RGS Rear Brake Bleed

murphus

murphus

Senior member
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Lost in the Midwest
I know this has been covered to death, but this is the first time I've not been able to bleed out the rear brakes on an RGS, despite having done it successfully multiple times previously. Replaced rear master seals, new brake line, new pads. Can't get the air out. I see people mentioning bleeding with the entire system off the bike, also raising the rear caliper, and saw Piet's past note about leaving the caliper in place and raising the rear master so it's the highest point. If removing the entire system or just the master, it strikes me one would want the reservoir at the highest point. I've tried everything so far except removing the entire system, to no avail. Even tried a reverse flush, but no joy. In fact, wouldn't move any fluid at all, leaving me to suspect plugged return port. Removing and disassembling the master showed the port open as I could be blow through it easily, so no idea what that was about. Never had one like this, any pointers welcome.
 
When I've hit this problem I gave in and stripped the complete assembly to bleed off the bike, with m/cyl the highest point. Couldn't get it to work raising m/c on the bike with caliper in situ
 
If all tricks fail to yield results, the M/C seals are probably shot. Seems that once old seals travel over the limits of previous movement, they just start leaking. This was a very common problem with the older Brembo rubber compounds, it seemed to me that the rubber bits improved considerably later on and were more forgiving. If the seals are more than 15 years old, chances are high they are at fault. Everything will actually look fine when disassembled, but they still leak, just one of those unfathomable things. To my knowledge, 14mm repair kits are available, 12mm not. On the bright side, I may be able to source NOS 12mm M/Cs.

piet
 
Hey Piet. Seals are new, transferred from a 12mm piston kit for different M/C with solid piston instead of hollowed out for pushrod. Bore is clean, no corrosion. I tried a pressure bleed using a setup I have to push fluid from the caliper to the master, then to reservoir. It did not want to push fluid the first time, so removed the master and checked for flow through the return port with the piston removed. Passed air no problem. However, once installed and back in place, no fluid is pushing through using reverse pressure. Light pressure on the piston resulted in a flow, but inconsistent. Fluid pushed through, then stopped and could not reliably or consistently get it to pass fluid. Not sure what gives there, but might explain why a vacuum bleed failed to pull fluid, the reservoir level remaining unchanged.
 
Covered previously but as a reminder.
Remove caliper, raise so level with reservoir. Place 2 x open ended spanners between piston and fixed side of caliper.
Bleed as normal and then tie down the rear brake lever. I tie it to the center stand.
With spanners between piston and fixed side of caliper, leave overnight with reservoir lid loosely fitted and any residual air should bubble out through reservoir.
I find this gives a good rear brake.
Bob
 
murphus said:
Hey Piet. Seals are new, transferred from a 12mm piston kit for different M/C with solid piston instead of hollowed out for pushrod. Bore is clean, no corrosion. I tried a pressure bleed using a setup I have to push fluid from the caliper to the master, then to reservoir. It did not want to push fluid the first time, so removed the master and checked for flow through the return port with the piston removed. Passed air no problem. However, once installed and back in place, no fluid is pushing through using reverse pressure. Light pressure on the piston resulted in a flow, but inconsistent. Fluid pushed through, then stopped and could not reliably or consistently get it to pass fluid. Not sure what gives there, but might explain why a vacuum bleed failed to pull fluid, the reservoir level remaining unchanged.
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Attempted exactly the same about 18 months ago, I was so disgusted after 6 hours of fruitless mucking around that I ordered a complete new M/C (Moto Guzzi Breva 1100 clutch), which I was trying to avoid because the sucker costs almost €300. New M/C was bled in a matter of minutes.

Either it'll work immediately... or you've lost by TKO.

piet
 
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Brake line must be straight without any loop. Maybe you have to move the caliper from the bracket so that the brake line will not go up and down, just one way. The air is in the loop when it is the upper point. Use a vacuum bleeder tool, cheap and usable tools cost about 20€.
 
sfcpiet said:
Attempted exactly the same about 18 months ago, I was so disgusted after 6 hours of fruitless mucking around that I ordered a complete new M/C (Moto Guzzi Breva 1100 clutch), which I was trying to avoid because the sucker costs almost €300. New M/C was bled in a matter of minutes.

Either it'll work immediately... or you've lost by TKO.

piet
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I had the exact same experience two years back with my '88 Paso. Uses the same M/C as the RGS, but without the routing issues. At the time, I found a Brembo copy with 50mm mounts for something like $90. Sadly, no longer available. Interesting we've both had this experience, the round with the Paso's been ringing in my ears as I've tried to get this M/C to work. TIme to switch gears, me thinks; I'm going to get a 40mm mount 11mm M/C and adapt it. Only question I still have is, what gives? The Paso was just as you described. Spent hours after the rebuild trying to get proper operation, no joy. New M/C bled in minutes.
 
Had similar issue with the Yamaha R6 Brembo rear m/cyl and Monster rear caliper on the SFQ. Nothing seemed to make sense other than the m/cyl was fukt. In the end I flooded the m/cyl manually by squirting fluid into every available orifice (of the m/cyl, not me!!) and this FINALLY allowed the thing to pump - once even a tiny movement of fluid or air at the caliper was evident it gradually increased and it all functioned normally - never worked out why std methods didn't work (like back flush, raising and lowering things), but it's been perfect ever since - and i don't wish to go back there any time soon!!
 
