Thread: Noisy overdrive even when disengaged

Sounds as if a bearing in the overdrive has collapsed - probably either RTC7179 or more likely RTC7171 - or a circlip failure has allowed RTC7171 to move endways so it is not supporting the shaft. The clue is the jumping out of fourth, indicating the back of the gearbox output shaft is not supported. A less likely possibility is that failure of a circlip on the input shaft has allowed the shaft to partly disengage from the gearbox shft, although I don't think it can move far enough. End movement on the quill shaft could also have this effect, again allowed by a circlip failure.

Remove the top cover plate from the T/C and check if it is possible to move the quill shaft with the gear on it sideways at all. In any case, I would remove the overdrive for assessment, and to check the rear gearbox bearing, which is another possibility, although unlikely given the association with engaging and disengaging the overdrive.

John

Thanks John. I think it is not related to the rear bearing as all the trouble began with engaging the OD. Gear box was rebuilt about 7000km ago. OD has always been noisy so my money is on it. Checking the transfer box not an option for me at present (injury). Will I damage the gearbox if I drive this another 60km to repairers? I am thinking the OD is a quite separate unit so its troubles are somewhat isolated. Everything else is (or appears to) be working well.

Depending on exactly what has gone wrong, it may be OK to drive 60km. But the noise is most likely due to the fact that the output gear on the overdrive is no longer meshing correctly with the intermediate gear in the transfer case, and driving any distance with this may cause wear to the gears, although this is unlikely in that distance. The more serious concern is that particularly if, as I suspect the problem is a failed bearing, this may allow the gear to come completely out of mesh, with both loss of drive and possible tooth failure on a gear. If I owned it, I would not drive that distance if there were any realistic alternative!

The previous noise from the overdrive may not be a valid indicator - these overdrives can be quite noisy for a long time without giving any other trouble, although the noise may reflect it having been run dry, which could well be the ultimate cause of a bearing failure. But I still think the problem will be found to be in the overdrive, not the gearbox rear bearing, although this may have been damaged as a result. (Not likely, it takes very little misalignment for gears to get very noisy!)

John

I got it to LVS at Silverdale with no dramas. They will sort it out for me next week. really good guys there. I think my preference will be for the OD to be removed. I lack trust in it and it gives, in my opinion, very little advantage.