draining diff oil

[iggy]

i want to drain the oil from my rear diff, i do have a 12v pump which was made for draining in board boat engines where theres no access to a sump drain, but id like to fit a 3/8 bsp plug in the underside of the diff casing, can the cast casing be drilled? ive never drilled a hole in cast iron before also what size hole should i drill for a 3/8 bsp taper tap?

[piman]

Hello Iggy,

Cast iron is normally easy to machine, it's quite soft although some castings can have hard spots but you will be unlucky if a differential casing has any. The only problem is how thick the casing is. I can't remember if there is a portion that looks as though it should have a plug but is not machined for one?

Tapping drill for 3/8" BSP is 15.25mm. Are you planning to drill with a hand drill or take the unit to a bench drill? The reason I ask is that you will probably get away with a (much more common) 15mm drill especially if you don't do a pilot drill first.

Alec

[JohnD]

Cast iron is easy to machine and drill, because of all the carbon in it.   In graphite form, carbon is an excellent lubricant.
And the swarf comes out as dust, so easy to clear.

This CT blog shows a 2000 dfiff (about of a quarter of the way down).
The author didn't fit drain plug then - perhaops he has now?
[Sorry, link no longer available]

John

[piman]

Hello Iggy,

just to elaborate on my previous post, my concern about the thickness is not related to the difficulty of drilling but if there is sufficient material to tap and secure a plug, too thin and it's not very feasible.

Alec

[iggy]

thanks for the info john and pinman, didnt realise cast iron would be easy to machine,i was intending to drill from under the car with the diff fitted, i can see a flat part on the diff nearer the alloy mounting plate. i have a spare diff and was intending on trying to measure the thickness of the of the flat part with a pair of calipers, if i can get a measurement il report back 🙂

[GT6 M]

its about 7/16 th thick,  and hole will be offset frae the CW by aboot 1/2 inch,
There will be v little swarf going inside, its mainly chippings/ dusty stuff wid cast, butt, for peice o mind, stick a magnet onto drill, it,ll catch the stuff.
it wont come pouring oot when yer thru either, just a dribble doont drill bit, it,ll come moer whenst ye tek bit oot.

if bung,n in a taper plug, is it one of the square heeded orrid things.
if so, get a 1/2 nut, and file some flats onit in the thread area wid a  square file,  but not too much slack, needs to be tight.
then bung it int vice, and press the 2 into one,
if no got a welder, then bung some epoxy glue into nut as yer squashing up
if got a welder, weld top bit, stops it coming off.

this way, ye got a 3/4 nut thats easier to tek off.

And whilst yer at it   bung a magnet init, and also a magnet int fill
plug too,    Same nut can be done on this too.
alott easier to get off.

For some odd reason, there moer gunge collected on fill plug magnet , than there is ont sump one.

Ohh, fill it, run it a 100 miles, get oil hot, then drain it.
reason, there could be a good chance that the inside has got thick crud
sticking to things,  this will loosen wid new oil, and then clogg things up,  so a re fill is in order

remember, oil is cheeper than diffs.

M

[Richard B]

Plenty thick there to fit a sump plug. I have done it. I prefer a 3/8" NPT x 18 (or is it 19). This is then the same as all the other Triumph plugs.

That boss is there for such a fitment, presumably dropped on cost grounds as not neccesary in production use.

[iggy]

thanks guys, i cut the end off a normal drain plug spanner and welded it to a 22mm socket so i can use use a ratchet on both the gearbox and diff plugs

[nang]

Easiest thing to use is a 3/8 NPTx 18 tpi socket head plug. Much easier to use an allen key   than that horrible cast square headed thing. I've done a spare diff case to see if it is doable. It is 🙂 I've actually made some brass hex plugs for my cars.
Tony.

[piman]

Hello Richard,

3/8" NPT is 18 tpi, 3/8" BSP is 19 tpi.

Iggy, you'll need a 9/16" drill to tap if you go the NPT route.

Alec

[Richard B]

Thanks Alec that explains it, I have an 3/8 NPT (18 tpi) tap here which I have used for diffs.

I then acquired a 3/8 (19 tpi) tap and did not know what it was.

