Not quite what we had in mind!

[Peter and Sandra]

It has cracked right on the edge of the weld. Bush in the front of the tranny shows even wear as does the spigot, no signs of misalignment.
The flexplate was dialled in when fitted and hasn't moved. The converter spins freely without any wobble when flicked with the fingers when the bolts to the flexplate are removed. The flexplate to converter bolts all screw in freely by hand with no binding and when we had the injectors out originally the whole engine trans combo could be turned freely by hand. No signs of anything moving or flexing when it is all bolted up together either.
Coolers are plumbed directly to the trans not through the radiator so no chance of coolant ingress.

[supersparky]

So what is the next step? Do you just replace damaged components and re-assemble it all and head off again, or......?
Is it possible that the engine/ transmission mounting configuration allows flexing through the adapter plate or bellhousing area when travelling over corrugations or chassis flexing?

[T1 Terry]

The only power transmitted through that snout is the drive the pump, so it is not a torque over load crack, that only leaves a flexing force causing the crack so something is moving between the parallel drive from crankshaft to transmission and the body of the transmission itself.

[Peter and Sandra]

Yes that is what the transmission bods said too. Problem is the whole thing slides together and bolts up really well, no juggling to line stuff up and no forcing. Everything spins freely when installed, as the 4L80E like most GM trannies is only mounted top half of the circle it has been fitted with the diecast TC cover to stiffen the whole thing up and give full circle mount.
Are you coming over Adelaide way Terry as you're most welcome to have a look as we're not going anywhere soon ))
Peter

[T1 Terry]

Yes that is what the transmission bods said too. Problem is the whole thing slides together and bolts up really well, no juggling to line stuff up and no forcing. Everything spins freely when installed, as the 4L80E like most GM trannies is only mounted top half of the circle it has been fitted with the diecast TC cover to stiffen the whole thing up and give full circle mount.
Are you coming over Adelaide way Terry as you're most welcome to have a look as we're not going anywhere soon ))
Peter

I think you are on the right track regarding the full circle bell housing giving the required stiffness. Perhaps look at the problem from the other direction, a truck bellhousing that suits the engine and then adapt the transmission on to that. The size/thickness of casting on an Alison transmission compared to a car transmission says to me that they have had to go to that extent to solve a problem.
Much as I'd love to come and cast an eye over it, I have 3 jobs to finish before the next job arrives either Sunday night or Monday morning, so not much change of even seeing daylight for a few weeks..... plus I'm required to go house looking tomorrow to make sure the house we have selected is the best available, just to make sure we haven't jumped at the first one we looked at...... more tomorrow night on its own thread

[supersparky]

Peter, I have just googled images of your trans, it looks like the evolution of the turbo 350/400. I had a few of them fail through the bellhousing area many years ago when I was doing things that they weren't designed to do. Is it possible for you to fabricate another mount at the rear of your engine block to stop the pitching effect of corrugations or heavy landings on your front suspension.

[Peter and Sandra]

Already done and fitted from the start, the Oka had SAE type saddle mounts on the side of the original bellhousing and I've made similar to suit this engine/trans. The mounts come down the side of the block (they are bolted at various points) and then pick up the SAE mount on the chassis.
As the trans adapter also stops at the same point as the trans mounting circle I made a bracket which attaches to the sump bolts down each side and also the adapter, which then allows the alloy torque converter cover to be bolted in to complete a full circle mount.
The weird thing is though that there are at least two other Oka's running the same engine/trans combo that do not have any mounts between the front engine mounts and the rear of the trans/transfer case, no SAE mounts at the rear of the block and no full circle mount at the engine trans. They must flex quite a bit but one has completed over 40k all over Oz with that setup.
When mine was passed by the engineer he was underneath watching while I held it on the brakes at 1500-2000 rpm three times in each direction and he stated there was no movement of the drivetrain at all under load. The he wanted to know whether I was looking for a job as I did neater work than some of his employees. I pointed out that I had the luxury of unlimited time to make and finish stuff and wasn't on a timeframe.

[supersparky]

Sounds like you have that more than covered then. So, what's next?

[Peter and Sandra]

Hopefully will hear from the torque converter fella today as to a replacement, then refit and probably head home, don't trust it much now ))

[T1 Terry]

Hopefully will hear from the torque converter fella today as to a replacement, then refit and probably head home, don't trust it much now ))

Maybe swap it out for a 4 speed Alison with an overdrive and lock up converter instead, you won't break one of them in a hurry, I think they come in 7 or 8 speed units these days. How about one of those hybrid drive electric auto trannies, the house batteries and traction battery all the one pack