Vibration in 3rd and 4th Gear

Hello all. Got a problem that I am hoping you can help with.

My 1995 Defender 100 300TDI has recently had a reconditioned transfer box fitted due to excessive backlash. All has been well for the last 3 months.
Recently it has developed a vibration under acceleration, but strangely only in 3rd and 4th gear in a speed range of 30 to 50 mph.
I have tried greasing the UJ's which seems to improve matters, but only for a few days. I have also checked them for play (3rd gear move it forward and back). Nothing doing.
I have noticed a chirping sound as the grease wears off and the vibration gets worse. It did remind me of failing UJ needle bearings, but as I say all appears ok in that department.
Any help gratefully received.
All the best & Thanks Jerry

The uj's might look ok under tension mate but they wont when you take the pressure off. the only way to check them proper is to take them off. it does sound the likely cause to me especially as you say it goes when you grease them.
quite an easy and cheap job to do to boot.

Thanks for quick reply will try changin them as you say cheap fix. Will let you know how it does.

it's definitely the UJs.

I've just started having the same problem on my 97 300tdi 90.
was that what the problem turned out to be ?
How easy a job is this to fix ?
Any help is much appreciated !!

UJ's for sure had the same problem. Its worse if its the rear prop shaft.

Parky91, there is some press fitting or hammering involved in removing and fitting the UJs, could take you the whole afternoon if you've never done it before, but for some experienced Landrover mechanic, it would take about 40minutes or so.
But if you want to try fitting it yourself, make sure you put some grease to hold the small pins when fitting a new UJ otherwise they will keep falling off and may miss out a few.

hmm, well i've got a mate who has a reasonable amount of experience, so will get him to help me out.
So what stuff will I actually need to buy ? just new UJ's ? or anything else needed also ?
Cheers for your help !