No rear brakes

After my Wr450 sat for five months waiting for the snow to melt.

I took the motorcycle out for a ride.

I had no rear brakes.

After riding 60 miles or so with no rear brakes I took the Yamaha home and tried to bleed the rear master cylinder.

No such luck it with not pump up at all.

My question is seeing how a new rear master cylinder is about 100 dollars and the rebuilt kit is about 20 dollars is it worth trying to rebuilt the master cylinder?

If you're sure the problem is in the master, it certainly is worth a try to rebuild it.

Personally, I almost never use the rear brake, so I dont know if I would miss it.

But from my experience, I would just pay the $100 and get a new master cylinder....... if that is the problem.

You should start by checking the brake pedal pivot and linkage... try to find out what excatly is wrong..... it may be something easy and inexpensive.


I would guess the piston in the master cyl is blocking the resivoir port . ether the spring inside is weak or the linkage is not letting it come up all the way.

If the linkage is working I would take off the rear brake and push the pistons back and try to back flow the fluid in the system. Could be a little air in it not allowing the master cylinder to work at all. Take the cap off the fluid res. pushing the pistons back and watch for air coming back through the system.

That sounds like a semi common problem....'

Bleed the brake this way:

1. attach a piece of clear hose to the bleed valve on the caliper, run that into a jar of some sort, open the valve.

Remove the reservoir lid, top up if needed

slowly depress pedal fully, slowly release, repeat, you should see fluid coming out into the clear hose, this fluid will move out/in with every depress/release, but it will suck in less than what it pushed out. You should see air bubbles coming through here and there as well which is a good thing.

Always keep an eye on the reservoir - fill it when you're down to a 1/4 level.

Just keep doing this for 20 or so reservoir fills or about 3 fills beyond where the fluid coming out changes to the cleaner clear look of fresh fluid - remember to GO SLOW on the pedal - if you go to fast, you're just going to keep pulling those air pockets back in and it will take 3x as long.

There is NO need to close off the bleed valve, you can actually let the system gravity bleed this way too, however, it takes really long when working on the rear brake because there isn't a big height difference between the caliper and reservoir and you have to be around to keep the reservoir topped up....

it may be as simple as a collapsed brake line

it may be as simple as a collapsed brake line

super highly unlikely

it may be as simple as a collapsed brake line

collapsed brake line normally locks the brake , because the pressure will push fluid thru , but when you let off the brake the fluid can't return to the master.

If you can borrow a pneumatic brake bleeding tool; do so. It is the best tool I've found for the job. They are, however, pricey. The Motion Pro unit retails at over $100. The brake master piston kit is a cheap way to overhaul the master. It's an easy chore which is outlined in your service manual.

Alright then a rebuild master cylinder is up next for the 450.

I was hoping to hear if this might be a common problem for the Yamaha or not.

I had the hot start plunger stick on my WR450 last year and nobody in here had ever had anything like that happen to there's.

I would just take a very close look at it before buying anything . It maybe the spring in it is a little weak not allowing it to return quite all the way. That would just take a few minutes to rear down . Then stretch the spring out a bit , clean everything and put it all back together. I have seen this one before. or the piston seal is bad.

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