Front brake bleeding help

Hi all,
Over the winter I bought a stainless rebuild kit for the front caliper (OEM MK3). The rebuild went fine, bled it down and it was just ok, a little soft but not too bad. Over time the brake became too soft. I just figured I had some air in there. I tried bleeding again, and quite a bit of air was bubbling out. I have run at least a quart of DOT 3 through the brake and the air bubbles continue to appear. Now I am at the point where there is practically no brake at all.
If I had any hair I would be pulling it out at this point. BTW I rebuilt the OEM master when I bought the bike 4 years ago and it has worked well. The brake lines are original and tight. There is no sign of fluid leaking. I think that if air is getting in, fluid would be leaking out. Thanks in advance for any advice.
Terry

I just went thru a similar episode with the rear disc on my Vincent project bike. This brake is from an 03 gsxr. Could not get it to bleed, nearly wore out the bleeders with all the tightening and loosening.

The problem with that brake was an upward hump in the brake line. I guess the fluid from the resevoir would pass by under the trapped air pocket without pushing it out. I went thru three bottles of fluid, had fluid everywhere, but still no back brake.
Internet Gixxer forums talked of similar bleeding problems. The fix seemed to reverse bleed be using a brake fluid filled syringe with tube attached to the open bleeder. To do this you must use teflon tape on the bleeder so that the threads dont leak when open. You need to be careful to keep the tape away from the end of the bleeder so that teflon doesnt plug things up.
You squirt the fluid thru until there are no bubbles showing up in the resevoir. You need to have some freeboard in the resevoir to start, otherwise the brake fluid will overfill the resevoir.

This might work for you, it did for some on the Gixxer forum. It didnt work for me tho. In te end I pullled te rear brake off and put it down on the floor, that way the hose was heading downhill all the way. Then I bled it in the normal way. It took about half a bottle of fluid and then the bubbles stopped, pedal was rock solid and has been ever since.

Hopefully there is some info in there that will help.

Glen

tban52 said:

Over the winter I bought a stainless rebuild kit for the front caliper (OEM MK3). The rebuild went fine, bled it down and it was just ok, a little soft but not too bad. Over time the brake became too soft. I just figured I had some air in there. I tried bleeding again, and quite a bit of air was bubbling out. I have run at least a quart of DOT 3 through the brake and the air bubbles continue to appear.Now I am at the point where there is practically no brake at all.

Click to expand...

When you say there's practically no brake at all, do you mean the brake lever is coming back to the grip, or that you are pulling the lever but getting little or no reaction from the caliper? During the bleeding process, when the bleed nipple is slackened off, air can be drawn into the bleed tube from the around the outside of the loose bleed nipple by the syphoning effect of the draining fluid which can look as if air is coming out of the caliper.

tban52 said:

The brake lines are original and tight.

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If the hoses are the originals then they are about 27 years overdue for replacement. Old brake hoses have been known to collapse or delaminate internally.

tban52 said:

There is no sign of fluid leaking. I think that if air is getting in, fluid would be leaking out.

Click to expand...

It seems more like a master cylinder problem, especially if the brake lever is coming back to the grip easily. If you remove the cap and diaphragm, and then operate the brake lever do you see tiny bubbles rising in the fluid reservoir each time the lever is released?

I had exactly the same happen.. Must have bleed it 20 times still the same. Was fine before rebuilding the calliper. I run a brembo master cylinder which is a major improvement on the girling. In the end I shimmed out the lever on the master to give me longer travel And it now it works fine. Still have no inkling what was the problem to start with.

Old brake hoses are great for trapping air bubbles.

I've had some success with removing the front wheel - or unbolting the caliper, pumping the pads down on to a tyre lever, then levering them back as far as they'll go - this does help get trapped air out, and a good deal of tapping the hose with a spanner also helps.
It can take days for all the air bubbles to migrate their way out, but I never have this problem with new hoses.

I bought the CNW Brembo conversion for both the front and rear brake. I was having no luck getting any pressure on the rear and never got useful pressure on the front bleeding the brakes the traditional way. I called CNW and they told me that it is very difficult (impossible for me) to bleed these newer brakes in the traditional way. I bought a brake vacuum kit (which connects to an air compressor) and bleeding the brakes is a breeze. The kit is $25 at Harbour Freight:

http://www.harborfreight.com/brake-flui ... 92924.html

Yes I never bleed the brake the traditional way anymore. The syringe-kit method is awesome , a one attempt affair and quick. Buy that Harbour Freight item if you have a compressor and try it as I am curious. Original lines must be pushing 40 yrs. old by now , dinosaur trash. Go braided stainless line.

+1 for the reverse bleed with syringe , worked a treat on my brembo .
I think from memory brembo describe the process on their website .

