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Brake bleeding help
smart51 - 16/5/15 at 10:47 AM

I've just replaced the brake master cylinder on my trike and bled the brakes but the pedal pushes to the floor with just finger force.

No bubbles come out of the bleed nipples, the fluid is nice and clear. There's no obvious signs of a leak. With a 19mm bore and I guess 40 or 50mm of stroke, I'd expect quite a puddle of fluid to come out if there was a leak. What else could be wrong?

rusty nuts - 16/5/15 at 12:56 PM

Did you prime the master cylinder before fitting ? Might be worth cracking off the unions at the master cylinder and giving the pedal a few pumps and possibly working your way downstream before finally bleeding from the nipples

Smoking Frog - 16/5/15 at 01:37 PM

Make sure the push rod is not applying pressure to the cylinder when at rest.

theprisioner - 16/5/15 at 02:20 PM

I had the same problem with the Sylva, had to slightly pressurise the system via the reservoir using an easy bleed (15ibs/sq in). If you have any loops in the system this can happen IMO.

smart51 - 16/5/15 at 06:15 PM

Thanks guys. I removed the reservoir from the MC and pressed the pedal slightly to remove air bubbles. After that it was just a matter of bleeding at the wheels and it is now fine. I need a bit more fluid to top up the reservoir so no test drive but it seems fine.

[Edited on 16-5-2015 by smart51]

907 - 16/5/15 at 07:41 PM

When I fitted new seals to my master cylinder I did a bench bleed.

Googled it and followed the video instructions.

Then did the normal beed from the nipples.

I think this is what Rusty Nuts is suggesting but he's doing it on the car.

Paul G

rusty nuts - 17/5/15 at 06:20 AM

quote:
Originally posted by 907
When I fitted new seals to my master cylinder I did a bench bleed.

Googled it and followed the video instructions.

Then did the normal beed from the nipples.

I think this is what Rusty Nuts is suggesting but he's doing it on the car.

Paul G


I would normally prime a master cylinder before fitting but as it was already installed my suggestion would work just as well , just me being lazy

907 - 17/5/15 at 09:08 AM

It was good to do it off the car. The M/C was off anyway as I had fitted seals.

By connecting nuts with short copper pipes and clear tubes into the reservoir I could see when the bubbles stopped,
about ten push-ins with a screwdriver. I did about ten more, just to be sure, then bolted it back in the car.
Swopping the stub ends for the main brake lines (ahem, crossed over) spilt some fluid but the wife was there to mop it up.
Bleed as normal, job done.

Paul G