Gearbox rear oil seal

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jagnut66
Minor Legend
Posts: 3635
Joined: Fri Apr 11, 2008 7:28 pm
Location: Mansfield, Nottinghamshire.
MMOC Member: Yes

Gearbox rear oil seal

Post by jagnut66 »

Hi,
I just had to change mine, as it was leaking like sieve.
Before doing this I trawled the internet / MMOC forum and couldn't find specific topic on the best way to remove the old one and install a new one.
I found a good video on 'YouTube' about the removal and refitting of the diff oil seal (which I've posted up a link to in a separate post) but none for this.
So I thought I'd start this, I will explain what I did and then others can add their thoughts / preferred methods.
This way, when someone looks for advice on this, there will be a specifically titled post for them to look at, which hopefully they will find useful / helpful.
Anyway, after perusing what bits I could find, I made a mental note that the seal might be crimped into a groove in the tail of the gearbox, which may need to be addressed before you can remove the seal and a warning to be careful not to damage the tail of the gearbox.

Fortunately I have my dead gearbox to practice on, so choosing my weapons of choice, a screwdriver with a metal cap at the top of its handle to facilitate it being used (hit) like a small chisel (not sure of this type of tools name) and a mid sized hammer, I set about prizing the old seal off.
Of course the advantage of this box being off the car is that you have all round access, so I worked my way round it carefully, a bit at a time, creating a gap between the metal body of the seal and the gearbox tail. Sure enough this seal popped off fairly easily (it wasn't crimped) with a bit of added wiggling by hand.
It revealed itself to be in remarkedly good condition, the inner rubber seal still being pliable and not rock solid. The gearbox didn't drip from the rear when in use, so I have kept this, as a good used spare.

The gearbox rear oil seal on the car proved a different matter though.
First, of course, I drained the gearbox of oil and removed the propshaft.
I don't think that the old seal had been replaced for a long time. It was rock solid and no amount of chiselling around the edges would produce a gap, nor would it budge (rotate) when gripped with mole grips. It felt like it was welded in place.
Yet I couldn't find any indents where it might of been crimped in place to hold it, anywhere around its circumference.
In the end I had to gently tease it with a cutting disc (a well worn down one note, that I keep for small jobs like this).
I slowly cut through the front of the seals casing, where it sits around the splines.
However, I was careful not to go through into the felt seal.
At the back half of the seals metal casing I 'grazed' my way through it, so as not to dig into the gearbox tail itself. Then I used my screwdriver and hammer to get under it and prize it up / split the seals casing. After which I was able to tap it off relatively easily.
I could see why it had leaked straight away, the inner rubber seal was widened through use and had set rock solid.
Having cleaned the tail of the gearbox up, I smeared some multi purpose grease around the inner lip on my new seal, that presses over the tail of the box and then drifted it into place using a 30mm deep impact socket, so that it went on evenly.
I found the 30mm deep impact socket ideal, as it is narrow enough to sit just inside the outer circumference of the new seals metal casing but has enough internal clearance to allow it to pass over the splines where they stick out of the tail for the front of the prop shaft to mate up to them.
I then reattached the propshaft and refilled the gearbox (1.3 litres engine oil).
So far no leaks have reappeared.
Touching lots of wood.......... :wink:
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
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