WOTL: Brake bleeder won't hold vacuum

[Blrfl]

Hit a bit of a snag this morning while doing the brake purge and need some troubleshooting advice:

Drained and cleaned the brake reservoir on the handlebar, filled it and purged the left outer pistons just fine.

For the clutch and the front left outers, I ended up using tubing over the nipple because the C-sized adapter that came with my Mity-Vac was too small to fit over it. (And I have the cuts to prove it!) On the front right outers, which is a pretty tight area, I couldn't get it to hold vacuum. I did manage to get the right-angle adapter over the nipple, and that wouldn't hold it either. Capping off either the adapter or the tubing with my finger resulted in the vacuum holding.

I re-capped the reservoir, pumped it up and found that the lever gets nice and firm, much better than it was before I started, so I'm reasonably sure there isn't a leak in the system, at least when it's closed. I'm wondering if maybe the bleeder screw is damaged.

Any suggestions on where else to troubleshoot?

Thanks.

--Mark

[BigTom]

Mark

Sounds to me like you have a handle on it. I think probably you have a tubing leak over the brake nipple. If the pump/tubing/adapter hold vacuum with finger pressure, it is ok. I think I'd take the caliper off before I'd go get a new bleed screw...It could be a crack in the 'inside' part of the screw, but not too likely to me. How hard did that screw loosen? I have broken them, but usually end up with two pieces:) And no questions...

[Blrfl]

Wasn't any harder to break open than the screw on the other side.

I did find some suggestions in this thread (http://www.st-owners.com/forums/showthread.php?t=8110) (should've searched first, posted second). Since opening this part of the system results in the least pain in the tuchus, I think I may pull both screws and do the teflon tape trick.

ETA: I've bled a lot of car brakes and don't think I've ever had this happen.

--Mark

[tdeboeser]

It's happen to me, on more than one bike. I do use a air compressor bleeder so it's probably too much for the line. That said, when I'm done I don't have any visible bubbles, and the brakes are good.

I once watched a MC tech do brakes with a air compressor, same thing, lots of air in the tube, but brakes were great.

EDIT: Seems like your vacuum was high, pulling air where your tubing met the nipple.

Tom de

[BigTom]

Quote by Blrfl
ETA: I've bled a lot of car brakes and don't think I've ever had this happen.

You obviously haven't worked on old enough junk! In my 'private' practice, I did a lot of work on 40's, 50's and 60's Fords. Some of those bleed screws were in deep and hard to pull:)

I had a 'pressure bleeder' (a dentist compressor and tank on a lawn mower body) so I could blow out the whole system and push clean fluid through. The 'Mighty Vac' works just as well or better on short runs, I've never had a problem with the unit, and I have abused it:) Problems I have had have always been with getting the hose fitted tight enough or the fittings themselves.

[Blrfl]

Yeah, well, Tom, we can't all be as old as you. :) My experience with cars starts with a '73 model and works on from there.

Still no love:

Tried several times to get the bleeder screw taped with the system still full and had no luck. To keep my wife from losing her thumb (she was keeping the hole plugged), I drained it and worked on the screw. While I was at it, I attached the screw to the vacuum pump and covered the hole, and it held no problem. With just the right amount of tape I got it to hold vacuum without leaking. :woo

At this point I'm doing it Honda's way: drain, fill, pump, suck. Ran two or three reservoirs of fluid through the left side and got nice, clean, solid flow. Moved on to the right side and after more than 12 ounces of fluid, it won't do better than fluid with a nice topping of bubbles. The lever does pump up, just not very well.

I'm almost out of fluid, so I think I'm going to break for lunch, buy some more and see if anyone has any ideas. Perhaps the tape isn't keeping the threads sealed while the screw is open? Not enough tape, maybe?

--Mark

[HankSTer]

Mark,
coincidentally, just did my brakes and clutch. I bought one of those things like a Mv, but had trouble getting the thing to keep the vacuum.

I now use one of those little one way valve things, and enough hose so I can snip off an end after it's been used a bit. I was able to get a good fit on all of them except the right front outer, I had to loop the hose over the caliper so it came down straight on the bleeder.

It may be overkill but even with the one way valve I still do it the old fashion way, open bleeder as I press pedal, close bleeder before pedal reaches bottom, repeat repeat repeat.

I was able to get to all of em pretty easily except the right front middle which is actuated by the rear brake. Had to crawl under the bike for this one, right hand actuating the brake and left opening and closing the bleeder.

One thing everyone might want to think about, the clutch bleed has made shifting alot less notchy. I actually thought I was due for an oil change.

anyway, just my report on how mine went, hope you get things sorted out where you are.

Regards,

[gene]

Might have to do the old pump and crack routine. you still need a fuel pipe ? I got a mapsoure dics for you next time I see you , maybe saturday ?

[gregj]

The vac might also be sucking air in around the bleeder threads. I have to put teflon tape around the bleeders on the front calipers on my VTX when I bleed them.

