CRF450R Back Brake Problems!!!

Alright, I'm on here posting for my boyfriend (he's not very internet savvy LOL). He's got an 04' CRF450R and he's been having MAJOR issues out of the master cylinder. He's just about ready to kill somebody :smirk:. Several months ago the MC went out on it and one of his friends told him to go to ebay, which was stupid we know now, and he bought a new (cheap) one. He installed then blead it and couldn't get anything. He thinks he blew a hole in the hose somehow bc it wasn't leaking before at all. So he replaced the caliper and the hose, put it all together and the cheap MC started leaking. But other than that it was working. He wasn't happy with that so he went ahead and bought the factory one, thinking that he wouldn't have any issues out of it. But now he can't get the new one to work. There's no air, moisture, or debris in it and the brake fluid is brand new. He's blead it manually and with a syringe. In the past several days we've read thru a million posts on here and seen that a lot of people have similar issues so we realize that the 450 back brakes are a pain in the ass. Anyway, he's tried a lot of the things other people have suggested and nothing seems to work. So we'd appreciate any advice we can get!

Thanks.

Edited by streetsavage

MC has is own rebuilt kit comes with the seals but since youve got a new one its time to check the caliper it has it own rebuilt kit also it might be youre seal on the piston on the brake caliper check that

How much wear is on the brake pads? If they have a lot of wear and the caliper is fully extended bleeding will be difficult. In most cases if the mc is good the line is next weak link, but if it has been replaced trouble shoot the caliper.

The brake pads are fine. But the caliper the line and mc have all been replaced so I don't understand what the hell is going on. I think I'm just going to buy a bleed kit and see if that will do any better

so your the internet savy one AND the mechanic?? lol.. (its' ok to just ask questions..)

"you" are not bleeding the line well enough more than likely, especially if you have changed parts. It isn't easy as part of the line at the mc is higher than the rest of the system and air gets trapped there. It is easier with a mityvac or $20 harbor freight bleeder.. It takes patience and practice to bleed the line without. The amount of pad left would have nothing to do with how hard the line is to bleed really, unless you took the pads out and pushed the piston right out of the caliper. I have replaced the rubber plungers inside the mc a couple times. Also the line at the fitting can be a weak point, but usually would have to have some line pressure to force fluid out there, it will feel the same as if the mc is letting fluid by the plungers..

open bleed valve put hose on it let gravity bleed air out. may take hours

I know that it might sound kinda dumb, but when he replaced all those parts, did he replace the crush washers for the banjo bolts?

If you have been having rear brake problems you might want to replace the rear brake line. had similar problems, rebuilt master cylinder, caliper finally replaced the line. It was the problem the whole time, bleeds quicker too. I will change fluid at least once per season.

Yeah I'm definitely NOT the mechanic. He asked me to post the question for him (the second post was him). It's just easier that way especially when he's out there trying to work on the bike and not getting anywhere. Sorry maybe internet savvy wasn't the right wording for what I was trying to say. And I did ask a question, didn't I? :smirk:

I asked him about the washers, he said he didn't replace them but he's pretty sure that's not the problem. And the rear brake line has been replaced! That's whats so crazy, everything is brand new. His Grandfather is over now and brought a vacuum bleeder (I think that's what it's called). He bought a regular bleeder and thought that had them working but when he took the bike to go ride over the memorial day weekend, the brakes were gone again. So they're hoping that the vacuum will do the trick. If not, I think they're out of ideas.

But thanks everyone, for all the advice and we will let ya'll know if the vacuum doesn't work!

always replace the washers when un-torquing the bolt(s)....after all they're cheap so what can you really say?

always replace the washers when un-torquing the bolt(s)....after all they're cheap so what can you really say?

unless leaking, crush washers are not the issue.

Melk-man it looks like you were right, the vacuum worked. He didn't think it would really work any differently because he had already bought a bleeder. Anyway, we appreciate everyones help

Edited by streetsavage
gave credit where it was due
Melk-man it looks like you were right, the vacuum worked. He didn't think it would really work any differently because he had already bought a bleeder. Anyway, we appreciate everyones help

awesome that it got it fixed. It is super easy to get air trapped in the line, especially when changing parts.

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