I just installed a new Michelin tube with a threadless presta valve. When I try pumping the tire, the head of the pump pops off when the PSI reaches about 100. The seal doesn't seem to be gripping the valve tightly when I lock it. I've only used threaded tubes before and never had this problem. Could the seal be worn from the threaded valves? The pump is a Topeak Joe Blow Sport but it's only 3 months old and used twice a week. Is there anyway to fix this? Thanks for the input!

Topeak offers rebuilt kits for most of their pumps, also are you sure the pump is compatible with a threadless valve?

Are you sure you have the chuck latch in the correct position?

You may need a new "O" ring or whatever is inside the chuck.

I use a Joe Blow with Michelin tubes.

are you sure the pump is compatible with a threadless valve?

I believe it is but not 100% sure. Are there pumps made specifically for threadless valves?

Are you sure you have the chuck latch in the correct position?

Yes, it still works fine with the threaded valves.

I'm just surprised that after 3 months the parts would wear out. Does anyone else use their pump on both threaded and threadless valves without problems?

there is a threaded ring on the head of the pump, it compresses a seal around the stem, which is even further compressed when the pump head lever is closed. Try giving the ring a turn or two if possible, to increase sealing pressure of the pump head onto the stem.

I tried that but no luck....it was already as tight as it would go.

this is why a buy tubes with threaded stems

Vredestein Race tubes are great

What if you took a bit of sand paper to the non threaded metal portion of the stem to roughen it up and give the pump head a bit more grip. Also, might give pump head and stem a good cleaning, maybe grease on either part is allowing head to pop off.

...or you can do this for the time being.....

It's a PITA, isn't it?

I have a similar problem with my TopDog pump. My path-of-least-resistance solution is to buy threaded stem tubes whenever possible.

jee, you've even got matching brown thingies on your brake adjuster doovies

Just the pump head is the Pista, which can be purchased separately and attached to any pump. Rubber ring on mine is a bit worn (actually from using this type of pump head on THREADED valve stems). With a new ring, it'll slide onto threadless valve stems without slipping back out.

Yes, definitely a PITA (Fixer - I think he meant Pain in the A**). Good to know I'm not the only one with the problem. I'll try sanding/cleaning as jsharr suggested but I think it's back to threaded stems for me. Thanks for the input!

Sorry for the confusion. Yes, I meant pain in the a**. An acronym I picked from my Dad.

I've tried wrapping a little electrical tape around the valve stem, and that works a little but not much.

Always buy threaded stems, it's just not worth the trouble you are having. Conti makes good long stem, threaded tubes.

I've never had a problem with threadless stems and my Topeak Twister pump. Note that the Joe Blow Sport uses the TwinHead pump head whereas the midrange and higher end Topeak pumps use the SmartHead. It could be that the cheaper pump heads don't hold unthreaded stems as well. If you want to continue using unthreaded stems then you might want to consider upgrading the pump head to a SmartHead. I personally prefer unthreaded stems since they don't chew up my seals and actually a good pump head and an unthreaded stem is probably going to provide a better seal than with a threaded stem. Also, I know this might seem like a dumb question, but are you certain you were using the correct end (presta) of the TwinHead and did you make sure to turn the valve lock the correct way?

I just double-checked and am definitely using the presta side of the pump and locking it in the right direction. I also tried sanding/cleaning and even the electrical tape but no luck. I did come up with an interim solution. I attached a presta/schrader adapter to the threadless valve so I could use the schrader side of the twinhead pump. Works like a charm! It's a few extra steps but at least it'll get the job done until I'm ready to change the tube. My luck this tube will last forever

Buy 99 cent adapter from presta to schrader. Although I think roughing or cleaning surface of stem will help.

Sounds like the presta side of the head is shot. I use unthreaded valved Michelin tubes with my Topeak SmartHead and have never had a problem. I regularly pump to 130PSI.