CBX550 brake bleeding issues...

**ellipsis** · 19th September 2010, 14:56

..... bled the front brakes on my wifes new(1986) cbx550 ....took a lot of air out...lots of pressure , fairly hard on the lever...next day , bugger all pressure, but could pump a bit of pressure up with lever...bled again , same shit..replaced everything in the master cylinder with new...seals , piston etc...no leaks...discs ok....lots of pressure from lever...short ride...good pressure on front brake when pulled on in one squeeze...but...when you just feather the brakes or give it a couple of gentle squeezes, it pulls right up to grip with no pressure whatsoever....have repeated bleeding procedures to only get same result.....any suggestions as to what could be happening, cos its got me stuffed....

**tri boy** · 19th September 2010, 16:17

All the bits around the right way in the m/cyl?
(cup seals etc)
Is the m/cycl piston returning all the way back on release of the brake lever?
Something is definitely fishy.
Also check all the banjo bolt copper washers for dishing or uneveness causing air leakage into the system.
Good luck

**F5 Dave** · 22nd September 2010, 17:51

You have a leak which is sealed when applying pressure. I'd replace all the banjo washers for a start but I'd be critical of the hoses & maybe the calipers or mc has a track that allows air in, like if there is a corroded surface. The lines should be replaced every 2 years (or so my old manual used to tell me). ok that is ridiculous, the lines will probably last 20 years. But 24 years have passed. . .

Only other idea is (memory fading), the CBX has an antidive mechanisim (4 way adjustable). Buggered if I can remember how it is actuated, if there could be a leak there.

. . .or did it have a mechanical pivot that pushed when the brake was applied so it didn't affect the fluid like the silly Suzuki one of the same era? think it may but too many beers ago.

**imdying** · 22nd September 2010, 18:33

If there was a leak, the fluid level would go down.

Get some brake hose clamps, clamp off the calipers (when the lever is soggy), and report back on what that does to the lever.

**tri boy** · 22nd September 2010, 19:15

Just another quick thought.
If there is no obvious leak, but the pressure is irregular, then possibly an internal piece of brake hose rubber is causing the fault.
Either way I think a complete strip an inspect is required.
It's a hassle, but don't compromise with brakes.

**ellipsis** · 22nd September 2010, 21:07

....got all that..thanks....am about to throw a borrowed master cyl on which will hopefully either cancel that end of things...but it may mean a complete strip....brakes and carbs had supposedly been done when we picked it up but i could get fuck all top end when i brought it home...carbs did have new bits but diaphragms had been put in all arse about face...cool bike ...just gotta suss the previous owners stuff...cheers...

**ellipsis** · 23rd September 2010, 09:07

.....thanks for the input....have found the master cylinder to be a bit stuffed....the piston bore has been corroded and therein lies the mystery....will be sorting new hoses also...

**imdying** · 27th September 2010, 11:52

Go see CBC and have a sleeve put in it. Hoses aren't usually a problem to sort.

**ellipsis** · 27th September 2010, 12:08

.....cool...will do that...trying to find a m/c for it is becoming a pain in the arse...only because we need one now tho....probably find a box full of them when its sorted...thanks..