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Gearbox Overhaul

Updated: Apr 20, 2020

The gearbox had a nasty whine, which increased in tempo and pitch as you moved up the gears and increased speed. Thought it thus might have been a diff (didn’t sound like that’s where it was coming from), or transfer case, or gearbox output shaft bearing. So, I knew I was going to find something nasty when I opened this baby up! As I had run out stuff to do on the chassis (and we were in he middle of a global Covid-19 lockdown!), I knew it was time to bite the bullet and get stuck into the gearbox overhaul. I had done a Landy Series 2 gearbox way back in about 1995, but was pretty nervous of the task ahead, especially as after the last overhaul I had half a dozen parts left over after closing the box back up again! However, the gearbox did seem less daunting than the engine overhaul, so I decided to begin with it...

Gearbox ready on the workbench
Gearbox being removed from the engine

Following the workshop manual closely, I stripped the box down to its individual components, taking lots of photos (else she wasn't going to get back together in any way resembling the original!) and observing each bearing and component in detail hoping to find an obvious cause of the horrendous whine. To my disappointment (ironically), every bearing was a smooth as silk, and every gear was crisp and clean, as if brand new. The elusive cause of the whine was not making itself known, and I was becoming worried that I'd have to reassemble the box not knowing if I had found the cause or not (not ideal, as the gearbox is probably the hardest part to get to once the vehicle is assembled and complete).


Main box, transfer box and output shaft housing

One issue I found (which I secretly hoped would result in a terrible whine!) was that the housing for the main shaft bearing was loose in the main gearbox casing, and rotated quite easily by hand. It also appeared as if the circlip retaining the housing had scoured the casing during rotation. I was not convinced this was the cause of the whine, but it was an issue that would need to be addressed during reassembly.

Whilst pondering over the possible cause of the now infamous whine, I noticed that the 1st gear in the main gearbox had some heat marks on it. It was a black/blue colour, indicating it had reached fairly high temperatures at some stage. On trying to remove the 1st gear, I noticed it was stuck on its bearing, and had to be encouraged off using a press. Once off, it was immediately apparent what the issue was. The bearing had cracked through in several places (no doubt due to the heat) and was binding on the 1st gear. As the 1st gear spins on its bearing at all times other than when the vehicle is traveling in 1st, this would explain the observed effect.


Heat marks on 1st gear and main shaft due to seized bush

The obvious question then was, what caused the bearing to get hot in the first place. on close inspection it became apparent that the bronze bush had been inserted onto the main shaft backwards, and the oil feed holes in the 1st gear did not line up with the grooved oil passage in the bush. In the picture blow, one can even see the black heat mark inside the gear where the (somewhat dry) oil passage on the bush ran, and it is offset from the oil feed hole. If oil could not feed the bush as designed, it must have overheated and failed.


Bush inserted backwards so oil feed holes don't align with oil passage/groove in bush

The only other issue found on the gearbox was some wear on the high gear wheel and intermediate gear in the transfer box. This results in some play in high range. I need to decide whether I replace the gear and shaft (if I can source them), or I live with some amount of play in the drive-train.

Wear on high gear wheel and intermediate gear in transfer box

As I need to wait until lock-down is eased before I can place an order for parts, I decided to leave this job for now...

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alaub
alaub
2020年6月01日

Very neat

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