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Old 01-18-14, 03:36 PM   #1
deacon mark
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Pump Chuck blows off

I have a Bontrager Pump that works great it is maybe 4 years old but the chuck when clamped down leaks air pumping tires. I then pull the chuck off my other pump and this one does not leak but it will not hold with smooth presta valves. It gets up to 80-100 psi and blows off drives me crazy. I can hold the chuck on the valve and get air to my usual 120 rear and 110 front but this is crazy. It works for thread valve stems but I just got a new bike and I hate to give up two new tubes. I could buy another pump but the reviews are all over the place. This is not rocket science I just want a floor pump and not pay a huge amount. Can I get another chuck that will stick on smooth valves. I hate to ditch a pump that actually works except in these cases.

BTW, new Wilier GT but 10 degrees and snow so have to hold off. I hope the shimano 6700 will shift as well as my 6600 and 7800 dura ace. The FD is better that the 6600 at least on the trainer but the rear seems a bit sticky at upshifting but downshifts great. It took awhile to dial it in but I am hope it will operate as well as my others. The 7800 just is rock solid and great the 6600 is almost as good but a little more strength with the left hand to get from the small to big ring.

While I am at it this is my first go around with internal cables and they look good but wonder if in the long run it really is any better. I am my own wrench a wheel builder so my OCD can kick in on my bikes.
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Old 01-18-14, 03:37 PM   #2
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you open the Presta valve lock nut and tap it and break the seal stiction?
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Old 01-18-14, 03:43 PM   #3
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Needs a new rubber........
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Old 01-18-14, 03:44 PM   #4
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Originally Posted by deacon mark View Post
I have a Bontrager Pump that works great it is maybe 4 years old but the chuck when clamped down leaks air pumping tires. I then pull the chuck off my other pump and this one does not leak but it will not hold with smooth presta valves. It gets up to 80-100 psi and blows off drives me crazy.
This is usually a sign of a worn gasket in the pump head.
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Old 01-18-14, 03:50 PM   #5
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Sounds like a simple traction problem. The threaded valves offer a gripping surface that smooth ones don't.

I don't know how much more traction you need, but start with the basics. solvent on a paper towel to wipe of any residual oil that might be left on the valves from the manufacturing process. If you have it, Acetone (not nail polish remover) is great for this, but uou can also use detergent and water.

Then remove and clean the pump's gasket the same way, so you end up with clean, dry rubber gripping on clean, dry brass. If possible, set the gasket as tight as necessary to work.

If that isn't enough, you need to creatively buy yourself more friction. There are nylon paints that offer good traction, or you can scrape some fine grit off sandpaper or Scotchbrite, and mix it into nail enamel to make a grip paint like that used for stair treads.

No need to use a whole bottle, just mix a dab on a piece of aluminum foil. Paint a traction band on the valve where the gasket holds, let cure 24-48 hours, and you should be fine.
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Old 01-18-14, 03:56 PM   #6
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Get thee one of these and never look back..http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1 Best pump on the market today. It takes a minute to screw to the stem but you'll not lose any air.
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Old 01-18-14, 04:09 PM   #7
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Needs a new rubber........
You reuse these??????
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Old 01-18-14, 05:08 PM   #8
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Topeak threadlock pump head

maybe this?

http://www.topeak.com/products/Pumps...ck_upgrade_kit
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Old 01-18-14, 05:16 PM   #9
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A Velcro strap wrapped around the valve and pump head is the cheapest anti-blow off method I know of. Otherwise a new gasket for the chuck or better yet, the absurdly expensive Hirame pump head if you can find one.
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Old 01-19-14, 09:44 AM   #10
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You reuse these??????
Depends on the circumstances, and actual need. Any port in a storm.....

But ---------- I think I wrote "needs a NEW rubber"....
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Old 01-19-14, 01:55 PM   #11
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Topeak or Lezyne thread on chucks are very good, and can be added to just about any pump. I have both. I also use a Topeak Twin Head on one of my pumps and it's worked well, though it recently needed the seal replaced after ~4 years of regular use.
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