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85 GL1200A: Front brake bleeding problem

2K views 22 replies 9 participants last post by  PAPete 
#1 ·
I have been using a pump on the caliper bleeder valve to bleed the left front brake and no fluid will flow. I have had the pump pulling -- and holding -- 20" Hg, which should be plenty, I think. I drained the reservoir and loosened the banjo bolt, but still no flow.

The attached is a close-up of the bottom of the reservoir. Is that loose metal tab in the hole in the bottom supposed to be there? What is its purpose? Any suggestions for clearing the blockage? Thanks.
 

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#4 ·
Thanks, IR.

After my first post, I disconnected the upper banjo bolt and put a little fluid in the reservoir, which I was able to pump out. I also was able to pull a vacuum down at the brake bleeder valve with the upper banjo still loose.

To me, this means there's a problem in the calipers, which I had just cleaned and installed new pads and spring. The picture below shows the calipers and new pads. Note that the pistons are retracted all the way into the housing. Is that supposed to be that way? Could this be the problem? If so, would compressed air in the lower banjo hole move them out? Any other suggestions? Thanks.
 

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#5 ·
Yep. Wrapped it in Teflon tape too because the vacuum was very slowly leaking. Our posts crossed; do you have any idea what I might have done to the calipers to create this problem, Ken? Thanks.
 
#9 ·
Thanks, Ken. I've "sorta" done that I think with (1) the fluid through the MC and (2) through brake line with the lower banjo bolt loosened. But, I'll remove those components and try to blow air through them as well as the caliper. Thanks for the suggestion.
 
#16 ·
Hi,
I am new to the web site and therefore have only just read your problem. May sound like a stupid question, but are you aware that only one of the front calipers is activated by the front lever. The other side is activated by the foot brake ?.
Another thing is, you can block the pads, get a large syringe with a suitable tube on it, and loosen the bleed screw. Then pres brake fluid backwards up to the reservoir. This will definitely get any air out of the system.
Good luck if you still have a problem.
 
#11 · (Edited)
Update

Well, you may remember that the pistons were stuck all the way into the caliper. So I took it off and blew air through the fluid intake and that moved them out to the proper position.

Then I unscrewed the bleed valve, cleaned it out and blew air through it. It wasn't completely plugged, but the flow was improved. Then I noticed there was brake fluid on the floor from the lower banjo bolt which I had neglected to tighten enough, thus confirming that the problem was in the caliper, and sure enough, after I filled the system (using a pump), they are working fine (on the lift).

So Dave, Ken and Iraqi Ram, thanks for your input. Problem apparently solved. Hoping for a test run this afternoon. :cheerssmall:


Edit: Not sure how the unhappy face got in the title.
 
#14 ·
Well, you may remember that the pistons were stuck all the way into the caliper. So I took it off and blew air through the fluid intake and that moved them out to the proper position.
.
It doesn't matter if the pistons are all the way in, they don't block the bleed hole, and you can put way more pressure on them with the brake than you can with air pressure.
 
#18 ·
Just wanted to chime in that not only is pushing the pistons all the way into the caliper ok (provided you clean them first), but it's also the recommended state for bleeding the brakes. With the pistons retracted all the way and clamped in place with a C-clamp or something along those lines, there is a bit less space for air to hide in the caliper. Just make sure there is a bit of extra room in the reservoir first because fluid will get pushed up the line.
 
#21 ·
It would be so lovely if you could just bleed at the screw without doing anything and get consistent results, but for some reason the 1200s can be weirdly challenging, which is why the web is full of so many reports of people rotating the caliper a bit, clamping the pads back, and doing a little voodoo dance to help things along. Looking at the inside of the caliper, it is actually possible for little bubbles of air to get trapped in the piston chambers when they're extended and the caliper isn't at the perfect angle to get the bubbles to rise through that single little channel. Dunno, maybe it's an old wive's tale - but I've had to flush the brake system a few times in the last week and thus had a chance to experiment with a few styles of bleeding. Placebo or not, feels like I got better results with the clamps on.
 
#20 ·
when did they move the bleed screws up to the master cyl- the high point? (surely you meant high point of the caliper?)(finally! a chance to poke fun at someone else~)

Its smart to replace the special washers for the banjo bolt if you have removed pressure from them by separating hose from master.

Also- burp the master at the banjo fitting if the line was off. Air likes to get stuck there and mess with you bleeding the system.

I realize this is side-note type info, and am thinking about future readers who may skip the first pages of a thread. Gurus please be kind
 
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