Thanks all,

Yeah, I think it's time for some new lines... This may be a stupid question, but do the lines come in standard lengths? Or should they be made up custom?
Who is a good supplier? I am going to try the syringe method too. Yesterday being Mother's day the prudent thing to do was stay out of the garage for a while .

Terry

When did you last overhaul the master cylinder :?:
I only expect these sealing rubbers there to last about 5 years, after that, you are living on borrowed time.
As for bleeding out, unbolt the calliper and insert a piece of wood, metal between brake pads, and hang it ABOVE the master cylinder by a piece of wire on to a door e.t.c. and then bleed out. Air will only go one way, it will rise.
I now use a slightly modified Easy Bleed kit to reverse bleed the fluid from the forks mounted m/cylinder

Rebuilt the master about 4 years ago. The front brake has been fine until I rebuilt the caliper. I am going to try the reverse bleed method, makes more sense to push the air up rather than down....

First thing I do when I put the caliper back on the bike is to take a plastic straw like the ones used on DW-40 cans. I afix it to a plastic syringe. With the hose off the caliper you can insert the straw through the hose port into the rear piston and force fluid into it until it pours out. Then you can do the same with the outer piston through the bleed port. The air in the rear piston has to travel upward and be forced back down to get to the bleed port on the outer piston. So I prefer to make sure both are filled as well as possible before I start bleeding.

Russ

PS-get a stainless brake line, you won't be sorry.

Terry it sounds like your wallet will be undergoing some bleeding and bloodletting before this gets resolved. Happy Mother's day to yours.

Quite often the problem is that when you pump the lever, the air bubbles go a little way down the pipe, then come back up again when you let go of the lever. There is often a high point in the brake hose that is slightly higher than the master cylinder.

You need to position the bike so the brake hose runs uphill all the way.

I do this by putting it on the sidestand and turning the bars all the way to the left. Then I pull the brake lever quite hard and put a zip tie around it. Leave it for about half an hour and release the zip tie. That often fixes it. If not you may want to try it a couple of times.

I won't guarantee it will fix your problem, it depends where the air is trapped, but it often helps and is free.

I ordered a set of braided stainless lines. Hopefuly they will be here by the weekend. Plenty of new techniques to try, I'll let you know. Thanks for all the good info.

The Procedure is to fit a ' bleed tube ' to the NIPPLE , about 1/2 a metre long , and throw the end in a can .So As it doesnt ' back feed ' on ea. stroke .

A new system will typically have residual atmosphere in . Leaveing it overnight after bleeding , then refitting the tube , and about four strokes should clear the ' atmosphere ' .

A nipple open more than say 1/4 turn tends to rattle , so bleeds back through the threads . SO , I check its clean , open it TWO turns , finger tighten closed , and open ONE QUATER
AND sit the six point spanner there hanging steady , ready to flick shut with a finger .

Youll get nowhere without a tube to take the discharge ( to inspect - Flushing Brakes ) as the barstwerd bleeds back every stroke of the brake lever . :lol: Sucks air in the caliper .

Some'll squirt fluid UP at the Resivoir , so untill you sure it doesnt ( Never trust te sucker though ) it can pay to sit the cap on. Unless youre intending to do a resay . :mrgreen:

Matt, how does the air get in when the bleeder is shut on the up or out stroke?
For me, the procedure has always been the same with a car as a motorcycle, open bleeder, push down brake pedal or pull lever, close bleeder, release brake pedal or lever, repeat until fluid coming from bleeder has no air bubbles.
The air and fluid go out on the down stroke when the bleeder is open, new fluid without air gets drawn from the resevoir when the pedal goes back up or lever back out (bleeder shut)
This works fine as long as there is no hump in the lines, then the air just sits there letting fluid run underneath.

I think it is a great idea to use a hose on the bleeder tho, keeps the fuid in a bottle rather than all over everything!

Glen

Yea , observeing the brother when he was 15 bleeding the brakes assembling a hot rodded 105 E Anglia with his mate whos a 747 pilot now , caused a degrre of thought to occur . It was a week and they still hadnt got em sorted . :lol: :lol: The back flow being the issue , and air locks / bubbles . Theyre attempts to refit the gearbox were a similar serial installation .degressing , but laying under the vehical , feet aft ,
sighting the bellhousing / rear block face , at mosat it needs a twist on the output shaft to slip straight on ( Most Days :lol: :twisted: ) .

Long and short of it is the length off arms to eyes , often cant be in two places at once .particuarly on many wheeled contraptions . Flushing them the rears together ( both open 0 , fronts ) often
turn a soggy pedal hard and increase responce & action significantly if old grotty fluids in it , I syphon the resivoir , wipe clean & start with fresh fluid rather than pumping sludgey stuff through .

The olde hydroscopic bit means if the colous soupey it moisture contents up .Most fortunate there was a gap in the traffic for the right turn when the pedal went to the floor in the 1951 Rover 75 .



more annon .