Brake fluid change issue with front brake

[Gray]

Hi,

I have replaced the filthy apple juice coloured brake fluid in my rear reservoir. Pumped it out through both nipples and the rear brake feels very good now (not tried it on road yet though)

Moved to the front brake which I have had a problem with recently. The lever pulls in quite a way before the brakes would bite. Pads are ok though bought new front and back sets to fit later this week.

I've bled both calipers and the fluid is coming out clear along with having topped up the reservoir above the minimum line during the process.

However what I've noticed is that when I open the nipple and slowly squeeze the front brake lever the fluid is pumped out but a few seconds later, with the lever still held in, the fluid starts moving back in as though its being sucked back to the reservoir.

I've listened to the front reservoir whilst pulling and releasing the front brake lever and there seems to be a slight squelchy noise coming from it though there are no fluid leaks anywhere on the front braking system. Every so often tiny little air bubbles come upwards in the reservoir through the little moving part at the bottom.

Any ideas what this could be? Is it worth getting a rebuild kit for the front reservoir?

thanks

Graham

[Tango]

For the price of a front reservoir rebuild kit I'd be inclined to fit one......and give the whole lot a good clean out whilst it's apart.....

[Mr Fro]

Master cylinder kits are only £20ish so are well worth replacing on an oldish bike (did mine recently).

You could try reverse bleeding the brakes - i.e. use a syringe to push fluid through the nipple and up to the M/C. You'll be forcing the air upwards - the way it want's to go.

[Matt Strange]

Pull the lever as far back as you can then tye it in place with a piece of string. Tap the cables, calipers etc with the back of a screwdriver (the handle) and leave it for a few hours.

All the air should float up to the master cylinder.

[Gray]

Thanks for the replies.

I've put a cable tie around the front brake lever and I've ordered £20 rebuild kit for the front master cylinder.

I'll go back in the garage shortly to gently tap the caliper/hoses etc and leave until tomorrow morning.

Sat on my bike free wheeling up and down the drive and the rear brake has a major improvement already with just a fluid change/bleed.

Hopefully I can get the front sorted out by weekend with or without the rebuild kit, change the pads and clean the calipers and then I can move onto rebuilding my carbs!

Learning as I go but its all good fun!

thanks again

Graham

[Gray]

Ok so I went out to the bike this morning and removed the cable tie. The front brake is back as it was, pull about 2/3 back before the brakes engage.

So I bled both front caliper again by pressing the brake lever a few times in each and the fluid came out then started going back in again.

Now I'm back to last night whereby the lever goes all the way to the handlebar without engaging the brake.

Earlier I removed the front right caliper and pulled in the brake lever. The 2 silver pistons are protruding around 4-5mm. These extend around a mm when lever is pulled fully in then return when lever is released.

Is it right for the pistons to be so far out or do they need to be flush with the caliper wall?

I'll work on rear pads in meantime as I'm waiting for the master cylinder rebuild kit for the front (hoping that's the cause of the air being sucked back in)

Thanks

[Mr Fro]

Daft question... How are you bleeding the brakes?

The procedure should be:

Attach tube to nipple and make sure M/C has a good amount of fluid in it.

Crack off the bleed nipple half a turn or so and squeeze the lever until it's back to the bar.

Re-tighten the nipple.

Gently release the brake lever.

Repeat until you have a good, solid feel on the lever and no more air appears from the nipple.

[Gray]

That's exactly as I do it. Had no problems at all with the back brake bleeding.

As soon as I open the nipple on the front, even without pushing the lever, an inch or two of fluid comes out into the tube. I push the lever slowly inwards and the fluid pushes along another few inches but if I leave the lever pressed before tightening the bleed nipple the fluid starts moving back towards the nipple!?!

[Chrissb6]

Hi you need to put the end of the bleed hose into a jar of hydraulic fluid to stop the bled air re entering the brake system. Top up the reservoir pump up the system and hold the brake lever tight, crack the bleed nipple open you should see the air come out and into the fluid into the jar repeat until theirs no sign of any air bubbles . Not having the end of the bleed pipe submersed will allow air to go back into the brake line.

Hope this helps

[Gray]

OK so I've learnt that the fluid is not moving back upwards towards the nipple. Its an airbubble in the tube which moves back upwards and doesnt reach the nipple so its not an issue. The fluid drips out into the bottle.

I've completely drained the front brake system. Starting with the MC I've cleaned it out of fluid and put my thumb where the banjo bolt goes and pulled in the lever many times.

