Do your oleos leak?

06-26-2009, 12:58 PM

seawally | Do your oleos leak?


With only 10 hours on my plane, this is my first oleo encounter. After experiencing seepage, I decided a rebuild and addition of Granville Strut seal was called for. During the process I found a couple of interesting discrepancies. #1 - Page 38 (July 1996) of the MLG manual calls for adding 17 cubic in. or 245 cc. of oil. Well, 17 ci. is actually 278 cc. I found over 300 cc. in each. #2 - After having had the oleos modified years ago, Page 19 Special (June 1994) by shortening the piston tubes by 4 inches, they now have 4 inches of tube showing that can penetrate the cylinders. Trouble is, the cylinders have over 6 inches of available travel space, so if gas pressure is lost, the piston tube over-penetrates the cylinder and stops when the Schrader valve 90 degree fitting hits the top of the cylinder. ( with the weight of the airplane on it) The piston will not bottom out as it used to.

Questions: #1 - What is the proper amount of fluid to use (Bob Darrah - how much extra did you add per your post #2683, 5/10/07), and #2 - why not inflate to 700 psi before installation?

Suggestions: Don't let leaks get bad before rebuilding, and make darned sure to keep oleos inflated. Wally

07-15-2009, 03:09 PM


Well now is a good time to answer since I have another leak. There has always been a very slowwwwwwwww leak in the starboard oleo. Not bad untill now. There is fluid on the outside top of the oleo. So today I went back into some old notes for the plane and discovered that Grandville had already been added to the strut However that was before I rebuilt it with new O rings last year. So, I guess tonight I will be adding Grandville to the oleo.

On another note, I talked to Alan and wondered why a second O ring was not added to the oleo for a double seal. Good question.....

Hey Wally, Yep the book does say to fill to 16.66 - 17 cu in. So that would be 278. ml, 9.4 oz, 278.5 cc, or 56.519480519 teaspoons. I guess 245 cc is wrong..!!

At last we enter the nitrogen much...? Well I guess that depends on that toe in or out thingy calculation. At 650 the wing is low, at 700 the wing is just right......

07-15-2009, 04:08 PM

Tom Saccio | Oleos

Hi Guys, I'm having the same problem. Mine are leaking and I can't seem to stop it. I put new seals, added Granville, none of it seems to help. I called PlaneMakers and they said that the Seals are a specific size. They get them from McMaster Carr. They are going to send me some and I will try that to see if it works. I'll let you know the results. What was the answer to double sealing? Are you going to try that? Tom Saccio

07-15-2009, 08:34 PM

Fred Lohr

i have had problems with leaking oleos, but mostly on the nose gear. I tend to pick up scratches on the inner tube and once you do, no amount of sealer or replacemnt o rings will help. Same applies to the maingear oleo. If there are any small scratches in the inner tube/sleeve, you may as well just replace it with a new one from alan at evansburg tool. otherwise just a few landings will ruin that single o ring and you will leak again. the surfaces of these things are anodized aluminum and are not really very hard when it comes to a resistance to surface scratches. A second generation design would be welcomed. that design might include a "wiper' seal, two o rings, something to resist "toggle" between the inner and outer tubes especially on the nose gear,

and maybe consideration of hardened chromed surfaces on the inner tube.

I wonder if we have anyone with oleo engineering background to look at this.

07-20-2009, 01:53 PM


I did some searching.... I assume we all use the Aeroshell Fluid 4 - 60421 which replaces Mil-H-5606A. This is most likely used in the brake and hydraulic reservoir also.

The following was taken from the AeroShell site:

AeroShell Fluid 4 is intended for use as a hydraulic fluid in undercarriage

retraction mechanisms, flap jacks and control mechanisms, brakes, shock

absorbers, automatic pilots, oleo legs, tail wheels, servo units, etc.

AeroShell Fluid 4 is also suitable for lubricating de-icing pumps and


AeroShell Fluid 4 should be used in systems with synthetic rubber

components and must not be used in systems incorporating natural rubber.

The latter systems require castor base fluids with which AeroShell Fluid 4 is

not interchangeable. Refer to the General Notes at the front of this section

for more information on compatibility.

AeroShell Fluid 4 is compatible with AeroShell Fluids 31, 41, 51, 61 and

71, although it is not recommended that AeroShell Fluid 4 is used in

systems which require the use of a superclean fluid nor should it be mixed

with superclean fluids for operational reasons.

Chlorinated solvents should not be used for cleaning hydraulic components

which use AeroShell Fluid 4. The residual solvent contaminates the

hydraulic fluid and may lead to corrosion.

AeroShell Shock Strut Fluid (SSF) and AeroShell Landing Gear Fluid (LGF)

are mineral hydraulic fluids (MIL-PRF-6083 and MIL-PRF-5606 respectively)

to which additional additives have been added to improve the extreme

pressure characteristics and the fluid’s natural lubricity. The lubricity agent

provides a stable thin film layer to the metal surfaces at mild operating

conditions. When severe conditions exist (landing/touchdown), the extreme

pressure additive supplies the load carrying needed at the metal-to-metal

surfaces to prevent the occurrence of such phenomena as "ladder cracking"

and "slip stiction" of the piston component of the landing gear.

AeroShell SSF is AeroShell Fluid 71 plus additives.

AeroShell LGF is AeroShell Fluid 41 plus additives.

At this point I am wondering if SSF would be a better fluid to use in the oleos. One of the reasons why the SSF was not used is because untill recently it was not available in the US. The viscositys are the same between the fluids at 14.5 @ 40c. Since they are the same the leaking most likely would not dissapear. If the viscosity were to be increased to 22 @40c this might stop the leak or as discussed before a second seal with a wiper seal...........

I recently added Grandvill's to my leaking oleo, at 1st it wasent holding. After a few laps around the pattern with a few touch -n- go's, it seems to be holding.