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Pulsating front brake level

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Pulsating front brake level

PostAuthor: Marko Sharko » Sat Jan 13, 2018 7:53 pm

My 81 750 is on the road after 18 months, has new break pads.
The front lever pulsates when braking.
When I push the Nike the rotor scraps the pad in one spot during the revolution of the wheel .
Could this be the issue? Can the disk be machined or does it need replacing?
Thanks

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Re: Pulsating front brake level

PostAuthor: bstig60 » Sat Jan 13, 2018 8:44 pm

The disk is warped. It will cost less to replace it. Used ones are available on Ebay. Here is the part number and the list of bikes that use the same disk.
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Re: Pulsating front brake level

PostAuthor: mark75 » Sat Jan 13, 2018 8:59 pm

you could have the disc turned by a machinist - minimum thickness is 4.5 mm (0.2")

if the disc is warped --- max deflection is 0.15 mm (0.006")

this info should be in your service manual. [downloadable (pdf) ones are available on site]
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Re: Pulsating front brake level

PostAuthor: Marko Sharko » Sun Jan 14, 2018 6:45 pm

bstig60 wrote:The disk is warped. It will cost less to replace it. Used ones are available on Ebay. Here is the part number and the list of bikes that use the same disk.

Can you please attach the list.

Thanks

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Re: Pulsating front brake level

PostAuthor: Hellgate » Sun Jan 14, 2018 7:22 pm

My guess is the rotor is glazed. Scrub it with Scotch Brite before you replace them.

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Re: Pulsating front brake level

PostAuthor: Flyingdog » Mon Jan 15, 2018 12:34 am

:yup:

Good idea before turning/or replacing rotors. Should also look at the flatness and cleanliness of your pads. But be aware.. oem pads are angled, don't do what some have and try to flatten the material parallel to the backing plate. Ruins your day real fast. Just because their fairly new, they're probly organic and will ball up with chunks of brake material and road debri. Making pads cock off just enough to make em feel squishy and wobbly. Specially since oem rotors are solid and don't do much clean/scraping the pads when applied. Not much you can do bout it unless you switch to slotted rotors and/or sintered pads. Which is kinda pricey since you should "only" use sintered pads with pure stainless steel rotors. Which Virago 'oem' rotors are not.
Oh yea, as you probly have noticed, be mindful of the mounting of those (Type I) single pin caliper systems.
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Re: Pulsating front brake level

PostAuthor: Marko Sharko » Fri Feb 09, 2018 11:59 pm

Man am I struggling here.
Had the disk checked by a custom motorcycle builder, disk is fine but run it on his lathe anyway.
Got a braided line fitted, cleaned up the new pads as per advice on the post, had another bleed sessio.
Just took it for a squirt down the road and there is no change, still pulsating.

I have after market billet levers and master cylinder fitted, is there any chance that the problem will lie in the master cylinder bore/ piston size?

It scared the hell out me, slowly pulled the front brake on, it pulsated and then pulled back to the bars.
While the bike is stationary I pull the level and it works fine.
Thought ?

Cheers

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Re: Pulsating front brake level

PostAuthor: Flyingdog » Sat Feb 10, 2018 12:35 am

Damn..master cylinder causing this? I couldn't see it, as that's "upstream" so to speak. There's nothing up there to cause a movement. I can't see it, as something's gotta fluctuate at the bottom to send the pulsations to the master. But I have been wrong, before. Have you put the bike on the center stand and tried taping a wire one of the forks..extend the tip of wire to the brake disc, wheel, tire to check for trueness? Maybe a problem at the caliper mounts? I assume, since you had your discs turned, they were mounted to the wheel, ok. With a disc lock at each mounting bolt. (And torqued correctly) Distance between the rotor and wheel (at all circumference points to points on the wheel). Caliper parts, seals, piston all nice and straight? Caliper, itself, correctly mounted and torques on the sleeve & bolt that mounts to fork leg. Have you grabbed the caliper and tried twisting it? How is that bolt/sleeve? Straight? You are using the correct pads, I assume. Contact surface to disc.. flat? The correct pads? I'm sure you're aware those pads' friction material are angled, relative to the backing plate. Just throw'n stuff out here. You saying the lever pulled back to the bars, sure sounds like air in the line. Hmm..there's only so few moving parts in that system.
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Re: Pulsating front brake level

PostAuthor: Marko Sharko » Sat Feb 10, 2018 1:28 am

Wheel is true and balanced.
I will have a good look at the calliper tomorrow and see what I can fine.
I think I will bang the old master cylinder and lever on and see if there is a difference, doesn't help that I did not ride the bike before the project so unsure if it was there prior.
Thanks for the ideas, will let you know how I get on.

MK

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Re: Pulsating front brake level

PostAuthor: Flyingdog » Sat Feb 10, 2018 2:19 am

JMO..I'd be more concerned bout the disc being true to wheel and the pads are true to the disc. Hope you find it.
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Re: Pulsating front brake level

PostAuthor: Marko Sharko » Wed Feb 28, 2018 12:30 am

Found, sort of.
Replaced aftermarket m/c with an omc, released all bolts and pushed bike up and down, re tightened, removed the tarrozza folk brace and went for a whip down the road, brakes are fine.
Not "new bike brake" but hardly any movement in the lever.
I may have been expecting too much from a 1981 bike to be honest.
I placed the fork brace back on and tightened up, pulsated again.
Released the pressure on the bolts a bit and all good.
Measuring the fork brace compared to the aftermarket billet yoke there is 4mm difference.
Loc tight on the fork brake bolts with less pressure and all is " to Micky" NZ slang for mint.
Thanks for your help folks.

Marko

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Re: Pulsating front brake level

PostAuthor: Flyingdog » Wed Feb 28, 2018 1:09 am

Marko Sharko wrote:removed the tarrozza folk brace


Whoa..didn't know you were using fork brace. Tweaked forks would definitely mess with stuff. Not entirely sure bout how caliper/pads/disc aligning with each other since they're all on one leg...But glad you're track'n it down.
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