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Bleedin' brakes!

  • Thread starter Thread starter oldrookie
  • Start date Start date
I am becoming remarkably good at taking the master cylinder off, disassembling-reassembling and reinstalling the little bugger.

Now if only I could do it right for a change. Have the lever tied back now and am hoping that will help with the bleedimg process tomorrow.

I no longer live in fear of that snap ring, so progress is being made.
 
I've worked for 30 years in research testing of vehicle brake systems. I don't understand how the belief of keeping the brake applied overnight does anything.

The little air molecules will not be beaten into submission of staying smaller molecules once the pressure is released.
 
The little bubbles will eventually float up hill to the upper end of the brake lines, they end up right by the master cylinder. That way when you release the lever, they go through the return port into the reservoir, instead of staying in the lines.

Sometimes it takes several times, but the brakes will get a lot more firm.

It's not like a car where the lines are mostly horizontal.

Try it, it works.
 
It appears to have done so. Brake lever travels smoothly through about the first third of its travel and then firms up quickly.

Not as solid as the new bikes, but I may be close to done. I've thought so before and been wrong, but this time it feels more firm.

I don't see any leaks from the piston bore, so it could be that I've finally got the seals back in correctly.
 
I read the whole thing here, and maybe I missed it, but you did try a vacuun bleeder that runs off an air compressor???
not a hand pump version... you may need the contious "pull" of a vacuum bleeder to make the air bubbles dislodge from where ever they are hiding.
I rebuilt, then replaced a Honda V45 hydrolic clutch m/c due to your same symptoms, then replaced the slave, and still no workee. ( total almost $350) Then someone told me "the air bubbles stick in the banjo bolt, and will never leave without a vacuum bleeding."
I was riding the bike 5 minutes after I bought the vacuum bleeder. And then realized I probably wasted $320... :-(

pS... don't buy the $20 Harbor Freight one, buy the $35 "name brand" model.
 
Last edited:
Well, a quick update.

I am still fighting with the system. I have a MightyVac and have been using it to bleed the system.

BWRinger suggested that I bench bleed the MC, so I did that tonight. This consists of taking the banjo bolt out and placing a thumb over the bolt opening. Push in the plunger a few times and ensure that all the air is pushed out of the MC. Important not to let any air back in while the piston is on the out stroke.

I did that process, reinstalled the banjo bolt and started bleeding the system again. Cranked the vacuum up to about 15 psi, open the bleeder slightly and kept an eye on the level the MC.

Got some air, but not a lot. Bled enough fluid out to fill the MightyVac container about 3/4 full.

The lever will not pull back to the handle bar, but still more travel than it had before I started on the rebuild.

Put the cover back on the MC and tied the brake lever back and will let it set until tomorrow.
 
I thought I had this beat, but I don't.

My starter quit, which diverted my attention for a while. Took the bike out for a ride today and the brakes were not what they should be. May still have leak.

This is just frustrating.
 
While waiting for starter rebuild parts to come in, went back to bench bleed the master cylinder again.

Old friend (literally) who is a Master Mechanic--worked on AJ Foyt's cars in the early sixties-- listened to me whine about the symptoms and said, "It's the master cylinder. Go back and check it again."

He was right, apparently. I'm going to qualify this until I get some more time on the road. Still more lever movement than I expected with stainless steel brake lines, but it stops much better now. Only put about 20 minutes on and only in the neighborhood (don't judge...was afraid it would stall with no hill around and bump starting on flat ground is a younger man's game,) but it seems much better.

Got the starter rebuild done this evening, so just one small solder job left to do and that will be it until the next thing breaks.
 
Does your bike have the dreaded 'anti-dive" mechanism? I recently did the brakes on the new to me 550 and couldn't get the lever to firm up either. On my 750 and Kat the anti-dives are disconnected (prior to me getting the bikes) so I thought I would do the same with this one, thinking it may help. It does. The calipers were easy as pie to bleed and the lever firmed right up.

As the bike is still running rubber hose, its not a nice 2 finger pull like the 750 & Kat but not too far off.

I don't know anyone else's experience with bleeding brakes attached to the anit-dives but I had heard (and now confirm) that they are a biotch to bleed.

Just something else to consider.

