Lt77 gearbox

[Alan Slater]

I have a LT77 gearbox in my MGB V8. I need to refill the oil, but I cannot find the fill plug. I have searched the internet, and all the photos show the filler plug near the drain plug, but it isn't there. Nor is it on the other side of the box. There is a plug on top of the box, about 12 - 15 inches in front of the gear lever. Is that it.

Hope you can help, it's driving me nuts!!

[nta16]

the filler plug hole is on the same side of the g/box as the drain plug

the filler plug is about halfway up the box and not vertically in line with the drain plug

the plugs can be whatever someone has put in them so not necessarily exactly the same fittings, one might be a recess socket the other a hexagonal head or a square socket or square raised head or any combination

always fully remove the filler plug first - if you take the drain plug out first and then find you can't remove the filler plug there will be swearing, plus if you take the filler plug out it helps with the draining

to do a thorough oil change (engine, g/box, r/axle) have the existing oil as warm as possible for draining then leave it to drain for as long as possible - both are to get as much existing oil and muck out at each change

notes:
• for all jobs allow loads more time that you think it will take, never be in a rush

• check for the correct oil to buy before buying it and before preparing for the work

• get the right tools to fit drain/fill plugs

• have the gearbox oil as warm as possible before draining (protect yourself from hot oil)

• clean around both plugs and spray with a penetrating/releasing fluid such as PlusGas (ordinary WD40 is not as good) and let it soak in then try to slightly tighten to break any muck seal before undoing, let the chemicals do the hard work for you

• take the filler plug out first as it will help to drain faster and to check it will come out before you remove the drain plug and empty the oil out of the g/box to find you can’t get the filler plug out to refill it!

• leave oil to drain for as long as possible

• clean plugs and threads, refit the best condition plug as the drain plug because it’s easier to replace a filler plug later if required

• plugs go back in hand tool tight

• refill with about two thirds of stated quantity of oil (refills never take the dry fill quantity stated), top up very slowly, better to need to add more than overfill

NOW the big debate is what oil should be in the box or best for it

[v8250]

Alan, here's a photo of my R380 'box. Zoom in and you'll see the filler plug. If you're not sure when the oil was last changed do drain the existing oil and replace with new. Now, there's great debate as to which oil to use. You may like to visit the V8Register.net website and search the technical notes...most folk nowadays choose the Castrol SMX-S. Others use ATF fluids which appear to ease any 2nd gear notchiness, but, are thin oils and so have lesser lubrictaion.

If you PM me I'll email you a copy of the R380 [LT77] overhaul manual and a copy of how to adjust the gearbox selector remote.

[v8250]

PS if your remote rubbers are badly worn replace with nylatron sets available from Rimmer Bros et al as per pic below.

[nta16]

well because of the black on black I'm struggling to see the filler plug on that photo and I know where it is!

still very usefully for a photo to have been put up, well done V8250

I've added an orange arrow pointing to the large headed hexagonal nut of the drain plug and a green arrow pointing to the (looks like) hexagonal socket of the fill plug

a note about the oil, in my Ford Type-9 gearbox it's always recommended to use Comma SX semi-synthtic 75w/90 (GL4) which I did for the first two years before swapping to Castrol Syntrans Multivehicle 75w/90 Fully Synthetic MTF and the gear change were instantly better even though I changed in an April so it wasn't the cold winter months when the better change would have stood out more

this oil replaced the SMX-S sometime back (us youngsters know these things )

I don't know what the oil change intervals are on the box but even with using the current fully synthetic Castrol I'd look at changing at least every 3-5 (more if scheduled) as a thorough oil change washes out muck and metal bits plus it keeps oil in the box that is still in good condition rather than old and worn

having driven a LT77 box through a couple of winters I wish the current Castrol was about then as I tried various oils to help with 2nd gear when cold (and reverse crunching)

Edited by nta16 on Sunday 8th June 10:29

[Alan Slater]

Thanks for the info, I will attach an image that shows there is NO filler plug on the side of the gearbox where the drain plug is. The second photo shows the plug on top of the gearbox, but I don't know if that is the filler plug. Hope you can help

[Alan Slater]

Second photo doesn't show, so here it is again

[v8250]

No, that's not the filler. Yours is an early gearbox used on some Rover P6 3500 & early Range Rovers...and some have mentioned these being seen on early SD1's. Have found another pic' c/o Google; see here

http://www.classicroverforum.net/viewtopic.php?f=2...

The filler should be on the alloy part of the gearbox extension. It sits [left hand side] slightly higher than the drain plug [right hand side].

If in doubt contact Tony at TM transmissions...he'll confirm for you.

PS where's your gearbox tunnel? Looks like there's a gaping hole?

Edited by v8250 on Sunday 8th June 15:12

[nta16]

oh, er, older stuff, I was thinking of later 5-speeds and a B (roadster) rather than factory BGT or conversion using an older box, my mistake

my P6 3500S was 4-speed (manual) box, I thought they all were, tbh I never checked or changed the gear oil on it as it was in the days when I could afford to pay someone else to get there hands dirty so didn't realise the fill was lower and elsewhere

sorry for confusion but a little more initial detail would help, there are lots of converted Bs so the variation can be wider

Edited by nta16 on Sunday 8th June 16:20

[Alan Slater]

Thanks V8250 , found it and removed it. Sorry I was a bit vague, but the recon gearbox was fitted to the car before I bought it. The hole in the tunnel is what you have to do to fit the gearbox into an MGB. It will be plated over later and is hidden inside the car.

Given it is an early LT77, although it has been reconditioned, what is the best oil to use. I was going to use either 5w40 cast roll RS or 0w40 Mobil 1 plus moly slip gearbox treatment.

Thanks again, I've been under the car 20 times looking for the bloody thing!!

[v8250]

Alan Slater said:

Thanks V8250 , found it and removed it. Sorry I was a bit vague, but the recon gearbox was fitted to the car before I bought it. The hole in the tunnel is what you have to do to fit the gearbox into an MGB. It will be plated over later and is hidden inside the car.

Given it is an early LT77, although it has been reconditioned, what is the best oil to use. I was going to use either 5w40 cast roll RS or 0w40 Mobil 1 plus moly slip gearbox treatment.

Thanks again, I've been under the car 20 times looking for the bloody thing!!

Re' the gearbox tunnel - you can buy a gearbox tunnel extension from BMH in Witney. This may be your best bet if a previous owner has butchered a hole to get the LT77 bell housing to fit. The gearbox tunnel area is important as it carries structural rigidity for the centre of the car and the front area is the common structural point and will ensure no scuttle shake.

Re' oil - the Castrol SMX/Syntrans option is best. Do a Google shopping search and you may find a supplier who'll deliver FOC.

[nta16]

SMX-S will be old stock if in small bottles