5 speed (LT77) gearbox question.......

[busheytrader]

Hi,

I've bought a LT77 gearbox on line. It was described as. " This is a gearbox I purchased off eBay some time ago as spare unit for my Cobra replica but I haven't ever used it so cannot guarantee it's condition. I seem to recall the last seller said that it was reconditioned and to be fair it does look like it has new gaskets fitted. All gears can be selected and both input and tail shafts seem to be rotating nicely without any sloppiness"

It's a CL prefix gearbox meaning it started its life in a 1979 or later year TR7.



The gearbox is exactly as described by the seller. It turns fine without sloppiness whilst the gears are selected easily. The oil has been drained and the magnetic oil drain plug has a some swarf on it. I can't tell what it was last filled with. (The predictive text kept wanting to spell dwarf, not swarf!) As advised on the forum, I want to check out the oil pump and replace if necessary. My Haynes manual describes the process required for a complete stripdown so is not a lot of use. Is it a simple process of just taking off the rear cover, then removing and inspecting the oil pump or is it more complicated than that? http://www.rimmerbros.co.uk/Item--i-GRID006106

Thanks in advance,

Adam

[Peter Nuss]

Yes, that pretty much what you need to do. I would also check to make sure the oil pump is pumping fluid before I installed the trans in the car.

[Hasbeen]

Being a lazy type, I'd be finding some way to turn the thing over out of the car, & check the pump by removing the bung. It would also tell you if it was in reasonable condition.

I'd be thinking about a radiator hose from the PTO of the tractor to the input shaft, with the box set up behind, or the mates huge 100 year old lathe. If it spins OK, & pumps oil, it should be OK.

Then again, a mate bought a Dolly sprint, with an overhauled engine & gearbox. Just as well he stripped them, both were "overhauled" but very badly assembled.

Hasbeen

[busheytrader]

Thanks Hasbeen, I'm in London suburbia so tractors are a bit thin on the ground here and my double garage doesn't hold a lathe. I'm rebuilding a 1994 Mini Cooper so there's no room for one.

I'll take off the rear cover and check the oil pump to see what state it's in. Once reassembled, how would I know the gearbox is pumping oil correctly before I fit it? I could put it in 4th and hand crank the output shaft but the revs would be very low. I was thinking of filling it with ATF to flush out any cr4p then after 200 miles or so replacing it with a recommended MTF.

My wedge passed its MOT several weeks ago but there were unnatural noises coming from the transmission in every gear but 4th on the way there and back. At best I have a replacement gearbox at a bargain price, at worst I have one to be rebuilt. The LT77 boxes are still being sort after for V8 kit cars etc and are being rebuilt by the likes of JRV8 in Northern Ireland , however the seller had just bought a T5 box for his fake snake and never having used this one, put it up for sale. I think he'd also changed his engine from Rover V8 to a Chevy V8.

[Hasbeen]

There has been quite a discussion about flat towing a 7. From it I gather the output shaft does not turn the oil pump. I could be wrong about that, but it's the message I got.

I guess you wouldn't have access to the petrol engine driven large usually 1/2 inch to 1 inch drills we use for drilling holes in hardwood fence posts out in the bush, would you? However perhaps a heavy duty electric drill with a high reduction could do it at the other end. You should be able to hire one of them, even in somewhere as civilised as London.

Of course I last passed through London 44 years ago, so have no idea of what it may be today.

Hasbeen

[Peter Nuss]

Do you own a 1/2 inch drill? If so attach the drill to the input shaft and put the trans in gear. Remove the oil galley plug and start the drill. You should have a steady stream of oil coming out the oil galley, if you are turning the drill in the right direction. Tractors and lathes might be a little over kill to simply turn an input shaft.

[busheytrader]

According to my Dad, most of London was just fields back then......... Yes, the LT77 box can't be towed for more than a few miles without the propshaft being disconnected.

I must apologise to Mr Haynes, I now have the rear cover off the box. It was as clean inside it as per the pics.


I'll have to get longer bolts that locate the remote gear housing since some ham fisted person has managed to strip off the first few mm of the thread. I'll replace the fibre gears. The pump housing and gears appear to have some light marks.



It has a black speedo cog so probably has had only the 2.0L engine to deal with so far.

if I had the tools and experience to open up the box further I would but I'll see how things go from here.

Thanks,
Adam

[Peter Nuss]

Well, since you have the rear cover off. You might consider getting a real oil seal installed in the rear case for the shifter shaft. And thread inserts for the stripped bolt holes. All simple things to do with the case off and some simple machining.

[busheytrader]

I ordered RTC2057A which is on the delivery note and as far as I'm aware is the fibre oil pump gear kit.

However, these steel gears turned up............with a different part no.

[jeffremj]

I ordered RTC2057A which is on the delivery note and as far as I'm aware is the fibre oil pump gear kit.

However, these steel gears turned up............with a different part no.

I heard that the original items are no longer made

Whilst the steel ones will pump oil nicely, they fail badly on the filtering side of things. Basically, if a bit of swarf gets to the fibre pump, it will get amalgamated with the pump gears and go no further (up to a limit). With the steel ones, the swarf may either lock up the pump or get passed through into the oil ways.

Note that when I reconditioned my gearbox, there was swarf embedded in the pump gears.

[busheytrader]

Well, since you have the rear cover off. You might consider getting a real oil seal installed in the rear case for the shifter shaft. And thread inserts for the stripped bolt holes. All simple things to do with the case off and some simple machining.

Hi Peter,

The stripped threads only affect a couple of mm for the remote housing bolts, so no serious issues there. I wasn't aware there was an problem with the shifter shaft and the rear cover as its well above the gear oil level. Is it a case of oil leaking out of the rear cover or contaminants getting in?

Adam

[Peter Nuss]

In my experience, the gear oil leaks out of the shifter/selector shaft and runs down the case and turns the gear box rubber mount to a sort of mushy kind of thing. The seal for the selector shaft is just an o-ring. A little machining and a press in oil seal with a lip could be installed to stop the leak. If you choose not do that, insure you get a really good o-ring to replace the one in there and protect it while you install the rear case on the gearbox. It will save the rear gearbox mount.