been Dazed and Confused

[Shred Astaire]

1978 Suzuki gs750E front brakes

They don't work. Rebuilt the calipers and master cylinder. When we bleed them, the fluid flows nicely into the cup. Clean and no air bubbles. The pistons both grab the disc but there is no fixed pressure in the system. No fluid leaking anywhere.

Any help is always appreciated.

[Big T]

Do you still have the original brake lines?
If so, they're probably swelling up under pressure
Time for new brake lines

[Shred Astaire]

Do you still have the original brake lines?
If so, they're probably swelling up under pressure
Time for new brake lines

Thanks Big T!

I'll check that out! They are probably the originals with the bike judging on how they look.

[Rich82GS750TZ]

I second the new line idea. Go Stainless Steel braided. Lots of companies sell them. You can measure yours and order new lines. Make sure what the company uses for measurement. The line plus the fittings, or line including the fittings. You can get banjos of different angles. Try to get the same as what you got. You can get swivel ends so clocking them properly isn’t important. Get new banjo bolts and copper washers too. Lots of colors of lines available from companies like Venhill, where I got mine. Ordering was pretty easy and their customer service was great. Some guys here put their own lines from lengths of hose and fittings from Earls. I’m sure there’s some savings there if doing more than one line.

If your line is original, replacement at some point is going to happen. Do it before it fails (I guess it already has). Just for fun, Tonight tie the lever back to the grip with a bungee or other cord. Leave it that way overnight. See what it’s like tomorrow when you unstrap it from the grip.

[Nessism]

Be sure to make sure the small return port in the master is open and you also may want to try priming the master. If that doesn't help, did you use OEM caliper seals or aftermarket like K&L. If aftermarket, that might be the issue. K&L seal dimensions are sometimes such that they grab the piston too tight and won't allow it to move close enough to the disc. You may be able to fix it by pumping up the lever and tying it back against the grip and leave it over night. If you can't get pressure that may not work though.

[Shred Astaire]

Be sure to make sure the small return port in the master is open and you also may want to try priming the master. If that doesn't help, did you use OEM caliper seals or aftermarket like K&L. If aftermarket, that might be the issue. K&L seal dimensions are sometimes such that they grab the piston too tight and won't allow it to move close enough to the disc. You may be able to fix it by pumping up the lever and tying it back against the grip and leave it over night. If you can't get pressure that may not work though.

I got the caliper pistons and seals from the UK. The seals were grabbing the piston at first (primed the caliper w/brake fluid) but the next morning I was able to install the caliper piston past the seal. Checking the seals at the caliper piston they are all seated properly and what appears to be fitting nicely and doing their job. I just don't understand why there is no leak. I purchased a 3qt (approx) brake fluid dot 3.0 and have been flowing a lot of fluid through the system.

At first the fluid came out blackish with small dots of black material but it's clear now. I started the front brake repair a month ago with the Master Cylinder rebuild as the front brake had no pressure. I noticed in another thread you mentioned pitting. I have pitting on the back of the master cylinder where the large boot covers the end of the cylinder but I can't remember if there was pitting on the cylinder itself.

Another oddity that has happened twice now is, the great suction holding the cap on the fluid well the next day after a bleeding session. I have to use all of my 64 yr old muscles to remove the damn cap.

[Shred Astaire]

I second the new line idea. Go Stainless Steel braided. Lots of companies sell them. You can measure yours and order new lines. Make sure what the company uses for measurement. The line plus the fittings, or line including the fittings. You can get banjos of different angles. Try to get the same as what you got. You can get swivel ends so clocking them properly isn’t important. Get new banjo bolts and copper washers too. Lots of colors of lines available from companies like Venhill, where I got mine. Ordering was pretty easy and their customer service was great. Some guys here put their own lines from lengths of hose and fittings from Earls. I’m sure there’s some savings there if doing more than one line.

If your line is original, replacement at some point is going to happen. Do it before it fails (I guess it already has). Just for fun, Tonight tie the lever back to the grip with a bungee or other cord. Leave it that way overnight. See what it’s like tomorrow when you unstrap it from the grip.

Thanks Rich, I'll check out those new line types.

[Shred Astaire]

When I untie the brake handle, what am I looking for to happen?

[Rich82GS750TZ]

Looking for the brake lever to firm up and for the pads to settle very close to touching the pad when the lever is free.

[Shred Astaire]

Looking for the brake lever to firm up and for the pads to settle very close to touching the pad when the lever is free.

No change. Brake pads touching disc rotor.

[Rich82GS750TZ]

But does the lever have a firmer feel when squeezed? Can you get the front tire off the ground. Spin the wheel. It's OK if the rotor sings against the pad lightly when you spin the wheel. That's somewhat normal. Is there any change in the operation of the brake lever/pads after having it tied to the bar overnight?

[Shred Astaire]

But does the lever have a firmer feel when squeezed? Can you get the front tire off the ground. Spin the wheel. I't OK if the rotor sings against the pad lightly when you spin the wheel. That's somewhat normal. Is there any change in the operation of the brake lever/pads after having it tied to the bar overnight?

Just finished up breaking the left one down and checking it over because I found one drop of fluid after pumping it a bunch this morning. There is even less pressure now than the feeble pressure it had. This sucks.

[Nessism]

Sounds like your master isn't pumping. You might want to remove it from the bike and hold it in your hands over a pan while pumping until it's shooting out a nice full stream with each level pull. Again, if the small relief port is plugged the pumping chamber won't fill.

[Shred Astaire]

Sounds like your master isn't pumping. You might want to remove it from the bike and hold it in your hands over a pan while pumping until it's shooting out a nice full stream with each level pull. Again, if the small relief port is plugged the pumping chamber won't fill.

If the master pump wasn't working would I still be having fluid pumping into the cup when I loosen the bleeder. I'm flowing a lot of fluid through the system. My wife does the hand brake while I do the bleeding. I'm wondering if it's the O Ring on the axle. I have one axle with a groove for the O Ring and one axle without the groove. Currently I have the axle and O Ring installed closest to the bleeder on both front calipers.. Should it be installed closest to the Hose Connection instead?

[Nessism]

What O-rings?