Pre war differential casings

[Brucegirvan]

We’ve had a second diff casing go in the same manner. Is there something we should know? Is there a fix?
Polly - 1929 7hp went heading home after a trial. We were on a long hill and had had to drop to second and after a minute or so there was a bang and the result was the diff casing had gone. I had put this down to trial wear and whilst frustrated, accept that that is a risk. However yesterday on a regulation road rally the same happened with Eddie - 1930 7hp Economy. Again heading up a hill in second. Eddie has been ultra reliable and there was not warning on this. Eddie’s result showing below. Both have failed upwards. Thoughts please. And I’m now after a diff casing set! Unless someone says these can be repaired.

F3047B53-846B-4955-A498-690685BEABD7.jpeg

[Forumadmin]

The crack looks new, rather than one that has developed over time. Before you put the next one in give it a crack test!
As you say, it looks like a vertical force, rather than axial, that has caused it. So are there any signs elsewhere, such as a scraping on the bottom of the diff or rubbing on any part of the chassis?
Perhaps some suspension rubbers or components are worn allowing the axle and case to somehow be put under more strain than usual. You need to consider how such a force could be transmitted to the case. Perhaps a wheel got stuck in a rut and the other wheel was put under load creating a bending moment. A sideways impact on the wheel rim might cause such a bending moment.
Other than that it could be just old age.
I should think it could be welded or stiched.
But you might have to take it to Asia https://www.youtube.com/watch?v=BK2Tw_M2KuQ
https://www.youtube.com/watch?v=dnpHtkzT2Rk

or perhaps not
https://blaker.co.uk/axle-straightening-services/

[Nick Webster]

I'm not very well up on pre-war, but I take it that is a rubber coupling disc on the drive flange? It does not look very distorted.

Nick

[PJGD]

Surely the natural force on the pinion is upward, is it not? Driving forward, the pinion is trying to climb up the crown wheel and it is the diff casing that is holding the pinion in place. Nevertheless, it is surprising that the case let go before some other component such as a half shaft etc.

[AlanBartlett]

Ouch!

Extremely bad luck to happen twice! I may have a spare casing. I'm in the slow process of rebuilding the axle for the eventual lorry in between everything else!

Still puzzled as to how that should happen though.

Regards
Alan

[Tony Fearn]

Hello again Bruce, and what an intriguing state of affairs.
As Alan says, "OUCH" , or even "OOPS-A-DAISY".
I'm as surprised as anyone that you should suffer the same problem twice on different cars.
I've never heard of this problem before, so I'm as much in the dark as you.
Nevertheless:-
I wouldn't bet on repairing the casing by welding, or stitching. It would be, in my opinion, a last resort, without understanding why it happened.
The rear springs seem to be rather 'meaty', similar to a Bradford. Are they correct for the car?
Is the jaw connecting the pinion to the prop shaft the wrong way round?
Is the disc connecting the prop shaft end to the pinion shaft flexible? It looks from the photo to be made of solid steel.
Does 'Eddie' have Hartford shock absorbers, and are they in good nick?
I can't understand why the pinion shaft, and presumably the prop shaft points towards the ground in the photograph you posted.
Regarding Philip's reasoning, could something have become trapped in the differential gears? Although this is very unlikely as both cars have had the same problem.

If you can't source a diff casing from elsewhere, I have delved into my stores and have found one.

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I also have more than one rear axle, but the backplates will need fettling.
Whenever (or if) you wish, email or phone me using the details in the membership leaflet.
All the rear axles are pre-war. Vintage I think are different, but I've included a photo of the casting number on the diff casing in case these are common.
Regards,
Tony.
P.S. Have a look again at viewtopic.php?t=6005

[Forumadmin]

Is the disc connecting the prop shaft end to the pinion shaft flexible? It looks from the photo to be made of solid steel.

That was my next question. The prop shaft must be able to flex to take up the axle vertical movement and possible chassis flex. Rear axle location might also be an issue. On a Jav the Panhard rod does this, but if there is excessive side to side movement of the axle this might also exert extra stress.

[BarryCambs]

As pointed out by Tony, there should be a Layrub coupling both ends of the prop shaft, but from the photo it looks like a solid disk??

[James Baxter]

The usual rubber coupling has been replaced by a solid disc, but that disc is an adaptor for a Hardy Spicer propshaft, fully flexible, I think.
It would be interesting to know if all the teeth are in place, since a stray tooth getting jammed in, would be my first guess of the cause of failure.
Jolly unlucky. I am not aware they are particularly weak. .......?

[James Baxter]

The usual rubber coupling has been replaced by a solid disc, but that disc is an adaptor for a Hardy Spicer propshaft, fully flexible, I think.
It would be interesting to know if all the teeth are in place, since a stray tooth getting jammed in, would be my first guess of the cause of failure.
Jolly unlucky. I am not aware they are particularly weak. .......?

