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Discussion Starter · #1 ·
OK, this is my fault, I over tightened the big assed U-bolts I use to clamp my trailer hitch to the seat post, so I cracked or split it......

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I'll be buying a new seat post tomorrow.

This one was aluminum, and until I crushed it, it had lasted a LONG time, like 15 years, but I'm wondering if there is something stronger out there on the market?

I plan on putting some hard rubber on the face of the red steel part of the hitch that goes against the back of the seat post, and not over tightening it, but still, is there something or some brand I should be looking for that is stronger?

Cheers!
 

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there were a couple cromo seatposts made awhile back, tioga, syncros maybe?
material's kind of irrelevant, whetehr cromo or aluminium or titanium, if it's designed for xc use... ;)
get a DH seatpost, diabolous or somesuch.
 

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You could likely use a similar seat post to the original if the load was spread better and you didn't over do the tightening. Especially with a mod or two on the u-bolt clamp.

A couple of ideas use them or not:

1. Spread the load: use the tubular part of the old seat post cut into about 1/3 sections lengthwise to go under the u-bolts and on the clamp side to reinforce the post and spread the pressure up and down the post and clamp it in a more radial fashion and not crush the post flat against the clamp. Some J. B. Weld on the shim (former post) might make one or more guides (bumps) for the u-bolt side to keep it in place while assembling/tightening, and a bed/fastening to keep the clamp side one from shifting doan until you get it tight as well as transfering force to the whole shim not just a narrow vertical contact point.

2. Use a torque wrench and test for the minimum setting that prevents the hitch pivoting or walking down the seat tube and use another 2 foot pounds or whatever is equal in N-m.

An alternative to a torgue wrench setting is to use a short stiff spring and tighten and test until the hitch is stable, ideally the spring should just fully compress at tight enough to prevent pivoting or walking of the hitch on the post. Then you know you are tight enough when the spring is compressed.
 

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weirdo
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I don`t know about seat posts, but I have a few other ideas too. I was thinking along BrianMc`s line of spreading the load with another piece of tubing between the post and your clamps. I have no idea if you can get a little bit of machining done on the cheap around there, but if you can`t find a tube with the same ID as the OD on your post, it would be a quick job to bore a smaller ID to fit. Or just let it stretch to conform when you clamp it on. Also, your rubber might do a lot of good bt not needing it so tight. Except that personally I`d try for soft rather than hard. I`ve used little pieces of inner tube from time to time when clamping stuff onto my bars because it grips much better that way. Like Brian says, use them or not- I don`t think either of us can offer guarantees, but at least we`re cheap :D
 

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Discussion Starter · #5 ·
Thanks guys for all the ideas, I'll update you all on it when I get something worked out! :thumbsup:
 

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Discussion Starter · #6 ·
OK, I got a new seat post, made by SRAM, it was the heaviest walled unit there, so I hope it survives, I also reworked the hitch, I'll post pics later.

I could not resist the temptation, and I bought new wheels too! :D
 

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Another idea, combining Rodar y rodar's:

IF you are free to replace the heavy chunk of steel mounting plate that the U-boles mount to, as part of 'rework the hitch', this idea might help:

Find a length thin walled of steel pipe or thick wall steel tubing with an ID close to the seat post's. It only needs to be thick enough to survive welding to the hitch, that thickness will be strong enough. Cut it to most of the length of the exposed seat post, or as much of it as you want to 'sandwich' with the hitch mount. Cut it lenthwise in two. If slightly smaller ID that the post, use the part you cut off the lenght as a mandrel to hammer the halves a bit wider. If a bit larger in ID that the post is in OD, put these wider pieces in vise and cold set (a little at a time and test fit) until the halves nicely fit the outside of the post. Weld one half to the hitch after removiing the square plate, at the height you want it. Use four stainless steel hose clamps, two top and two on the bottom to clamp the seat post with the free piece of half pipe on the front of the post. You could use U-bolts but if you do, I'd suggest lighter ones with the saddles on the back side to fit round pipe. The pipe pieces spread the load, the clamps are a radial force that uses the strength of the round seat post rather than crushing it, and four wider bands (if you use hose clamps) spread the force more than two or four U-bolts and you'd really have to work at overtightening them with a socket and ratchet when a nut driver will give you all you need because of the screww drive they have.

As before, this is use at own risk or not. This should lose some weight, at least covering that added by the thicker seat post.
 

