Technical Gearbox jammed

[bugsymike]

After a month ’off’ I finally got the chance to fit the new 4th gear/bush and resume battle with the setup. After a bit of faffage I was pleased with the pinion/crown contact/backlash so moved onto the preload. Using the very helpful 2018 post started by @fiat500 I got to ‘enjoy’ the relationship between the two and starting again. But I got the lash back to where it needs to be with the max preload I can exert but I cannot get enough preload to hold 1ftlb no matter how brutally tight I try to make it. What am I missing?

Is this the preload on the pinion gear shaft or with the crownwheel assembled also after doing your contact/backlash side?

 

[cinque500]

Is this the preload on the pinion gear shaft or with the crownwheel assembled also after doing your contact/backlash side?

This is with the diff assembled. What I did first was get the pinion shaft shimmed to get the correct contact pattern and adjusted the serrated rings to get the crown lash at 0.1mm.
Then I looked at adjusting both rings to get the lash and preload simultaneously correct. Just the output shaft is assembled and one drive shaft ‘locked’.

 

[bugsymike]

This is with the diff assembled. What I did first was get the pinion shaft shimmed to get the correct contact pattern and adjusted the serrated rings to get the crown lash at 0.1mm.
Then I looked at adjusting both rings to get the lash and preload simultaneously correct. Just the output shaft is assembled and one drive shaft ‘locked’.

The preload measurement, is it to measure pinion gear preload only , in which case crown wheel should not be involved, or crown wheel bearing preload?
From memory depending on axle design it may be two different settings.
Generally the pinion preload I would have thought most critical as it prevents pinion moving in and out of mesh position depending on load.
This is why in the old days you could hear axle whine change depending on if foot was on accelerator, or off on over run.
On the crown wheel preload setting it would involve slight tightening of both serrated rings a small amount and then rechecking gear mesh etc. as well as preload setting.
Once correct it is a good idea with lubricated gears and bearings, to turn them over several times and then recheck settings.
Do note I have not rebuilt one of the transaxles, so what I am referring to is general axle/diff rebuilding practice. So I defer to those more familiar with your model.

 

[cinque500]

The preload measurement, is it to measure pinion gear preload only , in which case crown wheel should not be involved, or crown wheel bearing preload?
From memory depending on axle design it may be two different settings.
Generally the pinion preload I would have thought most critical as it prevents pinion moving in and out of mesh position depending on load.
This is why in the old days you could hear axle whine change depending on if foot was on accelerator, or off on over run.
On the crown wheel preload setting it would involve slight tightening of both serrated rings a small amount and then rechecking gear mesh etc. as well as preload setting.
Once correct it is a good idea with lubricated gears and bearings, to turn them over several times and then recheck settings.
Do note I have not rebuilt one of the transaxles, so what I am referring to is general axle/diff rebuilding practice. So I defer to those more familiar with your model.

Thanks for this Mike, good stuff
I’d say I’m on part 2 of your process above, that is “On the crown wheel preload setting ….”. I’m not able to get enough pressure with the serrated rings onto the taper bearings to pass the 1ftlb test described in the Haynes manual and Pete’s thread on 1/12/18 and the @Bleeding Knuckles method https://www.fiatforum.com/threads/setting-up-the-diff-differential.463644/

 

[shera2025]

Gearbox locked solid recently doing the hill climb at Brooklands, no neutral either. Took the box apart and found the pinion bearing in very poor condition. Changed that and set the shims etc. All good on that front but having put the rest of the gearbox back in I find a still can’t select neutral and when I try to select other gears it just jams the box.
I know from my description it sounds very much like the interlock things, the two little kind of oval ballbearings and the pin in between could be at fault. But I’ve done those a few times over the years so I’m pretty familiar with those strange parts.
So then thinking I may perhaps have a bent fork I also looked at overriding the selectors by removing the 8mm bolts to manually (albeit perhaps moving things out of sync) try and find a neutral in there somewhere but I can’t no matter what I try.
Here’s a video, hoping it will help find a solution that evading me!

That sounds really frustrating after doing all that work. If you can’t find neutral even when moving the selectors manually, it does point to something still out of alignment inside, possibly a selector fork or something not sitting where it should after reassembly. Even if you’ve done the interlock setup before, it might be worth double-checking everything there again. Hopefully the video helps others spot what’s going on.

 

[bugsymike]

Thanks for this Mike, good stuff
I’d say I’m on part 2 of your process above, that is “On the crown wheel preload setting ….”. I’m not able to get enough pressure with the serrated rings onto the taper bearings to pass the 1ftlb test described in the Haynes manual and Pete’s thread on 1/12/18 and the @Bleeding Knuckles method https://www.fiatforum.com/threads/setting-up-the-diff-differential.463644/

Is it possible there is a correct C spanner that engages with the serrated rings to provide the force required?

