seatpost slipping: suggestions?

[Climb01742]

Originally Posted by azrider

Hey Climb.....what ever ended up happening with your slippage issue?

I'm obviously bumping because I'm having same issue with my CSI.

I believe I found a post that didn't slip. Which highlights how much variance there is in seatposts and seattubes. I'm now dealing with a seattube that's too tight. Aaaargh!! I find that Fizik carbon posts have an annoying habit of being larger than 31.6 or 27.2.

[azrider]

Another 2hr ride an no slip!!




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[azrider]

Originally Posted by Doug Fattic

Azrider, another frame builder chiming in, how long is the binder slot? I couldn't tell from your picture. If it is not longer than more than an inch it can be too short and won't hold your seatpost.

Hey Doug. Funny that's my name in real world.....No binder slot to speak of......its steel lug on my CSI

Or am I not understanding your question?




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[Doug Fattic]

Originally Posted by azrider

Hey Doug. Funny that's my name in real world.....No binder slot to speak of......its steel lug on my CSI

Or am I not understanding your question?

Sorry I didn't make my question clear enough. I wanted to know how long the slot is on the seat lug. I was referring to the slot between binder on the seat lug. In my experience if it is only 1" or less it may not be able to grip the seat post properly. Let me explain with an example.

Many years ago when I made one of my own frames I used an investment cast seat lug. For some reason I thought a short slot would look good so I only made it 1" long. I was careful to ream the hone the seat tube so it exactly fit my chosen seatpost. It had a tendency to slip under some circumstances. I asked a framebuilding friend of mine and he said a seat lug binder slot should be at least 1 1/8th inch long (28mm). So I extended my slot just those few mm and my slipping problem totally stopped.

[Steve in SLO]

OP, I'm glad it sounds like your problem is solved.
I was half tempted earlier in the thread to tell you to place the seatpost at the proper height and drill a hole through your seattube/seatpost from the side and stick a bolt thru it and tighten. Call it a direct binder bolt. I have seen it done, but on a bike that was so rusty I don't think slippage could have occurred.

[azrider]

Originally Posted by zmudshark

Doug, head over to Harbor Frieght and get their digital calipers.

Thanks Z. I'll do that. You back yet? Switch was flipped yesterday and temps are pretty amazing.....

Originally Posted by Steve in SLO

OP, I'm glad it sounds like your problem is solved.
I was half tempted earlier in the thread to tell you to place the seatpost at the proper height and drill a hole through your seattube/seatpost from the side and stick a bolt thru it and tighten. Call it a direct binder bolt. I have seen it done, but on a bike that was so rusty I don't think slippage could have occurred.

So unfortunately while on a 'bumpy' ride yesterday, my seatpost has indeed decided to slip yet again

Instead of drilling into my CSI, do you think i could drill into the seatpost only a few millimeters above the lug and have the screw 'head' act as stoppage point......like Alessandro Ballan did to his seatpost for Roubaix circa 2007

[David Kirk]

I wouldn't do anything until you know the actual measured size of that post.

dave

[azrider]

Originally Posted by David Kirk

I wouldn't do anything until you know the actual measured size of that post.

dave

Yay homework!

Thanks DK. That's a much more rational approach.




(deep breaths....deep breaths)

[Doug Fattic]

Doug, I am repeating myself but there is one thing I think you should try that will not hurt your frame and may solve the problem and that is to lengthen the slot on the back of the seat lug. It looks like they used a Henry James investment cast seat lug. They are cast with a built in slot. I just measured the slot length on a HJ lug in my inventory and it is just a bit short of 1". The slot length should be extended with a round file until it is at least 1 1/8" or more long. This is measured from the top of the lug to the bottom of the slot. My guess is that after the frame was brazed (so the seat tube now has to be slit to match the slot in the lug) the worker did not extend the slot any lower than the slot already in the lug.

Extending the slot will not hurt your frame in any way and is a lot more logical and easy to do than about any other more extreme remedy being suggested. I'll remind you again that I've found too short of a seat lug slot to be the source of seatpost slipping problems including the case on my personal frame that I mentioned before.

[azrider]

Originally Posted by David Kirk

Here's what I'd do -



With the post in place in the frame put a sharpie mark at the top of the seat lug point. Now remove the post and measure the O.D. of the post just below the head up top and make a note of it. Next measure the O.D. about 1" below the sharpie mark and make a note of that.



Both should be in the 27.15 - 27.17 range for a proper fit. If it's right up top but small in the clamped area the post is all done. It's been compressed. The post looks like it's a LaPrade which were made out of butter and necking down was common.



Without those numbers you are shooting in the dark.



The grooves that were made in this post no doubt didn't help. You may have made the effective OD very slightly larger but you also cut the surface area where the frame and post meet by a large percentage. For this reason alone, even if the post is the right size, I'd toss it and put a new post in place.....and I'd measure it before installing it.





dave

OD at top of sea lug



And 1” below that




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[FlashUNC]

So its either a big 27.0 post or an undersized 27.2 post.

[azrider]

Originally Posted by FlashUNC

So its either a big 27.0 post or an undersized 27.2 post.

Any seatpost's or oem's you metallurgists would recommend?

Should I avoid used?

[David Kirk]

very good. Now we are getting somewhere.

A post labeled "27.2" is meant to fit into a seat tube that is 27.2 I.D. and it is not supposed to actually measure 27.2.....it is a nominal measurement. A 27.2 post will not fit into a 27.2 hole and it needs to be just a bit smaller.

The actual diameter of a 27.2 post should be 27.15 so it looks like your post is right on.

This is of course good to know but it doesn't answer the problem of your properly sized post moving in your frame and this leads me to my follow up question - when you slip the post in does it take some work to get it in? Do you need to push and twist a bit to get it in or does it just slip or fall in?

dave

[Peter P.]

Originally Posted by Doug Fattic

Doug, I am repeating myself but there is one thing I think you should try that will not hurt your frame and may solve the problem and that is to lengthen the slot on the back of the seat lug...

I agree with Doug.

I had a Salsa Ala Carte ATB frame with a slipping 27.2 seatpost. It had what I considered a short slot in the seat lug, as compared to my 2 other bikes. I extended the slot by drilling a strain relief hole 5-10mm below the existing slot, then using a doubled up hacksaw blade to cut the existing slot to reach my drilled hole. Worked like a charm.

[azrider]

Originally Posted by Doug Fattic

Extending the slot.

Hey DFattic. Sorry for not responding earlier, and I appreciate what you had recommended, but once I read the part about taking a file to the frame I got a little too nervous. I have since measured the slot and it's rougly 1.10"

soooo......................