Changed rear pads years ago on my Pantah and couldn't get a pedal after. I spent 2 full days trying everything I could including pushing fluid backwards, nothing worked so I took it to the pros, and they fixed it and lightened my wallet by $400, a hell of a lot of cash back then but at least it was fixed. Somehow my homemade rearset had 1 too many washers and somehow wasn't allowing the return port to clear the piston. Now the bad bit, I rode the bike home but suddenly lost the rear problem brake mid-trip. I get off the bike and see the calliper hanging down under the bike by its hose. The fuckwit that did the job had failed to tighten the calliper bolts after bleeding it. I was lucky it had not fallen into the rear wheel and locked it up. I had a very tense phone call with that bloke's boss.
 
Vince said:
Changed rear pads years ago on my Pantah and couldn't get a pedal after. I spent 2 full days trying everything I could including pushing fluid backwards, nothing worked so I took it to the pros, and they fixed it and lightened my wallet by $400, a hell of a lot of cash back then but at least it was fixed. Somehow my homemade rearset had 1 too many washers and somehow wasn't allowing the return port to clear the piston. Now the bad bit, I rode the bike home but suddenly lost the rear problem brake mid-trip. I get off the bike and see the calliper hanging down under the bike by its hose. The fuckwit that did the job had failed to tighten the calliper bolts after bleeding it. I was lucky it had not fallen into the rear wheel and locked it up. I had a very tense phone call with that bloke's boss.
Click to expand...
This is why I always put Loctite on the caliper bolts when reinstalling after anything that requires their removal.

cheers,

bazzee
 
Just tightening them enough to ride 30k would help as well. Who the hell doesn't check your work after doing brake jobs? It fell off 20 minutes after I left their shop, not even finger tight I guess. I love the shop boss, a really helpful and knowledgeable bloke but at that time they were expanding, never saw that Mechnic again. They moved across Sydney and virtually became a one-man band after that, not going to name them but it's pretty obvious who.
 
murphus said:
I had the exact same experience two years back with my '88 Paso. <snip> I'm going to get a 40mm mount 11mm M/C and adapt it. Only question I still have is, what gives? The Paso was just as you described. Spent hours after the rebuild trying to get proper operation, no joy. New M/C bled in minutes.
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Same here. Gave up with my Corsa. Life is just too short. Never did work out what the problem was ...

(Ducati Paddy sells a PS11 50mm unit, but I suspect it's not worth it for you in the USA.)
 
Thanks for the heads up, didn't think anyone had them anymore. Worth checking into, but yeah, might be a bit pricey with shipping. Anyone adapted a 40mm mount ps11c (I think that's the one)? Tips?
 
Check that the master cylinder piston is fully retracted when the lever (or pedal) is released. I've had a similar issue after fitting new M/C seals. If the new seal is slightly wider than the old one, the piston might not move far enough back to uncover the tiny little intake port when the lever is released. That makes the thing impossible to bleed.
 
Found the issue. I did not appreciate that there are two bleed ports, one roughly 1mm and a second roughly .25mm. You can't access the small one without first removing the reservoir feed fitting and grommet, which carries the risk of damaging both. Removing the fitting and grommet showed the small port plugged. I learned of this thanks to Paddy, whom I'd contacted for a possible 50mm mount master (thanks for the tip, Ventodue). I explained my issue and he told me that if the small port is plugged it will never bleed. Cleaned up and now passing fluid and getting function, although still not completely bled. Thanks Paddy. I'll never cease to be amazed at the collective knowledge that abounds in these parts. Pic shows the two ports, doesn't really illuminate the plugged small port, but it's the one on the right.
 

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Good job murphus. It's always a relief when you find the problem is so simple and easily fixed.

Yeah, that little port can catch you out. It's the one I was referring to in my previous post. The master cylinder piston has to move far enough back to un-cover it when the brake is released. You sometimes need to adjust the cylinder stop position when fitting new rubbers to the piston. Doesn't help if it's clogged with muck though.

When disassembling and cleaning brake systems, I use the little nozzle cleaners for oxy-acetylene and LPG gas tips that you can get for a couple of bucks at welding or BBQ shops. The smallest one will go through that little M/C port. They're also handy for poking through carby jets, but don't be too vigorous with them. They're actually serrated like tiny little round files and can file out the jet bore size if you keep rogering the little holes with them.

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Nozzle and Tip Cleaner for Oxy Acetylene and LPG Gas gear - BBQ - Carburetor jet | eBay

Nozzle Cleaner Carburetor Jet. - Welding tip cleanerï¼This tip cleaner is specifically designed to clean out the tiny jets and carb passages from all dirt to help your machine running fine and not starving for fuel or flooding.
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On some Japanese rear mc I have had to remove the circlip and let the piston come out a bit further and pump it by hand to get it to bleed from dry, once bled work properly.
 
Tippie said:
On some Japanese rear mc I have had to remove the circlip and let the piston come out a bit further and pump it by hand to get it to bleed from dry, once bled work properly.
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Sounds like what Cam mentioned, with the seal partly obscuring the small port - but you'd reckon it wouldn't function properly once bled when the piston goes back and the circlip is fitted?
 
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