What I've found is the air pressure, patheticly low as it is, is forced against my thumb around the same lever position as when I was riding the bike with the brake problem in the first place.

Am I right then in thinking that I should feel a lot of pressure against my thumb when I start to pull the lever and not when the lever is near the handlebar? This is with the reservoir seal/lid screwed tight on.

If I am right then, with the MC rebuild kit hopefully arriving tomorrow, that stripping down the MC and rebuilding it should solve the issues.

As an aside I read it takes around 500ml brake fluid for full system flush. So far I've used 700ml approx and now my bike is empty Can see me going to halfords for another 1L Castrol bottle. Most of the drained/used oil ended up on the garage floor when I kicked the bleed bottle over when walking around the bike! Doh.

[Tango]

Rebuilding the MC isn't a bad idea.......but it also sounds like your caliper pistons are sticking on the seals a bit.....which is causing them to retract a bit when the pressure is released. I'd pop the pistons out and clean them....and then refit them with a bit of red rubber grease on the seals first.....

[Stu]

Tokico calipers by any chance?

Strip everything and clean it up and start from scratch

Tokico calipers can be a twat to bleed up

[Gray]

Yep they are Tokico 2 piston calipers.

I've now got both front calipers off, the MC disassembled and the brake hoses completely drained of fluid.

I am going to take the calipers to a local garage and see if they can get the pistons out for me. With that done I will overhaul the calipers replacing seals etc as required then work on the MC.

I will then fill the MC with fluid, bleed that, connect the banjo bolt/hose from the MC to the calipers and bleed each caliper in turn.

I hope that I will then get some pressure back or the whole thing is going in the canal!

(well not really, I will get a mobile mechanic out to do it lol)

[Stu]

you cant bleed a MC without the hoses connected!

once you get everything all sorted connect all the lines back up and start filling the system and just bleed one side at a time back and forth till no more bubbles come out

[Gray]

Sorry, listed in the wrong order.

Will let you know how I get on tomorrow

I'm enjoying working on my bike as this is all new to me but I'm get a tad frustrated as I'd hoped to have it ready for the weekend.

Not cutting corners though, especially with the braking systems, so will do what is needed in the correct order!

Thanks

[Stu]

just make sure you clean where all the seals fit in the calipers as this is where the problem is

the alloy corrodes and pushes the seals against the pistons

[Gray]

I'm taking both the front and the rear calipers to my local garage for him to sort them out along with my new pads which they can fit for me too.

The rear caliper has lots of corrosion inside and the pad retaining pin is seized solid.

I've had enough. If I get these sorted out by someone with experience and the right tools then at least I can keep on top of them in the future by cleaning regularly etc and not wasting 3 nights like I have so far.

Hopefully when I pick them up later this week it will be a case of just mounting them to the bike then adding/bleeding the fluid.

I can only hope it will be so simple.....

[Gray]

I had a local bike mechanic remove my pistons from all 3 calipers this morning.

My rear caliper was a bit of a mess. I couldn't even remove the retainer pin due to corrosion.

Fitted new seals into the front calipers, cleaned the pistons and fitted the new brake pads. The pistons slid into the caliper housing easily.

Put them back on the bike and tightened the caliper bolts and banjo bolts to the correct torque.

After a bit of pumping the fluid and removing air bubbles the right brake pad started to lose the slack but the left brake pad remained loose ie could put my finger through the brake disc and wobble it side to side. There was also a bit of fluid dripping down from somewhere in that caliper.

So I removed the caliper and pressed the brake lever looking for a source of a leak. Couldn't find any more fluid leaking out but I did notice that the pistons were starting to protrude ever so slightly with each lever press. I decided I'd better put the caliper back on the bike.

After several lever presses I started to feel the pressure building. I bled both calipers again with no air coming out just fluid.

Kept on pressing the brake lever until the pads were against the discs.

I walked the bike up and down the garage to check the wheel was moving freely. Then I checked the brakes and crikey they were a lot better than early in the week. I don't have to pull the lever in as far for them to make contact.

So I am happy. I have wiped down the outside of the calipers and locked the garage for the night. I will check for leaks etc in the morning. Then it's onto the rear caliper. Should be straightforward. Then its road testing riding slowly and stopping every few minutes to check for leaks etc.

I feel really glad that I replaced the fluid and pads on my own and see the benefit. Been a bit frustrating the last few days but thanks to the advice here and my local garage I know what to do for future.

Thanks!

[Stu]

Great news

Its always the same with tokico calipers of that age

I swapped mine to nissin 4 pots they are miles better almost fit and forget