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TB20 GT main landing gear gas shock seal kit, and overhaul

One of mine has lost all the air, and there is some fluid visible, and while I am getting it gassed up (nitrogen) the two are probably not unrelated. So at some point the two gas units will need a seal kit overhaul.

This turns out to be a nontrivial topic, despite me having the Socata TB IPC and the CMM because some P/Ns have changed.

The gas shocks appear to have been made by MECABASQUE who went bust c. 2020. So many of the TB mfgs have gone bust; many were tiny companies. Socata still sell the parts per the CMM but there is no document detailing the current P/Ns for say a TB20GT. I spent a while on the US user group but the owner is avoiding posting the P/N list, presumably because of concern for it leaking out of the “exclusive group” He is supplying it via PMs only.

The seals will definitely be standard parts because nobody will be making stuff like o-rings and similar seals. Only special machined parts will be custom. The problem is the same old one: to find the mfg you need to open up the unit and when it is open on the bench, you cannot fly the aircraft That is the #1 factor which prevents a comprehensive OEM cross-reference being created, like I have here.

The distributor (Troyes, for Europe generally) does not assist; they only order by P/N and back to back, and with no checking for applicability. And Socata will ship whatever you ordered, again with no applicability check possible. And apparently some people got wrong parts. The IPC was last updated 2006 (I have the CD, if anyone is interested) and subsequent changes are kept inside Socata only.

If anyone knows, I would appreciate it.

Shoreham EGKA, United Kingdom
Why not open the shocks and find hydraulic or pneumatic seals as required ? My guess they are metric so not a problem at all. If you cannot find any , send the shock to the maintenance, no need to fly the thing there . We don´t use nitrogen in shocks, just plain air from bottles. Air is 80 percent nitrogen anyway, so forget the last 20 percent. When seals fail, so for a reason: Scored chrome and /or dirt in there ruining seals and chromed faces. Vic

Interesting. Why is nitrogen used at all?

Apparently a lot of the time the actual leak is in the valve at the top, and this is easy to replace.

The other curious thing is that nobody wants to refill the shocks unless the plane is on jacks. That way you can fill them to the specified pressure correctly. But surely an equivalent way is to fill both fuel tanks to the same level and gas up the shocks until a) the required extension is visually achieved and b) wings are level. That would save a huge amount of hassle because going on jacks requires a hangar.

Shoreham EGKA, United Kingdom

During my last annual my mx shop was of the opinion that the ac feels „dizzy“ on ground and recommended a MLG OH during the wintertime. However I asked that in the SO‘s group aswell and it was not generally recommended to without bigger reason. However it was suggested to send in both MLG struts to Gomolzig (I know that you reported no overwhelming experiences according to your exhaust repair), but maybe you should give it another attempt at [email protected] – de facto still the Q how to exchange the struts if this can‘t be done in your hangar and without jacking it up…

TB20 Airman
Borkenberge EDLB, Germany

If I had two spare units I would happily send them somewhere, but this is otherwise too risky.

Maybe it is a good idea to look around some breakers. I have spare avionics already… But these have done 21 years, averaging maybe 150hrs/year (more nowadays) so they have done ok.

You need to jack up at least one side to change the strut – same as changing a tyre.

Shoreham EGKA, United Kingdom
Yeah, airfield politics – but I wonder what these idiots might say when even so you put the aircraft on jacks . Just tell them you got a flat tire , take the wheel home and the shock as well and you wait for spares. They cannot expect to drag your plane into their own workshop for taking on the job in near future I guess. At least this is the situation in my country, no company is interested in some more customers for jobs like yours. They just don´t have the time and staff for more jobs in backlog. So then, I have never come across stories when aircraft owners had any troubles from companies because maintenance was done in owners hangars. This is possibly due to most airfields not owned by maintenance companies but either run by clubs or towns and counties. Just extensive maintenance by aircraft owners is not wanted for safety and insurance matters in hangars – basically. Seems there are just a few o-rings in the shock plus a dust wiper seal. Ebay could be useful for finding this. The filling valve could be modded for an o-ring possibly when they are known to leak . You could replace the shock by a mild steel strut while repairing the shock, so nobody will notice anything in the hangar – but I would not mind.

The shock could be pressurized by some company with filling adapter to 30-50 bar, don´t know. Later you put the aircraft down and bleed the shock at filling valve for correct standing height, simple.



It is obviously easy to calculate how much pressure is needed to gas them up without jacking. Empty weight plus fuel plus contents, work out the surface area of the gas shock rod end… and gas them up to achieve some reasonable position.

One reason nobody wants to do it is because they are filling them using a simple hose with no pressure regulation upstream of the final pressure gauge i.e. they have no “stop pressure” facility. So it is really sensitive.

Shoreham EGKA, United Kingdom
Well, I could not calculate air pressure in shocks when there is a lot of linkage and leverage in the maths. There should be some numbers from Socata in handbooks about an idea of required pressure in shocks. So for a fillup you´d need an adapter hose from compressor to shock and a manometer for stopping fillup. Also the adapter would have a screw for reducing pressure and opening the fill valve. I guess there is a pin in the valve for bleeding it or adding air on aircraft. So that´ll do for setting ride height of aircraft once back on wheels. In photo the brass hex is for opening the valve when the adapter is done up to the shock . Vic


I use These people all the time.
Make a steel rod to temporarily replace the shock (obviously you can’t fly it like that but it keeps the busybodies away) strip the shock to ascertain the seals you need, order them for next day and Bob’s your Uncle.
Do them one at a time so as to minimise your risk.
I’d be very surprised if there was anything bespoke about them.

Last Edited by Stickandrudderman at 02 Feb 18:42
Forever learning

I agree with all great tips above, but my main problem is that arranging a hangar is hard so what I do to the plane has to be “one shot”. Basically stuff needs to be done over a maximum of 1-2 days.

Incidentally, are seals on sliding surfaces (like the ones here) normal o-rings? I think they normally have a rectangular cross-section, and a special profile like this (with or without the spring)

The Socata CMM shows a few o-rings, the top seal, and item 140 which is unclear.

I am informed that the only change from the latest available IPC (dated 2018) and the CMM is that P/N 70661080747 has been replaced by 40422015. No idea why this should be secret

Shoreham EGKA, United Kingdom
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