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Brake Bleeding issue

  • Thread starter Thread starter MotoNew
  • Start date Start date
M

MotoNew

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I have read all the tips and tricks I could find but my brake lever will still pull all the way to the grip. I have replaced the seals and piston in the calipers, replaced the master cylinder, replaces lines with stainless steel ones. I also went to a double banjo at the MC and ran one line to each caliper. After replacing all the parts I pushed new fluid from the calipers up to the master cylinder. It still felt soft so I took off the calipers and bleed the brakes with them above the master cylinder. Then I tried strapping the lever all the way down for over 24 hours and then bleed the brakes again. After that I tried removing a caliper and pumping out the cylinder a little, let it sit overnight then c-clamped it back to where it would fit back on in hopes that any air near the MC would push up through. After everything the lever is still pulling all the way to the grips. It's on a 1983 GS750e.
Please help me with any advise I am out of ideas.
 
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I would go back to the conventional approach ie calipers on disks and just keep adding fluid as you continue to bleed.Keep a towel on your tank to protect from spills / drips. Keep tapping the calipers and MC with a rubber hammer to shake the bubbles loose. I think you need the resistance of the pistons clamping on the disks to get adequate pressure and flow.

Your pads have adequate thickness?

Does the lever ever get firm during the process?
 
I have done the normal bleed process as well and have run two large bottles of brake fluid through the system and was tapping on the calipers throughout the process. Also, during the other bleeds with the calipers off I had a large c-clamp holding pressure on the pistons. I know it sounds crazy but I have tried everything I can find!
The pads have enough thickness, they will need to be changed fairly soon but I was wanting to take care of everything else before making the purchase.
 
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Did you purchase aftermarket caliper seal kits (K&L) or OEM Suzuki parts? Did you make sure the small return port in the master cylinder is open?
 
Suzuki OEM caliper seal kit with new piston, seal and dust seal. The small return port is all clear.
 
Were the brakes ever good whilst you've owned it?

If not, it may be a possibility that the MC is too small to feed twin calipers (IE it's sized for a single caliper).
 
What master did you install? I see it says you changed it. I ask because I bought a remote reservoir unit and basically had to replace everything rubber besides the seals in the master itself. The hose from the master to the reservoir was cheap the clamps were cheaper and the o ring that sealed the hose barb in the reservoir was fouled with metal shavings and needed replaced. Another thing to be mindful of is what size master you installed. Twin disk bikes need a 5/8 or 16mm master.
 
I bought an OEM master cylinder and then rebuilt it because I was concerned it had a problem. I also disconnected the anti-dive units to give the brakes more bite. Could the brake pads be too old and be compressing?
 
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Negative on the pads compressing.

Do you have another bike you can test the master on? If so, do the swap and figure out if it's pumping fluid like it should. Assuming it does, the problem is the pistons are binding in the bore, or maybe the caliper isn't floating on the sliding pins. You need to grease the pins with black moly caliper grease. Not clear silicone grease. And speaking of silicone grease, I think you can use that stuff on the caliper pistons to make sure they slide out and position themselves close enough to the disc. Caliper pistons binding and not sliding close enough to the disc is why you get the spongy level feel.
 
I don't have another bike but I think the master is pumping fluid fine because the bike actually brakes just fine. It just makes me nervous when the lever goes all the way to the grips. I will pick up some black moly caliper grease this week and get those sliding pins greased up. I think the pistons are sliding fine too, they seem to move freely and if I pump the mc when they are off they slide out and I can push them back with my hands.
 
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are you using the old brake lines ? perhaps they are expanding enough to cause the lever to go all they to the bar ?

I don't want you to go through the expense of new brake lines, but if the ones you have are original, it might be good to change them out

.
 
I just bled the brakes on my '84 750, same system as yours except for not having 2 lines from the master. The procedure I did, and do for most bikes, once there is fluid in the system from the initial refill and bleed if things don't seem right is to start at the master cylinder banjo bolt and bleed each and every fitting. Squeeze the lever gently and just crack the banjo bolts loose slightly until you can see a few drips of fluid around the washers and then tighten the bolts. Continue through the brake system with each banjo bolt and even redo the bleeders as you go ending with the anti-dive assembly. You would be surprised where little pockets of air can hide.
 
I just greases the caliper slides and it helped stiffen the lever but it still feels a little soft. I have already replaced the lines with ss ones. I will try cracking the bajo bolts tomorrow.
Thank you everyone for all the advice!
 
I let a few drops of fluid out at the banjo bolts while someone slowly squeezed the lever. It let air into the system so I clamped a hose on the bleeder and on a large syringe and pushed fluid up into the MC. When the reservoir filled I took some fluid out and kept pumping more from the bottom. I did this several times at both bleed screws. The handle is fairly firm but I can still pull it to the grips. I test rode it and it stops fine and I can even lock up the front tire if needed it just still feels squishy. Don't know where to go from here.
 
Just throwing this in there...
Ok, if you're sure all the air is out and if you look down at the calipers when you squeeze the lever and if you see them moving on their pins when they clamp the pads to the discs - that's lost motion caused by wear between the sliding pins and the body of the caliper bracket. That lost motion feels like spongy brakes.
Nothing much you can do about it, except replace the brackets with lower mileage ones, or do an upgrade to later / different calipers, as Salty Monk's conversion on here.
I rebuilt mine with newer brackets and the closest-fitting sets of pins I had and it was like 1980 again. :)

<edited to add>
The single most useful upgrade I did, after stainless hoses, was to fit a NOS Yamaha XJ900 master cylinder. The dog-leg adjustable lever that came with that helped enormously. That was then, this is now. Now, I'd fit a Deauville m/c with a span-adjustable click-stop lever.
 
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The calipers do move a little when I squeeze the brakes. I think that is what is causing the problem. Once again you guys are regular sherlocks when it comes to this stuff. Many thanks!!!
 
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