Excessive play in transfer box KZJ90

[BobMurphy]

You think its worth going further into the box then Bob ?

Yes, I found it easier to remove/replace the chain if the front prop drive was also removed.

With the sprocket out of the way its only a matter of removing three 6mm set screws to take the oil pump pick-up pipe out so that the magnetic trap can be reached.

Just to warn you . . With the rear cover removed, half the output shaft, complete with differential, can fall out .

You are right about the box twisting when trying to remove the Stake Nuts. I end-up standing on the locking bar and box to hold it all down!

Bob.

 

[Shayne]

But the chain looks good so my theory is shot down in flames and i've plenty to do without taking it apart just for a look if i'm unlikely to find anything to cure in there ?

Still reading about the recall thing , some suggest splitting and greasing the props cures the problem though i'm now thinking i should be looking at the front diff .

 

[Shayne]

Can't sleep and still racking both brain cells i hit upon the idea it could be the inner cv joints .

Web searches weren't helpful until i removed Toyota from my search pattern and then i started to see some relevant results .

 

[Shayne]

Right it's not the transfer box it can't be , with the rear prop removed the rotational play of the front prop is mimicked exactly by the rear prop flange .

If i hold the inner CV joint and twist on the front prop i can feel the slack so the box is going back together .

 

[diggerdave]

I feel for you, there's nothing more frustrating than a hard to diagnose problem.

On mine, with the front propshaft removed and with the centre differential locked (which should lock the front and rear propshafts together), if I hold the rear output flange firmly in position, I can rotate the front output flange by what feels like a lot (probably 10-15mm) before it locks up against the chain. I would expect a small amount of backlash to be normal, but this feels like w-a-y too much and would entirely account for my transmission shunt.

If you do the same thing Shayne, if I understand right, you feel no significant play between the two flanges? Where I have 10-15mm of rotation, you will have none or very little? If so, I think that is how it should be, i.e the chain is locking front and rear output shafts firmly together so they move as one when power is applied (have I understood that right...Bob Murphy?).

The photo shows what I mean (my box is still on the car and fully attached! Apart from the front prop being removed).

Given that there is no side-to-side movement on either front or rear flange that should mean the bearings are sound (i.e. both the front and rear output shafts within the the transfer box are held firmly in the correct position), I think the only answer is that my chain is slack... This would fit with the slightly graunchy noise I can hear when rotating the front flange with centre diff unlocked, the noise presumably of a worn chain.

What you are feeling by holding the inner CV and rotating the front prop is either backlash in the front diff, worn splines on the part of the driveshaft that's inside the diff or movement inside the inner CV joint (depending where you are holding it). However, there needs to be a fair amount of backlash within the diff - the question is, how much is too much?

 

[diggerdave]

P.s I'm feeling my way here and learning (hopefully) as I go. If anything I've said sounds wrong anyone, please say.

 

[Shayne]

We are all feeling our way here as you put it Dave .

What you say sounds about right to me but whats inside of these boxes is Bob's retirement hobby would you believe so i would wait for his input if i were you .

What is most baffling about mine is the lack of noise , i know Bob swapped a chain because the owner could hear it jumping teeth so chains can stretch .

Getting to that inspection hole like i did yesterday is no big deal , removing the prop is probably the hardest part - the stake nut can be removed and replaced far easier when the box is still fitted to the truck .

I can find no play in the box which is why i have abandoned that side of my investigation .

Now i think i have 15 years of wear giving some backlash exaggerated by inner cv joints that probably should have been replaced long before i bought the truck about 14 months ago .

I favour the joints over the diff because i can feel the knock inside the joint .

 

[diggerdave]

Getting to that inspection hole like i did yesterday is no big deal , removing the prop is probably the hardest part - the stake nut can be removed and replaced far easier when the box is still fitted to the truck .

I think that is my next step.

 

[Shayne]

Heed Bob's warning though and drill a couple of holes in a length of steel that you can wedge against something to lever against when your at the stake nut .

Ironically i did this while replacing the nut but only after tightening it with a normal socket bar just enough to make it tight without feeling i was in danger of breaking anything . Then i bolted my homemade tool on and wedged it against the chassis so i could go at the nut with a torque wrench and i don't think the nut moved 1mm more before hitting 118nm

 

[BobMurphy]

I think that is how it should be, i.e the chain is locking front and rear output shafts firmly together so they move as one when power is applied (have I understood that right...Bob Murphy?).

Errrrr not quite.

Its the locked Centre Differential that is making the front and rear prop flanges turn together.

The rear propshaft is driven by the rear half of the main shaft that runs the length of the Transfer Box. This acts as the 'Sun Wheel' in Epicyclic Gear terms.

The drive from the front of the Transfer Box (from the gearbox, via the High/Low Ratio epicyclic cluster at the front) drives the outer drum of the Centre Differential - The Anulus in Epicyclic gear terms. The front and rear sections of the main shaft are separate and run together on a caged roller bearing. This means that the Anulus and Sun wheel can turn independently.

Between the Sun Wheel and Anulus you find the Planet Carrier. This has three pairs of gears, the inner three run on the sun wheel and the outer three run on the inside of the drum (anulus).

Having paired Planet Gears reverses the direction of the drive, thus when the Anulus is turned the Sun Wheel and Planet Carrier try to turn in opposite directions.

