Tech & Wearables

Technical FAQ: Riveting carbon frames, sticky titanium frames, and bleeding Shimano disc brakes

Lennard answers questions about riveting carbon frames, freeing a frozen seatpost, and tricks bleeding Shimano disc brakes.

Dear Lennard,
Any idea what type of rivet gun is used for fastening cable stops to carbon frames? I have a cable stop that has corroded off and can’t find a tool to replace the 1/8” diameter rivets. It shouldn’t be this hard to find a tool.
—Rick

Dear Rick,
We always used a standard rivet gun and aluminum rivets when attaching stops to magnesium and aluminum frames.

This is what Alchemy Bicycles does on its carbon frames:

“We just use a standard rivet gun with aluminum rivets; steel rivets are too aggressive. We had to machine a custom tip so we could get rivets down into the stop but that is a function of the shape of the stop, nothing to do with carbon.”
Matt Macuszak, engineering director, Alchemy Bicycles

It’s not clear to me why you are having trouble finding a rivet gun for this purpose. A standard rivet gun will install 1/8” aluminum rivets and will even come with lots of them.
― Lennard

Dear Lennard,
I discovered your article online while looking for advice to remove a seized seatpost. My issue is that I have a titanium seatpost stuck in a titanium frame. I am not sure what to try at this point. Anti-seize spray hasn’t budged it.
— Tom

Photo: Logan VonBokel | VeloNews.com

Dear Tom,
I don’t know which online article to which you’re referring; I’ve discussed this frequently here, in 2003, 2007, and 2009, among others.

This one, from 10 years ago is the most thorough; it describes the action of ammonia, anti-freeze, and Coca-Cola, discusses many methods for getting it out, including clamping it in a vise and using a slide hammer, and explains how to do it if you resort to cutting off the seatpost.

Here is advice from Moots and from Eriksen Cycles, both of which make titanium seatposts as well as titanium frames, and from titanium frame makers Dean, Merlin, and Black Sheep.

From Moots:
“We would recommend Coca Cola. It makes a sticky mess but can get in there and help break the bond. If the bike is down to the frame, the post can be clamped in a vise and use the frame as leverage to “twist” the post free. Sometimes it works, sometimes the post needs to be cut (in several pieces) out of the seat tube.”
—Jon Cariveau, Marketing Director, Moots Cycles

From Eriksen:
“Liquid wrench dripped into the seat tube from the bottom bracket shell and let sit 24-48 hours. If it doesn’t come right out, then use a heat gun to do 8-10 hot/cold cycles. If it still doesn’t work, cut off the seatpost and use a reamer to remove material.”
—Brad Bingham, owner/framebuilder, Bingham Built/Kent Eriksen Cycles

From Merlin/Dean:
“One option is to set the frame up on either a lathe or horizontal mill and bore the post out. It’s a chore! The other option is if the seatpost isn’t too deep into the seat tube, you can bore out the entire seat tube and then weld in a seat tube plug. Seat tube plugs are available through Paragon Machine Works.
Either way… both are a chore.”
—John Siegrist, CEO Dean/Merlin Titanium

From Black Sheep:
“I would try dry ice inside the seatpost, to try to get it to shrink just a bit. If that doesn’t work, the next step would be to cut it off flush and start reaming the post from the inside with an adjustable-blade reamer. That is time-consuming, but will get the post out, and preserve the frame.”
—James Bleakley, founder, Black Sheep Bicycles

Dear Lennard,
I just did my first bleed job on my Shimano RS785 road discs. Wow, that was so much easier than my old Avid brakes, and a lot of it has to do with Shimano’s decision to put the bleed control on the caliper, not to mention the use of mineral oil. But it also has something to do with the way the brakes actually function, in that the lever never has to be moved during the bleed process.

Next time I won’t wait 4 years and 15,000 miles. And I have to say, it was a pretty impressive difference in the way the brakes feel. They still seemed to work just fine before, but I didn’t realize what I was missing. I’ve been adding fluid and removing air in the levers every 6 – 12 months, but the difference with the new fluid is impressive (I’m sure the new pads all around helped as well). I noticed last week, for the first time, that I was getting some pump up in the brakes on a long downhill, which I guessed was air in the lines expanding. That (and four years of procrastination) was the motivation to finally do a real bleed.