Good luck.
Spyug
 
No anti-dive on the GR. Had some cool tech for the time, but Suzuki went with pretty basic forks on the lower end model. The high end had air adjustable forks, but no anti-dive.
 
Can't believe I started this thread in March and I finally think the brakes are right as of Labor Day.

Drained the system at 8:00 a.m. this morning and pulled the caliper. No leaks evident there, so pulled the stainless line off the bike again. Cranked on the banjo bolt connections and found one of them was not as tight as I thought it was.

Got it tight and bled the MC. Reassembled the system, filled the MC and immediately noticed how much less air I was getting. The lever firmed up very quickly and it has far less lever travel.

Rode about 15 miles and the lever stayed firm the whole time. That is a first.

Kickin' myself in Indiana.
 
I'm going thru the same problem with my GSXR. Tried all the same things you have. My next step is I'm going with 2 SS lines from the MC to each caliper. Bypassing the splitter. I'm getting irritated over this but trying to keep my cool. It's got to be something easy that I'm over looking.

Glad to hear a happy ending with your dilema.
 
tas850g said:
I'm going thru the same problem with my GSXR. Tried all the same things you have. My next step is I'm going with 2 SS lines from the MC to each caliper. Bypassing the splitter. I'm getting irritated over this but trying to keep my cool. It's got to be something easy that I'm over looking.

Glad to hear a happy ending with your dilema.
Click to expand...

Sorry to hear about your difficulties. This had me completely frustrated. Still not sure I'm ready to believe it is fixed.

The crazy part is that the system is really fairly simple. Bench bleeding the MC really helped, but just on simple slightly loose bolt had me chasing brake pressure for months.
 
Well, guess who "prematurely whoo-hoo'd" again.

They get firm for a bit, then go soft.

I did feel some brake fluid under the upper banjo bolt this a.m., so it is either the front seal (which I suspect) or the upper banjo bolt isn't tight enough.

I suspect the seal because I have cranked that banjo bolt down so hard that I feared shearing it off.

So, when I get time this weekend...the system comes apart again. Has to be the front seal, or the MC has a crack in it. I'm pretty sure it is the seal.

May just order a GS 500 MC off ebay and start with that. Tired of messing with it.
 
I would recommend getting a silicone based brake grease and coating the O ring seals with it, then reassembling. Same with the MC. Pull the piston and seals out and give them a light coating

You'll find the pistons go back in much easier and slide better.

Be sure and get one that says it is compatible with seals and/or can be used on all brake parts

My machinist turned me on to this. He rebuilds MiniCoopers and does this to all his brake systems

I see Autozone has some in small packets

http://www.autozone.com/autozone/ac...lubricant/_/N-268d?itemIdentifier=193245_0_0_

Also, when reassembling, leave the brake pads out and have the pistons slid out part way. Fill the caliper with some fluid (get a $4 oil can from HF for this) until it appears in the MC.

Then, use a clamp and push the brake pistons all the way back in. This should expel any air in the calipers
 
Thanks, Big T.

I've bid on a GS500 MC, but I think I really want to figure out what was wrong with this one. I'm going to tear it back down and try your suggestions. Hope to do it this week--supposed to be cold and rainy anyway.
 
Not to Hijack your thread, but along the same lines: I too have lost brake pressure, only it was after I replaced the fork seals.

I had it jacked up for over a week while my local shop messed around with one of the tubes (long story), which includes having the calipers at an elevated position while secured by bungees. When I put everything back together the brakes no longer had pressure. Worked fine before I started the job. Bleeding didn't help.

Just wondering if anyone can point me to an obvious reason for this, or did I just damage something in the process?

Thanks.

(PS let me know if this should be posted in a new thread. I am new here and not sure of the protocol)
 
No problem with me having it here, but you'll get more help with a new thread with a good thread title.

Something like "Didn't touch the front brake system, but lost pressure"
 
Gotcha, thanks. Next time. I can close the book on this, anyway. I didn't realize that bleeding the master cylinder was an option. This wasn't mentioned in my manual. Anyway that's where all the air was!

Any luck with your problem? As you can see, I won't be of much help. Other than emotional support.
 
I bought an mc off a gs500 on Ebay. Should be here on Friday. Hoping a newer mc will solve the issue.
 
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