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Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:31 pm
by Ufgators
I have a Parlee z0 fitted with the proper size Thomson masterpiece seat post and I notice that the post slips a
Couple millimeters per a 2 hour ride with 6nm of force on the clamp and a generous coat of carbon paste. Any suggestions? Thanks

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:37 pm
by Devon
May be a silly question but are you 100% sure it's the right size post? Should be 31.6mm

Is the post/inside of the seat tube worn at all?

How much do you weigh?

A quick/easy temporary fix would be to wrap the inserted end of the post in a thin layer of electrical tape.

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:37 pm
by Weenie

Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:51 pm
by Ufgators
alexh wrote:May be a silly question but are you 100% sure it's the right size post? Should be 31.6mm

Is the post/inside of the seat tube worn at all?

How much do you weigh?

A quick/easy temporary fix would be to wrap the inserted end of the post in a thin layer of electrical tape.


Just measured it with digital calipers. The post measure 31.6 millimeters so probably within tolerance. The post isn't worn and the frame is new.

Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:51 pm
by Ufgators
I forgot to add I weight 155 pounds

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 1:54 pm
by Devon
I see no reason why it should be slipping in that case, unless there is an issue with the clamp? Try some threadlock/a new bolt maybe?

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:08 pm
by MajorMantra
Could be your torque wrench is out?

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:19 pm
by Rick
There has to be something else going on here. There is nothing about a Thomson seatpost that should allow unusual slip.

Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:33 pm
by Ufgators
Should I try more clamping force? Say 6.5nm?

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:48 pm
by Devon
Ufgators wrote:Should I try more clamping force? Say 6.5nm?


I'd personally check the clamp first.

Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:53 pm
by Ufgators
alexh wrote:
Ufgators wrote:Should I try more clamping force? Say 6.5nm?


I'd personally check the clamp first.


What do I look for in defective clamp?

Re: Thomson post slips even with tacx

Posted: Thu Jun 13, 2013 2:57 pm
by Devon
Ufgators wrote:What do I look for in defective clamp?


Shearing of the bolt/nut, or the clamp may be slightly too large for the frame and therefore unable to provide suitable clamping force.

Posted: Thu Jun 13, 2013 3:25 pm
by thisisatest
Grease between the clamp and frame. Grease bolt threads fully, and under the bolt head. As before, Tacx paste on post to frame.

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Re: Thomson post slips even with tacx

Posted: Fri Jun 14, 2013 8:24 am
by ghisallo2003
I have always found that the Masterpiece posts are marginally smaller than the normal posts from Thomson. I wonder if the extra machining takes a small amount from the overall diameter. I know it is not the principle of WW, but if the torque is correct and the clamp ok, I would try another Masterpiece to see if it is a case of upper-lower tolerances, and then think about a non-Masterpiece. The weight savings are modest compared to having a robust seat fitting.

Re: Thomson post slips even with tacx

Posted: Fri Jun 14, 2013 11:20 am
by 1415chris
If the Masterpiece is not robust, nothing is robust :wink:

Re: Thomson post slips even with tacx

Posted: Fri Jun 14, 2013 11:20 am
by Weenie

Re: Thomson post slips even with tacx

Posted: Fri Jun 14, 2013 11:25 am
by sungod
i had a similar problem with my ax europa post

6Nm, maximum rated torque - wrench checked against calibrated one at work
clamping bolt/nut threads clean and lubed
inside of seat tube degreased
the post is a tight fit

tacx paste didn't solve it - pink paste

finish line paste didn't solve it - white paste with gritty feel

but a mix of the two pastes did, at 6Nm the post no longer slips, been ok with this method for 3 years now

have to reapply paste mix any time i remove/refit the post, i.e. after boxing the bike for travel, otherwise it will slip without fail