Lost rear brakes

[RyanJ]

I picked up a 1983 GS550E a month ago that didn't run and needed some TLC. Got it running w/ the carb guides on the site. On my list of things to do is to change out the brake fluid. The front went fine, bleeding the brakes in the order the manual says. When I got to the rear, I bled 2 or 3 squirts of fluid out and then lost all pressure in the brake pedal. It will go all the way down without any brake fluid coming out of the bleed screw. There is fluid in the resevior and no leaks anywhere. Would this indicate the problem lying in the master cylinder? That's my assumption, but I was hoping I could get a 2nd opinion before I start tearing into it, since it looks like there's a bit of disassmebly involved in getting that off.

Thanks for any advice,

-Ryan

[twiggy2cents]

if you pump a ton does it eventually build back up, two things first: Did you close the bleeder pump and then open or leave it open the whole time? Second: the dispersion or main hole in the MC might be plugged not allowing fluid to refill the MC bore, you should be able to check t his with a light after removing the fluid f rom it

[Dave8338]

I think your instinct is correct but just to be sure, fill the rear master up and leave the bleed screw open with a piece of rubber tube attached to it. Leave the cap off the master and walk away for the day. If you come back the next day and the master is empty, we can move onto step two.

Welcome to the fourm. Your bike issues will be solved here.

OH...a Mega Welcome is in order!

[RyanJ]

if you pump a ton does it eventually build back up, two things first: Did you close the bleeder pump and then open or leave it open the whole time?

Pumping the break a bunch doesn't seem to increase pressure. To bleed I 1) Depress brake pedal, 2) Open bleeder valve, 3) Close valve when pedal goes down all the way, 4) Release pedal, 5) Repeat.

I think your instinct is correct but just to be sure, fill the rear master up and leave the bleed screw open with a piece of rubber tube attached to it. Leave the cap off the master and walk away for the day. If you come back the next day and the master is empty, we can move onto step two.

Welcome to the fourm. Your bike issues will be solved here.

OH...a Mega Welcome is in order!

Done, I'll see what it looks like tomorrow. And thanks ;-)

Second: the dispersion or main hole in the MC might be plugged not allowing fluid to refill the MC bore, you should be able to check t his with a light after removing the fluid f rom it

I'll give that a shot tomorrow after seeing if it's drained itself.

Thanks for the advice!

[almarconi]

If the bike has been sitting for any length of time, it would be wise to disassemble and clean your rear brakes. The rebuild kits for the calipers and MC are not that expensive. At the very least flush everything out with clean brake fluid. Both my bikes were sitting for years and the MC's were filled with a coffee colored, sandy goo. The ports in the MC are tiny and easily clogged. It is also highly recommended to replace the brake lines. There is lots of information on here about stainless steel brake lines. Good luck on your project.

[Nessism]

Yup, what almarconi said...

The brake fluid needs to be changed every other year or your brake system build up sludge on the inside. Flushing the system does NOT remove this sludge so a full tear down is the only way to remove it.

Most likely the master cylinder piston is stuck in the bore due to accumulation of sludge on the inside. Your brake lines have this same sludge so they need to be replaced. The fronts are similarly affected even though you think they are fine. A full tear down and replacing all the lines is the proper service procedure.

[RyanJ]

Dave8338:
The MC is still full. What did you have in mind before I drain it and check for blockages?

almarconi & Nessism:
The old fluid didn't look bad at all (nowhere near as bad as my car's when I did it). It may have been changed by a previous owner. I wasn't sure so I wanted to do it myself. I'll tear down and clean everything if needed, though I'd of course like to avoid it at least for now. It's hard to get motivation to do excessive work on a bike I haven't even been able to ride yet.

[Nessism]

Dave8338:
The MC is still full. What did you have in mind before I drain it and check for blockages?

almarconi & Nessism:
The old fluid didn't look bad at all (nowhere near as bad as my car's when I did it). It may have been changed by a previous owner. I wasn't sure so I wanted to do it myself. I'll tear down and clean everything if needed, though I'd of course like to avoid it at least for now. It's hard to get motivation to do excessive work on a bike I haven't even been able to ride yet.

I've rehabbed a half dozen GS bikes so far and don't even take them out of the garage before performing a full brake system and carb rebuild. My "motivation" is in knowing that everything is "right" before risking breakdown and/or brake failure.

[almarconi]

My "motivation" is in knowing that everything is "right" before risking breakdown and/or brake failure.

I agree completely, you definitely don't want to neglect the brakes. Even if cash is tight, take it apart and clean it. The two things I would never cut corners on are brakes and tires.

[RyanJ]

Ok fair enough. One thing I've learned is it's usually a good idea to listen to those with more experience ;-) In searching for braided brake line info, I found your thread on Homemade steel lines. I'm going to give it a shot and replace all the lines, and am putting an order together on AN Plumbing. I have a question though(let me know if I should post this in the other thread).

I'm going to go ahead an unhook the anti-dive unit while I'm at it, since I've seen that recommended several times, and it'll make the job cheaper anyway. The brake line from the junction at the triple tree doesn't connect to the caliper using a banjo hose end - it connects to the end of the bolt. For the new hose, should I use a banjo hose end, and if so, should I get a 90-degree one so it's coming off the caliper at the same angle as the current hose?

Thanks again for all the advice,

-Ryan

[Dave8338]

Dave8338:
The MC is still full. What did you have in mind before I drain it and check for blockages?

EXACTLY what Ness & Al have suggested. There is no room for error on a bike. If the rear locks up, you're in for a fun ride to say the least.
If the front locks up you're in for potential DOA at the hospital.

The test was suggested to ensure that it flowed through the caliper and MC. As it has failed the test...tear it down and do it right.