[GT6 M]

This why I said drain a few times,
most of the diffs im getting in are like this inside.
even cars that ev been run of late









M

[iggy]

GT6 M. when i get round to doing the drain plug i was going to use a 3/8 bsp tap cause i have one plus i can get almost any bsp fitting from work, do you no how long that diff in the bottom picture had been run before draining the oil? do you recondition diffs your self?

[MarkDeTriomphe]

Quoted from GT6 M

most of the diffs im getting in are like this inside.

That's shocking - how do people let their cars get into such a state (whistle)

Quoted from iggy

do you no how long that diff in the bottom picture had been run before draining the oil?

I bet it's been standing around in someone's shed for 20 years and was of unknown condition before that  (whistle) (whistle)

[Nick Jones]

That's a good one...... still got most of it's teeth.....  

Nick

[GT6 M]

Quoted from MarkDeTriomphe

That's shocking - how do people let their cars get into such a state (whistle)



I bet it's been standing around in someone's shed for 20 years and was of unknown condition before that  (whistle) (whistle)

> > > > >

M

[GT6 M]

the ones that ev been run, but with nee oil changes
then the oil goes like a tar, as when it cools, it litterally sticks to every thing,
slowly building up, bit like the sludge ye get in rocker gear/ sumps of oour cars
if not looked efter

As to teeth as Nick says,  got loadsa 3.7   -  3.45 diffs ,
all wid teeth missing oft Pinnion, just like the smaller Spitty type diffs.

must be a problemo with the Pinnions on the Triumphs.
v v few loose teeth of the CW ive had thru

M

[Rod 2500S]

A lot of the sludge is the result of the extreme pressure additives in the oil doing their job, but the rust is awful.

[Jonny-Jimbo]

On this subject, I noticed my Mk1 had a small puddle of oil under the nose of the diff over the weekend. The car has been parked there for about 6 weeks (weather too bad to take it out - not that I don't want to drive it in the wet, but because there is no hard-standing outside my workshop so I'd just get stuck in the mud!).

Should there be a gasket between the diff body and the nose piece in the subframe? That seems to be where it is leaking from and there is no gasket there that I can see.

[Clive]

Which car?

if herald etc based, certainly a gasket or some decent silicone sealant. No idea on the saloon stuff, but it needs a seal of some description!

[Jonny-Jimbo]

Sorry, this was on my Mk1 2000. When I took the diff out for inspection I used some silicon sealant on it and it seemed to last okay but has obviously failed. I was just wondering if there should have been a gasket in there in the first place?

[Clive]

A decent silicone should last indefinitely. After all it is used in the factory for most (all?) modern cars.

But here needs replacing. Worth checking bolt tightness too. I know the smaller diffs use a funny tapered bolt which is often replaced by an incorrect "normal" bolt.

[CRAJ]

Quoted from Jonny-Jimbo

On this subject, I noticed my Mk1 had a small puddle of oil under the nose of the diff over the weekend. The car has been parked there for about 6 weeks (weather too bad to take it out - not that I don't want to drive it in the wet, but because there is no hard-standing outside my workshop so I'd just get stuck in the mud!).

Should there be a gasket between the diff body and the nose piece in the subframe? That seems to be where it is leaking from and there is no gasket there that I can see.

No gasket there as the oil shouldn't get there either. The oil seal at the front of the diff is the culprit. This is accessed by removing the diff nose piece along with the quill shaft.
Leather lipped original seals  (from CW) are best. If it has been leaking for a time the oil will wash the grease out of the quill shaft bearing in the nose and ruin that too.

I did it on the pi a while back and it shows some pics and explaination on my blog.

Colin

[Jonny-Jimbo]

Would it not just be easier to remove the diff from the body than taking the nose piece and quill shaft out of the subframe? I'll have to check what condition the quill shaft is in. I don't think the diff has been leaking long.

This also calls into question, if I fit the current 4.11:1 diff that is in it, or stick in the (I think) 3.45:1 diff that came with the car when I bought it...

I was going to put an order in with Chris for some bits, but sadly he's not coming to Stoneleigh this year so his free courier service is not available. Luckily my other half's family live in Chard, so I may arrange for us to go and visit and make a detour to Chris' place.

[Richard B]

Diff can come off in situ leaving the subframe. Supposed to be 40 mins by the book.


3.45, slower off the mark. But you big ends will be gratefull! 😀

Whichever you use fit a new leather seal.


or compromise, look for a 3.7 from a late Auto 2000