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Discussion Starter #1
So I rode my 2010 Mv f4 last week with my cousins and it rode fine. Today I took it in the afternoon to get it inspected at a place about 7 miles from my house. I was a few hundred feet away from the shop that the rear caliper seized while I was riding around 20-30 mph n locked the wheels and the engine died. I got so scared thinking maybe the engine seized or the chain came off. I had to push it really hard to the side of the road in a parking lot. There was little smoke coming from the rear calipers. I waited and called my cousins to bring the truck to pick me n the bike up but as usual they didn’t answer the phone. I tried to push the foot brake lever but it was stuck. It wasn’t depressed at all. I waited for the bike to cool down and tried the foot rest and it was working again. I got it inspected and slowly rode back home without even touching the rear brake pedal. I’m gonna soon take it to cycles 128 for new tires so if it needs something I can have them do it since the wheel will be out anyways.
 

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Put a 8mm ring spanner on the bleed nipple then a length of clear hose over the spanner on the nipple, crack the nipple open while pushing down on the rear brake lever. Close the bleeder with the rear brake lever still pushed down. Let the lever up and repeat a couple of times. This will lose a bit of fluid if it's overfull.

Then check the lever adjustment where the brake lever activates the rear master cylinder. You'll see a threaded portion and a lock nut on the shaft. Flick the clip up and pull out the pin (it's all one piece and attached). Then hold the forked piece the pin came out of, undo the lock nut and screw the forked shaft clockwise into the master cylinder. This will change the stroke and engage the rear brake later in the stroke. Sounds like your problem is a combination of too much fluid and too much adjustment on the brake pedal.

If you're not confident and are going to let a dealer do it then have them check all of the above. I don't have an F4, but to check my rear master cylinder level the tank has to come off. Others more knowledgeable will tell you if the fairing has to come off to adjust the stroke on the pedal.

Bear all this in mind as it's easy enough to do but takes a few hours labor so a dealer will charge accordingly. I'll post some pictures when I get a chance.

Cheers

Deano
 

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Majid, @Deano is spot on.

The other thing that you should do is completely change your brake fluid. If there is moisture contamination then the brake fluid will expand more with heat and it could cause your symptoms.

It has happened to others.

The position of the master cylinder near the exhaust and the heat added from braking contribute to this.
 

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Not just fluid change....the return hole in the master cylinder is blocked so pressure in the system cannot release when pedal is at rest.....

Check the free play at the master cylinder piston and brake pedal....the piston MUST return to fully extended when at rest.

If there is not at least a minimal amount of free play between the pedal and the piston you will continue to have this problem, even with fresh fluid.
 

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Firstly,has any work been done to the rear brake recently?
If not,you need to diagnose the problem if it is the master cylinder or the caliper.More than likely it is the master cylinder.
To work out which is causing the problem is as follows-
When the rear brake is locked on,release the brake line to the caliber at the master cylinder,if the brake frees up the problem is in the master cylinder,and it will be not enough pedal free play or the seal in the master cylinder is blocking the compensationing port which means the master cylinder needs a repair kit fitted or a complete new cylinder.
 

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Discussion Starter #7
Sorry to get back late. Hope everyone had a safe weekend. Thank you everyone for all the replies and help. All of you guys are correct. esqz’me is spot on. I came today after work took out the fairing to inspect the lever and master cylinder. I noticed that piston doesn’t return all way so the brake lever isn’t returning all the way to push the brake light switch which is why my brake(stop) light is always on.(very dangerous cuz people behind me won’t know when I’m braking). I can easily take the tank off and bleed the rear brakes. I have never rebuilt a master cylinder. So my next question is can I get a link to a master cylinder I could buy or if the rebuilding is easy and if u guys can guide me a link to the rebuild kit. Also should I use racing brake bluid??
 

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Just check first the pivot of the brake lever is not seized.
It's pretty dirty in that area.
 