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Discussion Starter · #8 ·
Thanks for the idea Brian, if what I've done results in failure again, I might just use you idea :thumbsup:

What I did was use some putty to make a support around the back half of the seat tube.

First I sanded off all the paint on the back of the thick steel plate, and then I drilled some shallow holes to "Dimple" the plate, this will give the putty something to hold on to.

Machine Wire Cylinder Steel Household appliance accessory
Sorry for the lousy pic, I was in a bit of a hurry.

I then put the old seat tube in place, the non-oval section that was in the bike frame (I did check it too, it was still round!) I first wrapped the seat tube with some clear wrap stuff, in retrospect I should have just waxed the seat-tube, that would have worked better.

I used this putty, it is a two part stuff, comes in a stick, the outside and inside of the stick of putty need to me melded together, then you have about 5 minutes to work with it until it gets rock hard. The putty stuff is very good, I've used it on motorcycles before, when something broke, I've drilled and tapped this stuff and it has held up for many years.

I melded the putty, and then I put a blob of it on the back of the hitch, I put the seat-tube in place, and tightened (lightly!!) the U-bolts, I then pushed the molded the putty into the shape I wanted, making sure it got pushed down into the dimples on the steel too. After about 5 minutes when the putty was hard, but not rock hard, I removed the U-bolts and did some adjusting. Once the putty is set and hard, it is almost like steel, thus working it a bit when it is still somewhat soft, has it's advantages.

I removed the seat tube and then I put some #240 grit sandpaper on the seat tube and sanded the inside of the putty a bit to make it smooth and to enlarge it just a touch. I let that set a side and harden for about an hour, then I put a thin piece of rubber around the seat tube.

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(you can see the hitch with the putty on it sitting on the rack of the bike, the pic makes the curve in the putty look oval or something, but I assure you, it is round)

I am hoping that this will take up any slack in the hitch to seat post connection and might even provide a bit of a damper to the clackity clack of the connection between the hitch and the trailer.

I then mounted the hitch, and I carefully tightened the U-bolts. I do not own a torque wrench that goes down to a very low number (on my Christmas list!) so I was careful and consistently tightened them down in a crisscross pattern. When I had it tight enough that nothing moved, I turned each nut an extra 1/4 turn. I also checked the tube above and below the U-bolts, front to back, and side to side, with my vernier caliper to check. It measures 27.2 front to back and side to side, so it is still round.

The old seat post, in the area that it was clamped, now just sitting on the bench is certainly NOT round, it is 27.8 side to side and only 26.4 back to front, so I certainly squished it.

Here is how it looks now.....

Bicycle accessory Bicycle part Bicycle Bicycle frame Metal

Time will tell if this holds up, or if I have to go something more like Brian suggested.

I also bought new wheels :D

The Shimano WH-M505 wheel set....

Bicycle tire Bicycle wheel Wheel Bicycle wheel rim Bicycle part
I know, budget wheels, but they are strong and should last a while, that is what is important to me. I haul around a trailer full of beer for deliveries and I still weigh 266 pounds, so I'm not what you would call "Concerned" about the wheels being a bit heavy.

This is the fourth set of wheels I've had for this bike, let's see, 22 years and four sets of wheels, five and a half years a set, not bad I guess, but the first set only lasted about a year (cheap, and I did lots of off-road riding at that time) I paid about $177 USD for the set, including tax, I think I got a good price.

Now I just have to wait for the spacer for my 7-speed cassette to come in, the wheel is designed for 8 to 9-speed cassettes, but I'm told with a spacer the seven speed cassette I have will work fine. I sure hope so, because the shifters I have are also 7-speed, I really don't need or want to upgrade to an 8 or 9-speed cassette and also have to buy new shifters, no need for that.

This bike will continue to see daily use as a workhorse, one day, down the road, when I get down to say 185 lbs (I've lost 36 pounds so far!) I will most likely celebrate and buy my self a new bike, but the old Cannodale will keep on being used.

Cheers!
 

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Same comment as rodar y rodar, pretty much.

One suggestion/question: did you measure the old post at the u-bolts' contact points on the front of the old post as compared to between them or above and below them? The reason I ask is I think that would be telltale for whether the u-bolt pressure points are OK in your current setup or you need a shim shaped like the post under the hoops of the bolts to help spread the force on the front. It would be easy to add to what you have. If all the deformation of your old post can be attributed to the narrow vertical pressure point on the backside, your current setup should work well. Time will tell.
 
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