Hi All,

A friend of mine is interested in a TD6 and as we all know, one of the (many ) weak points is the gearbox which has a habit of going pop every 100k miles or so.

Question: If a gearbox has already been refurbished with a "SONNAX KIT" does that mean that it's fixed "forever" and unlikely to fail again? Or does it not really mean anything?

I use the "forever" term loosely here of course! I am just trying to establish whether this kit fixes the bit that usually fails. So in other words, if the advert says "gearbox refurb with Sonnax" does that make it an attractive car over one that makes no gearbox reference at all?

Thanks in advance. 2006 4.2 SC
2019 Renault Zoe Dynamique Nav

There are quite a few Sonnax spool or spool & liner kits available for the 5L40-E transmission so I guess it depends upon how many of these have been fitted.

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The gearbox fails as the alloy used in the valve block is softer than normal, so the bores wear and deposit filings into the oil, which then causes other parts to wear. The reduced pressure then causes the other parts to have accelerated wear and the circle continues. At least that's my understanding.

Sonnax kits involve machining the valve bores and then sleeping the bores with harder steel, hence the issue should be resolved for the duration.

That said, if the box has failed and the lines and cooler and torque converter etc have not all been replaced, the metal deposits could still be in there.

I also understand that not all the valve bores are lined with the kit, but just the main failure items.

I also understand you can have an upgraded sonnax oil pump too.

At the end of the day, I'd take one with the kit fitted over a standard one, but make sure everything else has been replaced too.

There are a few threads on here regarding prices and what's what. I assume you searched for sonnax ?

Is it 2 n's ? 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

Ah, there you go, rrphil is the man. I don't know one end of the gearbox from the other.....  2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport