| RETRO-FITTING PLUS
8 GEARBOXES
by Lorne Goldman OPTIONS LT77(1977-1994) The LT77 gearbox (from the
Rover SD1) has many different reputations. There were many variants made
(A, B, C, D & H [aka the LT77S]) and the later ones The LT77 was introduced to Morgans in 1976. It is the same box used with the Rover SD1. The early boxes are not great. A LT77 variation was introduced to Landrovers in 1983 with the suffix 'D' box (which was a big step forward) and was developed over the years to the suffix 'H' which was last used in 1994. This was improved upon (suffix E) which used a wider reverse gears. Then came the suffix F which used larger diameter laygear bearings. The suffix G was uprated with all the gears being widened. Then the last of the LT77 was the suffix H (also known as the LT77S) It used a dual synchro on 1st and 2nd gear. This is the best version is the last, the LT77S..or those with the G or H suffix. YOU NEED A SD1 VERSION for a Morgan, TVR, Marcos.
LT77 WEAKNESSES The LT77 biggest danger area is its particular sensitivity to the viscosity of the oil used.This is because of the weakness of its internal pump. After only a bit of experience, Rover used to specify ATF (Ford Dextron 3) to overcome baulking when cold. That is very thin oil for a manual gear box and the smoothness suffers..but at least the LT77 last. There are those who use Redline MTL or Castrol SMX-S with reported success and much smoother shifting. There is a now synthetic oil specifically designed for this gearbox from a company called Difflock. The product is called Difflock Evolution 1 Fully Synthetic 5 speed Gear Oil - 1 litre. These oils are fully synthetic with friction properties designed especially for gear syncros. They reportedly make gear changes like a knife through butter and synchro engagement is really good. The box is rated to 245bft. torque..but this reflects manufacturer caution. Morgans present an extaordinarily light load and stress on a gearbox. . R380 Gearbox
So there is no need for extensive chassis mods if replacing a Morgan LT77 with a Morgan R380. A small part of the chassis mounting plate for the LT77 will have to be cut away but the new mounting position arrives just above the crossmember making the installation easy and better. The propshaft is same as the Morgan R380 is the same length as the Morgan LT77. HOWEVER, the R380 used on the Morgan is a special version made for Plus 8s, later Plus 4s, some TVR Chimaeras and Sherpa vans only. The oil required is a MTF94, either castrol SMX-S, Texaco MTF-94 or Amsoil Synthetic Manual Synchromesh Transmission Fluid (MTF) SAE 5W-30. The shifting becomes as smooth as anyone could want. The R380 is much stronger than the LT77 with a overly conservative limit listed at a 280 lbs/ft..pulling a 3 ton 4x4.
R380 CLOSE RATIO OPTION (once from Ashcroft but not longer made. If a sufficiently large group gets together, I can approach him)
Note due to the nature of straight cut gears they will be noisier than a normal R380. Ratios are :
The ratios have been chosen to be ideal for racing and Morgans, ie higher 1st, 2nd and 3rd etc but still keep 5th as a reasonable overdrive ratio as this is often required for running between sections at lower engine RPM's. The gear kit includes the layshaft, Pinion, Mainshaft, 1st, 2nd, 3rd and both 5th gears. Borg Warner T5 (Tremec) Gearbox  The
World Class T5 'box is rated at 300lbft of torque. (Other T-5s can be considerably
weaker). This version is generally acknowledged to be a stronger 'box than
the LT77 abd is 12 pounds lighter. To fit this you can use a bellhousing
for an automatic SD1. This is shorter than the manual bellhousings and
can be fitted to the T5 with an adapter plate. The easiest way to operate
the clutch is to use a concentric hydraulic release bearing that is attached
to the gearbox front over the input shaft. Alternatively, you can
buy an aftermarket specially cast bellhousing from John Eales Developments.
The advantage with T-5 is easy accessibity of parts and a huge range of
gearsets. In the UK, ask for the type used in the TVR. |
The
'G' was further improved by all the gear teeth including the pinion getting
approx 20% thicker. Also a much wider pump was used to increase the lubrication.
The 'H' (termed the LT77S) was the same as the 'G' in terms of strength
but used a different syncro set up called the 'Double Syncro', 
The
R380 was developed to replace the LT77s. It hassthe same ratios as the
LT77. It's super rare 2 wheel drive version (Morgan, TVR, MGV8, Marcos
& the Sherpa Van) uses the same Sd1 bellhousing/clutch as the
earlier LT77 Plus 8s and the same input, output shafts and remote.
Other than that..there is no similarlity between the
boxes. The internals are completely different.
