Gearbox Rebuild

The bottom panel and hand brake assembly were removed from the transfer box, allowing the removal of the intermediate gear cluster. This, in turn, allows access to the internal nuts securing the transfer case to the gear box.

The front bearing cover of the gearbox was removed. This allowed me to see the suspect circlip on the primary pinion. I had expected to find it broken or dislocated from its groove, but it was perfectly intact, so the pinion could not be sliding aft after all. This raises the question over what is pushing the gearbox out of fourth.

The gearbox was fully stripped and cleaned. The lay shaft was checked over and is fine. There is no adjustment on any of its components.

The main shaft and its components were scrutinised before rebuilding, with careful checking of all the clearances and end floats. The second and third gear end float on the bronze sleeve is critical, as is the final amount of combined end float of these assembles parts.  It is set by shortening the length of the bronze bush to suite each gear’s end float on the bush, and then using the correct thickness shim bend the assembly’s retaining clip on the main shaft.  The end float of the first gear is set in a similar fashion, though this is a simpler operation because there is only one gear on the bush and there are no shims or clips to worry about.

The synchro units were carefully inspected for wear.  This included stripping the 1st/2nd synchro down completely and thoroughly cleaning all the splines and detent holes.  The synchro baulk rings were inspected for wear and found to be in near-new condition, so were retained.  Both synchro units were treated to new springs (three coil springs on the 1st/2nd unit and three leaf springs on the 3rd/4th) before being fitted to the main shaft.  WHn stripping the 1st/2nd synchro unit, do so on a flat bench, ideally inside a large box, with a cloth over the top to prevent the springs from propelling the detent ball bearings out as the central hub is removed – the balls shoot out at high speed and could easily be lost.

The whole gearbox has been rebuilt with new bearings throughout. The new lay shaft and main shaft bearings were drifted into the casing with the aid of heating to the casing to expand it. The main shaft rear bearing actually sits in a steel carrier, held in place with another large circlip. The bearing was seated in the carrier and the carrier seated in the casing with a generous application of Locktite “Lock n’ Seal”, which should prevent any bearing slip or spin and also help with preventing oil migration into the transfer case.  There was no trace of any type of sealant being used on the bearing carrier previously, and the carrier had been found to be easy to rotate in the casing during the strip down, suggesting the Locktite had been missed by LR Gen Parts when they rebuilt the unit several years ago.  I believe this explains the oil migration from gear box to transfer box when in use.  New clips were used throughout, on the main shaft, primary pinion and rear bearing carrier, on fitting.

This work has slightly reduced the main shaft end float, but not greatly. I do not believe that to be the cause of the trouble, though, otherwise other gears (especially second) would also be jumping out. Closer inspection of the spigot bush in the back of the Tdi’s crank shaft reveals a wear ridge at the inner-most edge, suggesting the problem may have been caused by the pinion being allowed to move off-axis. The new bush will eliminate this possibility.

The selector rods were reassembled with more new seals, this time of the correct cross-section and smoother inner faces. The previous seals had a rough texture and appeared more like cut sections of rubber hose, but these have a bevelled interior that matches the description in the Green Bible. I also used a thin smear of RTV sealant on the top cover, with more on each side of the lateral detent seals, so leakage should be reduced (it can never be eliminated form these boxes). I am now waiting for new bearings to rebuild the transfer box.

I have included a couple of photos of the splines on the 3rd/4th synchro hub and the inside of the pinion gear which show how the teeth on the Suffix D and E gearboxes (ECM gears) are. Earlier gearboxes have straight cut teeth.