Spongy Brakes??

[Fil]

I bled my brakes last weekend in readyness for my bike's return to the road after a long lay-up, and they seem quite spongy. The lever seems to come a long way back to the bar (not touching though!). There were definately no bubbles coming out of the tube when I finished the bleeding.
Has anyone got any tips for improving the feel of the brakes?

My bike is a 98 model - should I just rebuild the master cylinder as a matter of course?

[keithcross]

The front brake has been quite spongy on my Baggi from new, so this may be normal. Not sure with the scorpian models though.

Keith

[LWS66]

Do the brakes work fine, other than a long lever travel?
Try tying a zip tie around the brake lever and throttle grip (not excessively tight to blow seals, but firmly enough that the brakes are applied) and let it sit over night. That sometimes improves things for a while, but most likely it will return. One thing you can do is remove the calipers from their mounts, remove the pads, stick a small piece of wood or similar item the thickness of the "rotor and one brake pad" in between the caliper pistons, and apply the front brakes. This will drive the pistons outward yet they will stop from popping out of their bores, and you can then clean the grunge off of the pistons sides and clean the seals. I had a 95 Speed Triple with the same issue, and doing this helped big time and pretty much eliminated that from returning.I think the brake dust and grunge buildup on the pistons over time prevents the pistons from retracting into their bores. Learned about this on another mc site and it works. If they're spongy from new then maybe steel braided lines would help? All out of ideas.......

[phlat65]

you can also push the piston all the way in, and pump to extend it a few times ( with the master cap off ) and see if it changes.

my bleed proceedure: put a 1 ft piece of clear tube on the bleed fitting, make a loop with the hose so it goes above the fitting, then loops down into a bottle (to catch the spent fluid). the hose does not need to be submurged. while keeping the resevouir topped with fluid, slowly apply and release the brake lever completely, until you have passed 4-6 ozs of fluis through the system. no need to pump and open/close the bleeder fitting, the loop keeps air from being re-introduced into the system.

I use the Motul 600, dot 4, 594 deg F boiling point fluid in all my bikes, and have found no equal!

[DAVID THOMPSON]

rear brake lamp switch died on my rt125 2 times
i had a hell of a time getting
the air out of it after replacing the switch both times

what a pain

[Fil]

Thanks for the tips guys!

Keith - sorry, I should have said it's a '98 Mastiff (same brakes as your Baggy)

LWS66 - The brakes work ok inspite of the long travel/ sponginess, but I'll try cleaning the pistons in the caliper. It has steel baided brakelines as standard, so I'll not be needing to upgrade them!!

Phlat - I used virtually the same bleeding procedure as you've described, except I have a hose with a non-return valve in the end, and I flushed enough fluid through to completely replace what was already in the system. I will try the piston pumping idea though.

I'll let you know if I manage to improve things...

[F0ul_Oli]

Is it new fluid? There could be water in the old stuff.

I had a problem with another bike where the air was in the section just by the master, and the movement of the lever wasnt enough to get the air out at the caliper!

If you still have problems after trying everyones tips, let us know!

F0ul

[whysub01]

I draw the fluid through from the caliper with the aid of a biggish syringe-works a treat all the time.. Would also suggest using MOTOL 600 brake fluid. Expensive, but top stuff-can lock the front on my Skorpion with a two finger squeeze.

However, the brakes on my Baggi are very poor in comparison, with not much feel. I have a VFR750 caliper and bracket that I bought about a year ago, which is said to be superb, but remains in a box in the garage. I will get around to fitting it…….one day.

[keithcross]

Whysub

Will the VFR 750 caliper and bracket fit straight on teh Baggi? I have tried a few 4 piston calipers but they seem to foul the front wheel spokes.

Keith

[boysie]

Hi, I think you will find the brakes have a spongy feeling as the piston in the master cylinder is quite small,, not a bad thing as it gives a good ratio, a bit like using a small gear on your bike,,, if you just fit a master cyl from another bike, it will not make it more powerfull, just less spongy...


Hi keith,, long time no see

[phlat65]

the one way valve in the hose can allow air to be drawn in through the bleed fitting. try it without the valve...

[cat]

the one way valve in the hose can allow air to be drawn in through the bleed fitting. try it without the valve...

have you tried Speed Bleeders?
apparently they really work well. i bought some for the GS project but i never used them. if i can find out what the thread size of the MZ Grimeca ones is, ...i might be able to use them. or if i knew what other bikes use the same calipers - like some Ducati, maybe.

$7

>>>>
SPEED BLEEDER®, the patented bleeder screw with the built-in check valve. It is truly a one-person bleeder screw. Once installed, it becomes a permanent part of the brake system.

When it is time to bleed your brakes, you loosen the Speed Bleeder 1/4 turn and pump your brake pedal. When the pedal is depressed the pressure generated opens the check valve letting air and brake fluid out of the end of the Speed Bleeder. When you release the pedal and it returns to the up position, the check valve closes and prevents any air from re-entering the system through the Speed Bleeder.

When bubble-free fluid is evident you close the Speed Bleeder. In the closed position it works just like your stock bleeder screw and prevents any brake fluid from leaking out. It generally takes about 5 pumps to purge each caliper or wheel cylinder. That is all there is to bleeding your brakes. If at a later date you need to bleed your brakes, the patented thread sealing system makes it easy to open the bleeder screw to perform the bleeding operation.
>>>>

[phlat65]

without the thread sealing compoound, air will leak back through the threads, thats why I recomend bleeding without the check valve.

[cat]

without the thread sealing compound, air will leak back through the threads, thats why I recomend bleeding without the check valve.

but won't that happen even with the looped tube?

the syringe method sounds good, because it's more like the brake specialist thing where they have those pump machines. (or any good car service place, i suppose.)

[phlat65]

with the looped tube, the resistance on the reverse flow is very little, and it does not create any issues.