Well, my gearbox broke, so a great excuse for a rebuild thread. It's in a 109 with a 3.9 on carbs, has been fine if a little noisy (they're notorious for this as they use ball bearings rather than tapered roller) but finally gave up as I was towing a newly bought Sankey back from Tewkesbury. To cut a long story short, I as bumbling along on the A417 when I heard a little "ping" noise. You know, that kind that really make you nervous and you spend a minute wondering if it's just a stone flung from the tyre? Then another and the a nasty, heavy clattering noise from the gearbox. I was in fourth at the time, and still driving fine despite the noise. Pulled over, transfer in neutral, run through the gears. I thought the layshaft rear bearing might have collapsed, but it turns out fifth has popped off its retention ring and was flapping about in the breeze. Pics of that will follow when do my actual post-mortem of that box - I ended up rebuilding my spare.
The spare is interesting. On first inspection, it looked great inside - clean as a whistle. But the input shaft had a little more play than I'd have liked, so I took the front housing off to find this:
The cage has busted clean through the spot welds and come apart. Not ideal, so apart it came. I have a video of this, which will need some editing before it goes up as it's quite long! In order to disassemble the solid case, you have to make up some puller tools. Main and input shaft bearings are press fit into both the housings and onto the shaft, and being ball bearings you can't separate the inner and outer track like a taper roller.
So a few bits of box section and a little machining later:
I also made up the tool required to press the rear bearing along with the case onto the output shaft. The official tool is vaguely tube shaped and supposed to engage on the rear face of the inner bearing track, picking up on an internal thread in the end of the output shaft. I couldn't find a bolt to match, and didn't like the sound of this anyway, so I went a slightly different way:
The collet picks up on the radius of the output splines and gets retained by the outside taper into a collar, just like valve spring collets. No chance of it slipping off or stripping threads here! You'll see the finished article in action later.
After some cleaning measuring and faffing about I won't bore you with (the manual covers this far better than I can), it's time to reassemble. I did have some remedial work to do on the iron front housing that contains the oil pump and takes the thrust load of both front bearings. As you can see, there's a few thou of fretting there, and it's not even. It's too shallow to maching, so the best solution is to rake out the surface plate and get lapping:
A half hour later:
Much better. Now it can be assembled with new seals, pump, oil feed ring and O-ring:
Next up is pressing the bearings into the front plate and main case. No pics as it's pretty banal. I do with I'd taken some photos of the bearings from Ashcroft, though. They've used different style -and longer lasting - bearings that are the right width and ID, but too small on the OD so they're pressed into a machined collar. Lovely work and fitted tighter than the proverbial.
Input shaft goes in, baulk rings and bearing on:
Preassembled mainshaft goes on, layshaft and gasket get put in place:
The front layshaft bearing is cylindrical roller bearing, the outer of which gets pressed in sitting 5mm proud of its final position to make fitting easier.
Reverse gear gets fitted, but retained temporarily by a screwdriver This allows it to be wiggled around the layshaft as the main case is fitted. Spot the deliberate mistake; I fitted it backwards and realised just after I took the pic:
Main case goes on. There are supposed to be guide pins, but these would have interfered with my stand:
Now the home made special tool goes on:
And the whole lot gets pressed together by winding the two nuts up against the plate:
The tool worked like a charm. The gearbox is now taken off the stand and the layshaft front bearing gets tapped home, then the front housing goes on with a fresh gasket:
Torque to spec and we're done. You can see the front bearing plate is temporarily retained with a couple of bolts and spacers:
Now work starts on fifth gear. Both my boxes has sheared the pin in the synchro hub that drives the plate slipper pad retaining plate and output seal collar. Dave Ashcroft was kind enougb to supply an updated part with a 5mm pin, rather thin the 3mm, but I couldn't hunt down or didn't want to pay for the plate, pin or collar to match....
The plate was worn from spinning against the hardened hub and collar due to the sheared pin, so this was scrap. The fit on the shaft was also a frankfurter down an alleyway - not acceptable. A 3mm bit of plate got turned up, outside first:
And fits snugly:
Now for the pin hole. I could have measured, but it was simpler to use the pin as a punch. Anneal, the grind a piece of tool steel with a point, fit to hub, give plate a tap against it to leave a punch mark:
Check and drill:
Lovely. Grind the pin flat to remove the point and massage the keyway in the collar to suit:
The angle grinder is too cumbersome for this operation, so I made an arbor for an old slitting disk to fit into the die grinder. A much more delicate tool:
Polish up the seal collar on the lathe:
And it all fits together beautifully:
Because the plate is slightly thicker, a new "selective washer" needs to be made to give the right clearance against the retaining clip. This is the clip the had let go and caused my breakdown, so worth getting it cock on:
At the time of writing, I'm still waiting for a new clip. These should, under now account, be re-used.
Having got all that ready, attention turns to the layshaft. As you can see, a spacer is used to retain it in lieu or fifth. This allows the bearing retainer plate to be fitted. Two problems here: Firstly, it's fretted like the front housing. Second, it doesn't match the curve of the smaller main bearing OD.... It's not special steel, so I decided to build up with weld; both to eliminate the wear, and to add some extra to engage fully with the bearing outer track:
Fitted, spacer removed, fifth fitted, new stake nut torqued to 160 lb ft. I quick gripped the box to the bench to do this:
Staked with a round punch:
The fifth selector assembly retains the top of the bearing too, and this had the same issues as the other plate:
Spot the *cough* deliberate *cough* mistake: I fitted the selector ring the wrong way round. Easily rectified:
As the 1st/2nd selector fork is steel, and the collar lands are quite skinny, it had suffered from wear. I built up with some silicone bronze and linished back until it was flush with the steel again. I didn't take enough pics
In go the selector forks, interlocks, rods and retaining roll pins. I'll let the pictures speak for themselves:
The rest is just a case of bolting covers on, which was a bit too banal for taking pictures!
Oh, apart from getting the reverse gate spring back on:
I hope it's interesting, anyway. I'll make the special tools are available for rent in return for a donation to the forum fund. It's really not too bad a job, and I actually really enjoyed it.
For reference, a 109 with a sankey fits on large recovery lorry. RAC were really good about it - no problem at all.