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Re: [ST] bleeding brakes



On May 22, 2007, at 8:20 PM, Antonio Bird wrote:

> Despite modest mechanical abilities, I decided to try to bleed the  
> brakes
> myself.  Bought and installed speed bleeders.  Seemed to be going OK
> until I drained the reservoir too low and let air in the system.  Then
> got floppy lever which did not push through the fluid when I added  
> more.

I once let air that way into the hydraulic clutch system on my car,  
which was further complicated by the hydraulic buffer loop that  
system included with its own bleeder.  It took almost a full liter of  
fluid to bleed that system enough to actuate the clutch again.  If  
I'd known it would take that much, I would have gone to the store to  
buy some cheap fluid instead of use my $9/liter racing brake fluid!

Anyway, here's what I'd do.  Set up to bleed the caliper closest to  
the master cylinder.  Fill the reservoir with brake fluid (have at  
least a liter on hand, you can use cheap stuff and once you have the  
system properly bled, it will be easy to flush the old fluid with  
better stuff later).

Open the bleeder screw enough for fluid to come out with no  
resistance, .5 turn is probably enough.  Operate the brake lever  
through its full range of travel quickly and repeatedly until you  
have fluid coming out the bleeder screw.  If there is much  
resistance, open the bleeder a little more.  Once you have a good  
squirt of fluid coming out of the bleeder, then close the bleeder and  
see how soft the brakes feel.    If they stop before contacting the  
bar, then you at least have brakes, because it is only stopping  
because it is pushing the pistons to the rotor.

Once the brakes can actuate, then I'd continue by closing the bleeder  
a little, until you can feel some resistance when you squeeze the  
lever, but it allows fluid to pass so that the lever will go to the  
bar when you squeeze.  Squeeze the lever quickly and firmly several  
times.  When you stop seeing bubbles in the lines, then open the  
bleeder until fluid goes through with no resistance and activate the  
lever quickly several more times.  You want fluid to move through the  
system quickly, so the air bubbles don't keep rising back up the line.

After repeating those steps a few times, the lever should be getting  
more firm.  Obviously, watch the level of brake fluid in the  
reservoir at all times.  If you suck in air, you are starting the  
process all over again.

Once the lever is pretty firm, and you've repeated these steps for  
both calipers, then move back to the first caliper.  Squeeze the  
lever hard, and then open the bleeder very quickly.  You want a sharp  
burst of fluid coming out of the bleeder, carrying with it the last  
bubbles.  Repeat this as necessary for both calipers.

You can repeat the final bleeding procedure the next day for even  
better results, as overnight tiny air bubbles will coalesce together  
into larger bubbles that will be easier to bleed.

Hope this helps,

Jim

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