wingman1946
1978 XS 650e
I have flushed out the MC and got the fluid to finally flow down to the bleeder nicely but can not seem to build up any pressure. I have probably run a whole can of fluid thru it without bubbles. Any ideas welcome.
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brake won't pump up
- Thread starter wingman1946
- Start date
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- Tags
- brakes
NONclow
Confirmed Laquer Breather
If you had good pressure before the fluid change, then you probably still have air bubbles in the system. As was suggested in the link offerred by NONclow, just walk away from the bike for a day, and let the bubbles migrate upwards into the M/C. Gently adding some high frequency vibration ( just snatch your wife's vibrator when she's not looking 
) to the components could help the bubbles move.
) to the components could help the bubbles move.
wingman1946
1978 XS 650e
I guess I should have started the story from the beginning. At first I had some pressure at the lever but not enough to stop the bike. Trying to bleed the system at first was flowing some fluid but the flow stopped. I could not get fluid to move down to the bleeder any more. That is when I flushed out the complete system with brake cleaner. MC, hoses, caliper, and replaced the pads. Now I have good flow but pressure won't build up. I am not seeing air bubbles any more. Also removed the caliper piston and cleaned out the hole.
Hopefullly you got all the brake cleaner out. If you have any doubt about that, I would continue with your flushing procedure, and use a full quart of the brake fluid, if necessary.
Check to see that you are getting adequate action at the MC plunger by checking the clearance to the brake lever. Reduce the clearance to the proper measurement.
A plunger rebuild might be in order.
Make sure that the shim behind your new pads is exactly in place.
Check to see that you are getting adequate action at the MC plunger by checking the clearance to the brake lever. Reduce the clearance to the proper measurement.
A plunger rebuild might be in order.
Make sure that the shim behind your new pads is exactly in place.
wingman1946
1978 XS 650e
I have the brake lever with about 2mm free play before it touches the plunger. That about right? Has anyone tried the Asian MC units? They are available for about what a rebuild kit cost.
Just flushing usually doesn't clean all the goop out of a MC. You really need to take it apart. If it's not leaking any fluid, chances are good that the rubber bits inside are still OK. When servicing a caliper, one of the most important areas to get clean is the groove for the square sided o-ring seal. It gets a crusty build-up of dried out brake fluid down inside it and that forces the o-ring out more, causing the brake to drag and piston to stick. I'd try this thorough cleaning before I started replacing things.
wingman1946
1978 XS 650e
I did have the complete MC apart. Maybe I will give it another go. Cleaned the square groove in the caliper plenty good. You are right lots of bad stuff in there. Can you advise me as to what is suppose to hold the rubber piece onto the small end of the spring. do I just put it down in there and hope the plunger will hold it in place? Just wedged in between the plunger and spring?
Yes, cup fits over spring end \\\\\\ ]
did you read through all the brake rebuild threads in tech?
Did you check to be sure the caliper mount slider is lubed and moves easily?
Double check that tiny little second MC port from res to bore.
angus67
Welder's penetrate deeper!!
If you had good pressure before the fluid change, then you probably still have air bubbles in the system. As was suggested in the link offerred by NONclow, just walk away from the bike for a day, and let the bubbles migrate upwards into the M/C. Gently adding some high frequency vibration ( just snatch your wife's vibrator when she's not looking
Actually done this, even the vibrator part. Empty lines are a bitch to bleed
My old standby; bike on sidestand, bars turned full left. WALK AWAY, come back in 1/2 hour, brakes work. Key is making sure the path from caliper to reservoir is uphill all the way. Gravity sends the light bubbles upstream to the reservoir. if you really feel the need give the lever a single pump now and then till it's hard.
vr3506
vr3506
Start with an empty pump and fill from the caliper (through the bleeder) up to the pump
Use a syringe about 60cc for this job.
Use a syringe about 60cc for this job.
It sounds like you got air still in the system. Last time I changed lines/cleaned up the calipers, it took what felt like FOREVER to fully bleed the system and get pressure back.
What seemed to work for me was this: Fill reservoir...pump the lever and HOLD IT and at the same time, open the bleeder valve...even after what seems like all the bubbles have stopped, keep it open and hold the lever and wait another 30 seconds- 1 min. you may be surprised that some more bubbles start to finally come out.
Close the valve, then repeat. Note: I was second guessing myself after a while...but after about 30 min...it finally worked. I know there are faster ways, but this has always worked for me, and it's what I know.
Also, I'm sure this is common practice, but I always attach a 1/4" clear tube section about 2' long to the bleeder valve, with it looping into a cup... and I fill about 6" of it w/brake fluid so that at no time will air have a way to get back into the system...and bubbles rise to the top of the tube.
What seemed to work for me was this: Fill reservoir...pump the lever and HOLD IT and at the same time, open the bleeder valve...even after what seems like all the bubbles have stopped, keep it open and hold the lever and wait another 30 seconds- 1 min. you may be surprised that some more bubbles start to finally come out.
Close the valve, then repeat. Note: I was second guessing myself after a while...but after about 30 min...it finally worked. I know there are faster ways, but this has always worked for me, and it's what I know.
Also, I'm sure this is common practice, but I always attach a 1/4" clear tube section about 2' long to the bleeder valve, with it looping into a cup... and I fill about 6" of it w/brake fluid so that at no time will air have a way to get back into the system...and bubbles rise to the top of the tube.
rainycity
XS650 Addict
I had that same problem a while back and what I did was (from the advice of others on this board) was remove the bottom banjo bolt, took a few syringe`s and filled them with brake fluid and started from the bottom and pumped it up and through and after that my brakes worked great.
Whenever it comes to bleeding the brakes the first thing I do is remove the bleed nipple and wrap a small amount of ptfe plumbers tape around the thread this stops any air getting in via the nipple, I connect a 60ml syringe full of brake fluid to it and force this though the system, I then pull it back through using the syringe and topping up the reservoir as I go, I learnt this off of my dad who was a Royal Engineers heavy vehicle fitter in the 1950's, takes me about 45minutes per brake.
