Blooming Series half-shafts.

I have to say that in many years of trialling I never broke a half-shaft on an 88" - though I did do a front diff once playing silly buggers (twice actually, I did the Stage I's as well).

109's with a Rover rear axle will snap as easily as a very easy thing, but a Sailsbury is almost indestructable - hence why Sailsbury's were fitted I presume. I've always had 7.50's on my 88's - so I don't think that is a problem as such. I have a Sailsbury on my 88" currently (because I happened to have a 109 rolling chassis sitting around), and would heartily not recommend it for laning or trialling - the bottom of the Sailsbury makes a very effective ground anchor!

If you want to break an 88" rear shaft then driving off a kerb (or rock, or mound etc) such that one wheel is free to spin, however breifly, is a good way of doing it.

As said above, I'm firmly of the opinion that driving style, on or off-road, is the key. I can well remember going to my first inter-club trial (at Trentham) and whatching bog standard Series motors thrashing toyed-up 90's. After a while I twigged why - a careful right foot is far more effective than a V8 or agressive tyres.

Just my 2p.

Richard

On or around Thu, 10 Aug 2006 09:03:29 +0100, beamendsltd enlightened us thusly:

There's a good deal of truth in that. also fat tyres only make sense in very soft conditions, when they might make the diffence between sinking and not-sinking. all the rest of the time, normal-width tyres work better.

There used to be available, as I remember, a replacement hub which absorbed shock (a bit like the springs in the driven plate of a clutch, I guess) in the transmission. If they're still around and not too expensive, it could be a quick and easy way to prevent weakening or fracture of half shafts. Never heard of a freewheeing version for the front, though :-)

While on the subject, btw, can anyone tell me the reason for the dire warnings about damage to transmission if using 4wd with the hubs set to freewheel? I can't see why when in freewheel the hubs should lock the front half shafts whether driving or driven in either direction. If this is the problem, however, is it the case with all makes? - I use superwinch.

Arthur (and "Mikey", my '67 SIIa SWB)

Free-wheeling hubs for the front of Series vehicles are two-a-penny, there were some automatic ones, as per the Series I, but they didn't work in reverse. All the rest are just variations on a theme. There is/was a kit available for Defenders that involved a mod to the transfer box. In fact, the very, very early 110's had selectable

4wd as per Series motors and freewheeling hubs are in the parts book.

Because there would be some very interesting loads in the transfer box, which it was not designed for, plus I *think* the front diff would very confused with no load at all on the half-shafts with the prop being driven, but then that might just be me!

Richard

IIRC the warning was only about using low ratio if the front wheels weren't driven. Because the rear half shafts were a known failure point having the greater torque delivered to them rather than shared between front and back was too much. This is why the Range Rover moved to permanent 4wd.

The other issue was the yellow knob. This is essentially a sprung loaded release mechanism to engage a dog clutch and was designed for use on the move. If free wheeling front hubs are in use then the front transmission drive train is stationary. Engage the clutch via the yellow knob, on the move, and all this has to be accelerated to road speed instantaneously.

AJH

I'd wondered if the rear half shaft loading was the issue, but in this case, the rear half shaft loading would also be too high if in low transfer one of the front wheels lost traction and all torque was delivered to the back. This is practically what 4wd is for and will occur frequently off road, so it would seem strange if it was guaranteed to cause damage. If, on the other hand, all wheels retain full traction, then the front/rear windup would surely put even more stress on the transmission.

As an aside, I've often thought that the torque due to windup must be quite large. I wonder if this is what sometimes causes the initial damage in some cases of half shaft failure and it's only a shock (such as a careless left foot or spinning wheel) that finishes it off. I'd always assumed that eliminating windup was the main reason for moving to using a centre diff, and if you've got a centre diff you might as well have permanent 4wd as well.

I agree that the dog clutch will have a nasty shock if engaged with the vehicle in motion but the front transmission stationary, so I can understand the yellow knob warning. However, the shock would be even worse if the yellow knob were to be pressed down when the vehicle is stuck with the rear wheels spinning, which must be a likely reaction for anyone, who, for example, loses traction on a snowy road.

Maybe, as another contributor has suggested, there's a potential problem with the axle. Although the pinion and crown wheel are designed to drive in either direction, maybe there's a problem if the pinion is driven, but the crown wheel is unloaded and rattles back and forward between driving and driven tooth engagement. Can any diff experts comment?

