Folks, my 03 td6 has developed a fifth gear fault where by it feels like it wants to change up and down constantly, the result is a juddering when under light load in fifth gear. All is ok under heavy (ish) exceleration and smooth getting into fifth gear. Is this a rebuild/ recon box or an oil change? I fear recon box??

You could try changing the oil only as its a small outlay and you can establish the condition of your box by the oil condition i.e if its just black / brown colour could just be burnt and not serving much purpose in which case an oil change could cure it or if its as above but with particles in it an oil change could help but how long it will last befour a major failure is anyones guess but at least you know and it could give you enough time to put a bit of money to one side for a rebuild hope this helps  onto no6 Range Rover

Everyone needs a hobby

oh that dont sound good, mine has just done the exact same thing. i dropped the oil and noticed alluminium fillings in the sump, i took the gearbox off and its in being rebuilt as we speak. it drove perfect apart from the little jerk every now and again in lock up at about 1500rpm, i thought it best to get it done soon as rather than risk any more damage to the box.

Is it possible to purchase the Sonnax unit and fit it yourself - or does it have to go to a transmission specialist ? If it is a DIY option I would do it myself - even though my box is ok.

i spoke to a company that supply the sonnax parts to gearbox rebuilders and they said it is a specialist job and cant be done by the diy mechanic, they also said there are a lot of sonax upgraded parts and they only fit a selected few parts because of cost. i then spoke to a company in kettering that supply a gearbox with three selected sonax upgrades installed for 1495 + vat, the valve body is your original part that is reamed out to take the two sleeves from sonax for the torque converter and box pressure solinoids then the oil pump is machined to take the third upgrade from sonax and thats it. the other five valves in the valve body are your origanal parts and not changed neither is anything else in the gearbox so i have since decided to have a local guy that i have been dealing with for years do my gearbox, he fits a brand new valve body, machines the pump for new internals and replaces all the clutch plates and seals, rebuilds the torque converter all for 1400.00 quid. i did ask him about the sonax parts but he says they cost a fortune and are not proven to fix the reliability issues with this gearbox and that after a rebuild and yearly oil changes the box should cover another 95k ( what mine has done) before any problems if any and not to worry. looks like where stuck with a chocolate gearbox and the only thing to try and help is to keep it well serviced and not do any traffic light grand prixs.