UN1 Leaking oil from a big hole

[NIGEL S]

Driving back from Sywell classic on sunday i heard a bit of a whining noise on deceleration from the gearbox,got out and found a hole in the rear casing.
About 2 mile from home i ran over a brick in the road that rattled under the car.
I don't now much about gearboxes but looking at the picture should there be a nut on the thread visible through the hole.
I am not sure if the brick broke the casing or maybe something letgo in the box.Still able to engage all gears.
Any of you UN1 experts thoughts would be greatly appreciated.
Nigel.

 

[David]

Is there actually a thread on that end section?

Looks more like there should be a bearing on there.

 

[NIGEL S]

What you see through the hole has a thread on it and at the base is a loose chunky washer.
Nigel.

 

[Jac Mac]

What you see through the hole has a thread on it and at the base is a loose chunky washer.
Nigel.

Its spat the pinion nut off ( where it states 'secondary shaft' on attached drawing, during the time it was loose it would have been causing the Ring & Pinion to get out of alignment particularly on deceleration which would have caused the whine. Total teardown/rebuild likely unless your really lucky/brave and want to to chance your arm with another cover & replacement nut/washer, but having run for a few miles I don't like your chances.

 

[Malcolm]

What Jac Mac says. You are not the first to have this issue and won't be the last!

 

[Jac Mac]

Was re-visiting this thread, this failure which is apparently fairly common could be reduced somewhat by changing your driving style..... when in 5th gear do not use engine braking.... use the brakes. With engine braking the torque reversal loads induced by the helical cut 5th gear puts all those loads on the 'nut' & threads and then tries to 'tip' the 5th gear on its splines, once a small amount of clearance is created a 'rattle gun' effect takes place until the nut gives up and is forced out thru the cover, while Nigel states he still had all his gears the lower 5th gear would have been walking back and forth on the splines each time he accelerated/decelerated.