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Heads up! Brake lines rubbing

Y

yankee-flyer

Well Known Member
Bolted the master relay, etc., onto the firewall today and just by chance discovered that one of the bolts used in installing one component (relay?? check tomorrow) is pushed into the bundle of plastic brake lines right where they're held to the instrument shelf by an Adel clamp. Gotta get in there tomorrow and see if the clamp can be mounted another way. Current setup will eat through the plastic lines in no time. Anybody else find this

Wayne 120241/143WM
 
Master contactor bolts

Wayne,
I went out to the garage to check. I see what you mean. The master contactor bolts are very close to the brake lines, perhaps 1/8" to 1/4" from touching. I do not think it will be a problem as long as the brake lines do not move. The plans specify AN4-4 bolts. Using AN4-3 bolts would help. So would using a couple of thick washers under the bolt heads.
Joe
DSCN4187.JPG
 
yankee-flyer said:
Bolted the master relay, etc., onto the firewall today and just by chance discovered that one of the bolts used in installing one component (relay?? check tomorrow) is pushed into the bundle of plastic brake lines right where they're held to the instrument shelf by an Adel clamp. Gotta get in there tomorrow and see if the clamp can be mounted another way. Current setup will eat through the plastic lines in no time. Anybody else find this

Wayne 120241/143WM
Click to expand...

Yes, I noticed this as a potential chafing situation. The starter relay bolts through the firewall can touch the nylon brake lines. I installed a pair of adel clamps around the brake lines directly behind the relay bolt nutplates so that the bolt ends touch the center of the adel clamps and not the brake lines.

Don't have a picture, but can get one next time at the hangar.
Tony
 
Thanks for heads up

I intend to find that location today.
From the looks of it I would think a nylon tie to pull the brake lines together
and a large dollop of red RTV on the offending bolt would protect the lines.
The RTV should not restrict the bolt from being removed later.
 
Cushion clamp

Wayne,
Is the cushion clamp bent in such a way that one side is flat and is up tight against the sheet metal? I am trying to figure out why there is clearance between the parts on my RV-12 and not on yours. After reading your post and taking the above picture, I removed the bolts and put 2 thicker washers under each bolt head. There is now about 1/4" clearance between the bolts and brake lines.
Joe
 
Clamp location.

Hi Joe,
Looking at your photo and at mine, I have about 1/4 inch clearance between brake tubing bundle and the wiring bundle coming through the avionics shelf and zero (or negative) clearance between the brake lines and bolts. It looks like your brake lines are up tight against the wiring bundle but clear the bolts. I'd think the final shape of the Adel clamp could cause that-- I'd like to do something that makes the brake lines clear both. I'm thinking about a 1" (or so) piece of 1/8" aluminum woth a tab on bothends to lower the Adel clamp below the bolts. Not "exactly like the prototype", though.

Wonder how many 12's are out there with those brake lines rubbing something?

Wayne
 
Suggestions

Wayne,
Just because the brake lines and bolts are touching does not mean that the bolts will wear a hole in the brake line. There has to be relative motion between the parts for that to happen. Since all parts are stationary, the only concern is motion from vibration. I do not know how much the brake lines will vibrate.
Here are some suggestions: Remove the cushion clamp and bend it in such a way to maximize the distance between brake lines and bolts. Elongate the cushion clamp hole to move the brake lines closer to the wire bundle. Replace the AN4-4 bolts with AN4-3 bolts. Smooth the ends of the bolts so that there is no sharp edge. Put 2 thick washers under the bolt heads. If there is still a concern, drill holes in the panel above and add wire ties or even two more cushion clamps. Good luck.
Joe
 
I suspect all have the same issue as we build to the plans. I've been thinking about it ever since first noticing months ago at brake installation. Now ready to button up the front pan so it's a good time to deal with what will likely be a problem somewhere down the road. I plan to bend the brake line bundle adel aft to add clearance. If that fails will add a umhw block spacer to move the brake line bundle down about 3/4in. Additionally if I am still anal about it will coat offending bolt tips with silicone to provide a cushion should contact ever occur. If I had it to do over I would consider routing the brake bundle aft of the wiring bundles eliminating the chafing possibilty.
Dick Seiders
 
You might also be able to use a 3/16 ID alum tube spacer under the adel clamp long enough to clear the bolts. This would obviously require a longer bolt in the adel as well. I've seen this on production airplanes several times.

Dick Sipp
Assisting a new -12 builder
RV-4
RV-10
 
I wrapped this section of the brake line bundle with a split, 4" long piece of heavy duty rubber hose and hose clamped it in place. (Same idea as used on the fuel supply and fuel return lines where they come together under the fuel tank) Isolates the brake lines from the bolts, nutplates and control cable housings.
 
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