Thread: Adaptor shaft

Thanks Sitec. From your description I can only imagine it must be an interesting driving experience bringing a 101 up to speed.

Where did you find your information about preload on the ZF output shaft?

I have removed 4 zf boxes out of Disco 1s for seals, filters, valve systems to replace kick downs etc. I replaced one of the boxes with an Ashcroft unit, paid a core charge to keep the old box, hence my ability to take references from it where practicable.

I've noticed all the zf autos have very floppy or loose output shafts. As said earlier I cannot find any evidence in the BMW workshop manual to show that the zf output requires preload. Off hand I would have said the zf output shaft remains loose at the end of the auto gearbox, and simply rests in the input gear ready to drive it.

I asked some questions on the forum about output shaft wobble. I asked whether the input gear in the LT230 imposed any load on the zf to stiffen it up. I wondered whether the zf wobble was actually LRovers way of building in a mechanism to allow for any slight mis-alignments. The response was not particularly edifying. The one thing I was told was that the torqued up nut and flange did preload the output shaft bearing on the MSA.

When I finally exposed the rear of the MSA, as you saw in the earlier post, I was interested to see how rigid or unyielding the output shaft was without the nut and flange.

Now that I've bumped the box and knocked things when putting on and off bits of the Outcast kit, I now find when I grab the MSA output shaft I can pull it a couple of mm out of the box. The bearing assembly comes with it for the same distance, but seems to be stopped by some retainer which I think might be what appears to be a split ring around the bearing in the picture. The MSA shaft however remains rigid with almost no ability to be moved up or down. Only when I put a dial on it at Lotza's request could you see it can be moved up and down by about 0.2mm.

I have a manual for the Isuzu MXA which looks to be very similar to the MSA. The manual says the nut has to be done up to 226 Nm but does not say one way or the other that this is for bearing preload. I have taken the comments from the forum to be that this is indeed preload. Putting the flange back on and tightening the nut a small amount seems to make no difference to the 0.2 up and down movement. So you tell me if you think the bearing is preloaded by the flange and nut or is already preloaded some other way, or is not loaded at all

Where did you find your information about preload on the ZF output shaft?

All this talk of preload but little understanding of bearings. The only common bearing system that needs preload is a pair of opposed taper roller bearings, or perhaps angular contact ball bearings. The only thing a shaft nut should be able to do on a plain ball bearing or a parallel roller bearing is clamp up the inner race to the shaft to prevent relative movement. Differential pinions (between taper rollers) for example either have a rigid spacer with shims chosen for the correct preload or a collapsible spacer for simpler assembly. Only in the first case the flange nut torque isn't particularly critical.

I've been waiting patiently for someone to show what sort of bearings and loading the Isuzu gearbox output shaft has, (sectional drawing anyone?) because that will determine the optimal design of the adaptor shaft. A gearbox designed to drive a universal joint directly has no need for a super precise alignment like one that drives an attached transfer case. Running a rigid shaft effectively in three tight bearings in a row means that shaft will require super tight tolerances to function adequately. Either that or the centre bearing (in this case the rearmost bearing on the gearbox) has to have extra clearance (or be removed entirely) to allow for the inevitable changes in dimension with loading.

And before someone pipes up again with "it's too rigid to flex, wow look at how big it is" remember there's an Isuzu engine in front of it. EVERYTHING flexes, just because you can't see it when you rotate it by hand doesn't mean that it doesn't deflect under engine load. The trick is to design the shaft constraints so that the flex does no harm.

A multi vehicle application gearbox like the ZF is so designed that the output shaft relies on either an attached transfer case or an extension housing with a second bearing to hold the shaft in alignment adequately. That second bearing could be either a simple bush and slip yoke or a parallel bearing and yoke.

Ah.... Poss a pit of confusion with the ZF side of things... Im using a ZF5-42 truck gearbox which is std behind a Cummins 6bt in the UK. Its a heavy duty 5 speed which is designed to cope with the engine in front of it. The preload of the output flange is more a case of 'being bloody tight' so as to stop the gears/bearings from floating on the main shaft. It is a requirement of that box and as Nick (nrs91) found out in his Cummins to Land Rover conversion in the UK. He used the 'floating spud shaft' idea and the box lasted 3000 miles. This is why I made my kit without a spud shaft, and with a tube nut.. Re preload on the LT.. well, that just has to be set up as original, but to retain this preload when bolting it onto a different box using a different system, account has to be taken as it will alter when bolted tight with a tube nut. Trust me, I thought about it.. It wouldn't have lasted 15000kms if I hadn't!

