Reply With QuoteThis weekend I took the LT230 T-box apart. As the vibration is most noticable from the handbrake area and my rear propshaft was vibrating like hell while stationary at 2400 RPM (new shaft with new UJ made no difference) I came to the conclusion that something might have worn in the T-box after having to cope with the vibes for nearly 200000Km.
reading various treads about changing the input gear with bearings with the box in situ, and changing the bearing on the rear output shaft I just did it. You have to remove the brake drum and rear prop shaft. Drain the T-box for oil. Remove bottom plate as it helps a lot removing the forward bearing race from the T-box casing. Mark the rear output cover (6 bolts) with a screw driver so that the outer cover and the plate that holds the rear bearing can be aligned later-on. remove the rear cover & plate and pull out the input gear. There is a drive shaft adapter that is bolted on the ZF autobox output shaft, p/n FTC5090 that can be replaced simultaneously. I did not know initially that this was a individual part, otherwise I'd replaced it too. By the way: noticed that the ZF shaft had a lot of float, could easily move it 5 mm side to side!Checked with helpful as always Dave Ashcroft from Ashcroft Transmissions and he confirmed it to be normal.
Spline wear inside the input gear was minimal, as it was the cross-drilled type. I modified a bearing puller to remove the front bearing race, and again, a great help if you can reach through the underside of the t-box to hold the puller. carefully drove the new bearing race into position after cleaning everything. You need a press to position the new conical bearings onto the new input gear, and there is a shim procedure (all described in RAVE) where you have to place the thinnest 3.15mm shim under the rear bearing race, put everything back together to measure end float of the input gear. The bearings should receive a certain preload. After that's checked remove input gear, grease-up bearings and use sealant between both cover plates and t-box. Job 1 done!
Next remove output housing (first vibration damper goes). Start by removing all bolts, they are a pain to remove as they are "loctited-in". Then with some knocks of hammer and a piece of wood the output housing can be removed from the t-box. Now remove output flange nut, and flange. Then remove large circlip. I removed spined output shaft with a hammer couple of hits and it is out. Used press to remove bearing. The bearing was SHOT. Could not even turn it freely, it was jamming all the time. Cleaned all, used press again to position new bearing. Circlip back in place. Then used press to position new output shaft. New oil seal, then used new prop flange with new mudshield, 4 new bolts etc. Flange back on the output shaft, anyway, this procedure is documented very well on www.discovery2.co.uk.
Output housing with sealant back in place, as well as bottom cover of t-box. read on US forums that slight overfill of T-box is recommended, so jacked-up rear of Disco and filled with correct gear oil. Finally propshaft back on and for the testdrive....
WHAT A DIFFERENCE!!!!! the "hot spot" around 2400 rpm IS GONE. It now goes through the whole range (under load) without any extra vibes.
I would well recommend replacing the bearing of the rear output shaft. It can be done in under 3 hours if you have the press and other tools at hand.
(Sounds familiar) If the engine is held at or near this critical rpm for any length of time the crank will probably suffer fatigue failure. This critical rpm must be avoided or at the least damped. 
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