Rover LT77 Gearbox

[chesterak]

What would you consider to be the reasonable maximum power/torque to put through this type of gearbox?

Happy New Year to all.

Stan

It's life Jim, but not as we know it..

[PeteV]

Firstly, you need to establish the condition of the 'box. Putting a lot of torque through a 'box with shot bearings isn't a very safe practice - these boxes chew up the internal oil pump gears & then begin to wear heavily.

As for torque figures - TVR did use the LT77 in the early Griffith. I've got a friend who runs a John Eales (?) built 5.0 Litre RV8 in his hillclimb Westfield & he told me recently that last season he & the other driver blew-up two LT77s which probably isn't bad going considering the amount of abuse they get during this sort of thing. He's looking at other options himself though.... The comforting fact was that when they 'gave up' the 'box casing remained intact !!!

So, if you have a good condition LT77 or better still the Vitesse version (which has a stronger bearing arrangement) & you're not being too silly with it then you can probably put 300 ft.lb throug it occasionally without too much worry.

Alternatively look at the R380 which I believe Russ uses in his Nitrous buring monster !!




Pete.

[chesterak]

Pete,
Thanks for the reply. The box I'm using has been completely rebuilt with new bearings, oil pump gears, seals etc. I'm not sure of the origin of the box - how do you recognise a Vitesse box?
I'm aware of the R380 box - I drive a manual Discovery - I wasn't aware of the 2 wheel drive application. Is this a 4WD box adapted with an output flange or specifically manufactured for 2WD?

stan

It's life Jim, but not as we know it..

[osgood]

Stan the SD1 box is fairy substancial, but if you use hydraulic fluid/power steering to keep it lubricated then it will blow, with any more than normal road work, trust me I have got rid of two. Use fully synthetic, or EP 80 gear oil which was previously stated in hand book prior to 1978. I have now got the replacement R380 sports box 28A which is a direct replacement for the old LT77 (SD1) unit which runs on fully synthetic; no more problems. Used in the TVR, Morgan, & MGRV8. The box fits but new mountings required as they are 2" further back, but prop and clutch okay. hope this is of some help!! Eric.

[chesterak]

Hi Eric,hows it going?
From previous posts I was aware of the lubricating issues for this gearbox, but I'm interested in where you can obtain the R380 box, any advice?

stan

It's life Jim, but not as we know it..

[russell_ram]

Stan,

There is nothing wrong with a well rebuilt LT77. Constant levels of high engine torque and vehicle mass/shock loading are what destroys a gearbox. In a Cobra, the mass is approx half that of the SD1 or XJ6 that the box was previously fitted to, and considerably less than a 2 1/2 ton Land Rover. The weaknesses in the LT77 are the main/lay shaft bearings and the synchros on 1st and 2nd gear. However, that didn't prevent the majority of boxes (in their heavy cars) lasting well over 100,000 miles! In a Cobra you cannot achieve the constant high torque, low speed input (because it accelerates too easily/quickly) and you don't tow a 3 ton trailer (well I don't anyway) and you haven't got the traction levels available like you have in a 4WD Range Rover. The box was good enough for Rover to degrade the lubrication spec to using an Auto g/box oil in an attempt to improve cold shift quality into 1st and 2nd gear (because the syncros are not really man enough). However, if you want to improve it's life use a good, modern 75/90W semi-synth oil (which were not available at the time) and be a little bit careful about shift speed when the box is cold (this is a 40 year old gearbox design in it's 4 speed variant remember) - oh and don't abuse the f*ck out of it!!!!!. You should have no issues with a 77 up to 250-300LbFt, power is not really relevant.

R380 (380Nm capacity in 4WD form) is basically the same gearbox - they are hard to tell apart at a quick glance. The bearings are bigger, it has triple synchros on the first three gears and reverse selection moves from 'next to 1st' to 'opposite 5th'. The differnce between a 2WD version (TVR,Morgan, Daf Van, MGRV8, Gaz/Volga, Chengdu and Sanyai) and a 4WD box is in the input shaft/constant pinion (different lengths for different applications), the main shaft (spline for 2WD flange or splined into t/box), rear output housing, and selector shaft (different 2WD versions and totally different between 2WD & 4WD). Even early R380 boxes also specified ATF, only recently changing back to semi-synth gear oil, Texaco MTF94.

You won't gain a great deal by spending nearly £1000 on an R380 if you've already got a good LT77.

Hope that helps a bit.

Russ

[osgood]

Hi Stan. I got mine from from DJ Ellis Nuneaton: http://www.djev8.com I think there are various ratio's for van application if purchacing from other places. Mine seems to be quite closer than I expected, marked 28A sports.

Reverse is over the other side and down & you dont use that spring loaded gate the old boxes have. The reverse light switch is also a seperate unit.

Yes I am fine matey will see you soon no doubt? All the best Eric.

[chesterak]

Russ,
Once again, many thanks for this information. The operating conditions of the original application are obvious - now that you have pointed them out!!!!. I have faith in the chap who rebuilt my gearbox (he is also a friend) so I'm reassured to stick with the LT77. The reason for my original concern was that I'm using a mildly tuned Rovertec/V8 developments 4.6L engine on a Weber carb but I have now sourced an injection system that I'll fit post SVA.

Stan
:7 :7 :7

It's life Jim, but not as we know it..

[osgood]

Hi Russ I must say your a mind of information on the old RV8 scene have printed your reply out for future reference.

I have seen this box advertised with ratio's of: (R380)

3.98:1
2.50:1
1.50:1
1.00:1
0.78:1 I asume this is commercial ratio speck as the gaps are bigger than the old box with 5th slightly lower.

Would you have any idea of what the ratio's is my particular unit (sports 28A) would be, as it seems to be closer than the old unit (LT77?

All the best Eric.

[russell_ram]

Eric,

28A g/box is morgan/TVR V8 long remote. Is same ratios as V8 MG(18A)/T16 Morgan(24A)/Chengdu (21A)and TVR 3.9 short remote (20A).

Ratios are 3.32,2.09,1.40,1.00,0.79.

As far as I'm concerned the ratio set you list above doesn't exist from the factory, unless they are a specially machined aftermarket set. All V8 R380 2WD boxes are the same ratios except Daf Van which has a slightly lower 2nd gear.

Russ