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As Mitchy said. From your photo the lever is not returning fully. You can see the rear brake light switch is not depressed, there's a gap between the lever arm and switch plunger. Before you go laying out on a master cylinder kit, check and do all the things mentioned above. Eliminate them first and maybe save yourself some money. Racing fluid? Don't waste you money, a good quality fluid is ample. This is on a back brake that for most owners never works anyway. It's a shame yours went the other way, albeit briefly. Also just check the disc isn't out of true from the heat. Mine cooked when my rear hub seized. Still ok and running if a funny colour.

Cheers

Deano
 

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Majid, loosen, or remove the hex holding the brake lever pivot, Clean the area with Brake Cleaner or Degreaser, lubricate the pivot bolt where is penetrates the brake lever, reinstall...BUT do not overtighten the bolt.

It is also possible that there is some corrosion or dirt on the push rod for the master cylinder. I'd spray some brake cleaner inside the rubber boot to loosen things up and exercise the piston.

If you end up needing a master...I probably have one here.
 

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Discussion Starter #11
So @Deano first I should check if the brake lever pivot is not seized. Then do a complete bleeding of the fluid and refill with fresh fluid. And also diagnose if it is the master cylinder or caliper.( the way @mitchy mentioned Sunday).

@if u have any picture on the adjustment of the lever and changing the stroke that will be great.
 

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Discussion Starter #12
Chuck I just saw what u wrote. I’m gonna do all that tonight n get back to u. Thanks a lot as always
 

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So @Deano first I should check if the brake lever pivot is not seized. Then do a complete bleeding of the fluid and refill with fresh fluid. And also diagnose if it is the master cylinder or caliper.( the way @mitchy mentioned Sunday).

@if u have any picture on the adjustment of the lever and changing the stroke that will be great.

That's what I'd do mate. I'll try to post some pics later today.


Cheers


Deano
 

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Here's some pics. Shows 8mm and clear hose on rear caliper, brake pedal and clip. Undo 10mm locknut (spanner down) while holding forked shaft with screwdriver. Back locknut down toward master cylinder a few turns. Turn fork 4-5 turns in your case toward master cylinder, retighten locknut, put pedal and clip back on and see how it feels. May need more, maybe less.
Cheers
Deano
 

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@Deano is that a hole in your exhaust, removed bracket?
 
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@Deano is that a hole in your exhaust, removed bracket?

Yeah mate, it is. Took a run up the Atherton Tablelands a few weeks ago and it pissed down. Bike sat for a couple of weeks before I could clean it. Noticed the bracket had broken off. It had been welded on by my son after it came off a while ago.


Unfortunately my boy's welding was much better than the original cos this time it's torn a hole in the muffler. Only noticed it when I posted the pictures. I was waiting for someone to notice and chip in.


Put my Arrow system on yesterday and will get him to repair the HP. Going to leave that bracket off. Never did line up properly anyway no matter what I did and not really needed anyway.


Cheers


Deano
 

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Discussion Starter #17
Sorry for the late reply. I had to give the wife a little attention.(she was complaining I was spending more time with the bike than her). So over the weekend I adjusted the brake lever exactly how @Deano mentioned and now it works properly engaging the brake light switch. My gas tank was full. I was being lazy. But instead of removing the tank to flush and refill with new brake fluid I just removed the 8mm bolt holding the reservoir to the bike and slowing moved it outside and secured it to my bike frame. After that I removed the screws to the cap of the reservoir and bled the whole brake system. I was extra careful not to spill any brake fluid. Took it for a ride but was too scared to use the rear brake at all. I will let u guys know if anything happens in the future. Thanks for all ur help.
 

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Sorry for the late reply. I had to give the wife a little attention.(she was complaining I was spending more time with the bike than her). So over the weekend I adjusted the brake lever exactly how @Deano mentioned and now it works properly engaging the brake light switch. My gas tank was full. I was being lazy. But instead of removing the tank to flush and refill with new brake fluid I just removed the 8mm bolt holding the reservoir to the bike and slowing moved it outside and secured it to my bike frame. After that I removed the screws to the cap of the reservoir and bled the whole brake system. I was extra careful not to spill any brake fluid. Took it for a ride but was too scared to use the rear brake at all. I will let u guys know if anything happens in the future. Thanks for all ur help.
I often ask the Mrs to help me when I am bleeding the brakes and clutch on my bikes.....She is very good at fault finding lol>:)
 
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