Front Brakes

scotty · Post by **scotty** » Sun Feb 18, 2007 6:43 pm

With the weathr being so bad up here at the moment I've been doing a bit of work on the bike and have come across a problem when doing the front brakes re bleeding the system. I have replaced the brake pads front and back and cleaned up the calipers. With the brake pads out I have crefully operated the front brake leaver to ease the pistons out of their bores in order to clean them up a bit and work in some red rubber grease which is recommended for pistons in hydraulic units. When I was doing this one of the pistons accidently popped out of it's bore on the left hand caliper and I was pressed back easily enough. I knew this would let a load of air into the system but I was intending to to bleed the whole front system to get new oil in there. I am using a syringe system so am sucking the oil down and out through the caliper nipple and topping up the handle bar resevoir as oil passes through the system. The right hand caliper bled ok and I am getting a solid stream of oil through but I am having problems with the left caliper and am getting a continual stream of bubbles with hardly any oil. I,ve tried syringing oil back into the left caliper to fill the piston housings and then bleed it back out but I'm still getting 90% air from the left caliper. There is no resistance on the front lever at all now. I must be doing something wrong but cannot figure out what. Is it better to bleed the system buy forcing oil down through the system by using the front brake lever ?

Any help in what I'm doing wrong would be greatly appreciated. I'm using the syringe and plastic tube as I don't have a brake bleeding kit so any advise on a decent kit would also be appreciated.

Regards

winger · Post by **winger** » Sun Feb 18, 2007 7:07 pm

Firstly you sure you didn't damage the seal when you put the piston back in,if the answer is no,it seems strange your getting so much in the system,i prefer the rubber bleed hose with a non return valve in a jar,cost a couple of quid,and then fill the res up and do the old routine of lever in left hand,spanner on bleed nipple in right hand,open bleed nipple pull in lever with left,lock it off,let lever out and keep doing it,the moment you've got the slightest bit of resistance,pull on lever keep pressure on and put an elastic band over lever and handle bar,leave over night and let it bleed itself.

Me-109 · Post by **Me-109** » Sun Feb 18, 2007 7:43 pm

Pretty much what winger said. I've got one of those vacuum kits and they always seem to stream bubbles into the fluid in the hose. The hoses don't seem to seat quite so well so are sucking air in around the bleed nipple. Confuses you into thinking it is actually coming out of the caliper.

Steptoe · Post by **Steptoe** » Sun Feb 18, 2007 8:31 pm

Have you got ABS, or ABS/servo brakes, or non ABS brakes ?

Jason M · Post by **Jason M** » Sun Feb 18, 2007 9:05 pm

I had something like this on my Thundercat - too much air in the system for the brake lever piston to compress. enough to bleed. I was told to get some mole grips, pull the brake lever and without letting it out, clamp the brake line just out of the brake lever, then let the lever out, pull it in again whilst letting off the moleys then when the lever is in, clamp the brake line again. Repeat until enough pressure has built up in the brake line to bleed. Might not be this, but it worked for me

Jason

r550s · Post by **r550s** » Sun Feb 18, 2007 9:36 pm

try putting a good dab of copaslip, or any grease, on the nipple threads - and don't undo it so much.

ChasesDragons · Post by **ChasesDragons** » Mon Feb 19, 2007 10:56 am

Just an idea, assuming nothing about our knowledge:

Piston seal check: Take problem caliper off, take any rubber piston boots off, wipe clean and dry the area by the pistons so you can detect any moisture, place a pice of metal/wood of sufficient thickness in between the calipers and squeeze. This should allow you to detect any fluid/air escaping out of a compromised piston seal at the caliper - this might be the origin of the air entering your system.

Do a similar check around the bleed nipple and the banjo union.

You can make this a wee bit more sensitive by wiping dilute detergent around the items so it bubbles in the presence of air escaping.

Get rid of the syringe, get down to any car place and buy yourself a piece of clear tight-fitting plastic piping for brake bleeding. Get a jar quarter filled with brake fluid. GRANDAD KNEW BEST!