[bcst1300]

Gregj has it. The air is getting in around the bleeder threads and into the MV. I had so much grief with about 1/2 of the bleeders. No air in the system so I am sure the air was coming in around the threads. Next time I do this I will drain out the system and teflon the bleeder threads or install quick bleeders they use a threadlock compound too.

[Pat Thompson]

The vac might also be sucking air in around the bleeder threads. I have to put teflon tape around the bleeders on the front calipers on my VTX when I bleed them.

I just did this procedure today and the ones that wouldn't hold vacuum wouldn't hold vacuum before loosening the bleeder. That right front outer in particular doesn't give much room to get the rubber fitting over it. All the center ones seemed to have trouble.

The ones that worked sealed before the bleeder was loosened. The ones that wouldn't hold vacuum wouldn't hold it before loosening the bleeder. So, in my case anyway, the problem wasn't that it was leaking from the threads. For some reason the adaptor just doesn't set right on summa those nipples. :shrug2:

[Blrfl]

Here's how it went down:

Took a break for lunch and got a new roll of Teflon tape while I was out. Pulled the offending screw, put a bunch on and screwed it back in. Like Pat, I was having trouble getting vacuum to hold with the bleeder still closed, and this cured it. I had to do the same with the center piston on both front calipers and the clutch. Both ports on the rear caliper behaved perfectly.

The fronts turned out about as it was before I started, which is not a big surprise since they were pretty good to begin with, the fluid in the reservoir was surprisingly clean and the purge went well. The big story is the rear, which feels a zillion times better than when I started. While braking was acceptable, I think they've been just a little spongy since I got the bike. I haven't been out for a test ride with yet, but based on the feel I think the brakes are in good shape. (I'll do that after the coolant change this morning).

I decided to re-visit the clutch and ended up doing a full drain, pipe tape and refill on that as well. I had to run quite a bit of fluid through it to get all of the air out, and it had to be run through pretty slowly to do it. In first gear, I get some drag on the rear wheel when the clutch is first disengaged, but it does break open after a few degrees of rotation and ends up with slightly more resistance than in neutral. I neglected to turn the wheel by hand before I started work for comparison, but once I put the seat back on I'll be able to test how it feels under Fred Flintstone power, which if how I paddle it out of the garage.

Some observations:

There's something I just don't like about the bleeder screws on the front calipers. It almost seems like there's a very slight mismatch in the threads that causes them to leak air when opened. Only one of the four on mine didn't require tape to seal up, which is a pretty poor ratio.. The screw on the clutch is another issue.

Rob's article was great, but I think I'm going to put together a one-page version that summarizes the steps and includes when to remove/replace the left caliper. It's easy to lose your place in 31 pages.

The noise the handlebar reservoirs make when you drain the fluid and pull air through them is phenomenal. I believe I now know what Ross Perot was talking about (http://en.wikipedia.org/wiki/Giant_sucking_sound).

My wife gets a big thank you for being the Wrench Wench for this project. Patti poured pretty close to a half-gallon of brake fluid and didn't spill a drop. ("I like this stuff, it's a very cooperative fluid.") With breaks, problem-solving and interruptions for things like a brush fire on the berm behind my house took pretty close to 11 hours. The next time should go more quickly if the pipe tape continues to do its job.

--Mark

[c-lapier]

My experience is similiar to Pat's. I used the pointed MityVac fitting that fits into the bleeder screw hole, vacume wouldn't hold before opening the screw. After opening the screw the fluid was foaming and it took longer to drain/fill, but the pedal/lever were firm. Does anyone know where to get fittings that work on the brake screws ?

[Blrfl]

Update:

Got the coolant and T-stat done today and took her out for a ride. Wooo-whee! The brakes are great! I think the clutch has improved the shifting enough that I think if I don't do the brakes every season, I'm at least going to do that. I'll post up about the T-stat elsewhere.

c-lapier: The silverline version of the MV includes a nice assortment of hoses, adapters and fittings that snap right over the nipples on the bleeders. They sell the sets as replacement parts.

--Mark

[Scooterb]

Rob's article was great, but I think I'm going to put together a one-page version that summarizes the steps and includes when to remove/replace the left caliper. It's easy to lose your place in 31 pages.

--Mark


Good, since it's only going to be one page you'll have it done by tomorrow?!?!?!:D

I think I'm going to go look for a MightyVac on Saturday.

[Blrfl]

Ha! I'm going RIDING.

--Mark

[c-lapier]

Mark, thanks for the info on Silverline fittings. Draining the clutch was much easier than the brakes simply because the fitting actually fit.

[Snoweyowl]

I had a problem getting firm pressure after replacing brake lines on one of my bikes. First problem was air at the Y connector for front brakes (dual lines). Tapped the lines with a wrench to free bubbles, still soft. Tied the brake lever to the grip with a bungee cord and left it over night. Next day all was well.

[rosast1300]

I just did mine and experienced the same problems, but now have fluid leaking out of the front bleeder screws. Will the teflon tape remedy an actual fluid leak?

[Blrfl]

It may if the fluid is leaking through the threads and the problem isn't with the screw itself.

--Mark

[rosast1300]

OK, thanks will attempt.