Thread: Adaptor shaft

Originally Posted by workingonit

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.

The end float of the main shaft is controlled by the clearance in the rear main ball bearing and the clearances around the snap ring holding it in position. I doubt that it's particularly critical. The size of these components means that they won't suffer from a little movement between acceleration and deceleration. This end movement would be generated by the helical gears under load from the engine.

As for my idea of loading, a torque applied to a gear set will tend to push them apart. Even a mighty Isuzu box will have some slight shaft deflection under full load. I remember from back at engineering school that gear teeth profiles are designed to function quietly over a small range of clearances, involute shape I believe.

Originally Posted by Sitec

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.

Well that's exactly how mine was done, and it snapped.

85 county.

As you say, and everyone agrees, the flange is torqued up. But some say it is also torquing the output bearing. I queried this, because to me it appears only torqued up to keep the drive flange on, and to grip the inner race - to me that is not torquing the bearing as you would a taper.

I've tried to buy the MSA manual from Isuzu, on line and a couple of truck supplies. All I've turned up is the MXA (which I've now got), or sites that present a generic photo purporting to be out of the MSA manual but with no Isuzu logo or anything indicating it might be genuine and want $10 from you.

Anyone know a proven source for the MSA manual?

Bee utey

The outer bearing race is 90mm o/d and 77mm i/d. The inner race is 52mm o/d and approx 47mm i/d.

The shaft is 20 spline, approx 36.5mm o/d. Total spline length without bolt thread is 80mm, but 24.5 of that is taken up with a spacer and the speedo worm gear - length does not include the smaller thread for the flange retaining nut.

Just to stir Vern (and others). How about a uni join combined with sliding spline? Where's my fire proof suit...

So is my 0.2mm wobble at the end of the outputshaft (0.016") good or bad or doesn't matter?

Sigh....

Just get yours going would you

Originally Posted by bee utey

Excellent, thank you. I see that the main shaft of the 5 speed is supported solely by the needle roller in the input shaft and the ball bearing in the back of the main casing. I see that first gear is near the centre of the main shaft, so any decent load in first gear would lead to the highest deflection in the shaft under load. Then I see the measurement for factory runout (page 7B-62) at the centre of the shaft (.002") and acceptable runout on a used shaft (.008") thinking that the design of the box allows for this perfectly. The 4WD transfer box is close coupled and would have no trouble dealing with this slight deflection.

Now if you bolt a rigid extension to the output flange this runout (plus any adaptor misalignment plus any load deflection) would be magnified by the time you get to the LT230 input gear. The maximum stress in the extension shaft would be where Vern's shaft broke. So a slightly flexible splined coupling allowing that runout to be accommodated seems like the best idea, to me anyway.

mine hasn't been the only one that has snapped, snapped in exactly the same place in very similar conditions

aulro - Vern - snapped - case not yet assessed?
aulro - Bee utey - snapped - case not yet assessed?
aulro - from memory I think one more - shaft damaged - case damaged

outcast - if I understand them two worn (not broken) Sheldon shafts - and two Sheldon cracked cases

Outcast and Sheldon shafts seem to get the tick in design. Query on final treatments. Cases are out in front as prime suspect?

Ahhh, I love these threads. This is bee uty on the 'Isuzu MSA gearbox to LT230'

'...An actual universal/CV/rotoflex joint might work too, not sure if you'd have the room.'

http://www.aulro.com/afvb/isuzu-land...-lt230-53.html