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Go Back   VAF Forums > Model Specific > RV-8/8A
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  #1  
Old 08-13-2022, 02:10 PM
jklusman jklusman is offline
 
Join Date: Feb 2013
Location: Lafayette, IN
Posts: 19
Default RV-8 Mixture Control Cable Replacement -- More Detail

Among us RV-8 drivers, and perhaps those who maintain other RV models, I suspect there are many who will have to replace the mixture control cable on their aircraft. I am very much indebted to Paul Dye and others on this site for their very helpful posts and responses to my questions on this subject. Paul’s description of the problem was identical to my issue, and I suspect he and the other responders saved me hours of research and maintenance effort with their posts. This post is intended to add some detail to the process for the benefit of those who, like me, have limited experience in aircraft maintenance.
The cable for my aircraft is connected to a Titan 0-360-A1A carbureted engine. While the old cable still worked, it was getting very difficult to move the mixture control lever, especially at low temperatures. While removing the old cable, I had to bend it considerably, and after that the inner portion would not budge. Obviously it was time for a change.
You must remove the top cover of the control lever quadrant to access the cable at that end. However, NEVER, EVER disassemble the control lever mechanism except under threat of death. If you do, you will struggle for a long time to get it back together. Don’t ask me how I know. Also, don’t remove the clevis from the control lever. Instead, you will want to unscrew the cable from the clevis by twisting it at the engine end (there are no jam nuts on the cables at the quadrant end).
To remove the old cable, start at the quadrant end. Getting access to the 11/16” nuts holding the cable housing to the quadrant bracket will require using a ratcheting wrench head fitted to a ratchet- wrench extension. It will take only a very small motion to loosen either nut, which will allow both nuts to be moved easily by hand. My friend Dave Gevers suggests using a punch and small hammer to strike the nut in a strategic place to loosen it if the wrench head won’t fit. Leaving the universal clevis and jam nut on the engine end of the cable will make it much easier to unscrew the cable at the quadrant end.
You can purchase a new cable at Van’s Aircraft. A 55” cable is recommended for the RV-8. Interestingly, the cable I removed was a 60” cable, and it had a couple of excess bends, rising 2-3 inches above level and then lowering to 2-3 inches below level as it ran to the cable mount at the engine end. These excess bends may have contributed to the binding.
Installing the new cable is pretty straightforward, and I found the 55” cable to be a much better fit than the old 60” version. I inserted the new cable through the firewall going nearly straight in from the front, and I left it in that position until it was secured to the bracket in the control quadrant. Then I was ready to thread the cable core to the clevis at the quadrant end. At the engine end, installing the universal clevis and jam nut will make it much easier to perform the next step. It may take two persons to reassemble the cable at the quadrant end – one to twist the inner core at the engine end and one to hold the clevis at the quadrant end in the proper position to assure a mate at that end. I was able to twist it myself from the quadrant end (I have long, thin fingers) and got it threaded on the first try. Then I routed the cable to the right side of the engine, maneuvering it among the various tubes, wires, parts of the engine mount, etc.
Once installed, the new cable can be adjusted easily. I took a photo of the old cable attachments at the brackets on both ends and made sure the new cable was similarly attached. Then, with the universal clevis firmly attached to the cable (but not the carburetor) at the carburetor end, the inner core can be easily screwed in or out at the quadrant end. If necessary, the universal clevis can be further adjusted to get the proper fit at the carburetor end. However, it is easier to adjust the cable where it is mounted to the bracket at the carburetor end to achieve the proper throw of the mixture lever at the carburetor.
The new cable is a big improvement over the old one. I hope this posting is helpful to anyone who faces the same problem.
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  #2  
Old 08-14-2022, 05:39 AM
rv8ch's Avatar
rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
Posts: 5,013
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Good post, Jim. I hope that I don't have to replace these cables, as it does look like it will be a lot of work. I recall installing all three at the same time on the quadrant, and then pushing them forward. That won't be helpful if I have to replace one cable.

If I had it to do again, I would almost certainly use normal vernier cables for the prop and mixture, with a single lever quadrant, since it is easier to make fine adjustments by rotating the knob, rather than carefully moving the levers.
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  #3  
Old 08-17-2022, 07:24 PM
jklusman jklusman is offline
 
Join Date: Feb 2013
Location: Lafayette, IN
Posts: 19
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Thanks, Mickey. It's easier than it looks once you get past all of the dead-ends, which is what my post is designed to help you avoid. I think the throttle cable will be next, but I'm sure I can do it in half the time.
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