You could try this: fill the fluid at the top, zip tie the brake lever HARD against the handle and leave for a night or a few days. Tilt the bike/handles so that the container at the top is the uppermost part of the system so the air finds an easy escape path to the top. This can be promoted by frequent gentle tapping of the brake hoses to help the air break off the hoses and move up......"someone" has been known to tie a vibrator to the hoses, overnight....hey, I am just giving you an idea, you do not have to do it.

I believe ABS and whatnot is going to grossly complicate this.

Regards
Udhi

scotty · Post by **scotty** » Mon Feb 19, 2007 12:33 pm

Thanks. I did take the caliper off to see if oil was coming past the piston that popped out and there was no problem. The piston seems to be moving ok and smoothly within its bore. If the oil seal had been damaged or pushed away from where it should be you would think that oil would seep out and that is not happening. I have placed a bit of wood between the pads and compressed the lever and there was a bit more pressure as the pads came in contact with the wood. Jason - I think you might have hit on the problem. There seems to be so much air in the system that it's hard to compress it out or indeed suck it out with the syrindge that I was using. It's worth a try using the hose clamps so I'll see if I get the chance tonight. The whole thing is pi**ing me off something else. Hydraulic brake systems can be really querky and you get to thinking a bl**dy great twin leading drum would be a lot less hastle !

gus · Post by **gus** » Mon Feb 19, 2007 5:34 pm

My top tip.
Tilt the handle bars so no air bubble can form where the piston for the master cyclinder is.Cant remember if its left or right!

Make sure the fluid is top upped.Gently squeeze the lever in and out whilst lighly tapping the master cylinder.You will see air bubbles.Keep squeezing until all air has gone.You should have a decent lever pressure.Once you have a that, bleed your brakes in the usual way using the bleed nipples and tube etc etc.Leave a lacky band on overnight to sort ouy any remanining air.
hope that helps
gus

jivebiker · Post by **jivebiker** » Thu Feb 22, 2007 2:33 pm

Try this..

If you have any pistons that are not pushed right back onto their bores..

Pull brake lever to bar and tie off.

Push pistons back in the good caliper, this will force an enormous amount of fluid compared to the handlebar lever across to the other caliper. Make sure the other caliper is angled so that all air, having risen to the top is also made to flow to the nipple side (you could have air trapped on the wheel side) and give the caliper a good tapping with a nylon mallet to loosen any stubborn bubbles.

As a rule I never use suction methods as if there is a leak they will introduce air into the system.

scotty · Post by **scotty** » Sat Feb 24, 2007 5:08 pm

Thanks guy's. I've been a bit low with a touch of flu lately so not managed into the garage but will do so over this weekend and try out some of the things posted.

scotty · Post by **scotty** » Tue Feb 27, 2007 10:33 am

Had a session in the garage last night and enlisted the help on my next door neighbour so I could do the standard way of bleeding the brakes. They are much better now with reasonable pressure at the lever. Even though we ran through quite a bit of new brake oil the lever is still on the soft side. The whole linkage on the front brakes seems unnecesarily complicated with the connection pipe going across to the left side caliper. Also the bike is a 99 model so there must be some swelling apparent in the rubber hoses by now so it might be time for a change to braded ones. I would reckon that running braded hoses directly to each caliper would result in better pressure at the lever and also enable a much easier time bleeding the brakes.

r550s · Post by **r550s** » Tue Feb 27, 2007 11:26 am

got the same year bike, and yep it does. Dunno if there's kits for a simple two line/double-banjo-at-the-master-cylinder set up, but you can get all the components from BSR Aerotek on-line for much less than £100 (and they're really helpful on the phone too). If you need guidance about making your own lines up - try the Goodridge website, they do a 'how-to' PDF. Wish I could post photos - my guess at routing/ line length/banjo angle has worked out okay and there's no chafing anywhere.

Boxered · Post by **Boxered** » Tue Feb 27, 2007 11:34 am

I have just fitted such a setup to my bike last weekend, goodridge do a kit, not sure on price as I got mine from them via ebay last year, I paid about £48 iirc, but I would guess at nearer £70 retail.

Steve