LT77 Gearbox oil

[adam quantrill]

simon_h said:

On the gearbox front, I spoke to Competition Transmission Services, who rebuilt the box, and they have asked me to try some different oil in it before condemning it. I’ve swapped it already and hope that sorts it as I can’t cope with the prospect of heaving the whole lot out again.

Well I've done a few thousand miles since my gearbox oil flush and change, including the long run to/from BBWF (I don't usually go over 100 miles on a run).

And I can report good news all round, my previous niggle with SMX-S, where after a long run the gearchange would get relucatant to change and crunchy, is gone. And the new oil is Mobil one 0W-40 with a dose of Molyslip.

For the flush procedure read here:

Strange gearbox/clutch problem

[adam quantrill]

ATF is too thin - I predict you'll have much the same sorts of problems. At least you can drain it out and use it as your "flush" before going over to the Mobil 1.

[adam quantrill]

I bought a gallon of Mob1 for 30 quid on offer, and it used just under half, so I have some for topping up and another change in 4 years time ;^) and I used half the Moly.

[adam quantrill]

Good stuff - nice to see an alternative - it'll be interesting to try it in winter too - we both have that final test to do - will it shift OK when freezing cold from startup? I shall resurrect this post on the first frosty day (at this rate, that won't be long....)

Graham, what is the exact brand and type of your difflock oil?

[adam quantrill]

TV8 said:

Hi Adam,
It is the oil recommended in the link below your question and this reply. Very pleased with the results of a simple change

Just for reference (in case the link breaks) Difflock Evolution 1 Fully Synthetic Gear Oil - 1 litre
[S031-3-60034].

It will be interesting to compare notes in the winter....

[adam quantrill]

Hamish - thanks for the tip - and another recoomendation - but I'm surprised you don't insist on your oil being tartan! ;^)

[adam quantrill]

Simon - what is it like going into reverse?

[adam quantrill]

Doubt it's the clutch then. Is the rebuild guaranteed in any way?

[adam quantrill]

So - I think it's almost winter now (well the central heating is on...) and we've had a few cold mornings. So far, I haven't had any crunching at all from cold with the Mobil 1 - most impressive! I guess the viscosity doesn't change very much.

I must have put 3 or 4 thousand miles ont he box now - not problems at all - and it even put up with a totally failed clutch for a few miles (the pipe broke) which is impressive.

[adam quantrill]

Yeah it's the standard 0W engine oil. Although you only need 2l it's usually better value as a 4l 'can' then you have enough for an oil change in a few years time. And yes, I am still happy with mine.

[adam quantrill]

This is weird we had one other post saying exactly this a few weeks ago - even posted photos and the casting is flat where the filler plug should be (usually)!

Maybe you turned the car upside down last time? ;^)

Well there's a removable plate on top which I think you can fill through, held on by a couple of screws. But it might be hard to get to in situ... possibly if you remove the gaiter.

OK I found this "the filler plug is on the nearside (l.h.looking towards the front) approx half way up and towards the back end of the box near the the speedometer take-off point." does that help? Must be a later style or off a different car where the original position wasn't convenient.

Edited by adam quantrill on Friday 29th July 18:47

[adam quantrill]

Yeah it should take 2l. I use a plastic pipe and then do it standing up, squeezing from a spare 1l oil bottle with a nozzle. The first litre can go in with no fuss but you have to start watching during the second litre because when it brims it goes all over the floor - a waste of oil apart from anything.

[adam quantrill]

What was in there (by the look of it) was it ATF? That stuff does tend to leak out.

[adam quantrill]

Yes.

Despite my recent box failure (it spat the oil out and I didn't notice) I still recommend it - did over 30k on it. And it's going into the next box too.

[adam quantrill]

andymadmak said:

I am a bit mystified by this. 30k on a gearbox is nothing, even an LT77!
I can understand the enthusiasm for an exotic oily solution, but the reality is that your gearbox failed prematurely.

Let me clarify.

1. When I got the car it has some oil in the box. This may have been ATF I would have to look through old posts etc.
2. I then put SMX-S in it. Mileage between 10k and 20k? I had problems with cold morning crunching, and hot long drives it would be reluctant to shift (e.g. coming back from BBWF). Otherwise better than ATF.
3. At around 50k miles on the box I put in the mobil 1 + moly. All previous symptoms at extremes went away. Now the box is at 83k miles. When I drained it prior to removal around 20ml of oil remained, this is what caused the failure.

[adam quantrill]

andymadmak said:

AHA! Thanks for the clarification. All understood. Nevertheless I still question the use of Mobil 1 as a transmission oil. I am not an oil expert but my understanding was always that the structure of transmission type oils allows it to cope better with the very high shear forces inside a gearbox. That's not to say that mobil 1 cannot cope at all, but it's not designed for the application. Perhaps the Molyslip helps with the situation?

Yes the Moly here is working as an EP additive. Note that Mobil 1 is known for quite reasonable shear qualities but I wou'nt use engine oil on its own - I did this once with a Rover P6 four speed box - it was great for a hundred miles or so but then shredded itself.

andymadmak said:

I was also under the impression that the seals have to be of a type that can accept the chemical properties of the oil, - is it at all possible that you lost your transmission oil because a seal has broken down?

Yes I was considering this too - many people have reported leaks from the top (selector) when using ATF. Maybe Mobil 1 could have affected the rear seal where the oil appeared to be splattered round under the car.

What probably didn't help with the box I have just extracted is that there's no top breather - looks like it was deleted by the time the E suffix boxes came in. So the box will be "pumping" i.e. pushing out air (and oil) while it warms up.

[adam quantrill]

Yeah it's '89. The box is the type with filler above drain plug on the same side. I reckon there were a few variants of LT77 for different RWD applications independent of the suffix on the serial number.

[adam quantrill]

Getting back to the question of how much molyslip I put in half of a 65ml cartridge (leaves enough for another oil change especially if you buy the oil by the gallon).

My current box is on this formula too, and going well on it.

Don't forget the "no load" flushing stage, this removes a load of crud from the box.

[adam quantrill]

Agreed, changing the gearbox oil won't fix a wobbly remote selector linkage, so check this first.

Most oils I have used over the years are fine most of the time, but I always had problems with these two scenarios:

- driving off cold, on a frosty morning, for the first few miles.
- driving on a hot day for a long distance - the usual one being coming back from BBWF.

In each case the gearchange would be difficult, syncro could get iffy, etc.

After trying quite a few official gearbox oils, mainly 75W, the best one I had found was Castrol SMX-S.

However it still suffered in the hot or cold range. When I changed to Mobil+Moly, the last problems were fixed.

It's not _like_ brewing your own, it _IS_ brewing your own formula. But it was tested out by the Rover SD1 boys too before coming here.

I don't know many other wedgers who use their cars in the winter, and I have no reason to continue testing different oils, so I suspect that even if there are better "official" gearbox oils out there, we won't have enough testing done to find out if they also fix the extreme hot and cold scenarios.

But if you do use any other oils, please do post your results up on this thread, so others can have a go.

[adam quantrill]

Yeah I have to agree. I'm surprised that you were having cold-running problems on ATF, as it's quite thin even on the coldest day. Where I found ATF really horrid is when the box gets very hot - long run on a hot day.

I got through quite a few boxes on my 350i's when using ATF, back in the day before we knew better, and I put a cumulative 80k+50k = 130k miles on the 350i's, they have tended to last better on SMX-S or (latterly) the Mobil.