Adding fluid after brake line change

[cecil_t]

I recently picked up a '77 XS650 with the factory dual-disk option, and I just replaced the brake lines with braided stainless ones. Cleaned out the fittings and reservoir while everything was apart (didn't seem too bad actually), re-assembled and everything fits nicely.

I added fluid to the master cylinder reservoir but it won't pump through the system regardless of what I do with the bleeders. I tried loosening the banjo bolt at the master cylinder and some fluid seeps through but I can get any to pump. I think the piston is stuck "in" and isn't returning.

What are my options, how do I get fluid back into this system? Once the fluid is moving I know how to bleed brakes, but I can't seem to get it primed.

 

[5twins]

One pump, or even a couple, on the hand lever doesn't move much fluid. It's often difficult to fill a drained system this way. Some pre-fill the new lines to help with this. I use a Mityvac vacuum pump to get a dry system full, then finish with the normal old fashioned hand pumping.

 

[cecil_t]

I think there's a larger problem with the master cylinder, the piston definitely isn't returning with the lever. I took off the banjo bolt and put an awl through there and can push the piston back manually. Maybe the master cylinder needs rebuilt?

 

[XSLeo]

Unhook the line from the master cylinder. With the M/C full, plug the hole the line hooks to with a finger tip, slowly pump the lever. As you pull the lever it should push any air out past your finger tip. As you release the lever your finger tip will seal the hole enough so fluid will be pulled out of the M/C.
Repeat till you get a good flow of fluid past your finger.
Hook the line back up. It may pump up from there.
If not try filling the lines with fluid. Syringes can be bought at a farm supply. With the line unhooked at the M/C use the syringe to fill the lines.
I have a Miti Vac tool. With the M/C full hook up a rubber line from the bleeder to the tool. Open the bleeder, pump the tool. It will draw fluid down the lines.
Some use a pump style oil can. Clean it out very well. Hook a rubber hose between it and the bleeder and pump fluid up the line.
Up in the M/C is a tiny hole, it is a bit toward the line from a larger hole. The large hole fills the plunger, the tiny hole bleeds a bit of pressure back when the lever is released. If this hole is plugged it can prevent pumping the pressure up.
Search the forum for master cylinder rebuild, you should find pics showing this hole.
I have had about a 50/50 success rate rebuilding M/C's I found it easier to replace.
On your M/C it should have the bore size marked on it. I think the stock dual brake system used a 16 mm bore. I have added the dual disc to my 75 and my 81. The 76 up single disc brakes use a 14 mm bore. I use this size on both bikes. Works very well.
If you can't get your M/C to work and decide to replace it, get the 14 mm bore M/C. Much stronger brakes. Better feel.
Leo

 

[cecil_t]

Thanks XSLeo. I tried my finger on the hole but the piston still doesn't return much, not all the way. At this point I have the line completely off and fluid in the reservoir and nothing is coming out at all, even when the brake is pumped. So one or both holes must be clogged I guess, and the piston doesn't return with much authority.

I wonder how these brakes worked at all before. I guess I'm going to order a new master cylinder then and rebuild the calipers while everything is disassembled too.

I was looking on Mike's and you're right the dual-disk option says it's 16mm. I don't see a 14mm option though, just 13mm for the single disk. Is the Magura or Yamaha OEM style better?

 

[cecil_t]

"Nissin 14" is what the MC has stamped

 

[schlakeandbake308]

Just get the mitivac... i had the same problem with mine. mini vac fixed it in five minutes.

 

[cecil_t]

I'm into a m/c rebuild at this point. It's all apart and is cruddy.

 

[5twins]

I guess I didn't read your 1st post close enough. I thought you'd cleaned the MC. That's what you need to do. Do that 1st before buying anything new. I've reclaimed some pretty nasty ones. As long as it's not leaking fluid, you shouldn't need seals either. That goes for both the MC and the calipers. Disassemble, thoroughly clean all the gunk out, re-assemble and go from there.

In my opinion, guys seem to throw the towel in far too easily on these original brake components. They're really not bad once they're set right. Yes, you do want new lines, which you've done, but there's usually no need for new MCs and calipers. The stock pads are very good as well.

 

[cecil_t]

I guess I didn't read your 1st post close enough. I thought you'd cleaned the MC. That's what you need to do. Do that 1st before buying anything new. I've reclaimed some pretty nasty ones. As long as it's not leaking fluid, you shouldn't need seals either. That goes for both the MC and the calipers. Disassemble, thoroughly clean all the gunk out, re-assemble and go from there.

In my opinion, guys seem to throw the towel in far too easily on these original brake components. They're really not bad once they're set right. Yes, you do want new lines, which you've done, but there's usually no need for new MCs and calipers. The stock pads are very good as well.

Definitely, I agree. I'd like to keep these stock components, so I ordered a rebuild kit. Got the mc disassembled, just waiting on the kit.

 

[5twins]

Like I said, if it wasn't leaking fluid, you probably don't need a rebuild kit. I've renovated lots of these with just a good cleaning and no new parts.

 

[gggGary]

+1 "up- nort MC's that always had fluid seldom need parts even after 40 years! BUT they always need a cleaning of the gunk! I use a 1/2 dowel with a hacksaw split lengthwise, and bit of 1000 grit slipped in it to "hone" the bore.