Strange brake behaviour - your advice please

[RetiredAndRolling]

My Riese and Muller Tinker has developed a strange brake behaviour recently. Any ideas of why and how to cure it please?

The bike is stored horizontally on a boat To get it on land it is tilted tail up at around 60° and passed through a hatch. This worked fine for years.

Last year, one of the hydraulic disc brakes was sticking on. A bike shop found some crud in the affected brake’s pipe, blew it out and refilled the fluid. Problem solved.

This year, the first time the bike was extracted from the boat the right brake was so spongy it was ineffective. The left brake was operating normally. After 10-15 minutes of riding the right brake returned to normal operation. This happened again the next time the bike was extracted and tilted.

As the brake lines should have no air in them, I can’t understand what is happening and what I should do to correct the affected brake. If air has got into the brake line, how does normal operation return without me bleeding the hydraulics?

Many thanks for your suggestions.

 

[Woosh]

If air has got into the brake line, how does normal operation return without me bleeding the hydraulics?

over time, air bubbles form inside the brake fluid and usually collect in the reservoir. However, because you keep the bike in an unsual angle, some bubbles may collect in the hose making the brake spongy.
You should burp the brakes first. It's a 5 minutes job.

 

[Nealh]

You still have air in the system , as most bike will . the reservoir as mentioned will often have an air pocket and inverting the bike will induce the air in to the brake line. Once the brakes are burped and working fine again one coudl top up the reservoir to reduce the air pocket

 

[saneagle]

My Riese and Muller Tinker has developed a strange brake behaviour recently. Any ideas of why and how to cure it please?

The bike is stored horizontally on a boat To get it on land it is tilted tail up at around 60° and passed through a hatch. This worked fine for years.

Last year, one of the hydraulic disc brakes was sticking on. A bike shop found some crud in the affected brake’s pipe, blew it out and refilled the fluid. Problem solved.

This year, the first time the bike was extracted from the boat the right brake was so spongy it was ineffective. The left brake was operating normally. After 10-15 minutes of riding the right brake returned to normal operation. This happened again the next time the bike was extracted and tilted.

As the brake lines should have no air in them, I can’t understand what is happening and what I should do to correct the affected brake. If air has got into the brake line, how does normal operation return without me bleeding the hydraulics?

Many thanks for your suggestions.

It's dead simple. The only way air can get in is when the bike is tilted so that the hose is higher than the reservoir. That's how the brake became spongy. Ebike hydraulic brakes are self-bleeding, so any air in the hose will get removed by pumping the lever (normal operation) when the reservoir is back to its normal position above the hose. That's how all hydraulic brakes work, so it's perfectly normal. Nothing to worry about.

 

[RetiredAndRolling]

Thank you Woosh, Nealh and saneagle. All very reassuring and I will get burping. Much appreciated!

 

[saneagle]

Thank you Woosh, Nealh and saneagle. All very reassuring and I will get burping. Much appreciated!

You don't have to do anything - just pull the lever a few times until it becomes firm again.

 

[AndyBike]

The only way air can get in is when the bike is tilted so that the hose is higher than the reservoir.

So how come brakes work out of the box ?. They've sat on a shelf this way, that way, on their side etc etc, been sent through the post where they've been turned and flipped over many times, and yet work perfectly

 

[chris_n]

So how come brakes work out of the box ?. They've sat on a shelf this way, that way, on their side etc etc, been sent through the post where they've been turned and flipped over many times, and yet work perfectly

Because at that point there is only fluid in the system, no air is present. Once there is air in the master cylinder and you tip the bike over the air tries to rise to the highest point.

 

[RetiredAndRolling]

You don't have to do anything - just pull the lever a few times until it becomes firm again.

Alas, the fitted Tektro Auriga Comp brakes do not firm up the brake when pumped repeatedly with the brake lever. i also tried pumping with front wheel raised then rear wheel but this made no difference.

I then topped up with hydraulic oil the unhappy brake (right brake, front wheel). It worked fine until the next tilt. Oh well .

When tilted, the handlebars are at the low end and the rear wheel goes high. This never used to be a problem in the past and the left/rear brake still works fine. I have now ordered a brake bleed kit and look forward to learning something new and seeing if bleeding makes a, er, bleeding difference. “I’ll be back”.

 

[Woosh]

When you get the bleed kit, try burping first. You'll waste a lot of brake liquid with each bleed which may not be necessary.

 

[Nealh]

For my Shimano's I use the cup that screws in to the reservoir then reverse pump the fluid from the calliper with a syringe, the reservoir cup will take up the unwanted fluid and the released air. Once done I use a bit of velcro to hold the lever in, fit the cup stopper and then unscsrew it . Refit the reservoir cap and then try the brakes sometimes one may need to go thru the process twice.

 

[RetiredAndRolling]

UPDATE - oil leak found
Thanks for all this advice. I was ready to do the bleed as described above but first tried burping as suggested by Woosh. To my surprise, the reservoir on the offending brake was low on oil, even though a bike shop topped it up on holiday. Burping produced bubbles and good braking action. I was happy. When I replaced the reservoir cap and checked the brake again, I was surprised to see oil coming out of the bleed bolt on the reservoir, even though I’d not touched it, it was snug and I’d never seen oil leaking anywhere previously. I looked for a tiny o-ring to try but don’t have one in my garage. I’ve contacted my bike supplier to ask if there should be an o-ring there before visiting a bike shop to get one.

 

[saneagle]

UPDATE - oil leak found
Thanks for all this advice. I was ready to do the bleed as described above but first tried burping as suggested by Woosh. To my surprise, the reservoir on the offending brake was low on oil, even though a bike shop topped it up on holiday. Burping produced bubbles and good braking action. I was happy. When I replaced the reservoir cap and checked the brake again, I was surprised to see oil coming out of the bleed bolt on the reservoir, even though I’d not touched it, it was snug and I’d never seen oil leaking anywhere previously. I looked for a tiny o-ring to try but don’t have one in my garage. I’ve contacted my bike supplier to ask if there should be an o-ring there before visiting a bike shop to get one.

There's no O-ring, as one is not needed. Just tighten the nipple.

 

[egroover]

UPDATE - oil leak found
Thanks for all this advice. I was ready to do the bleed as described above but first tried burping as suggested by Woosh. To my surprise, the reservoir on the offending brake was low on oil, even though a bike shop topped it up on holiday. Burping produced bubbles and good braking action. I was happy. When I replaced the reservoir cap and checked the brake again, I was surprised to see oil coming out of the bleed bolt on the reservoir, even though I’d not touched it, it was snug and I’d never seen oil leaking anywhere previously. I looked for a tiny o-ring to try but don’t have one in my garage. I’ve contacted my bike supplier to ask if there should be an o-ring there before visiting a bike shop to get one.

Did the rubber o ring get stuck on the bleed pipe screw when you bled the reservoir on the brake lever end ?

 

[RetiredAndRolling]

I didn’t touch the bleed bolt/ screw as I was burping, not bleeding. Even when i ensure the bleed bolt was snug, it already was, it oozed mineral oil. The bike suppliers say there should be an o-ring.

 

[Nealh]

Most bleed screws on the reservoir will have an o ring.

 

[RetiredAndRolling]

SOLVED - A visit to my local bike shop to acquire the tiniest of o-rings has sorted the problem. It will be interesting to see if a properly sealed reservoir will prevent sponginess when the bike is tipped in future. Thanks for all the advice and encouragement. Much appreciated.

Thinking back, I visited three bike shops while travelling, each time to do with this brake. I think the o-ring must have been omitted at some point. Bizarre that I did not see any signs of fluid loss.