 

[fiat500]

After a month ’off’ I finally got the chance to fit the new 4th gear/bush and resume battle with the setup. After a bit of faffage I was pleased with the pinion/crown contact/backlash so moved onto the preload. Using the very helpful 2018 post started by @fiat500 I got to ‘enjoy’ the relationship between the two and starting again. But I got the lash back to where it needs to be with the max preload I can exert but I cannot get enough preload to hold 1ftlb no matter how brutally tight I try to make it. What am I missing?

@cinque500 You woke me up!
Are you doing things the right way round?
The preload is set first. At this point you don't want the crownwheel and pinion binding on each other, but backlash perfection is not needed. Both castellated rings will need adjusting towards each other so that whilst the crownwheel is still just "kissing" the pinion the bearings are "tight" to that 1lb/ft turning torque. Then, by tightening one castellated ring, and loosening the other by exactly the same amount at a time, you push the crownwheel either away from or towards the pinion until you have the correct backlash, without losing the preload.
At that point the exact preload may in any case have been lost....but if you have done this carefully it should be only by a fraction. But then the same principle applies. Whether you need to increase or decrease preload you must move both those rings either towards or away from each other by exactly the same amount. This should not affect the backlash as at this stage, that additional loading on the bearings amounts to a microscopic amount of movement.
However, you may then want to recheck the backlash, and this can go on ad infinitum depending how patient you are, or how much of a gambler.
As with any bearings, if you apply pressure to them they will eventually tighten, bind, and then fail. So if the above guidance doesn't work, something is allowing "give" or something immovable is preventing the application of load.

 

[cinque500]

@cinque500 You woke me up!
Are you doing things the right way round?
The preload is set first. At this point you don't want the crownwheel and pinion binding on each other, but backlash perfection is not needed. Both castellated rings will need adjusting towards each other so that whilst the crownwheel is still just "kissing" the pinion the bearings are "tight" to that 1lb/ft turning torque. Then, by tightening one castellated ring, and loosening the other by exactly the same amount at a time, you push the crownwheel either away from or towards the pinion until you have the correct backlash, without losing the preload.
At that point the exact preload may in any case have been lost....but if you have done this carefully it should be only by a fraction. But then the same principle applies. Whether you need to increase or decrease preload you must move both those rings either towards or away from each other by exactly the same amount. This should not affect the backlash as at this stage, that additional loading on the bearings amounts to a microscopic amount of movement.
However, you may then want to recheck the backlash, and this can go on ad infinitum depending how patient you are, or how much of a gambler.
As with any bearings, if you apply pressure to them they will eventually tighten, bind, and then fail. So if the above guidance doesn't work, something is allowing "give" or something immovable is preventing the application of load.

@fiat500 I’m glad to be of some use at last
Sounds like what I need to do then is slacken off the crown wheel side so there’s a fair bit of lash, set the preload using the other side, then revolve the castellated rings equal amounts until the backlash is to spec. I was trying to get this done all in one go if that makes sense.
Question for you - Does it matter what rotation and which drive shaft I use for the 1ftlb test?
@bugsymike here’s the tool I’m using, a motorbike clutch holder. Not the biggest for leverage perhaps?

 

[bugsymike]

@bugsymike here’s the tool I’m using, a motorbike clutch holder. Not the biggest for leverage perhaps?

Should be good enough for that amount of preload I would have thought.

 

[cinque500]

My bad I was trying to get the bearing preload set without having the bell housing half attached, relying on what I thought was very stiff 7mm plate on those bearing carriers being ok bolted on one side only - but no!!
With both halves assembled I can now get 1 ftlb on the driveshaft, happy days.
Have to start again from scratch on all the adjustments but hey at least I know I can achieve the right preload now. Thanks all, will update in due course but in the meantime any advice always gratefully received

 

[fiat500]

My bad I was trying to get the bearing preload set without having the bell housing half attached, relying on what I thought was very stiff 7mm plate on those bearing carriers being ok bolted on one side only - but no!!
With both halves assembled I can now get 1 ftlb on the driveshaft, happy days.
Have to start again from scratch on all the adjustments but hey at least I know I can achieve the right preload now. Thanks all, will update in due course but in the meantime any advice always gratefully received

The fact that it all needs to be assembled is what makes it so hard to get access for measuring the final backlash settings. But great to hear that you're on the final leg.