LT77 into a 4-cyl P6?

There's quite a few sub-£100 R380 gearboxes on Ebay including delivery on a pallet, only thing to decide on is do you use the LDV remote or an SD1 remote if you went that route. The LDV remote is taller and chunkier, and sits further forward, but the SD1 remote would sit 3" too far back if used. A lot of the LDV remotes have lost the gearlever or had it gassed off on removal, so picking one with it complete would be adviseable.
 
I see what you mean about prices, they really don't go for a lot do they! After reading around a little, I have a couple of concerns:
Weight - apparently the R380 gearbox weighs 50Kg which is pretty hefty, but presumably the LT77 was the same (a Toyota 5-speed box weighs 35kg).
Ratios - I found someone saying they never use 1st gear as their box had probably come out of a van so had a very low ratios. Am I right in thinking that 4th will always be "straight through" and 5th effectively an overdrive? So it's only the lower ratios that could be an issue? Or is he talking cobblers and van gearing was lowered via the diff anyway?
 
R380 is heavier than the LT77, much of that is the gears are physically larger, there's two sets of gears in the rear casing on the R380 instead of the one set on the LT77. Fourth is straight through with overdrive fifth, like an LT77.

Confirming ratios seems to be a bit of a vague subject, though I'm running a 3.07 final drive I don't have any issues with first gear, which to me seems about right on mine. Vans generally have low ratio axles anyway, but there does appear to be two main ratios available:

1 3.985:1
2 2.519:1
3 1.507:1
4 1:1
5 0.831:1
R 3.816:1

1 3.321:1
2 2.131:1
3 1.396:1
4 1:1
5 0.77:1
R 3.536:1

I have no idea how accurate those numbers are?
 
Thanks Simon, I'm sure I have the P6 gear ratios somewhere to compare so will post when I find them.
I wonder how serious that weight difference would seem when on the move?
 
Willy Eckerslyke said:
Thanks Simon, I'm sure I have the P6 gear ratios somewhere to compare so will post when I find them.
I wonder how serious that weight difference would seem when on the move?
Click to expand...

The ratios for the P6 4-cylinder 'box are:
1 3.625:1
2 2.133:1
3 1.391:1
4 1:1

So the second 'box that Simon listed seems much closer - virtually identical in fact, albeit with a higher first gear (probably no bad thing!)

As regards weight, I can't see it would make any difference at all. Fuel economy around town might be marginally impacted, but that would be drastically offset by the high speed cruising economy. I certainly can't see it upsetting the balance/handling of the car either - the weight is too low in the chassis, and practically at the intersection of the roll/pitch axes.

Michael
 
Thanks Michael, that's reassuring. From those figures, it looks as if either version of the R380 would be quite acceptable. So next step is to see if I can find one locally at the right price. I'll leave with eBay as a last resort.
 
sowen said:
R380 is heavier than the LT77, much of that is the gears are physically larger, there's two sets of gears in the rear casing on the R380 instead of the one set on the LT77. Fourth is straight through with overdrive fifth, like an LT77.

Confirming ratios seems to be a bit of a vague subject, though I'm running a 3.07 final drive I don't have any issues with first gear, which to me seems about right on mine. Vans generally have low ratio axles anyway, but there does appear to be two main ratios available:

1 3.985:1
2 2.519:1
3 1.507:1
4 1:1
5 0.831:1
R 3.816:1

1 3.321:1
2 2.131:1
3 1.396:1
4 1:1
5 0.77:1
R 3.536:1

I have no idea how accurate those numbers are?
Click to expand...

The first set of ratio's are for an early LT77 box fitted to the ser 1 SDI's. The second set are for the later boxes from the diesel SDI's and LDV vans which had a 0.77 : 1 fifth gear. All other boxes had the following ratio's
5th 0.792:1
4th 1.000:1
3rd 1.396:1
2nd 2.087:1
1st 3.321:1
Rev 3.428:1
The gearboxes with the stronger casing and bearings and shot peened gears are from serial suffix D onward. These have a slightly larger casting with different ribbing, and are the equivalent to the R380, but that type designation, was as far as I can find out, only used on boxes fitted to four wheel drive trains.

I have done a lot of research into these boxes as I am going to put one into my Rover P6 2200sc. the bell housing is the major problem to be resolved, I intend to try and use the back end of the LT77 housing welded to the rear of the bell housing of the P6. This will mean I can use the clutch actuating mechanism of the LT77, the clutch arm housing on the side of the LT77 housing I'll cut off and weld onto the side of the P6 housing. Well at least that's the theory. will put up a topic as soon as I can.
 