[Tony Fearn]

Hi all.
This shows the necessity of more than one photo, so all of us can see what is really going on.
I also took a photo of the rest of the bits in the tub which contained the diff case halves, just for posterity.
It looks like there are bits from a couple of diffs.
Is there an anomaly in the number of teeth on each of the crown wheels as can be seen in the photos below.
One seems to have more than the other.
Why would this be? Are they from different models?

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And as a further comment, the three-pronged jaw originally used a flexible fabric-type disc, whereas the double jaw came later and used the Layrub disc. (I am open to correction).

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Tony.

[Brucegirvan]

Dear all - thank you for these. As i work away most of the week it can appear that i am a bit slow on response - believe me i am grateful for your words.

What I left out was that Eddie was over 60 miles into the rally, which was all on good surface B and C roads, so I am loathed to think that abuse from interaction with the environment is to blame, whereas I could understand that more with the failure on Polly. Eddie had also I had a very successful Madresfield event a couple of weeks earlier, which on the face of it could have shown up any underlying cracks etc.

OK so a few point on your points:
Pinion breakage - I agree ‘up’ is right’ due to the direction of forces.
Flexible disc - or lack of. As James noted, both Eddie and Polly have been fitted with props that have UJ’s both ends. VO on the other hand has the classic carden arrangement and flex discs. I am aware HSpicers are OK, though need care. We do maintain ours via greasing and checking bolts regularly. Interestingly this arrangement involved not only these ‘odd’ solid coupling discs, but also adding a significant weight. Many Kg’s. Not ideal. Was going over to UJ’s favoured for competition thinking that the fabric discs are not good under load? I’d be a little surprised as the fabric disc do not have that much play between the bolts. Thoughts?
Clean break - Again, I agree. When we looked at Polly’s break there was no obvious failure start point, it looks more like a massive breakage. The large crystal structure in these castings would not blunt any cracking very well.
Teeth - Not sure yet, James. I need to create room and retrieve Eddie to have a good look. Whilst we have seen that on Polly’s gearbox before (the gearbox side was jettisoned as a result), it was not the case with Polly, though there was damage probably from the sudden failure and resulting contact as the prop bounced around. I can update if different later
Diff casing casting number - Thank you, Tony. 915 is correct. I will contact you. This is a pre-war casing and has the 3 holes - drain, fill and height check.
Crown gearing - Where do we start on this conversation? I may as well confess straight up that Eddie has classic ‘back axle sitting on top of spring’, whereas Polly has it sitting under, which necessitates swapping the crown around to avoid 3 reverse and one forward gearing. I thought there were different gearing for trucks/lorries v cars. Am I imagining that?
Shock absorbers - I had not counted these, as they are Hartfords, were stripped and maintained about<1000miles previously and we’d had a great run up to the point of failure. We were certainly not suffering from ride issues or travelling in any ruts.
Springs - To my knowledge these are what were fitted at that time. These were brand new <1000miles ago (small mortgage required, though probably a lot less than today’s cost, thanks to Putin!). Again the happy mileage in use has not shown up any issues, including 350mile return trip to compete at the last Bicester driving test.

A few other things:
- Would ‘grabbing 1st gear’ have done it? Matt says he was preparing to/may have. Who knows. That is water under the bridge even if he did; it was not how I remembered it but I was face in a map at the time. However could that have generated enough ‘lock’ in the system for the weakest link to go? Give how beefy the drive shafts are, and that the pinion is a splined fit to the jaw rather than a keyed fit…. Thoughts?
- Jaw reversal - I want to check what you mean by this, Tony? From what I remember putting Polly’s diff back together, the 4 bolts have only 2 positions that work. Ie the flange can only go on in 2 positions 180 Deg apart.
Spline v keyway - Does anyone know when this came in and why? Splines would provide more strength surely. Does this explain the 2 v 3 jaw options? And what was the anticipated method of connecting a 2 bolt pinion jaw option to the prop?

Thanks again.

Bruce

[Brucegirvan]

Tony - many thanks for pointing to the earlier topic 6005. A mine of information is being built on JowettTalk. We’ll need it when the walking pre-war Jowett encyclopedias can only look down on our efforts in the years to come

[Forumadmin]

Dropping the clutch in first gear does put a lot of load on the transmission. Frequently doing this may have caused fatigue or just once may have been just too much strain. UJs also do not take up any axial movement which is why the rear prop on the post war prop has splines. CV joints are another solution.

[Brucegirvan]

Thank you, Keith. Both Props have a sliding joint in them, though at the gearbox end..makes me think whether it should be the other way round given the fact that the gearbox should not move quite as much as the diff casing!