lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> I've run into a problem with the gear hydraulics in my L235 that I have been rebuilding. Possibly someone out there has a solution or suggestion. When running a retraction test on jacks , the gear retracts nicely, until all is tucked away except the last inboard door (on the right). At this point I detect a slowing of the pump, and the upper (high pressure) switch activates, and the pump turns off. Gear lowering works normally, both pumped down and in free-fall. I have tried adjusting the upper pressure limit switch, but reach the internal pressure limit of the pump before retraction completes. All struts and doors operate freely, without any binding or friction. I have removed, inspected and returned the door sequence valve, and the system operated correctly only once immediately following this procedure. The following retraction cycle stopped at the same point. I have verified that the hydraulic reservoir is full. When replacing the pressure switches several weeks ago, I noted that even after opening the free-fall valve, their remained significant pressure in the system, and fluid was ejected from the loosened fitting for some time. I suspected that both the high and low pressure sides of the system were at elevated pressure, causing the shutoff with insufficient differential pressure. This evening, a released all pressure in the system by loosening a fitting at the high point (nose wheel well), and repeated the tests, with no change. I have also noticed that as the gear is retracting, the level in the reservoir rises. I assume that this is to compensate for the displacement of the pushrods in the retraction cylinders as they move, but I am not certain that this is the case. I admit that I don't understand how the system can "self bleed" as described in the construction manual by simply cycling the gear repeatedly. Given the amount of fluid I lost when replacing the switches, I suspect that I still have air in the system, but I fail to see how this could explain the symptoms that I am seeing. The system has been working without a hitch for months leading up to these final tests. The only things that I have done recently that could possibly have impacted the gear system were the replacement of the pressure switches, after which a successful retraction tests was performed, and recent replacement of the brake lines from the caliper body into the wheel wells. The system holds pressure well, as the pumps do not blip on continuously, in either gear up or down state. Any suggestions would be appreciated. Tom Low N31CD L235 thomas.low@sri.com LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com.