Brake bleeding-wrecked master?

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DanH
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Brake bleeding-wrecked master?

#1

Post by DanH »

Hi All,
I decided to tackle a few projects on my '79 over the winter. One of those being the twin piston caliper conversion. I was able to get a reasonably decent set from an '86 VT1100C for $35. I went ahead and ordered a rebuild kit for them and got them looking pretty good. Pistons were in decent shape, so just did seals and bleeders and lots of cleaning.
Prior owner had done a master cylinder rebuild a couple years ago, and I got the bike last April. The master cylinder is a rectangular type instead of the cylindrical. By the time I got the bike running late in the summer, I was able to put maybe a few hundred miles on it. The brakes worked ok, but rear would occasionally hang up a little and some associated squeaking, etc...
Anyhow, over the winter I rebuilt the rear and those new twin-piston fronts and was pretty excited to finally swap them out.
Weather becoming agreeable around here, I swapped the fronts out a few days ago and figured I would spend 10 minutes bleeding them and be ready for the road.
...and two days later, I am still at the "bleeding the brakes" step!
I got a lot of froth and bubbles initially, and after a lot of fluid I got through the froth and was still pretty bubbly.
I read on the forum somewhere (and I think also on Randakks) about the trick of cable-tie the brake lever, turn wheel to the left and let sit overnight. So I did that two nights ago, and next morning almost thought it worked. The lever felt maybe just a little firmer, and after a few more bleed cycles I was not getting any more bubbles. But When I pull the brake lever, I am barely getting any grab at the rotor - even if I pump a few times.
I did the same cable tie the brake lever method last night, and still same result - clean fluid coming out as I open the bleeders, but no improvement on the pistons really grabbing very much.
So one "no-no" I know I did was to pull that brake lever all the way back instead of stopping a little short. I probably did that at least 5-10 times before I looked again at the manual (and later in a number of places on forums) and saw that was not to be done.
So, now I am wondering if I wrecked the master cylinder? How would I know? Or is it possible I still have a rogue bubble somewhere (like in that manifold behind the Honda badge, etc...?). I have gone through one entire bottle of brake fluid so far (small bottle). I am thinking to maybe try that reverse bleeding method of injecting fluid through bleeders and up to the m/c. I am a little nervous about the potential mess, but maybe its worth trying?
'79 GL1000 - Rideable work in progress
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Re: Brake bleeding-wrecked master?

#2

Post by Track T 2411 »

My first thought is that the master cylinder is improperly sized for the calipers, although I'm not an expert on hydraulic formulas... Hopefully someone with more experience on that sort of thing will chime in.
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Re: Brake bleeding-wrecked master?

#3

Post by DanH »

Thanks for weighing in!
I am hoping that is not the case, but seems one possibility. All the posts I read regarding the twin piston swap indicated the original master could be used, though since my master cylinder looks to be not-original - maybe could be out of the range of what works? I hope to try bleeding again tonight (this time I have a big bottle 😃), and I will see if any better results.
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Re: Brake bleeding-wrecked master?

#4

Post by low-side »

Sounds like you're having a rough go of it. A couple questions: did the mc ever run dry while you were doing your work or bleeding; how old are your hoses; do you know what size your mc is; does the mc have a name on it or is it likely some off brand eBay thing (not trying to start anything with the $20 mc proponents)?
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Re: Brake bleeding-wrecked master?

#5

Post by Shadowjack »

I get bubbles if I don't put teflon tape around the bleeder threads. About the bad master, if you take off the upper hose and put a plug bolt in the hole, does it get instantly solid? Also, remove one caliper from the circuit and see if you get brake action at the other.
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Re: Brake bleeding-wrecked master?

#6

Post by pidjones »

What year GL1000 is this? The '79s had a rectangular-looking MC reservoir. I have a VTX MC that just won't work on my '78 (but looks great). Swapped back to the old, nasty-looking original and have great front brakes again. Shadowjack's suggestion of replacing the banjo bolt with a blank should rule out (or prove) a bad MC for you.
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Re: Brake bleeding-wrecked master?

#7

Post by DanH »

Thanks so much for the help! Well, the solution ended up being pretty simple - and I can't believe I missed it (well, yeah actually I can believe it). So when I swapped the calipers last week, they are a bolt-on swap - ...but the horizontal braces for the fender interfere a little bit. This bummed me out a little when I noticed this as I was installing them, but I figured I could just give them a slight bend and pull the back of the fender just a little bit forward and then use a longer screw to attach at the fork (and use a short spacer).
With the fender still on the bike and the calipers installed, I bent each of the braces just enough so I could get the longer screws in, and I temporarily added a short length of rubber hose on the braces so they wouldn't rattle against the calipers. My thought was I would at least get it running (and stopping) and would later take the fender off to make a more permanent mod.
Fast forward to last night: So after another hour or so of brake bleeding, and a ugly attempt at "reverse bleeding," and still nothing getting better, I decide I will take the calipers off and unbolt the manifold and see if I can get those close to the same height as the m/c. Step one was to unbolt the side braces of the fender since they now sort of wrap around the twin piston calipers (whereas the original calipers clear those braces completely of course).
After I unbolted those side braces, I figured I would get a good look as I squeezed the brake lever and see if I could see the pads moving at all before I went ahead and unbolted them. Well , what do you know - I barely moved the brake lever before it completely grabbed and felt nice and tight!! Turns out, I neglected to realize the calipers needed a little room to travel outward in order to grab the rotor. In my mind I was imagining them travelling the other way, but it all made sense when I looked at it in motion. Of course they need to travel outward! So after this eureka moment (I couldn't decide whether to cheer or to kick myself), I removed the fender and made a more permanent and slightly larger bend on the braces - just enough to allow the calipers to travel, probably about 1/4" of clearance there now. Brakes work GREAT now! Had a nice though chilly ride into work this morning!
Below are a couple pics showing the braces. I had the bolt out, but you can imagine as it tightens how it would pull the brace hard up against the caliper, even with the short spacer I had in there (not pictured).
Second pic shows the other side brace after I made the little bend, and now have clearance for the caliper.

By the way, just to respond to the question/suggestions (again, thanks so much!!!)
- Hoses are braided upgrades, though I am not sure the age
- I am not sure of the m/c size, though I am curious now. It may very well be a cheapo
- I had heard of others using teflon tape, and I am kicking myself for not doing that when I put in the new bleeders
- Great suggestion on the master cylinder check - I ended up not having to check, but am glad to know of a way how now
- Interesting to know about the rectangular m/c on '79 (which my bike is). For some reason I thought all were the cylindrical type and the rebuilt one on mine was not a match with the original - but looks like that is not the case!

pics:
LH - before bending
LH - before bending
LH.jpg (169.81 KiB) Viewed 200 times
RH - after bending
RH - after bending
RH.jpg (194.38 KiB) Viewed 200 times
'79 GL1000 - Rideable work in progress
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Re: Brake bleeding-wrecked master?

#8

Post by 5speed »

sometimes it's the simplest thing that chucks the monkey wrench in things
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Re: Brake bleeding-wrecked master?

#9

Post by low-side »

I just removed the brace when I did the conversion. It's been a few thousand miles now and the fender hasn't cracked and doesn't make any noise.
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Re: Brake bleeding-wrecked master?

#10

Post by DanH »

Well shoot, I didn't even think about just taking the brace off! I am glad to hear that is a viable option! That might look better than how I have it rigged now.
'79 GL1000 - Rideable work in progress
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