LT77 Leaking from rear oil seal

moppit · Post by **moppit** » Sun Apr 03, 2016 6:57 pm

Hi Folks,
My first post so be gentle! So far I've been browsing this forum and picked up loads of tips as I get my NG TC V8 (Rover 3.5, Typhoon cam, Edelbrock 500) up and running for the first time with a new engine and gearbox.

The LT77 seems to be dribbling oil from the rear seal next to the propshaft. Is it case of simply buying a new one and tapping it in around the output shaft? Sorry for the rather numpty question but just want to be sure. In my case the output shaft seems to slide in and out a bit - is this normal? Is it on a keyed shaft and designed like this to allow for movement in the prop?

The gearbox has a rather interesting history as it was once on display in the foyer in Rover. It seems to work ok but dont know how long its been sat around.

Any thoughts much appreciated!

DEVONMAN · Post by **DEVONMAN** » Mon Apr 04, 2016 7:44 am

I thought that the LT77 has a flange at the rear which connects to the propshaft with 4 bolts. If your has this arrangement, the shaft/flange should not slide in and out of the gearbox at all. If it does then the gearbox has a problem and probably need a rebuild.

If you have a sliding yoke arrangement, and you can see the oil seal, then with the propshaft removed, it should be possible to remove the old seal and tap in a new one provided you have sufficient access.

moppit · Post by **moppit** » Mon Apr 04, 2016 8:29 am

Thanks Devonman

Yes there is a flange held on by a big nut. When I took the propshaft off there was a load of oil that ran out.

The oil seal is visible. Surprised it is not retained in some way?

When you say 'sliding yoke' not sure what you mean?

DaveEFI · Post by **DaveEFI** » Mon Apr 04, 2016 10:29 am

At one time a propshaft would be a fixed length, and just pushed onto the gearbox output splines. BMC used this idea. These days, it's usual to have a splined joint within the propshaft, so the output from the gearbox fixed.

unstable load · Post by **unstable load** » Mon Apr 04, 2016 5:31 pm

moppit wrote:Yes there is a flange held on by a big nut. When I took the propshaft off there was a load of oil that ran out.

The propshaft is bolted to the flange and it has the sliding part in it. Did the oil come out of the propshaft when you slid the slip joint apart or the gearbox when you removed the flange?

moppit · Post by **moppit** » Mon Apr 04, 2016 6:14 pm

Oil came out of the gap between propshaft flange and gearbox flange when I pulled it apart and dropped the prop out of the way. On my old prop there was a sliding part in the prop. This prop seems to be fixed so I'm guessing the gearbox output shaft has to slide to allow the prop to be installed/uninstalled.

DEVONMAN · Post by **DEVONMAN** » Mon Apr 04, 2016 10:22 pm

The flange on a LT77 does not slide in and out of the gearbox to allow the prop to be fitted. If it does then something is knackered in the gearbox.

Propshafts used on an LT77 gearbox will normally have a slide section within it, or say on a SD1 Rover, the CV joints at each end will allow the propshaft to compress/extend slightly to cater for engine or axle movement.

The oil that came out when you removed the prop has seeped along the gearbox output shaft splines and got past the flange nut/washer. Some sealer on assembly would cure that.