Hydraulics

lwford

lwford

New member
Has anyone repaired or had a power pak overhauled recently. I'm having an intermittent problem with the left gear up light going out after about 45 min of flying. Recycle the gear and fine for the next 45 min. I think the up lock hydraulics on the power pak is slowly bleeding off and that is the problem. I put the crate on jacks and pumped the gear up sure enough after about a half hour the left gear went off the up limit switch and the right gear was close to the same. I get in and hand up the pak a couple times and the lights come back and the gear is locked in the well--only to repeat after 30 never been inside a power pack and really don't want to. Best send it out and get 8130 tag. Lynn the crate
 
Are you sure it's the powerpack? If it's only one gear, maybe the o-rings in that gear actuator are leaking. They're an easier and far cheaper fix. Tom Robinson
 
Tom, I'm sure. When you put the plane on jacks and retract the gear into the wells, there should be no movement of the struts. They are held locked up by the power pak. I got under the crate and can pull on both struts. If you leave it retracted and watch the strut very slowly lowers off the left uplimit first and then the right uplimit. The pak was last overhauled in 12/89. My logs say it was done again in 87. Rick Cox will overhaul it with an 8130 tag but it costs about three grand. The joys of aircraft ownership. Get er dun. Lynn the crate
 
I pulled the Pak, it took two days. This is a very messy job. I will tell you how I did it so you won't make too many mistakes. Pull the top part of the cowl to get to the firewall hyd. tank. My tank has a small vent hole in the filler plug, I assume to prevent lock. Drain this tank the best you can because it all flows down to the Pak and on you. Next pull the front seats. the Pak is now exposed and you will remove it up through the copilots seat. Disconnect the hyd. lines and use plenty of shop rags and a drain pan under the plane where the drip pan opening is. Let it bleed till it stops. The Pak is mounted on a plate with four bolts, they are different from the four bolts that mount the Pak to the plate. Disconnect the flap, gear and hand pump levers. I used a mirror to get the forward mounting bolts loose and the rear bolts are easy. Make a barrier of rags so that if you drop a socket or bolt it doesn't run down the fuselage. It took a good 45 min to find that socket! You will need to remove the heat duct under the copilots seat in order to get the Pak out. Once it is out it will continue to bleed 5606 so keep it on a towel. I removed the pipe fittings from the left side of the tank as pictured in Cox Airparts photo. I made it look just like the photo to send to them. Getting in to the Pak mount is a real exercise so make yourself some padding to ease the pain. Lynn the crate :wink:
 
I need to tell you that Cox requires the pipe fittings to do the overhaul. I discovered and was later told by them that the input line has a small ball and spring check valve. Cox needs this to do the Pak test. This is quite different than what I am used to. It seems every time I sent something out with fittings attached, the unit is returned overhauled sans fittings. I was surprised finding that check valve but next day Rick Cox e mailed and said to send him the fittings as there is check valve in there. It appears to me that the seat is custom made by cutting the steel fitting then coning it to fit the ball. WOW don't loose that thing. Make a note in your -2 Flightbook page 28 check valve in pressure line to the Power Pak. It also states a 750B mine is a 750N.I have no idea the difference. There is also on the gear struts a ring that is staked to the strut that holds the felt strut seal in place. My seals were RTVed in and after all these years with the crate they were missing the rings. AAC provided me a strut drawing and it clearly shows the staked ring. Sure as heck not a maintenance friendly design. Lynn the crate. :eek:
 
Thanks for sharing the process of removing the powerpack - it will be very helpful to those that have not been through this painful ordeal. As for the model number, to the best of my knowledge there was never a 750B, the "N" in 750N refers to Northern Aircraft, the owner of record and builder of the 14-19-2 in 1957/1958. The 750P was the variant used in the Pipers. Give me some time and we will have more history on this unit.
 
Certain models of the Aztec and the Apache use the Electrol 750-P. My assumption is "P" is for Piper. Yes, it is close, but with a few major differences... the reservoir bowl is taller in the Piper version and the manual pump handle is different. I am pretty sure the main casting is the same. The new Bellanca factory may acquire authorization to overhaul these units at some point in the future.
 
On a roll, I decided to overhaul the struts and check the gear over very carefully. I found the O rings in both struts pretty tore up and the left one was hanging up (lower leg not extending). I found that the O ring called for was AN 6227-25. Trust me that you will four letter word that to death. Use an AN 6227B-24 works perfectly and the lower struts will extend perfectly. The compression springs were fine but the left kickdown spring was 1/2 inch shorter than the right so I replaced that spring. Now we wait for the return of the Power Pak. Lynn the crate
 
I got the pack back and it had major trouble. Rick Cox did excellent job in refurbing it. I'm in process of getting it together in the old crate. Another word of caution, install the extensions before you mount the pump. I did not do this and it was like fixing a watch to put them on the cotter pins were the toughest. If I did this with pump on the bench it would saved me at least an hour. Lynn the crate
 
Pump is installed and serviced. With lines purged it took 3 pints of 5606 to get it to normal. It purged itself, start working flaps and then the gear after the flaps are operational. I swung the gear 10 times and left them retracted on jacks for over an hour. I then rechecked fluid level on the firewall reservoir. Do not attempt to check fluid in the pack as it is now under pressure a word of caution. This should be good for another 30 yrs. Lynn the crate
 
Well, this sucks, the pack has a weep on the nut that holds the filler plug! I removed it again and returned under warranty. All I want for Xmas is my Pwr Pak. The CRATE
 
The pack was returned with the problem fixed no cost warranty. It is now going back together and off the jacks. It has been a very long haul on this problem. The Crate
 
Good Going!
I just completed assembling 9800B after the annual inspection. There is always something. I found the left muffler rubbing on the lower cowl. Turns out the right muffler was getting loose too.
Your post on this topic caused me to give a second look to the hydraulics... Keep on posting!
 
I got the crate assembled only to find I had no brakes. Both cylinders had no pressure.sh--! I serviced the cylinders, and the brakes came back. I think the parking valve is the culprit and it has never been out of that plane since it was built. Has anyone ever messed with that unit? Lynn the crate
 
That brake thing has happened to me in the past.. after a long time out of service.
Something new to look at.
Thanks,
 
I've serviced my parking brake valves. It has 2 small o-rings, one of which is hard to take out and put a new one back. A piece of twisted safety wire helped a lot
 
lwford said:
I got the crate assembled only to find I had no brakes. Both cylinders had no pressure.sh--! I serviced the cylinders, and the brakes came back. I think the parking valve is the culprit and it has never been out of that plane since it was built. Has anyone ever messed with that unit? Lynn the crate
Click to expand...
Before you tear into the parking brake, look for any sign of fluid leaking around the unit. If there is no fluid leaking the bleed-down of the brakes can't be blamed on the parking brake, although the parking brake may not be holding brake pressure if the o-rings are shot. If you never use the parking brake then that may not matter.

You are going to need those angled head wrenches!
 
yeah Rob, the brake problem has me confused. When the snow gets deep, I'm going to rebuild the brake system. I have found no leaks so where did the fluid go, a mystery to me. The crate
 
In my case fluid was slowly leaking thru parking brake valves even when not in use. Had to bleed LH brakes every two weeks
 
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