Brake/Clutch hydraullic system bleeding

This topic keeps coming up time after time and I just thought it deserved it's own easily searchable heading.


Motorcycles are such a bitch to bleed brakes on since the amount of brake fluid that travels in a stroke is so small. The air bubbles just won't keep moving in the direction of the bleeder valves. Some guys have gone to some very unusual extremes to encourage the air bubbles to travel towards the bleeder screws including but not limited to standing the bike up such that the bleeder screws are higher in elevation than the master cylinder because the air wants to travel upwards.

If you look at the bleeder screws you'll notice that they kind of look like greease fittings and there's a reason for that. In the automotive world and quite possibly the motorcycle world on the assembly line after all of the brake components are installed, the guys on the line hook up the brake fluid filling hoses to the bleeder screws and back feed the brake fluid from the slave cylinders to the master cylinder. The brake fluid travels upwards pushing the air out in front of the brake fluid. One big air bubble moving upwards.

In a lot of automotive repair shops they have a brake bleeding chamber. Kinda looks like a round sphere which they fill with new brake fluid and then pressurize with air (maybe 20 lbs). The hose on the chamber is terminated with a cap that screws on in place of the master cylinder cap and then a valve on the hose is opened up. When the mechanic goes to bleed the brakes, all he has to do is open the bleeder valve and watch/wait for all of the air bubbles to escape then close the valve. The air in the bleeding chamber is pushing the new brake fluid in one big push and the air bubbles just can't stop and reverse flow back and up to the master cylinder.

So that's the theory. Now that you know this what can you do to better bleed brakes? I don't have access to a bleeding chamber anymore and if I did that's what I'd use. So I have come up with a cheap method to achieve a system similar to what they do on the assembly line. Get a piece of tygon hose or fuel hose that fits tight over the brake bleeder screws and a 4-8 ounce squeeze bottle with a nipple on the end of the bottle that will fit on the other end of the hose. Fill the bottle with brake fluid. place the end of the hose on the bleeder screw. Open the bleeder screw and then squeeze the bottle pushing brake fluid backwards through the system towards the master cylinder. ( I'll have to note here that you're filling the brake master cylinder so you need to make sure there's room in the master cylinder to accept the brake fluid.) At any point now you can close the bleeder screw. If the system has fresh brake fluid in it, and the master cylinder is getting too full, you can take the filling hose off of the bleeding screw and suck the excess brake fluid out of the master cylinder using the filling bottle and then go to the next bleeder screw and bleed that side of the brake system. So in effect you're constantly moving brake fluid in the direction of the master cylinder which is the highest point in the system and that's where the air bubbles are trying to hang around.

Here's a link to a video on using a brake bleeding chamber type tool
www.ecstuning.com/b-motive-parts/univers...pb-0101/Video247-HD/

Here's a link to back bleeding using a large syringe and hose.



Hope this helps.

KB

I've always maintained my brake system by flushing it regularly. This is likely why my M/C's and Calipers have never been apart and continue to perform consistently with no signs of leaking. Perhaps a bit of Luck, as well !
I've done this no less then 5 times over the years (1980). This includes using Q-tips to clean the reservoirs of the black residue that accumulates in the bottom. Never used paper towels !!!!
No argument that bleeding the air by yourself can be a pain but I somehow managed. Non-the-less, about three years ago I picked up a vacuum-pump designed for this purpose. Typically about $50.00+ I purchased mine on sale for $29.00 (Princess Auto - Canada). Made the bleeding task a piece-o-cake - so much easier and quicker and as far as I'm concerned paid for itself the first time it was used.
Brake lines have been mentioned. About 30 years ago I made a complete set of steel-braid lines because of the "flex" in the OEM's. The difference between the factory rubber lines and S/S was/is remarkable.
I think the last thing I'll mention is the braking performance of the system. One of the reasons I've not changed out the front or rear calipers despite so much controversy about their poor performance and alleged "locking-up" issues is because I've never had any concerns or frightening moments. Always firm, linear, predictable and consistent. I attribute this to the above mentioned maintenance. Will admit though, a "6-puck" on the front does look "cool" !
My philosophy however with this critical part of the bike is "If it ain't broke - don't try fixin' it".

Hey Scotch, thanks for the tip on the bleeder pump. I've been having a hard time bleeding mine and the pump might just do the trick. Unfortunately, they've gone up to $70. so you got a really good deal. Still, worth it for the savings in time.

Dogfight.

You can reverse bleed also with a piece of plastic tubing and a large disposable syringe. Push the pipe on the syringe, suck fluid in, remove any air by tilting upwards the syringe/tube. Prior to pushing fluid in, wrap some Teflon tape around the threads of bleeding screws, this will prevent seepage of fluid via the threads. Once you have filled the system and closed the bleeding screws, pull the lever in and fix it in place with a tie wrap. Leave it overnight, this will allow any remaining air to escape via master cylinder.