SIII Gearbox Noisy 4th Gear

Have reconditioned the gearbox, has new mainshaft. bearings and new gears.

Problem is the 4th gear makes a grumble marbly noise and is a bit vibrational most noticeable when coasting along. Seems to quieten down when accelerating. The other gears are working fine. No jumping out of gear.

ive tried shaking the rear prop looking for play in the transfer shaft but that appears nice and firm. Any ideas?

you havent got a 4th gear as such like 3rd 2nd etc its the connection of input to mainshaft ,other gears use input shaft through layshaft to gear selected out,hence noisy in gears except 4th were its quieter is common fault (layshaft bearings),were input shaft bearing would give noise all the time at engine speed, and rear mainshaft all the time but related to gears, possible bearing noise that only shows up at speed or load hence been noticeable in 4th or even diff did you do it yourself or somewhere else ,was it stood after been reconned before running for sometime

jamesmartin said:

you havent got a 4th gear as such like 3rd 2nd etc its the connection of input to mainshaft ,other gears use input shaft through layshaft to gear selected out,hence noisy in gears except 4th were its quieter is common fault (layshaft bearings),were input shaft bearing would give noise all the time at engine speed, and rear mainshaft all the time but related to gears, possible bearing noise that only shows up at speed or load hence been noticeable in 4th or even diff did you do it yourself or somewhere else ,was it stood after been reconned before running for sometime

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Thanks James, your right it was the transfer shaft bearing there. I removed a shim to provide a slight preload to the bearing and that has quietened it down considerably. Not 100% though.

I have a suspect rear prop shaft and uni joint. The front uni slides up and down on the cups although on twisting the joint it has the smallest bit of play. There is noticeable play between the two halves of the prop shaft which prob indicates flogged splines.

Considering that, James do you think its worth persevering with this prop shaft of should I order a prop shaft from Paddocks? Im a bit concerned that the yokes are worn in the cup area if it slides up and down. D.