I'm afraid i don't think Dangermouse's statement that the first set of ratios is from an early SD1 is correct. Those very wide ratios are much more appropriate for a van. The SD1 3500 ratios were 0.833, 1.00 , 1.396, 2.087, 3.321 and the TR7 ratios were identical
 
Dangermouse said:
sowen said:
R380 is heavier than the LT77, much of that is the gears are physically larger, there's two sets of gears in the rear casing on the R380 instead of the one set on the LT77. Fourth is straight through with overdrive fifth, like an LT77.

Confirming ratios seems to be a bit of a vague subject, though I'm running a 3.07 final drive I don't have any issues with first gear, which to me seems about right on mine. Vans generally have low ratio axles anyway, but there does appear to be two main ratios available:

1 3.985:1
2 2.519:1
3 1.507:1
4 1:1
5 0.831:1
R 3.816:1

1 3.321:1
2 2.131:1
3 1.396:1
4 1:1
5 0.77:1
R 3.536:1

I have no idea how accurate those numbers are?
Click to expand...

The first set of ratio's are for an early LT77 box fitted to the ser 1 SDI's. The second set are for the later boxes from the diesel SDI's and LDV vans which had a 0.77 : 1 fifth gear. All other boxes had the following ratio's
5th 0.792:1
4th 1.000:1
3rd 1.396:1
2nd 2.087:1
1st 3.321:1
Rev 3.428:1
The gearboxes with the stronger casing and bearings and shot peened gears are from serial suffix D onward. These have a slightly larger casting with different ribbing, and are the equivalent to the R380, but that type designation, was as far as I can find out, only used on boxes fitted to four wheel drive trains.

I have done a lot of research into these boxes as I am going to put one into my Rover P6 2200sc. the bell housing is the major problem to be resolved, I intend to try and use the back end of the LT77 housing welded to the rear of the bell housing of the P6. This will mean I can use the clutch actuating mechanism of the LT77, the clutch arm housing on the side of the LT77 housing I'll cut off and weld onto the side of the P6 housing. Well at least that's the theory. will put up a topic as soon as I can.
Click to expand...

The debate is more of what the actual ratio the rwd R380 gearbox is, I've had trouble finding accurate information, unless we assume that they share the same ratio's as the 4wd counterparts. What we can see is that the actual ratios whatever they may be are likely to not be a serious issue, but down to the persons preference who's doing the conversion, basically there is no right or wrong 'box :)

I'd be interested to see how you get on welding the two together. Will you be doing it yourself, or farming it out to a specialist welder and how will you align the two? I've seen a few welded bellhousings over the internet, there seems to be a bit of hit and miss as to how well they line up after welding, some are straight and others come out as warped scrap.
 
Hi Sowen
To line up the bell housings I was going to make a jig the bolted onto the front of the housing with the output shaft fixed in a bush, when the housing is transferred to the other box that shaft will fit into the jig centring up the bell housing to the gearbox, I hope , lol. Not sure what to do though, either use the rear end of the LT77 box welded onto the rear of the P6 bell housing or weld the P6 bell housing front bolt ring onto the front of the LT77 housing Or perhaps more simple make an adapter ring between the engine back plate and the LT77 housing. More thought required..... As one of my old teachers used to say, measure twice to cut once.
 
I really like the idea of welding up a custom bellhousing for the job, but I would say have a look round the internet as plenty of people have done it, and some have had problems doing so.

Here's one I did earlier :wink:

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The engine is a Mercedes OM606 inline 6 cylinder diesel, sat upright on it's crank pulley, with an LT77 sat above located in the crankshaft spigot. The bellhousing is a standard Land Rover 4 cylinder, but with the flange cleaned up a bit, and the original Mercedes gearbox was cut up for the first approx 40mm of the flange, and filed back to locate on the Land Rover bellhousing. I then used aluminium wire in my mig welder and tacked the two together. I haven't got any further, but now have a TIG welder of my own to finish the job. Engine is however currently bolted up and running/driving in the Land Rover awaiting completion and going back on the road :D
 
Progress is being made on the 5 speed gearbox conversion. after a LOT of measuring, I found it would be impossible to weld the front mounting ring from the P6 gearbox onto the bell housing of the LT77. so I decided to make up a conversion plate to use the P6 bell housing and clutch release mechanism.
 

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I've decided to let the gearbox oil lubricate the mechanism as per the original, and modifying the mainshaft to stop oil leaking to the clutch
 
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