Topic: Carbon fiber brake pull rod

[FunJimmy]

So here's my dilemma.

During my last visit to Kelowna, Frank generously gifted me one of his cool Da’Bomb rear brake adjusters, but upon trying to install it I found that the threads on my stock pull rod are either trashed or the rod is slightly bent causing Da'Bomb to bind. Say that (Da'Bomb to bind ) fast five times. 
Either way I need to address this if I hope to use Frank’s cool adjuster.



With the search function currently not working I wasn't able to find if anyone has made custom brake pull rods yet so it’s up to me. 
From the vast amount of carbon fiber tubing available online I ordered a couple of 3K roll wrapped, 6mm ID x 8mm OD carbon fiber tubes.



I’ll machine a couple of billet aluminum (anodized) end caps to accommodate a clevis at one end and a stainless threaded shaft at the other.



Hope to get started as soon as the carbon tubes arrive.

[slikwilli420]

How are you going to reliably bond the aluminum to the carbon fiber?

[firebane]

Since there there isn't that much force you could use a good 2 part epoxy and it would go nowhere.

[FunJimmy]

Since there there isn't that much force you could use a good 2 part epoxy and it would go nowhere.

Exactly! The end caps will have a sleeve that the carbon tube will fit into combined with a 6mm threaded rod down the centre of the carbon tube. Epoxy both interfaces should be plenty strong enough.

[edwardmorris]

I made a custom one using stainless steel rod and clevis. I had to use standard size (non-metric) stuff since the only stainless steel clevis in the correct metric size was only available somewhere in Europe and with shipping it quickly became cost prohibitive. CA may be a different story, but just my 2c.

Thread: http://forums.sohc4.net/index.php/topic,142367.msg1793878.html#msg1793878

[DaveBarbier]

Did something similar for my brake and shifter rod. Used a carbon arrow shaft slipped over threaded rod, added the joints.

You know that the swing arm will hit the brake actuator, right? Haha, just kidding, isn't this the picture you posed a while back where members were giving you sh*t about your swing arm interference and they wouldn't accept, or ignored, when you said this isn't actually how it's run?

[fantino]

Sorry if I'm repeating information you already know, but:

Make sure you give your bond surfaces good surface prep and make sure you have no exposed carbon at the bond interface. Alu + carbon fiber will cause galvanic corrosion if not isolated from each other. Metal parts are typically given a coat of quality primer in bonded composite assemblies (aircraft mfgs like to use that super toxic green stuff, alodine I think. I would just use a good epoxy primer on a sandblasted surface).

I would also recommend post-curing the resin for a couple hours (depends on the resin system, but probably ~150-200F). This will help your bond joint reach its maximum strength.

[drumstyx]

Huh...today I learned carbon fiber is in the galvanic series. I never really thought about the fact that it's actually just graphite.

[FunJimmy]

Sorry if I'm repeating information you already know, but:

Make sure you give your bond surfaces good surface prep and make sure you have no exposed carbon at the bond interface. Alu + carbon fiber will cause galvanic corrosion if not isolated from each other. Metal parts are typically given a coat of quality primer in bonded composite assemblies (aircraft mfgs like to use that super toxic green stuff, alodine I think. I would just use a good epoxy primer on a sandblasted surface).

I would also recommend post-curing the resin for a couple hours (depends on the resin system, but probably ~150-200F). This will help your bond joint reach its maximum strength.

Good tips. Thanks
Would anodizing the aluminum ends provide isolation?

[fantino]

I believe anodization does reduce the electrical conductivity of the surface, but I'm not sure to what extent. It's not a process I know much about outside of cosmetic use. If I were going to the trouble of coating, I would probably just powder coat it, guaranteed isolation with a high quality bond potential.

Really, the easiest way to prevent corrosion is to just make sure your carbon piece is resin rich at the surface, which I imagine a tube like that would be, except for the cut end. You could seal the ends with a little epoxy to be safe. With items like metallic fasteners, usually holes in the composite are made a bit oversize and the edges sealed or an insert is potted in place.

Oh, one last thought, less epoxy is more. Target a fairly tight fit between the tube and it's mating part, maybe 10 thou or so. Thick bond lines will have reduced shear strength.