Sun Mar 27 2011

Parking brake valve mounting

First task today was to make a clamping plate to go behind the parking brake valve which will clamp the valve to the cover and doubler. I made this from a scrap piece of 2024-T4 bar 1/8 inch thick. The instructions say to use some rubber washers and tighten the bolts until the rubber is under slight compression. I think the reason why they recommend that is the valve halves are just stock dimensions on either side and with the machining tolerances such as they are, the bodies could bind on the common shaft if they don't work out right. I clamped my valve in a vise and couldn't detect any binding, so I think this'll be OK. If all else fails, I'll just hold the valve bodies against the sander to ensure the sides are coplanar.

Another odd asspect to this valve design is that the "bolt holes" are actually formed by two grooves that have been turned around the outside of the valve bodies. One side effect of this is that the bolts won't do a good job of preventing the valve from twisting on the bolts a little. Since my lever arm is going through a slot, that would cause the arm to rub on the slot, so I want to prevent the valve from twisting. So, I made up a couple little tripler plates to go above and below the valve bodies. They're 0.040 inch thick and do a good job of keeping the valve from twisting.

Being satisfied with the way the mounting was turning out, it was time to transfer drill all the holes to the side of the cover. I also cut and filed the slot to match.

Last task for the evening was to countersink all the holes in the doubler and dimple all the holes in the side of the cover. Looking at this now, I think I may have gone a bit overboard with the number of rivets. Oh, well.