# Trek semi-integrated single bolt seat post slipping?



## machoman (Oct 10, 2014)

Anyone's single bolt seat post is slipping? I mean do you find your seat angling down or not being able to hold a level setting even after tightening the seat bolt? 

I looked at the design and while it's used both by Giant & Trek - the single bolt design it looks like a weaker design compared to the 2 screws at the end of the seat post. It relies on friction to hold ones seat rails and it's angle. You can only tighten the single bolt so much to increase the friction to hold one's seat angle. If you sit more towards the front of your seat there'll be more weight there and the seat post will angle the seat down.


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## Peter P. (Dec 30, 2006)

I had this problem with a Ritchey single bolt post. The only thing holding the saddle in position was compression of the saddle clamp to the shaft head.

It slipped a few times the first week I owned it, until I slipped the post into the dumpster.

Now, the only time I'll accept a single bolt post is if the interfacing surfaces are serrated.

Otherwise, it's 2 bolt posts for me.


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## ibericb (Oct 28, 2014)

The answer may be grease. Because of the way screws/bolts work and torque is developed, dry threads may not develop adequate tension upon tightening to proper torque. That means you will reach proper torque upon tightening, but the bolt will still be under tensioned. The answer is lube the threads, and the back of the bolt head where it seats before tightening. Basically grease (lightly) the entire bolt length from the backside of the head down the shaft to the tip, and avoid getting grease on the clamp/rail interface. . Trek offers this simple explanation.

It's not "friction" that holds things in place. It's bolt tension. Friction leads to higher torque when tightening at lower bolt tension.


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## Tlaloc (May 12, 2005)

The seat mast clamp isn't specified for high torque. If it slips you should reassemble it with carbon assembly paste and re-tighten it to the specified torque WITH A TORQUE WRENCH.

You seem to be describing the bolt that holds the seat rails to the seat mast. The torque required for this bolt is surprisingly high. As I recall it's 100 or even 150 inch pounds, but don't take my word for it. Get the correct torque from Trek and tighten it to the specified torque WITH A TORQUE WRENCH.


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## ibericb (Oct 28, 2014)

Well since this was posted in the Trek forum, I'll assume this is on a Trek bike. If not, disregard what follows.

First look on the post/mast for the clamp torque spec. If there isn't one printed there, the following comes from the Trek Bicycle Owner's Manual, page 18:

• One bolt across the seatpost head that uses a 5 mm allen wrench 120-130 lb•in (13.6-14.7 Nm)

• One bolt that uses a 6 mm allen wrench: 150-250 lb•in (17-28.3 Nm)

If it is a seat mast (e.g. Madone ) the spec's are different I believe. The following comes from Leonard Zinn:
Trek Madone saddle rail clamp bolt on seat mast cap 124-142 in-lbs / 14-16 N-m


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## machoman (Oct 10, 2014)

How does torquing to a certain setting help if when i've tightened all i can - the allen key won't budge anymore - and the seat still angle down. This is BS.


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## machoman (Oct 10, 2014)

Peter P. said:


> I had this problem with a Ritchey single bolt post. The only thing holding the saddle in position was compression of the saddle clamp to the shaft head.
> 
> It slipped a few times the first week I owned it, until I slipped the post into the dumpster.
> 
> ...


Unfortunately I"m screwed - my Giant Defy 2015 is an integrated post type so i'm stuck with it. There's no option of trying another brands seat post ect..... If i can't resolve this i'm getting it welded down.


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## ibericb (Oct 28, 2014)

Dry bolts tightened to a specific torque do not reach adequate tension if there is binding in the threads. The result is, a loose joint. It is the tension on the bolt that produces the clamping effect. There have been numerous studies done on the effect. A well lubricated bolt and head mating surface can be tightened to the same torques setting as a dry bolt, but with lube the tension will be typically 20-40% higher. The effect and problem is well known.

Take the bolt out completely, clean it, using a good grease lube it lightly from the thread tip to and including the back of the head, then also clean and lightly lube the mating threads in the clamp pieces. Be sure and keep the grease away from the rail an clamping areas. Then reassemble and tighten top to torque spec. If it fails to hold then, see your dealer because it is defective.


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## Tlaloc (May 12, 2005)

machoman said:


> How does torquing to a certain setting help if when i've tightened all i can - the allen key won't budge anymore - and the seat still angle down. This is BS.


You can't tighten the bolt enough with a hex key because the arm isn't long enough - you don't have enough leverage. When you lubricate it and then tighten it WITH A TORQUE WRENCH you will have a longer arm to apply torque. You will be surprised how much torque this is. Or maybe not. If you aren't going to listen to our advice, why did we take the time to try to help?

Don't even think about working on your carbon bike without a torque wrench. There's a reason that there are torque specifications.


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## ibericb (Oct 28, 2014)

I'll add as my final comment -- there are thousands of these style single-bolt clamp seat posts/masts in use without problem. The design is sound. 

You may have a defective post/clamp, but I doubt it. At this point, you may have damaged the bolt enough that even when properly installed it won't develop the right tension. If you have continued trouble, get a new bolt and clamp set, and then install it THE RIGHT WAY (clean it, lube it as described previously, and as advised by others use a torque wrench. If that isn't clear to you, then take it to your local dealer and have them do it for you.


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