Master cylinder bench bleed.

Hey Y'all

I've searched for this and I have found numerous mentions of bench bleeding a dry master cylinder, but I haven't found any details as to the process. So....................how exactly do I bench bleed a dry master cylinder? :?: I'm trying to swap my beat up mc for a used one I picked up from a fellow xjer who was parting out his bike.

Any help would be greatly appreciated.

 

Just fill it up with brake fluid and pump easily. For the rest bleeding is quite the same as bleeding the calipers. If you experience a soft handle, try bleeding the banjo's one by one. Let someone pump and hold the brake lever when it's got pressure, wrap a towel around the banjo, loosen the bold until the lever touches the handebar (HOLD IT THERE) and tighten the banjo again. Then repeat the procedure for all other banjo's, until the handle is nice and hard again.

I normally use a vacuum bleeder. Works like a charm, except for a sticking air bubble in the banjo's.


grz Thijs

 

Are you saying to bleed the MC after mounting to the handle bars? Will the piston return, you know push back out, as soon as the brake line is reinstalled and there's fluid in the MC?

Unfortunately, I don't have a vacuum bleeder and I'm on a very tight budget.

 

There is an air leak hole in het master cilinder which will ensure that it fills up properly. It can take quite a few pumps though. Pump easily en leave give the cilinder some time to fill up.

I don't see how you are going to bleed the MC without have it attached to the rest of the braking system/bike, since it will run empty then :wink:. Put the bike on the side stand for bleeding, since the reservoir has to be horizontal. (approximately)


grz Thijs

 

I guess I wasn't clear in my original question. Here's the issue.........

The plunger or piston in the guts of the mc isn't returning to the extended or release position. I have put the replacement mc on the bars. I then put my finger over the hole where the banjo attaches to the mc. I then have to push the piston in with my finger but it does not return. So I have to use a small screwdriver to pry the piston back out then repeat. This doesn't appear to be very effective. I can't install the lever to pump the brakes since the plunger/piston won't return on its own. I keep having to pry the piston back to the release position.

Any advice?

 

If I'm not mistaken there should be a spring inside the MC which makes the piston come back. I'm afraid you'll have to take it apart to be certain everything is OK inside. Maybe some heavy corrosion is making the cups stick in the bore somehow.

I know there is a spring in the '85 XJ700N, but for the '82 650 I don't know for sure, but logic tells me there should be one in :wink:.

I guess taking it apart and honing the inside + renew the cups is the way to go. Not too difficult, and will make your MC as new.


grz Thijs

 

I found it. The spring was in 2 pieces that were fused together. No wonder it wasn't making sense to me. Anyway, thanks for the heads-up I think I'm good to go now. This forum ROCKS.

Peace
J