But this brings up a few questions. Your book, and the Shimano manual, would have had me put on a second hose and do a reverse bleed, if you will, into a bag (or on my gravel, since it’s just mineral oil). However, the Park video I looked at skipped this step, and I couldn’t see why it was necessary, so I skipped it. The brakes are solid as a rock – like new, so I have to ask, what purpose would it have served? Aren’t I pushing out all the air during the bleed, or is there a way it can get trapped in the caliper? I did have the bike tilted up when I was pushing the fluid, so the input point was as low as possible.

Also, when I was doing the bleed, I ended up pushing through two syringes worth of fluid in both brakes, until I was sure it was coming out clean (I was glad I bought a full quart – a lifetime supply, as it were). The old fluid was a dirty, burnt color, which got me wondering. Does Shimano add the color as a way to show visually how worn the fluid is? I was wondering if the burnt color was heat-related, or due to contamination in the line. I’m inclined to believe it was heat-related, as it seemed to be spread uniformly throughout the fluid.

I did make one rookie error on the first brake. I didn’t change the pads right away, so I ended up basically overfilling the levers. When I spread them again to accept the new pads, I ended up with a little puddle of fluid on the ground (the bike being upside down). Next time I’ll make new pads be part of the bleed process. That way the levers end up perfectly filled. But from that I learned one thing – the Shimano brakes really are an open system, based on my being able to squeeze the fluid past the o-ring. I wonder if this is why the pads are so much easier to change than SRAM.

I did use the bleed block, but I’ve found it is just not quite thick enough to allow me to put in new pads easily, so once I injected the new fluid, locked the valve, and cleaned the caliper, I put in some old pads, so I could pry the pistons apart just a tad more, before installing the new pads and wheel. With just the bleed block, new pads are always just a touch too tight on the rotor. Maybe the bleed block is enough, but it’s always seemed easier to spread them as far as they will go, and then pump them back down. I always use my old pads to protect the pistons when I do this.

In getting the residual air out of the levers, I rotated the bike up and down in the stand, per the heads-up you gave in your column last year. Shimano says 30 degrees, but I recalled you said it should be more like 50. I just went as far as I could without spilling anything from the top cup.

Next time I’ll try the reverse bleed and see if anything comes out. Before closing the bleed valve, I tried pulling back on the plunger a bit to see if there was any obvious air I could suck out, but all I got was clean fluid. If nothing else, they feel solid as a rock.
— Steve

Hydraulic disc brakes
Photo: Dan Cavallari | VeloNews

Dear Steve,
I’m a bit surprised at the difficulty you’ve had fitting the disc in between your new pads after bleeding. Most of the bikes we bleed are brand new, where we have added longer hoses to fit a huge bike, so your used-pad idea is not applicable. We use the bleed block to hold the pistons apart when bleeding them and then just put in new pads. We rarely have to spread the pads to fit the rotor in. When we do, we use this tool, spread them wide, and pump them down with the lever to the correct spacing.

As you clearly understand, if you just stick a spacer between the pads when bleeding, that’s a bad idea, due to the potential of getting oil on the pads. The bleed block with the pads removed is the way to go.

I like putting a syringe on the caliper and looking at what comes down from the lever. While you had clearly great success just bleeding down from the lever, air can get trapped in corners of the caliper, and pulling and pushing on the caliper syringe can free it. We have had new Shimano brakes that had a big enough piece of stuff in the caliper that we couldn’t push fluid from the caliper syringe—the syringe plunger was hard as a rock. We had to keep repeatedly squeezing the lever and adding fluid to the funnel to push the black piece of who-knows-what into the syringe until it sat on top in there so that we could again push clean fluid with the syringe.

I don’t know why Shimano fluid is pink. Perhaps it’s to distinguish it from other fluids so you don’t accidentally put in the wrong stuff. Magura Royal Blood (also used in Campagnolo disc brakes) is blue, and it, like Shimano fluid, is also mineral oil, while SRAM DOT fluid is yellow and absolutely cannot be mixed with mineral oil. I’m betting the brown color of your fluid is due to heat, not contamination, since it’s on a road bike ridden in sunny SoCal. Not much opportunity for dirt to get in past your seals.
― Lennard


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

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