Trophy Brake Master Cylinder Problems?

This couldn't be anything to do with allowing for the movement of air above the level of brake fluid in the master cylinder could it?

 

Right. Do the bubbles arrive when you squeeze the brake lever, or when you release it?

Sounds like air is getting in somewhere it shouldn't, to me.

 

Yup sounds like air getting in. Small split in hose near connections maybe? Are the bleed needles , connectors screwed in tight?

 

This is just a guess, but it sounds to me like there might be an obstruction somewhere in the pipework not allowing the brake fluid to flow. To check for this you could undo the calliper bleed nipples to ensure the fluid is getting through?

PS Sorry mate I've just re-read your post no.6 and the fluid is obviously getting through.

Can't think of anything else, sorry.

 

Is there any fluid coming out of the Caliper bleed nipple? Is the diaphram in place when bleeding? , used to have this problem on other bike .. fill resovoir tie brake lever back and leave over night. If as you say everything is tight bleeding should be straight forward. Peace

 

Hi @TT600Des

Please don't be offended as I don't know if you've done brakes before, but this is how I work through a system.

When I bleed out brakes for the first time after a rebuild I usually top up the master cylinder and open the bleed nipples one at a time and let the fluid run through until I'm getting fluid flow at the caliper, whilst making sure the reservoir is kept topped up.

I also usually use a length of plastic hose over the bleed nipple so I can see fluid and bubbles coming out.

Do this on both calipers.

Then close the bleed nipple on each of the calipers and drop a coin or Stanley blade or similar into the master cylinder reservoir ( over the hole that's bubbling to stop brake fluid being ejected onto the paint work ).

I usually soak a rag in water wring it out and lay it over the paintwork as an added precaution against spillage.

Start bleeding one caliper till it runs clear whilst keeping the reservoir topped up, close up the bleed nipple and start all over again on the second caliper.

Check brake operation by feeling the lever pressure, check fluid level, if a little soft tie lever back to the bars.

A word of caution if your brake system is more than a few years old I would tie a block of wood to the grip behind the brake lever to limit travel as often old cylinders have a ridge of sludge and debris from the brakes built up on the internal bore of the master cylinder which can damage the seals.

Sometimes to fully bleed out the brakes can take several bottles of brake fluid.
** Don't forget to remove the object you have dropped into the reservoir **

Good Luck with the brake bleed.