901 gearbox visual inspection

kium · 04-11-2020, 03:22 AM

Hi guys,
what do you recon of this teardown gearbox?

Bought it on a wooden palet, for years unused, with a promise it was ok. Nothing too appealing at first glance.
It's a 901/13, 5 speed, maybe 1968.

Came apart quite easily, still had some oil inside, about 1L with a "good" smell and a golden color.
I have the impression it's the first time it's taken appart, the paper seals are extremely thin and came out in one piece, no sealants used. The rubber seals are all Kaco.
The magnetic plug was loaded the classic fine metalic sludge, no metal bits have been found inside.
All parts turn free and smooth.
The reverse switch looks brand new and the speedo gear refuses to leave it's home.

I'm not in favour of taking it all apart just to double check all is fine, I'm not sure I will put it back together as well. I can live with a used gearbox.
Having said this, now it's the moment to fix anything that's needed.

Please take a look and give me your opinion:

Reverse gear and needle bearings (complete and all fixed in place)

1st gear

Differential bearing, right Smooth but with a satin finish

Differential race, right side (lid) Smooth but with a satin finish

Differential bearing, left

Differential race, left Smooth, with a satin finish and oil marks from years not moving

Secondary shaft race

Primary shaft race

Gears 2 and 3

Gears 4 and 5

Cheers, Kium

Trackrash · Trackrash's Garage

You may want to ask this in the Tech forum as well.

I will say from the pics things look good from what you are showing. It is hard to tell the condition of the gear teeth unless you completely remove the oil. The thing to carefully look for on the gear teeth is any loss of the hardened surface. You don't show a picture of the pinion gear, that is something to look at closely. Did you try shifting into each gear?

Are you going to replace the two large ball bearings? Those are the main wear items in this trans.

The reality is, you can put it together an see how it runs and if there are any problems OR you can carefully inspect every part before hand.

kium · 04-11-2020, 09:45 AM

Thanks Gordon for your comments.
I forgot to take a pic of the pinion gear, I'll see if I can make one tomorrw.
In general to me the surfaces look good, but I haven't got an experts eye.
I wouldn't mind changing the bearings of the differential, as they seem a little worn and accessible.
Are these the ones you recommend, or the ones that go on the intermediate plate?

kium

Trackrash · Trackrash's Garage

I am talking about #25 and 26 in this diagram. Thanks Grady. Here is a good read on those transmissions. 1970 (911/01) transmission refurb issues
Probably worth closely examining those two bearings. You may want to check the availability of them as well. If you replace the diff carrier bearings it would be a good idea IMO to then check your R&P preload and backlash.
BTW, after looking closely at your pics, it looks to me like your synchro rings in the bottom two shots are worn out.

Trackrash · Trackrash's Garage

This looks like a worn out synchro band.

kium · 04-11-2020, 01:27 PM

Thanks for the diagram, actually I was working with a similar one, but this one is completely exact to mine. For example: it has an o-ring for the diff. cover -not a gasket.

yes, I see what you say about the synco band.

About the availability issues of the bearings.
Wouldn't they be available in SKF if we had the codes?

It's worth going all the way and getting all these issues sorted out now, my worries are to put it all together again if I go that far