I have a nearly pristine Specialized Allez (all original Shimano tri-color 600 components) but there is one problem. The seat post clamp has broken. It has been ridden with this temporary "repair" - a bolt with a big washer but I would like to do a classier repair. I've had this about a year or so and asked for some thoughts last year, but was hoping to get some additional ideas. If you have ever repaired something like this, please advise. I appreciate "out of the box" thoughts. Whatever is done, I will do myself and yes...I have considered stripping it and making use of the components. For some reason, I can not bring myself to pitch this particular frame.

Would be a stupid reason to toss a whole frame. What metal is the clamp made of? It's possible you could take it somewhere to have a bit of metal welded on to replace the broken part. Otherwise, your temporary fix may be adequate in the long term, though that's up to you. You could maybe get a cheap seatpost collar and slap it on there- if you did that along with the bolt it might be enough to fix the problem.

good idea, grind it all flush and use a seatpost collar, but if originality is your thing..i'm sure a good metal frabricator can duplicate the broken bit

The ST doesn't extend far enough above the TT to allow for a slide over clamp, so no grinding/filing down to do such. The carbon tubes suggest that any high temp solution like welding a bit back on will be fret with epoxy failure. But a welded bit is the most likely solution that has real merit and a very high cost. Besides the issue of keeping the heat located away from the epoxy is the question of the AL alloy and it's ability to be welded. I see aero space level skills...

Back in the day of Vitus and Alan bonded frames Harry H did many repairs on them. taking the junctions apart and replacing with new. For this frame I doubt that you'll find a donor "lug" without buying a complete frame. I don't think a year of pause will gather better answers. Andy

The ST doesn't extend far enough above the TT to allow for a slide over clamp

ah yes, very observant , andrew!

Buy a quill-type seat post.
Have someone who knows CF repair strengthen the seat tube where the wedge will end up.

A skilled welder WOULD be able to attach a replacement ear. But it would have to be done basically one tiny bead at a time, to avoid heat build up which would otherwise degrade the CF and the lug bond.
And getting a strong seam from layering up many, many tiny spot welds is really tricky.
There are also zinc based low temperature solders which will wet to aluminium.
Might be strong enough. Might not. Might let the CF/lug bond survive. Might not.

I would call/email carbon bike repair specialists like Calfee Designs and ask if any have experience or ideas on how to economically repair.

You could epoxy some kind of metal tubing, (a brass bushing, or an over-sized t-nut?) to the damaged ear. You can they build up an acceptable ear to trap the tube, perhaps with washers on either side to provide a bearing surface. Once cured, you could dremel the whole thing into shape.

West system epoxies are my go to products. You can even add aluminum powder for looks. I'm thinking G-Flex might be best. Look at the "Handy Repair Pack":
WEST SYSTEM | Repair Kits

However, grinding down the remaining lug (and remnants of the broken one) and then welding on a short extension of the ST so that a slide over clamp can be used might be easier/more effective than welding on a bit of metal to replace the original lug.

Dan

Good points. Perhaps epoxy a steel sleeve inside the seat tube to extend far enough above the top tube to allow a clamp?

That's a good possibility, probably the best mentioned so far. A smaller diameter seatpost would be needed to account for the sleeve's wall thickness.

Or what about this...if it's of the same metal, the slip-on clamp could be welded/brazed directly to the ST.

Dan

So I am happy to be wrong on two points. First that a year wait does bring a new and good suggestion forward and that there is a third option which has no chance of damage to the existing frame. I like the suggestion to epoxy a sleeve inside the frame. This sleeve could, before being inserted into the frame, have it's own binder brazed to it and it's ID that of common small diameter seat posts. Very slick and I learned something today. Andy.

I'd be tempted to find some nicer hardware and keep doing what you are doing. However, I assume that is putting a lot of stress on the other lug.

I would try taking a piece of stainless strap cut from sheet and loop it under the top tube against the lug and back to the seat lugs. Drill holes in the stainless to align with the lugs and run a nice bolt through the stainless and lugs. You will need to massage the strap over a mandrel to take the proper twist and shape to sit below the top tube nicely. You can polish the stainless to look like chrome.
I've done a lot of this making custom brackets and it's not hard. Might take a couple tries to get right.

