Technical Gearbox countersunk screws

[dapedza]

Got the 126 gearbox from Lukasz at LP Garage. It looked ok when peering through the cover. Yet on strip down, what a mess. Turns out the retainer for the layshaft bearing retainer had come loose. The gearbox was eating itself to death. It’s almost as if someone tried to drill the heads off, gave up & threw the box back together. Bizarre.
Anyhow, I’m guessing I can use my 500 casing which is good & quite a few other bits which are good to make a nice synchro box.
Which brings me to this question. Scoured the internet to locate a suitable impact bit to remove these screws. Can’t find anything. Any ideas? Thanks!

 

[Toshi 975]

The larger cross head bit from a basic impact driver set is a perfect fit. I use that in conjunction with a socket wrench , 8mm I think.
That bit also fits the two countersunk screws on the front main bearing.
I have got a couple of boxes of gearbox parts if you come up short on any bits, everything apart from actual gears.

 

[dapedza]

Thanks for the advice. Managed to rummage around & find a bigger bit. The screws came out easily enough. It’s nice to get the new bearing fitted. Now the fun starts - trying to fathom out where everything goes!
Speaking of which, a couple of questions if I may:
The first pic is of a couple of 1st/reverse gears. One has a step & is slightly thicker than the other. I’m guessing the 126 box uses the narrower gear?
The second shows some angled cutaways on the internal splines. They seem regular, so are they supposed to be like this, or is that damage? Thanks as ever

 

[Toshi 975]

Thanks for the advice. Managed to rummage around & find a bigger bit. The screws came out easily enough. It’s nice to get the new bearing fitted. Now the fun starts - trying to fathom out where everything goes!
Speaking of which, a couple of questions if I may:
The first pic is of a couple of 1st/reverse gears. One has a step & is slightly thicker than the other. I’m guessing the 126 box uses the narrower gear?
The second shows some angled cutaways on the internal splines. They seem regular, so are they supposed to be like this, or is that damage? Thanks as ever

Count the number of teeth, if my memory serves me well I think the 126 has two more teeth than the 500.

 

[dapedza]

Count the number of teeth, if my memory serves me well I think the 126 has two more teeth than the 500.

You’re absolutely correct. The wider gear, with the flange has two extra teeth

 

[124BC1]

Got the 126 gearbox from Lukasz at LP Garage. It looked ok when peering through the cover. Yet on strip down, what a mess. Turns out the retainer for the layshaft bearing retainer had come loose. The gearbox was eating itself to death. It’s almost as if someone tried to drill the heads off, gave up & threw the box back together. Bizarre.

Why didn't you bring this 126 gearbox back to the seller and insist on either a refund or replacement?
Businesses do have obligations (Sales of Goods legislation etc.) unlike private sellers...

 

[dapedza]

Why didn't you bring this 126 gearbox back to the seller and insist on either a refund or replacement?
Businesses do have obligations (Sales of Goods legislation etc.) unlike private sellers...

Good question. I didn’t intend to have a go at Lukasz. I’m sure he would have taken it back if I’d asked him. He probably knew as much about the box as I did until I stripped it down.
It would have been a hassle to drive it all the way back to Sudbury. Combined with my very good 500 box, I seem to have everything I need (assuming there is good interchangeability of most parts). I have a new bearing set, new seals & gaskets. The only things I had to buy were a new end casing, a bronze bush for the clutch shaft & a retaining spring for the synchro plates.
If I can do a good job, this will hopefully be a good synchro box for a fraction of the cost of an overhauled 126 box from Ricambio.
I’m learning as I go along, with the help of the manuals, YouTube & this excellent forum!

 

[dapedza]

Please excuse the number of postings on the forum, but your advice is very valuable!
Assembly seems to be going ok, but there are a couple of issues which I can’t find answers to:
The roller bearing for the output shaft is wider than the casing. It means it protrudes a few mm behind the pinion into the differential casing (see pic). I guess this is the case with the original bearings?
The other issue is the main shaft. Nothing seems to secure the top bearing, so the shaft is completely free to move forwards along with the bearing. Checked all my manuals, but I cant find anything. I must be missing something? Thanks

 

[Toshi 975]

The sectioned view of the gearbox in the Haynes manual clearly shows the roller bearing protruding into the diff housing so no worries there. The Mainshaft is restrained when the tailpiece casting is bolted on. Both shafts have bearings that are free to slide at the diff end to allow for any differential expansion or contraction, you have steel parts mounted in an aluminium case.

 

[dapedza]

Thanks for that, much appreciated. I’ll press on then.
I had a suspicion the end casing held the shaft in place, then thought ‘surely not!’ It looks like a clever bit of Italian engineering!

 

[dapedza]

I’ve finished putting the box together, and all appears to be ok. The diff is next, and that seemed to go together well. I used a bit of engineer’s blue on the pinion and the spread on the crownwheel seems to be ok (please excuse the poor pics).
Now the fun starts as I need to set up a rig to do the gear-to-pinion backlash

 

[dapedza]

Backlash seems to be within limits. Now we move on to the 1lb preload. One thing the manuals don’t make clear is what you do with the opposite driveshaft whilst you’re setting up the preload. My assumption is you lock the opposite shaft in place? Thanks (in anticipation of your advice)!

 

[fiat500]

Backlash seems to be within limits. Now we move on to the 1lb preload. One thing the manuals don’t make clear is what you do with the opposite driveshaft whilst you’re setting up the preload. My assumption is you lock the opposite shaft in place? Thanks (in anticipation of your advice)!

Yes, clamp or otherwise immobilise the oposite driveshaft.