A Transmission related poser for you.....

[chickenjohn]

Here is an odd problem of interest. A customers car turned up at my workshop the other evening on a tow truck, the symptoms being no drive to the rear, yet the prop turned when in gear and engine was running.

He immediately thought "aha broken half shaft" but on with drawing the half shafts from both sides both splined ends were intact. And to add to the confusion both half shafts were of the stronger "uprated" variety the idea being with his mildly tuned 60BHP 1098 to avoid such breakage.

What was the cause of the breakdown???

[rayofleamington]

By that description the first place to check would be the diff internals.
Anything including failed pinion, ring gear, or bevel gear could give loss of drive. It could be the gears themselves or their connections / mountings.

Depending on what had failed in the diff, it may have been a blessing that it came in on a truck rather than towed!

Alternatively this may be a trick question. When you say prop turns when in gear is this with the wheels on the floor?

[bmcecosse]

As above - must be something broken in the final drive - could be almost anything really - but probably broken diff pin -horribly common on powerful Minis. Assuming (as Ray has done) that the prop turning is a positive movement - and not just 'idling round'. Just for info -how do you identify the uprated shafts??

[dp]

Broken spline from gearbox to engine or gearbox tail to propshaft??

[MarkyB]

Completely knackered clutch would still turn the prop and back wheels yet not move the car.
You don't say whether the wheel turn or not with no load.

[chickenjohn]

I pulled out the diff and all the internals were intact. At first I also wondered if it was a very badly slipping clutch, but then the prop would not turn with the wheels on the ground the engine running and the car in gear.....and with the back wheels not moving!

[kennatt]

well shafts ok,diff ok,prop turning but not wheels,must be the uj prop to pinion,but would it stay together and not just let the prop fall.Can you see the pinion being turned,Aah , but then you would see that when you took the diff out,very strange I give up come on then tell us.

[MarkyB]

Does it make any strange noises when you try to drive it?

[chickenjohn]

The prop and UJ's were fine and no odd noises! Oh and the Diff while showing some very slight wear on the teeth between sun and planet gears was intact and working perfectly well.

Any more guesses??

[bmcecosse]

Could be centre plate ripped out of the clutch - I had that once..... But then the 'drive' to the prop would be very poor......

[liammonty]

I have heard of the toughened half shafts breaking at the hub end before, I.e.the shaft itself doesn't break - the weak point is where the shaft connects to the cap that bolts to the hub. Could have broken there?

[kennatt]

stripped spines on pinion shaft take some doing and would be noisy, is there a prize ,maybe a complete set of wood for a traveller

[rayofleamington]

the prop would not turn with the wheels on the ground

I'm still trying to work out if it's a trick question...

So does the prop turn when wheels in the air, and not turn when wheels on the ground with car stationary?

If prop not turning when wheels loaded (with engine running and gearbox in gear), then it's something from the front of the prop forward.
Anything from flywheel, Clutch disk, clutch hub, clutch cover, gearbox input shaft... broken gear hub or selector mechanism, gearbox output shaft* or even front proj uj mounting to prop tube is fractured**
I've yet to see a broken spline on transmission output shaft

* gearbox output shaft could shear but then you'd be unlikely to get any 'low friction' drive with wheels in air as the broken off end would slip further into the prop shaft female spline.

**not heard of that ever happening but in theory is possible...

[katy]

Pinion shaft broke.

[mikeysmorris]

propshaft failed at rear uj to tube weld

[simmitc]

I think that Katy has the answer, but in case not... does the whole shaft turn along with the flange on the diff, or has the shaft been sleeved in some way at some time?

[bmcecosse]

We are told the diff is fine...... I suggested diff pin way back at the start! But seemingly not that......

[taupe]

Splines stripped on the UJ flange to the diff?

Or if uprated half shafts have the outer splines or keyways failed on these?

Taupe

[chickenjohn]

Well done to Hammondty! and Taupe is on the right lines as well.

At first I could not understand why the car was not working as nothing seemed to be broken, but then remembering the problems th owner Matt had had with his uprated half shafts, leaking and rubbing on the hub nuts. I looked at these closely again. The left hand side half shaft on the inside of the hub end had been rubbing on the rear hub nut. And on the left hand side had completely worn the weld away that connects hub flange to half shaft itself, allowing the shaft to turn with the hub flange remaining stationary.

http://www.youtube.com/watch?v=qwaD2jroLik

Ironic isn't it supposed "uprated" half shafts which are sold on the basis that they do not break are of faulty design and actually fail in service due to faulty manufacture. We have a replacement pair on order from a different manufacturer. Luckily within one years warranty so the cars owner got them replaced for free.

Why they didn't put then welds on the outside, i.e. weld the nut and washer to the flange and shaft, I don't know....two piece half shafts seem s recipe for disaster...

[bmcecosse]

Good grief....so presumably shards of metal through the bearing? Was there no noise to go with all this carnage? Any chance of a picture or two?? And - we wre told the halfshafts had been inspected, and were fine !