Changing input/output shaft seals on SD1 LT77

DamianZ28

DamianZ28

Active Member
HI Guys, Am in the middle of my gearbox swap from BW35 to SD1 lT77 manual 5spd on my 72P6 V8, its 2600 police spec with V8 bell housing from a mid 80's SD1.

Is it a relatively easy task to do ? I'm not scared just want to know if once I remove the casings to do the front/rear seals, will a load if cogs fall out the box :eek: ?
Sorry to ask a dumb question like that, is the oil pump at the rear or front? will be replacing the gaskets too, I'm quite confident in doing the work, just useful to have some pre-operation info LOL.

One last thing, the front input shaft has a very tiny bit of play, is this normal, the box has about 55k miles on it, also this has been asked 1000 times but what is the recommended oil to use, the car will cover no more than 3k miles per year, if that really, thanks very much Damian
 
This is all from memory as I've done a few LT77's in the past, so worth verifying I've got the details right before you start :)

Changing the input and output shafts seals is relatively easy, undo the big nut on the output shaft and pull the flange off to replace the seal. The nut will be very tight, can't remember the torque figure off the top of my head. The front seal is also not a bad job to do, but easier to mess things up. Sit the gearbox upright with the tailshaft down and the input shaft pointing vertically up, undo the six bolts that hold the front cover on and lift it off, being careful not to lose or misplace the shims on the front bearings. The seal is inside the front cover and will need a new gasket when refitted.

There are two main casing gaskets in the centre of the gearbox. To replace the front one of the two, put the gearbox in neutral, support the gearbox vertically on it's tailshaft with the input shaft pointing vertically up. Remove the small plate on the centre of the top of the front gearbox casing (two 10mm bolts) and carefully withdraw it, it is the selector quadrant stop for the front selectors. Undo the all the bolts that hold the alloy tail casing through the centre plate to the front casing. Carefully lift the front casing off, being careful not to dislodge the reverse gear shim, idler shaft and oil pick up, and not lift the centre plate off the tail case. Replace the gasket, refit the front casing and put at least two bolts between the tail casing and the front casing.

Turn the gearbox over so the input shaft is at the bottom and the output shaft pointing vertically up. Remove the output flange and the speedo drive gear from the side. I cannot remember if the worm drive needs to come off aswell. Remove the small plate on the top with the two 10mm bolts (rear selector quadrant stop), and remove the bolts holding the rear casing and carefully remove it without letting the centre plate come away from the front case and not lose the square peg drive gear from the end of the layshaft into the oil pump. There is also a rubber o-ring that the selector rod passes through which can be changed at this point. Fit a new gasket and carefully refit the rear casing, taking care to align the square oil pump drive with the layshaft.

Not impossibly difficult, and should all become obvious as you go, and do not force it as internal parts can be broken easily. The small play on the input shaft should be acceptable, as it will be supported by the crankshaft spigot bearing once fitted. Main thing is whether it's quiet in operation and selects freely without crunching, only a road test can fully determine that without a full overhaul.

On mine I ran it on Castrol SMX, and had no problems but that 'box was very worn and I'm running an R380 now.

As I say this is all from memory, and there are plenty of guides and pictures on the internet on how to rebuild the LT77.
 
Hi Simon, brilliant :D many thanks for the this detailed information! certainly be a great help indeed, As there are no leaks evident then I may just do the oil seals including the selector rod if possible, just in case I bugger something up doing the gaskets, I'll let you know how I get on with it.

Thanks again Damian
 
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