our 399 has developed a problem with the four wheel drive.when ever you put the brakes on hard or are on wet ground and the front wheels are working to pull the tractor there is  banging and sharp vibrations coming from the front wheel drive system as the front wheels keep turning and then stopping.there is also a like a gear stripping sound.and does not stop very well it also bangs when you turn the front wheels with the four wheel drive on.it is nothing to do with the front axel as this has been looked into can anyone give me any advice on what could be the problem and is it a cheap fix?all peplies will be greatly appreciated

sounds like theres somthing wrong inside the main gear box were the 4 weel drive is engadged disingaged but dont realy know.

may have had a bearing or something broken up and then it has ended up around the drive gears sometimes geting in there!

thanks for the replies.but it would be good to have a few more.so does everyone agree that it is a main gearbox problem??

quick test for you jed if your trying to isolate the problem, if u have a spare hour, get the driveshaft of and drive around, if u still get the same results then its your axle thats suspect,

I would suggest that you have a look at the front diff and front axles before touching the main gearbox as when we have thought about getting another tractor we have always been told to steer clear from the 4wd ones as most of our work is on the road or hard ground where a it is not really needed. But the main reason we were told to keep clear was that at least in the old tractors when they did a lot of roadwork he found that he was for ever replacing front diffs and drives by the stub axles due to the vibrations and potholes shaking them and wearing them out.

I think he said at one point it was getting so bad that he was replacing them every month or so. But say that those were on tractors that were 5 to 15 years old at the time and would now be about 20 to 30 years old.

yyes it has done a lot of road work.and for a while the four whell drive sensor went and it was stuck i four wheel drive for a long time .but the front axel as all been checked out and has all been put back together with new bearings but it still hasent solved the problem but on the other hand when you put the brakes on it brakes on the shaft and so the fault cannot be the main gearbox as it must be between where the brakes break on the shaft and the front axel.but the sound is definatlycoming from under the cab so i suspect it could be the transfer box??