A good welder could "stack" a suitably sized fabrication on top of the existing aluminum clamp. You would definitely need to weld up the split on the existing clamp, so its movement wouldn't compromise the weld, and you'll still have the risk of softening the glue that's holding the parts together.

It appears to be a pretty poor design, overall, and one the manufacturer might want to address. I'd start there, but, if that goes nowhere, talk to your local biker gang, and see who welds their Harley crank case covers. That guy will know his scheisse.

Another thought: just grind off the existing lugs, and square up the top of the clamp. Have a welder weld on another split ring on top that will allow enough room for a standard band clamp.

As Andy points out: The lugs are of an unknown alloy, with unknown weldability -- possibly very poor, given that the lugged carbon construction needs no welding at any point in its manufacture. And as you too mentioned, heating of the lug for welding (and even more so for brazing, as was mentioned somewhere above) could well damage the adhesive joints around the lug -- a problem, by the way, which could not be jerry-rigged away with a long bolt, a nut and a big washer.

Do not attempt to weld. It will cook the bonding epoxy right away. I have done my share of welding over the last 35 years so i have a feel for this kind of thing.

Polishing the lugs with a buffing wheel will be enough to expand them and ruin the bond. My neighbor buffed his and his lugs disbonded and rattled around. Striking an arc would be instant death as the aluminum conducts heat super well.

I would remove both ears and machine a custom clamp. But i also have machine tools that allow me to do so. Maybe you have a machinist friend that could help you?

Since heat is the accepted way of getting epoxy to release all the warnings to not weld or grind really should be heeded.

How about drilling and threading a hole into the seatpost at the bottom of the clamp slot and torquing a nice allen bolt into place..?

I see: its epoxy bonded carbon fiber tubes in aluminum junctions, and the Aluminum seat post clamping ears cracked ..

repairs will be really expensive and may even be impossible without access to more of the Carbon Fiber Tubes
since you May have to cut one to begin to take the seat cluster apart

IDK if they Copied the 'screwed and glued' Italian AlAn frames or Not .. Those, the "lugs" and the Tubes were threaded

RH on one end LH on the Other so turning the Tube around Pulled it's end pieces into the final position ,
then the Epoxy Cured .

Had An AlAn , found Air Freight to & from Italy was Really Expensive But once there the replacement cost was not huge.

But including Shipping It was , so that frame was Retired..


File what is left smooth then make a seat post that will expand , like a Quill handle bar stem. inside the seat tube.

You may have to Hire a Machinist and their shop time to get that..

Or just Fix your saddle Height where you want It, and epoxy the seat Post in Place

with the bolt (or set screw) thru the seat tube and the seat post to make sure it wont Move, as Suggested above..

Good points. I would think the manufacturer would be able to identify the alloy (may even brag about it!), which is likely 6061 t-6, which is very weldable. I think it could be tigged, without overheating, especially just adding a narrow split ring for a standard band clamp. I've never welded aluminum that close to an epoxied joint, but I've done jobs that didn't melt the glue on stickers that were that close to the HAZ. They weren't structural stickers, of course!

The best that I come up with is to:

- grind/file lugs off, sand smooth

- in the same area, drill & countersink holes in lug on each side of slot

- clamp seat post in position, drill & tap through holes in lug, into seat post for machine screws

- install SS oval head screws, fixing seat post in place

Only adjustable by drilling/tapping new/more holes, but should work & look reasonably neat,

& needs only hardware store bits.

It all goes back the the fact the seat lug is glued to carbon tubes and any significant heat will destroy the bonds. Welding and brazing are out of the question.

Wouldn't that put an undo stress/pressure on the CF tube and cause it to crack?

Dan

Does that bolt actually hold the post in place? Maybe have a piece of thicker material milled that half wraps that collar. https://www.grainger.com/product/GRAINGER-APPROVED-Half-Clamp-6RNC1?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/6RNA8_AS01?$smthumb$

My Late Father was The Machinist... You have to machine the expansion device carefully ..

so it does not concentrate the force in any one place .... friction over a Wider area.

its Really ready to just strip and hang it Up, for wall decoration ..


I have made 2 bikes work better, with slipping Seatposts with a second Tube clamp band
above the frame Gripping the seat Post Itself.

on My Brompton It's a Second QR lever type.