Brake lever firm, but brakes are weak

[Guest]

I finished my cafe project, stock caliper, steel line, and an ebay Chinese master cylinder. Everything bled easy enough, and the lever is very firm, but stopping power is fairly weak. I realize it's a single piston single rotor brake but I know it's not doing the job it should. I put new pads in the caliper but it's performing the same. Possible glazed rotor? I'll get some brake cleaner and try that first.

77 GS750

[mmattockx]

1) Is your master cylinder the correct size for your single caliper?

2) Clean the rotor with dish soap, water and a scotchbrite pad. You will be amazed at the gunk that will come off. Hopefully your new pads aren't too contaminated to bed in on the clean rotor and work properly.


Mark

[Runeight]

What size is the master cylinder compared to the one you removed? Did you rebuild the caliper?

You could bleed some more, might be air in line.

[Steve]

Could be a glazed rotor.

Being new, shouldn't be glazed pads.

However, being new, the pads are not yet bedded into the disk(s).

Until they have been run together for many miles, the high spots on the new surface of the pads are the only parts that are touching the high spots on the disk(s). Until the pads wear a bit and conform to the shape of the disks, you will have limited contact area, therefore limited stopping power.

You can help bed them in a bit by dragging the front brake a bit while riding at a modest speed. Do it for a minute or so, then let the brakes cool. Repeat a few times, the power should improve.

Remember that Google is your friend. (click link)

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[tlscharlie]

I'm not sure of the bore size, no, and looking at the listed ones now, there is no description to say. I was thinking since it's a single piston that even if it's smaller than 5/8 it would be ok. Maybe not? I'll look at it when I get home and see if I can tell.

[tlscharlie]

I'm pushing almost 300 miles on the brakes as they are now, with not really any serious improvement. Should I put some effort into bedding them in more aggressively?

[Steve]

Only if you want them to work better.

It's not the number of miles, it's what has happened during those miles.

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[Nessism]

I'm not sure of the bore size, no, and looking at the listed ones now, there is no description to say. I was thinking since it's a single piston that even if it's smaller than 5/8 it would be ok. Maybe not? I'll look at it when I get home and see if I can tell.

With a single disc brake setup you should be using a 14mm master cylinder. If you have a 5/8" master the hand force will be higher than with a smaller master.

[Runeight]

Next time you do your brakes have your rotor done also. Just a future thought.

[mmattockx]

However, being new, the pads are not yet bedded into the disk(s).

Until they have been run together for many miles, the high spots on the new surface of the pads are the only parts that are touching the high spots on the disk(s).

I can bed pads to about 95% in one 20-30 minute ride. I go out on a back road where I can run highway speeds and there is no traffic to interfere with me. While riding along, I will brake down to 20mph or so at a medium effort level 3-4 times (equivalent to a firm street stop), then harder 3-4 times (equivalent to a hard street stop, but not a full on panic stop), then a couple serious efforts to get some heat into them (90+% of a full on panic stop). This has never failed to bed sintered pads to the point where the brakes are fine for daily riding with no drama (so far a number of sets of EBC HH pads, OEM Suzuki pads and one set of Galfers). The last 5% comes in over time as you say but this gets them good enough to trust while riding without worrying about emergency maneuvers.

I'm pushing almost 300 miles on the brakes as they are now, with not really any serious improvement. Should I put some effort into bedding them in more aggressively?

Clean your rotor as I described in post #2 then go out and follow my procedure above and they will be as bedded as you are going to get. Note that if your master cylinder is too big you will always need higher lever force than with the proper sized M/C.


Mark

[hillsy]

With a single disc brake setup you should be using a 14mm master cylinder. If you have a 5/8" master the hand force will be higher than with a smaller master.

This ^^^^

Probably even smaller than 14 would still work quite well.

[Steve]

I can bed pads to about 95% in one 20-30 minute ride. I go out on a back road where I can run highway speeds and there is no traffic to interfere with me. While riding along, I will brake down to 20mph or so at a medium effort level 3-4 times (equivalent to a firm street stop), then harder 3-4 times (equivalent to a hard street stop, but not a full on panic stop), then a couple serious efforts to get some heat into them (90+% of a full on panic stop). This has never failed to bed sintered pads to the point where the brakes are fine for daily riding with no drama (so far a number of sets of EBC HH pads, OEM Suzuki pads and one set of Galfers). The last 5% comes in over time as you say but this gets them good enough to trust while riding without worrying about emergency maneuvers.

If you look at the link to the Google search I gave in post #4, that is the same basic procedure that was shown from many sources.

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[tlscharlie]

Thanks for all the pointers! I dig this forum's responsiveness! So I bled the brake last night and the fluid was very dirty, which I thought was odd since the MC and line were brand new. I also scrubbed the rotor as directed and braking is definitely better. I haven't confirmed the MC bore size, but I'm guessing it's larger than is ideal. That combined with the "short" style levers that came on the Chinese MC/Clutch control would probably be responsible for the majority of the issue. Less leverage and incorrect ratio of fluid to piston would be my current theory based on everything so far. Thank you all again! I'll see if I can confirm the bore size and if need be, I'll get another set with a 14mm bore and report back!

[Nessism]

If your fluid is turning dark right away that means you have sludge inside your caliper. Time to pop out the piston and clean out the chunkies. Lubing the pins with dark black moly caliper grease is advised, as well as replacing the seals on the piston.

[tlscharlie]

Copy that! Thank you!