Sorry, the last sentence was meant to be a joke - although you could in principle have a freewheeling hub which shock absorbed when locked, it seemed a bit unlikely.

I can't see the problem with transfer box loading. The transfer box gears are ahead of the dog clutch, so the transfer gears only see the combined load and don't know anything about whether the load is from the front or back or both. The dog clutch looks too simple to worry about whether the front output is loaded or not. I've never heard of any problems with running with the front prop disconnected, which would look the same to the box as the front axle freewheeling.

Seems you're more likely to be on the right track in suspecting the pinion and crown wheel driving the front diff (see my other reply).

Back on the history track, the old Rover 75s and 90s (closely related to 4 cyl and 6 cyl Land Rovers) had a freewheel which disengaged the transmission on overrun, thus saving fuel and engine/transmission wear when going downhill or stopping. The lack of any engine braking, combined with single circuit brakes must have been a bit lethal, and Rover dropped it in favour of an overdrive. I think, but am not sure, that this change coincided with the 75 becoming the 80 and the 90 becoming the 100 and 110 (twin carb).

"ArthurC" >>

You've got it spot on there. Many farmers would tow large loads with series vehicles which needed low ratio to manouvre and also to start off from junctions and to climb roads. They were just so underpowered at that time. The torque loading from all this was massive, especially when turning with a heavy load where the wheels could not slip. The half shafts just couldn't take this for very long and were/are a regular failure item. Sometimes they ultimately failed when driven quite gently up a slight grade in 2wd.

I'd

Yes, the Defender was a major step forward and is still ahead of the game in this respect when compared with all other comparable vehicles. Same goes for the Discovery and Range Rover in all models although others have caught up in drive train design in this class, such as Toyota and Mercedes but the Toyota does lock the centre diff by default in low range for some reason.

Huw

I think the issue was more to do with using low ratio on a firm surface with a heavy load or trailer, it was to share the load between all halfshafts. On soft going traction is the limit on firm surface it's engine torque, clutch slipping or driveline failure. The half shafts were the known weak point and IIRC the manual stressed that low ration 4wd was only for off road use but we all used it when towing heavy loads.

Yes I am sure wind up does cause high stress on the half shafts but it was always the long one on the rear that broke and always with characteristic fatigue lines (and it leaves a sort of cone at the break). As I said spinning the rear wheel in mud and then suddenly lifting off to brake it on engine overrun and pulling the vehicle to a halt with the handbrake was the counter point to stressing it whilst under load. These combined to fatigue the halfshaft.

All sounds reasonable but off course you still get wind up when the diff lock is used.

Or in the mud. The thing is releasing the throttle when things start to grate with a stuck vehicle is a lot faster than bringing the vehicle to a stop when the yellow button has been pressed in anticipation of a muddy bit.

I don't know but I do have experience of another 4wd tractor where the lower 3 gears were for crawling and not full power use. The manual plainly states that the diff will not take full engine torque in these low gears. The manufacturer safeguarded the diff, half shafts and housings by using shear rivets from crown wheel to carrier.

AJH

Think of the kinetic energies involved with a free but stationary shaft being instantly brought up to speed - something would give, somewhere. Probably the dog clutch.

Karen

Not two a penny in Australia - they are really expensive for what they are. Last time I purchased some in the UK I bought direct from Mayflower in Tavistock for some £12 or so, in around 1970.

Karen

Karen

It would only be worse if the freewheeling hubs had been put back in fixed, otherwise it would be the same as the first case scenario, i.e. no load but stationary front drive train.

which must be a likely reaction

If there is so much play in the meshing of the crown wheel and pinion that they rattle with no load, then the diff would be knackered anyway.

Martin.

On or around 11 Aug 2006 12:06:23 -0700, "ArthurC" enlightened us thusly:

but only people who don't bother to read the instructions...

Best thing is to depress the clutch momentarily whilst pressing yellow knob if driving off road with rear wheels spinning but I would think most if not all would judge the conditions and already be in 4 wheel drive with the front hubs in fixed before getting into such a position.

Martin

It's a simple rule really - if you're going off road the hubs go in regardless of whether you think 4WD is going to be needed.