive been doing my own brake services.Has anyone ever had this happen, or heard of it happening, or maybe have an idea of what might have caused it.Ive since driven all over town this morning and they are working excellent again.
Its a VS with no ABS.
 
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88GreenVN

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Sounds like it had 1 small amount of air left in the lines. The second bleed did the trick hey.
 

Brett_jjj

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I didnt end up re bleeding them this morning though,because they are back to normal again,the pedal is firm with normal travel like it should be,and it was just as firm first up yesterday when I bedded the pads in,this is what I cant work out,the brakes were excellent first up yesterday,then last night they went to the floor and the brake fail light was on,then this morning they are back to normal again with no light showing..
 

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Strange indeed. Even if the booster fails you still have a firm pedal. The only way the pedal can go to the floor is if there is air in the line some place.
 

Brett_jjj

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Strange alright,I cant work out what could have caused it. Theres definitely no air in the system as the pedal is heaps firm like it should be and has the proper travel,the booster is working fine,when the brake pedal is held in and the engine is started,the pedal sinks in a bit like it should..Its got me stuffed why its happened.And I dont feel safe driving it knowing that it went to the floor just out of the blue, but now is back to "normal" again.Ive found from past experiences that if a bit of air is still in the system,it usually just makes the pedal a bit spongy with a bit longer travel,but last night it was nearly to the floor.
 

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possibly a master cylinder that is on it's way out.

was there a lot of pedal travel with the old pads or generally more travel then you have now?
 

Brett_jjj

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Yeah,there was a bit more travel there before I replaced the pads and fluid,but there usually is,the pedal always seems to get a little bit longer when the pads are near the end of their life.The travel was not excessive though,but you could tell the difference between how they were before and after the pad change,less travel and a good firm pedal.It "feels" just like it always has when Ive put new pads and fluid in,theres no difference there from any other time ive done it..I agree,I think its something up with the master cylinder.Theres nothing else that I can see,that would cause the pedal to just go to the floor just out of the blue and cause the brake fail light to come on.Ive been checking out the VT front brake conversion anyway,the VS is way underbraked at the best of times for a car that size and weight so I might kill 2 birds with 1 stone.Thanks for your time and input guys.cheers.
 

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The VT M/C booster upgrade is very much worth the effort. All 3 of my VN's have now had this upgrade and I'm very happy with the brakes on all 3. None had the calipers or rotos changed so still stock in that area. I figure we are not racing anyone so if we have to stop big time once we can give the brakes a while to cool while we change undies :) so no need for 1,000 worth of rotors/calipers.
 

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so whats happened most likely is that where the pistons was in the master cylinder it has worn into the alloy a little with the old pads, when you fitted the new pads the piston has moved back some in the master cylinder pack past the wear point. there may be a small ridge/lip in the master cylinder where it has let fluid past the piston allowing it to travel a lot further.

the VT style MC is a straight bolt on (to your existing booster) but you need a small spacer to go between the MC and booster to get the spacing correct. or you could adjust the rod as it has a threaded section on the end but i'm not sure what length it would need to be adjusted to
 

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The VT M/C booster upgrade is very much worth the effort. All 3 of my VN's have now had this upgrade and I'm very happy with the brakes on all 3. None had the calipers or rotos changed so still stock in that area. I figure we are not racing anyone so if we have to stop big time once we can give the brakes a while to cool while we change undies :) so no need for 1,000 worth of rotors/calipers.

i'll 2nd that. makes a huge difference to the brakes.
 
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