Bleeding front brakes

[daveb]

Hi everyone.
Getting my 85 350n1 ready for the summer. When I got the bike last year the front brake was not very good. The lever ran out of travel and it only just slowed the bike . So I've freed up pistons and put new pads in. The fluid was horrible so I've bled through new fluids . .After 3 hours of bleeding and a litre of fluid I'm still getting bubbles when bleeding.and no pressure on the lever.I've noticed every time I depress the lever and it returns a big air bubble comes up from the bottom of the reservoir. Is the master cylinder knackered or do I keep bleeding. Thanks all for your help in advance

[tomtom1]

Hi I've struggled to bleed front brakes before, so I ended up back bleeding them by filling a oil Can with brake fluid and putting it on the bleeding nipple using a peice of pipe, and pumping into the caliper, then once you have a brake lever, I put a cable tie around the brake lever and left it over night.

[tonyd123]

Does it still feel spongy? Try pulling the lever back to the bar and put a zip tie on it for a couple of days. Should release any air trapped near the top.

[midlifecrisisrd]

Keep getting the bubbles up out the master

When the bubbles stop you will have a brake

Try the tying back too

Last one I did took days.

Steve

[Chewie01]

The trick I used to get the air out of my front brakes after a complete replacement of all the parts was to just keep flicking the lever to let the air out the top.
Then when the top stopped giving me bubbles I used the standard method to get any remaining air out of the system.

[headcoats]

When you say freed up the pistons,were the pistons rust free,no pitting and were the seals changed

[daveb]

Thanks for your answers ... headcoats the pistons had black filth stuck to them . I pushed them out till I could see the chrome and cleaned them with brake cleaner. They looked like new. I put the red seal grease on pistons and worked them in and out till I could push them back with my finger. I didn't pop them out the seal . Doesn't look like my bike has ever seen rain!.
OK so the bubbles from the reservoir is normal in the bleeding process. So keep tinkering tomorrow and then tie the lever and leave over night . What a pain . Shall report back soon on progress. Thanks everyone

[elsiefan]

I am a little concerned that your problem may be due to old seals. If, as you say, the pistons were covered in black filth that needed brake cleaner to remove, that filth may have damaged the seals, which may themselves be many decades old.
I stripped and rebuilt the calipers on my 4L0 and it took an hour or so of flicking the lever and the brake hose, to get bubbles come up to the master cylinder and the fluid all the way into the system, then some standard bleeding cleared all the bubbles. I did tie the lever back overnight and gave it another bleed in the morning and just got fluid out. I used about half a 1L bottle of fluid. That was with all new seals in place. I believe Norbo does them for the N1 for a fiver a set.

[crigar]

There are many solutions. What seems to me the easiest:
-remove the master cylinder attachment to the handlebars.
-remove the cover and the rubber plate.
-Position the master cylinder as high as possible (if possible let the hose be as vertical as possible).
-move the brake lever a few centimeters (not completely). After a few movements, small bubbles should come up in the jar.
-Repeat the operation until there are no more bubbles.
-The operation is finished when the lever becomes hard.

Les solutions sont multiples. Ce qui me semble le plus facile :
-enlever la fixation du maître-cylindre au guidon.
-ôter le couvercle et la plaque en caoutchouc.
-positionner le maître-cylindre le plus haut possible (si possible que la durit soit le plus verticale possible).
-actionner le levier de frein sur quelques centimètres (pas complètement). Après quelques mouvements de petites bulles doivent remonter dans le bocal.
-répéter l'opération jusque à ce qu'il n'y ait plus de bulles.
-l'opération est terminée lorsque le levier devient dur.

Translated with www.DeepL.com/Translator (free version)

[chrisg]

Everyone has their own favourites, mine is to inject fluid from a syringe through the bleed nipple. Take care not to overfill the system. I put some ptfe tape on the bleed nipple to prevent the fluid track back out of the nipple threads. Make sure the second caliper nipple is closed. Fill 1st caliper and hose to the splitter, then fill from 2nd caliper.
Good luck.

[elsiefan]

Apr 22, 2023 10:50:32 GMT 1 chrisg said:

Everyone has their own favourites, mine is to inject fluid from a syringe through the bleed nipple. Take care not to overfill the system. I put some ptfe tape on the bleed nipple to prevent the fluid track back out of the nipple threads. Good luck.

You are correct there. and the OP has a number of options for bleeding protocols. 
My concerns lay in their comments about the filthy pistons, plus running nearly 1L of fluid through and still getting bubbles coming out when bleeding. It sounds like air is getting into the system somewhere, and the seals, or bleed nipples, are a potential culprit. It should be a sealed system, but the continued presence of air indicates this is not so. 

[daveb]

I spent 3 hours flicking the brake lever yesterday. Untill I could pull it at least 30times with no bubbles coming up . I then bled the brakes normally . Tied the lever up and left overnight. This morning I've tried the brake and boom . Got good pressure. Can only pull the lever about half way . The best its been since I've owned the bike .
When Ive done brakes on modern bikes they have been easy to do . Was there a floor in the design of the rd brakes. Where discs and hydraulic brakes a new thing?
Thanks to you all for giving me your time to give your experiences of bleeding the brakes . Right. now to go do the rear brake ... thanks

[chrisg]

These bike can be problematic and give us preblems but maybe thats why we love them so much 🤔

[Chewie01]

I replaced my front brakes with a Brembo master cylinder and Triumph calipers with Venhill lines. So no Yamaha parts were used and I had to do the flicky lever thing for a couple of hours.
I would therefore say it's not just an RD thing.

[JonW]

Indeed try bleeding Tockico 6 pots lol