The front propshaft is driven by the Planet Carrier.

This is why, when jacking up one side of the car (e.g. both nearside wheels off the ground) with gearbox in gear, The Centre Differential 'open' and handbrake off . . . Turning one wheel results in the other turning in the opposite direction .

With all road wheels on the ground, the load is split between front and back and when in 'drive' the entire Centre Differential assembly turns as one and both front and rear propshafts turn in the same direction.

When locking the Centre Differential, a sleeve is slid across the gap between the front and rear sections of the main shaft, meaning that the Anulus and Sun Wheel turn as one. The Planet Carrier locks up (as the Planet Gears are in mesh with both - with more teeth in the drum than on the Sun Wheel) so there is no differential action as the Planet Gears reach 'Transmission Wind-Up'.

There will be slack in the Planet Carrier and the Planet Gears whose needle roller bearings can get very worn and thin. Also, there will be some movement between forward and backward rotation as the Planet Gears jam-up - being asked to engage two different ratios at the same time.

Feeling rotational play between the front and rear companion flanges can therefore be caused by a combination of slack in the chain, wear in the Centre Differential Planet Carrier (which is not particularly strong) and a bit of natural movement as the Planet Gears jam-up.

I'm afraid it could be wear in one, the other, or both .

That was a long way around for a short cut - apologies .

Bob.

 

[Shayne]

Thanks Bob i was just thinking that and you saved me saying it

I only went to school once and that was on a Sunday so i think what Bob's saying is there are a number of reasons why play can be found in the transfer box and none of them good so it might not be as simple as just swapping the chain .

 

[diggerdave]

Feeling rotational play between the front and rear companion flanges can therefore be caused by a combination of slack in the chain, wear in the Centre Differential Planet Carrier (which is not particularly strong) and a bit of natural movement as the Planet Gears jam-up.

I'm afraid it could be wear in one, the other, or both

Bob, thank you very much. I understand a little more clearly now, and you've saved me a potentially costly assumption (that its the chain wot dun it). I think this also means that, even though Shayne's chain is tight (checked after removing the speedo extension), it could still be the transfer box causing his version of the shunt!

 

[BobMurphy]

I think what Bob's saying is there are a number of reasons why play can be found in the transfer box and none of them good so it might not be as simple as just swapping the chain .

That's about it .

There will always be some slack because of the way the Centre Differential works when locked. The question is . . What is acceptable and what isn't .

There is some shunt on my '95' but I ignore it. Mind you, when they do finally 'let go' . .



Bob.

 

[Shayne]

Bob, thank you very much. I understand a little more clearly now, and you've saved me a potentially costly assumption (that its the chain wot dun it). I think this also means that, even though Shayne's chain is tight (checked after removing the speedo extension), it could still be the transfer box causing his version of the shunt!

Quite possibly mate i'm not ruling anything out as yet but i am convinced there is a problem with the inner CV's that needs fixed and as drivetrain shunt is a known consequence of knackered inner joints it seems sensible to remove that from the list of likely suspects first .

 

[diggerdave]

Actually Shayne, I realised my mistake on the way out of the front door to work... Since you don't have any play between the front and rear outout shafts of the transfer box, the problem isn't your box (chain, planet gears or planet carrier) at all. I hope your inner CVs are the answer.

Bob, mine's probably more than a little shunt. I can and have lived with it for a while but either its getting worse or my tolerance of the 'gently let the clutch up to biting point, wait until the slack has taken up, fully release, power' rigmarole is wearing thin!!!!

Exploring second hand box route at the moment...

 

[Shayne]

Sadly its not the cv joints

 

[BobMurphy]

Exploring second hand box route at the moment...

The Transfer Boxes are not too difficult to re-build. The problem is, when they are apart on the bench its difficult to decide which bits need replacing (some are obvious) and the cost can escalate.

A new Centre Differential, Hi-Vo chain, gasket set, oil seals and a couple of bearings can come to £1,000 - what does a second-hand box cost, and is it any good ??

You could send the box to me if you're stuck (and not in a great rush for it)!

Bob.

 

[diggerdave]

Bob, that's a very decent offer. I've seen your threads on the other site (and after your last explanation on here, I'm actually understanding them a little better too!) and I realise that your expertise would be preferable to letting my local gearbox repair place loose on it. I'll see what's available second hand, but might contact you if I can't find anything.

I intend to test any second hand boxes before buying. All I can think of to do is a) check for endfloat and side to side movement in the flanges, b) check that the centre diff locks, and c) check for excessive freeplay between that front and rear output flanges as well as listening for noise and general visual condition.

Can you advise any more specific checks that could be done to a box that's off the car?

(Apologies to Shayne, I don't mean to hijack but I guess this could be useful if you find that it is your box after all.)

 

[Shayne]

No worries Dave finding the answer is all that matters .

 

[BobMurphy]

I intend to test any second hand boxes before buying. All I can think of to do is a) check for endfloat and side to side movement in the flanges, b) check that the centre diff locks, and c) check for excessive freeplay between that front and rear output flanges as well as listening for noise and general visual condition.

That's about all you can do, really. I would check for leaks and the condition of the oil as well - which should be clear.

If it looks like this, leave well alone .



Bob.