When I bought my FZR250 3LN1 one of the threads had gone on my front brake master cylinder so I decided to replace it and never checked if the brakes worked. I fitted a cheap japanese MC and bleed it but could not get the sponginess out of it and it was not very good at stopping the bike at the end of the quarter mile. As I have had this sort of problem on a Ducati clutch which turned out to be a hose problem I replaced the hoses with a twin set from Goodridge. Now I cannot get any pressure from the master cylinder, I tried two others but with the same result. Is there some black magic involved in bleeding the brakes ???????????????????
OK. Start with topping off the master cylinder with fresh brake fluid. Have a clean container with fresh brake fluid and line to the bleed nipple of the front left caliper. Get your spanner on there, fit the line. Pump the brake lever a few times and then hold it. Crack the bleed nipple until you feel the pressure (if any) on the lever, then tighten the bleeder. Repeat as necessary & top off the fluid in the master cyl. Same deal for the right hand side. Protip for spilt brake fluid - soapy water will neutralise it. Keep a spray bottle handy. With the age of the bikes, lines could be a problem. They are usually dated somewhere, and service manuals call for replacement every 4 years... like that ever happens.
No resistance at all when operating the brake lever, and if I pump with the valve open the fluid in the drain tube doesn't move. Tried three master cylinders. Lines are brand new stainless Goodridge.
Take the line off the master cylinder and put a finger/thumb over the outlet and pump the lever using your finger as a one way valve to bleed the master. It has to be on a near level to get air out of the cylinder. Once you have pressure refit the line and bleed to the calipers. Make sure the bleed nipples on your calipers are clean and fluid can get through them. I have had some that required taking the caliper off, fitting a piece of wood between the pads and holding in the air above the bike to get the last bit of air out. Brakes can be so frustrating sometimes, but worth all the effort to make them work well.
When you pump the brake lever , is there any air bubbles appearing in the reservoir ?. If so you might have air in the whole system. What work's for me is SLIGHTLY tie back the brake lever with a zip tie when it just loads up the piston etc in the master cylinder and leave overnight.In the morning remove the master cylinder cover and "slightly pump" the lever again , if there are air bubbles you will see them.Watch your painted part's when you remove the master cylinder cover , Dot 4 doesn't play well with paint.
Try screwing in an M5 or M6 thread bolt into the bleed nipple hole They look like M6 to me but i haven't had one out to check for sure https://www.ebay.co.uk/itm/2-x-Male...-00mm-Joiner/351634507848?hash=item51df0cc848 https://www.ebay.co.uk/itm/4-x-Male...-00mm-Joiner/351634507786?hash=item51df0cc80a https://www.ebay.co.uk/itm/Metric-B...M10-Choose-pack-qty-UK-FREEPOST-/191898489590 Bleed screw cap's- https://www.ebay.co.uk/sch/i.html?_...w=cap+bleed+screw&_sacat=0&rt=nc&LH_PrefLoc=2