Originally Posted by bee utey

All this talk of preload but little understanding of bearings. The only common bearing system that needs preload is a pair of opposed taper roller bearings, or perhaps angular contact ball bearings. The only thing a shaft nut should be able to do on a plain ball bearing or a parallel roller bearing is clamp up the inner race to the shaft to prevent relative movement. Differential pinions (between taper rollers) for example either have a rigid spacer with shims chosen for the correct preload or a collapsible spacer for simpler assembly. Only in the first case the flange nut torque isn't particularly critical.

I've been waiting patiently for someone to show what sort of bearings and loading the Isuzu gearbox output shaft has, (sectional drawing anyone?) because that will determine the optimal design of the adaptor shaft. A gearbox designed to drive a universal joint directly has no need for a super precise alignment like one that drives an attached transfer case. Running a rigid shaft effectively in three tight bearings in a row means that shaft will require super tight tolerances to function adequately. Either that or the centre bearing (in this case the rearmost bearing on the gearbox) has to have extra clearance (or be removed entirely) to allow for the inevitable changes in dimension with loading.

And before someone pipes up again with "it's too rigid to flex, wow look at how big it is" remember there's an Isuzu engine in front of it. EVERYTHING flexes, just because you can't see it when you rotate it by hand doesn't mean that it doesn't deflect under engine load. The trick is to design the shaft constraints so that the flex does no harm.

A multi vehicle application gearbox like the ZF is so designed that the output shaft relies on either an attached transfer case or an extension housing with a second bearing to hold the shaft in alignment adequately. That second bearing could be either a simple bush and slip yoke or a parallel bearing and yoke.

Here's a link to the MXA manual which is essentially the same box: [ame="http://www.weatherproof-windows.co.uk/nkr_repair_manual/PDF/LGMXA-WE-461.pdf"]http://www.weatherproof-windows.co.uk/nkr_repair_manual/PDF/LGMXA-WE-461.pdf[/ame]


Section view on Pg 7B-3.

You might find 7B-4 interesting too - it shows how Isuzu designed the input shaft to the transfer case in the 4WD versions.

Steve

Steveg. 7B-23 is where I got my flange bolt torque of 226Nm. I have a pdf that looks very similar for the same box.

Sitec. Thanks for the clarification about the zf.

Bee utey. Thanks for the info on bearings. The MSA bearing just looks like a plain ball bearing to me. I understand the principle of clamping to the inner race of a straight ball bearing vs torquing a taper.

I had my doubts about the flange bolt being a bearing tensioner - I queried it and end float examples. I was told the flange bolt is torquing the output bearing and not to concern myself about shaft float in zf and or MSA.

So in your view am I safe to go back to the idea that no preload is being applied to the MSA output bearing, but just clamping the inner race?

I guess it doesn't really matter - whether its just securing the drive flange and clamping the inner race or if its applying preload, just tightening it up will cover all bases. But some wanted me to tighten the bolt up and do some float measurements on the assumption that the bearings get preloaded. Sounds like the information I gave 'unloaded' should be just as valid.

Bee utey.

Been digesting your second paragraph.

The bearing on mine is marked 'NSK TM308-' on the plastic dust seal. On the outer race it is stamped '6308N'. The bearing has a ring groove, around the perimeter of the outer bearing, to take a flat profile split ring - my impression is that the ring stops the shaft from moving further into the MSA box. Maybe able to see that in earlier photo not far back. I cannot say if the shaft is supported by just one bearing, or maybe a second one inside the box - all I can say is the shaft-in-bearing is very solid for something that has been in service in an industrial truck (never saw the truck so no idea of mileage).

Not sure what you mean by '... and loading the Isuzu gearbox output shaft has.' If you mean the type of truck weighs, then 4 to 6-8 tonne - not 100% sure.

well that is interesting

Taper roller bearing have some slack, in not that tend to over heat. that's why you back off wheel bearing, clearance in the transfer case etc

angular contact are about the only bearings with pre-load, think spindal moulders or wood working machines etc.

look at the MSA box manual. the output flange but must be torqued up. because if you look at the manual you will see that this is the only pressure applied to the main cluster for the dogs. NB lt95 is shimmed.

Well, if I was using an Isuzu box, and length was not critical, this is how Id do it.... A simple adaptor shaft that bolts directly onto the original prop shaft output flange.