Gearbox oil refill plug.

Drivetrain problems

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Re: Gearbox oil refill plug.

Postby dapinky » Thu 17.08.2023, 22:33

Okay then to try and finish this post (for now) with some definitive information....... All measurements were taken at 'ride height' on a level garage floor.

Having used the 'D' plug to fill the gearbox yesterday, only to not get anything dribbling out, I did it the 'proper' way today....... and found (like others have mentioned previously_ that the bolt holding the clamp plate for the speedo drive had previously sheared off and the plate was missing - so the speedo drive was held in by gravity and friction (it was all covered in oily crud, so it's been like it for a long time). Anyway, there is about 7 or 8 mm sticking out of the gearbox with a good M6 thread on it (I checked with a new nut), but not enough to get at it to remove it.... so I will fabricate some sort of bodge tomorrow using an M6 female rod joiner to give a usable M6 female 'hole' albeit raised by 20mm so it will need some bent bracketry - can't see it being beyond the wit of man to make something that will work.

Anyway, back to the point of the post - when I got the drive out and the hole cleaned up, I couldn't find my old dipstick in the toolbox. so made up a new version from a length of aluminium plate, 38mm long, with rounded corners - this just fits into the top lip of the speedo drive recess, drilled a 6mm hole in the centre and bolted a length of M6 stud through it, with a pair of nuts locked together 25mm down from the plate (this is the distance I measured from the underside of the speedo housing and the 'MAX' level) the 'MIN' level is 5mm further down, and as the nut is 6mm thick, it's a bit of a measure of how much is needed.... the stud protrudes a further 15mm beyond the nut...... it has about 5" of stud out the top for a handle.

By sitting the plate in the hole, (you can get an arm down between the heater pipe and the coolant tank - it is easier if you loosen the 2 clamps on the heater control valve and swivel it round out of the way) it is easy to check the level of oil.

Filling it up was simply a length of plastic plumbing pipe (15mm PEX semi-rigid pipe) dropped into the hole with a funnel in the end, and pouring the oil in. As I was starting from an empty (or as empty as it is ever going to get without stripping the 'box) I knew that it should take 1.8L of oil (except some books say 3 pints, and don't say if they are UK or US pints, and all 3 quantities are different!) - in fact, the only useful thing I knew is that I had drained 1.7 litres out yesterday - but I didn't know if it had been filled to the correct level, so was really working a bit blind.

I put 1.5L in and then tried the dipstick - it didn't register at all, but I could see oil in the hole..... so I added another 100ml and it just registered. Another 100ml took it to the lower level, and a further 120ml took it to the highest level.

So, now we know that the difference between the lowest and highest levels is 120ml, which may be useful to anyone topping it up.

We also know that it took 1.82L of oil from empty to 'MAX', but anything between 1.7 and 1.82 would be in the right range....... so lets agree that it is a 1.8L capacity, but 3 Imperial Pints will get it to the MINIMUM level!

Okay, so now I decided to see how much I needed to add before the 'fill plug' overflowed...... and so I added oil 200ml at a time and never found out as it got to the top of the speedo hole before it flowed out of the 'D' plug hole. The only way to find out would be to put the speedo drive in, then fill through the fill plug till it overflows, then drain a load out and refill from that quantity until it is the right level, see what you have left and do some maths!

I can't see any point unless someone has literally stuck the speedo drive in with chemical metal or similar in the past and the only option is to fill through the 'D' plug - but in that case, I can assure you that from a drained 'box, just chuck in 1.8L through the 'D; plug and it'll be close enough - but don't wait until it drips out - IT IS NOT A 'FILL LEVEL' HOLE!

Anyway, it's now got the right quantity of new oil in (because I drained it again and refilled it by chucking 1.8L straight in and then checking the dipstick), and I just have to re-fit the speedo drive tomorrow.

Just the one now, but this one's mine! - and it will be finished eventually..... - but also temporary custodian of a project until it is finished enough for Angie to drive it

go on - click this link - you know you want to!
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Re: Gearbox oil refill plug.

Postby chrism » Fri 18.08.2023, 01:12

Yep this time last year I, too, was seduced - then befuddled - by the D-plug seeming to offer a 'fill level hole'.

I wasn't convinced either so I topped up with 1.8l (Comma 75w/80 GL4 fully synth) through the speedo drive (I recall needing to use a flexible drive on the fixing) and tho' I can't remember how I came by this volume I'm mighty glad that you've confirmed it in a very practical way :)

So I reckon...

Easy-peazy: From now on folks forget the D-plug complication. Chuck in 1.8l and get a slick gearchange and a much smoother ride...
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Re: Gearbox oil refill plug.

Postby jgbff7 » Fri 15.09.2023, 13:18

With the head off my engine I am changing the gearbox oil having reasonable access to the filler. My stud is also broken with about 6mm remaining and no retaining plate.

The removal of the speedo drive was not easy but I found the best method was a vertical pull. I protected the jaws of a mole grip with masking tape and managed to get sufficient purchase to lift the unit out easily without damaging the threads. The O ring was very loose and looked very old.

The piece that holds the speedo cable to the drive (looks rather like a long socket) was completey broken and disintergrated as soon as I put a spanner on it. I suspect I shall have to replace the speedo cable.

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