Saturday, March 14, 2015

Gearbox Rebuild - Part 2 - Mainshaft Rebuild

<This post is part of the 'Winter Project 2014/15 - (Gearbox Refurb)' project>

With the exciting arrival of a new package today from Guessworks comes the ability to press on with the next stage of the gearbox rebuild. Now I have the new baulk rings, I can assemble the mainshaft ready to insert into the case. At first, building the mainshaft seemed a little complex, but after watching this step by step video guide posted by Mini Mania and also this one posted by Guessworks, it turned out to be a very straight forward project.

Baulk Rings
In the post Gearbox Stripdown - Part 4 - Mainshaft Strip, I looked at how worn baulk rings affected the gap between the baulk ring and the gear face. If it's below 40 thou it would probably lead to gear crunch, especially going from 3rd to 2nd for some reason.

Well now that the new baulk rings have arrived, I can compare the difference between the worn ones and the new ones and see how it affects the internal face.

This is one of the worn baulk rings. It's quite evident that the 'ridges' have been worn down allowing it to sit closer to the gear making less effective.

Worn Baulk Ring

This is one of the new baulk rings and it's noticeable straight away that the ridges are much deeper.

New Baulk Ring

The Gears
While all the gears were out, I took the time to separate the synchro hubs and give all the parts a good scrub with a brush and some red diesel in a washing up bowl (old one of course!) to get all the old oil and debris off. Once cleaned they were then dipped in new oil and left to drain as the oil was cold and really thick..

Apart from just overhauling the gearbox, the other main goal was to understand the anatomy of the gears and also how they work, so searching through the pile of gearbox innards and comparing them to the videos and diagrams from books, I was able to pick out the 4 gears and line them up side by side.

The first noticeable thing is that 1st gear is straight cut whereas the others are all helical. Without doing further research, I am not sure why this is. The next thing to note is the descending size as the gears go from 1 to 4 which makes perfect mechanical sense. This is particularly useful to know as 2nd and 3rd can be easily mixed up and can be put on the mainshaft incorrectly as I nearly did. So remember that 2nd is bigger than 3rd.

Mainshaft Build
Anyway, now that I have the nice new baulk rings and the gears sorted out, I can finally get on and assemble the main shaft. I won't go into vast detail as the videos cover it pretty well, but I will cover the main points.

Starting with 2nd gear with it's two detents and locking ring. I found it quite tricky to press both detents in at the same time and push the locking washer down. To be honest, it's a three handed job, but even with the normal number of hands, it's just about manageable with two small screwdrivers, a lot of attempts and maybe the odd swear word here and there.

2nd gear.

Next to go on is 3rd gear, this also has a locking ring, but thankfully with only 1 detent making it easier to fit. Both 2nd and 3rd have a split needle bearing that sits on the journal first.

3rd gear on.

Thankfully that's the worst of it over as 2nd and 3rd are by far the trickiest gears to install. By contrast the 1st/2nd synchro hub is easy as it (and the 2nd gear baulk ring) just slide on the shaft with no faffing about at all. I did however need to make sure it was on the right way. If I were to guess, it would almost certainly be the wrong way, so I always check.

1st/2nd synchro hub and 2nd gear baulk ring on.

Next thing to fit is the 1st gear journal. It looks like a top hat with a hole in and is an interference fit with the mainshaft. I heated it on the hob first to expand it, making it easy to fit.

First gear journal ready to go on.

Once the journal has cooled, the 1st gear and its needle bearings and baulk ring just slide into place.

1st gear in place.

The final part of the mainshaft build is the 3rd gear baulk ring and the 3rd/4th synchro hub, again ensuring it's the correct way round, it just slides into place on the other end of the shaft.

3rd/4th synchro in place.

And that's all there is to it really, as the 4th gear cannot be put on until the mainshaft is installed in the gearbox housing.

All things considered, building the mainshaft was nowhere near as difficult as I thought it was going to be. Of course it helped tremendously having the videos on hand and working through them as I went, pausing, going back, resuming etc.

Once more a seemingly complex part of the car has been demystified as I have slowly learnt about all the various parts and how they fit together, making this a very pleasurable little project. Now to get it all in the gearbox...

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