Gear box problems


I have been having some problems selecting third gear in my F75. I checked the gear oil only to find the oil was all milky brown (water in the oil) I have since change the gearbox oil twice to ensure that all old oil has been flushed out. I am still having trouble selecting third gear on the odd occasion.
Anyone got any idea's

I had the occasional problems

I had the occasional problems with 3rd, cured completely when I put Fully Synthetic oil into the gearbox. If it doesnt leak its worth the cost.

3rd gear going can be the fir

3rd gear going can be the first sign of the dreaded mainshaft nut problem rearing it's ugly head. Don't worry yet. If however this problem persists, and gets worse, to the point where 3rd (or reverse is the other favorit) won't engage you may need this nut replaced. It usually happens around 50,000 miles. The main shaft nut in the gearbow stripes it's thred and workes it's way of the shaft, the shaft moves about, and the gears get missaligned. Typical simtom is gears that wont quite engage, much gear grinding noise, ETC...
It can be replaced by droping the transfure box off of the gearbox, allowing access to the rear of the box. Put on a new nut. Reattatch Transfure. Job, jobbed.

Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.

no nut probs yet but ....

My box has done 90000 without any nut probs, but in a previous post I told the story of the 3rd gear crunch/clatter. Funnily enough, just before this, I had changed the gear oil for semi-synthetic 75W/90.

This oil seems 'thin and weedy' but I believed that it does what it says on the box. Afterwards the gearbox was a bit noisier, but I still believed what it said on the oil pot.

After the big crunch .... (just before winter, so I put off doing the job until it was warmer), I checked the amount of metal filings stuck to the magnetic drain plug. There weren't many, so I persevered using all gears except 3rd. The semi-synthetic had turned a nice shade of brown in only 10000 miles and smelled as if it had been getting pretty darn warm.

A couple of days ago I did a long motorway run and thought the gearbox was sounding a bit noisier than usual, so I drained it again. Out came the semi-syn VERY brown this time after another 5000 miles and looking thinner than witchpee this time. Oh, BTW, the mag drain plug had collected the fallout from the crunch last back-end, to whit a couple of chunks of gear teeth .... OUCH !

Right .... enough of this hi-tech chemical stuff. In went 3 litres of straight 90 gear oil. Guess what, the box is as quiet as you like, needs double-declutching when cold, and is sweet to use when warm.

Now I know the prob with 3rd, I'll get around to fixing that fairly soon.

Hi m8 Would you be kind en

Hi m8

Would you be kind enough to direct me to the gearbox filler plug.

I know its on the right handside of the box as you look at the vehicle from the rear..i.e. the driver's side.

But how do you get to it Unknw