 | Home > Technical > 'Sight-glass' for MT82 gearbox oil level |
 
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| swt Member Since: 24 Aug 2018 Location: Cumbria Posts: 149   
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Like some of those in the 'gearbox dipstick' thread below, I've had a fluid leak from my gearbox (MT82) - indeed I've had one off and on for most of the life of the vehicle:
https://www.defender2.net/forum/topic82869.html So I'd appreciate a way to check the fluid level in the 'box. It seemed to me that the easy way to achieve this was a 'sight glass' arrangement. At first I thought this might be a bit exposed to damage (and therefore catastrophic lubricant loss) but actually even the drain plug on the MT82 is reasonably high up - and I don't drive seriously off road. It would be easy to contrive an M16 x 1.5 90-degree take off with a barbed hose connector to replace the drain plug and, for security against contamination, place another in the filler plug. A hose could then be run between the two connectors and, liquid finding its own level, the oil level in the box could be observed. The difficult part of this seems to be to find a hose which is (a) resistant to the oil temperature; (b) chemically resistant to oil; and (c) clear or translucent enough to show the oil level inside (I'm not really up for fitting a proper sight glass as well). Having been through all the options, it seems to me that PTFE tube is the only one that meets the criteria - but I'm completely ignorant in such matters. Can anyone with better knowledge advise? Yes, I could have the leak fixed, top up the box, not care, risk knocking my heath-robinson arrangement off etc., but please indulge me for a moment! Other warnings about safety and suitability from those more knowledgeable than I gratefully received. |
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16th Jul 2023 5:36pm |
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| The Zee Member Since: 26 May 2019 Location: Salisbury Posts: 288 
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PTFE (polytetrafluoroethylene) tube will withstand up to 125°C but starts to soften as the temperature rises, at about 200°C it's quite soft, and starts to properly melt at about 325°C, but decomposition starts at 250°C,
 it will be match the chemical resistance you need, but is not particularly transparent in the wall thickness that may be needed.
PFA (perfluoroalkoxy alkanes) would be a better bet, it’s more transparent, even less reactive than PTFE, but is slightly more physically fragile than an equivalent piece of PTFE. It’s also stupid expensive!  Zaid-M
www.DefencePhotos.com 2014 Defender 110 Utility, 2.2 Puma, Indus Silver Not just transport more like a religion |
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16th Jul 2023 6:16pm |
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| 1NRO Member Since: 22 Feb 2015 Location: cumbria Posts: 69
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A header tank type sensor that can be activated when desired? Requires a custom filler plug maybe?
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16th Jul 2023 6:44pm |
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| swt Member Since: 24 Aug 2018 Location: Cumbria Posts: 149
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Many thanks for all the useful input. Looks like PFA might be the way to go - and is a reasonable price per metre. No risk of deterioration from continuous folding in this application.
I got underneath and measured this morning. The drain plug is significantly higher than the bottom of the chassis at this point (far more than is required for a 90 degree pipe fitting). It's protected from physical impact on one side by a crossmember and on the other by the exhaust. So I think the risk is acceptable. My daily offroading is gravel tracks and grassy fields, so at least for me this doesn't feel like a problem. Agreed, that the impact of the risk eventuating is significant. It could be mitigated by a valve fitted close against the gearbox, opened only to inspect the level. Then the tube being ripped off by a branch would cause no significant oil loss. I looked quickly, but struggled to find a small, simple, oil-safe candidate. There are some great oil drain solutions (Stahlbus competitors) but they all seemed to have a straight take-off - and I really need 90 degrees to keep it close to the 'box and avoid a great loop of pipework. Pictures of the prototype to follow, when I have time to source the components. |
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18th Jul 2023 8:25am |
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