Preamble

When driving in 4th gear, the noise from the gearbox was becoming intolerable. This isn’t a new phenomena but it was getting on my nerves.

What I had (wrongly) assumed was that the noise whilst in top gear was coming from the input shaft and constant gear (4th gear). Thanks to the knowledgeable folks on the Series 2 Forum, I was spared a lot of unnecessary work. Transmission noise in 4th gear is coming form the transfer box not the main box. When in 4th gear, the power for the engine is transmitted straight along the main-shaft to the transfer box.

The plan had been to remove the transfer box and replace the intermediate and output gears with the original ones I took out in 2017. A friend reported that the noise could be reduced by replacing just the intermediate gear. This can be done with the gearbox in-situ and this is what we did, with positive results.

Why the noise? All the gears, bearings, and thrust washers were new (not Britpart or that ilk); the intermediate gear end float was set correctly as was the pre-load on the output gear. The box was noisy from day one. So this only leaves the quality of the parts open for debate.

Process

Friend Jeremy came over in his lovely, 6 cylinder, Series 2a Doormobile… fresh from a (not uneventful) trip to Sicily. This guy can fix anything!

Order of operations as follows:

  1. Disconnect propshaft
  2. Remove handbrake assembly and output flange
  3. Remove transfer cover plate and speedo cable
  4. Remove overdrive.
  5. Remove intermediate gear pin
  6. … catch the intermediate gear as it drops out of the casing and extract the thrust washers.
Remove the rear propeller shaft. This is best done by putting an axle stand under one end of the rear axle to lift a wheel off the ground. This way the prop can be rotated allowing easier access to the nuts.
  • Remove handbrake drum
  • Remove output flange and finally the hand break assembly
No photos of the OD removal but here’s the hole it leaves behind. The easiest way to remove the Roamerdrive is to extract the 6 bolts (taking care not to loose the seals) and rotate the overdrive until the “stiction” between the gasket is broken. It can then be withdrawn.

Fast forward 10 minutes and the intermediate gear pin has been withdrawn and the gear and thrust washers removed.

Intermediate gear and pin. When the teeth are compared to the original gear with nearly 200,000km of use they’re in better finish than the one with 5000km of use. You get what you pay for I guess. What was I thinking?

For comparison, we removed the intermediate gear and pin from Jeremys spare transfer case (still with the original steel cage roller bearings!!!) and found the best fit combination of parts (gear, bearings and pin)

The winning combination was the original pin, original gear and new bearings. There was as much lateral float with the same pin and bearing combination in the very used one from Jeremy and the pattern replacement. It would have been handy to have a bore micrometer to measure the diameter of the gear centres. I’m pretty sure the bore on the new gear is oversized.

Jeremys S3 gear and pin (top left). Pattern replacement gear and pin (top right). Original gear and new bearings (bottom)
The wear on the thrust washers was extraordinary. The top half of the one of the left and the bottom half of the one on the right were heavily worn. This supports the idea that the bore of the replacement gear was oversized fractionally and not running concentric on the shaft.

Knowing which gear and pin to refit, we set to putting everything back together using new gaskets and Hylomar sealant.

  • Jeremy cleaned the old gasket and sealant off the overdrive
  • I did the same with the cover plate. I think I had the easier job
Some comedian decided it would be fun to stick a knife in the tube of Hylomar. I got a palm full of the stuff. Sticky?… very.
Overdrive prepped and ready to be fitted. Nice work Jeremy.
Cover plate, OD, output flange, hand break assy and prop back in place

Conclusion

The transfer box is now noticeably quieter in all gears but could be better. That said, I am please things are a little quieter in the cab.

As an experiment, I refilled the box with EP140 (rather than EP90). This also helps to suppress some noise but not much… I would describe the sound as being “muffled”. What is noticeable, is it takes a lot longer to heat the thicker oil.

Hylomar sealant… I’ve not seen it for sale in Switzerland so it’s worth the longer delivery time and importation fee as it is amazing. The usual oil leaks from the cover plate and overdrive are gone. I have one small drip form the front output flange but thats a seal issue not a gasket issue.

I buy most oils and the Hyloma from Holden Vintage and Classics in the UK.

Since I took these photos, I’be also changed the oil in the main gearbox and sealed the drain plug with Hylomar… another perpetual drip cured.