AWD front rear differential problem

[shoo]

Hello
I have a 94 AWD non supercharged Previa and for long time I have knocking noise mainly at low gears mainly when high torque is delivered, apparently aside of the inconvenient of the loud noise and since there is no snow here… everything seems to be ok…but off course it is a matter of time until something will ‘give’.
I suspect it has to do with some kind of slippage at the differential that distributes the torque for the front and rear axles,at the output of the trannr and I know there is a chain there, so one option is that for some reason that chain is jumping over its sprocket –but somehow and based on intuition only and my motorbike experience, it is not that kind of feeling- again I might be wrong on that… but since I don’t have drawing of that final drive differential I am not sure what else can get wrong there.
So my questions are
1. Did anybody experience such phenomena?
2. Does anybody has or know where can I get access to a good drawing of that differential?
3. Aside of buying h whole tranny and take the necessary part any idea where to get replacements like chain, sprockets pinion etc. ?
4. if indeed i will need to replace that chain, is that a unique part for previa or there are more competiable like a chain of 4runner for example?
Thanks for any help
Avishay
p.s.
I will try to make a video of the phenomena and upload it to youtube

[pdgizwiz]

Have you checked the U-joints in your driveshafts? I'd rule out relatively simple things before suspecting the transfer.
If you narrow things down to the transfer case, drain and inspect the oil. If it's full of metal swarf, well, there you are. If not, re-fill with new fluid. Perhaps the oil itself had failed and the disks inside were doing a stick-slip dance.

[shoo]

i have had this for almost 2 yeas during this time i have changed the oil and the u joints and try to inspect it from below while the car was on the lift, i suspected the bearing in between the rear and front part of the FRONT drive shaft and nothing. i am pretty sure it is coming from the mid differential, - i will soon try to make some go pro clips and post a link.

[shoo]

Hello
i am going to try and fix this problem hoping it is only the chain from the transmission to the differential, however if that is not the case i may install a 2wd tranny fo the time being and fix the whole thing when it is outside. i have the tranny and actually this tranny was already installed in the vehicle prior to the current 4wd tranny, so i know it should be OK and will fit, the only thing is the rear drive shaft. where the rear drive shaft that connect the 4wd transmission to the rear axle is shorter then the one of the 2wd and when i replace the 2wd with the 4wd i had to rebuild it so i would probably wont be able to use it (there is about 4cm sliding ability or so but i think that the transmission end is different) anyhow, i can get another rear drive shaft but...there are 2 type of rear axles in Previa, separate suspension and solid axle, mine has one solid axle -as in pick-ups- and the drive shaft i can get as replacement is of a separate suspension type, and my question is will it fit? anybody has any experience or knowladge with this?
thanks

[TheMAN]

the one for the solid axle and independent suspension are different.... get the correct type

[shoo]

Thanks TheMan for the info, hopefully i will not need to replace the whole transmission. i took apart the transfer drive case:
Previa transfer case 02.jpg
it turned out that the silent chain that connect the main shaft- the one that runs from the transmission to the rear axle- with the front wheels shaft is very loose and causing the power loss as the chain is slipping when torque is delivered.
Previa transfer case 03.jpg
this chain usually cost around 450$ but i managed to find one place in Japan -called Amayama- that has it for 220$ and hopefully i will get it with in 2 weeks or so. -the hard part was to get the full and correct part number
as you can see in the pictures there is a fork that engage and disengage the front wheel drive from the main shaft -i dont know exactly how it works since there is no solenoid there and apparently somehow it is controlled by oil pressure, i assume that maybe it is connected in a way to oil pressure built in the torque converter i.e at high torque the front wheels are engaged and as speed built up and less torque is delivered the front wheel are disengaged....i am not sure about this mechanism and if anyone knows how it works i will be happy to learn...
anyhow apparently there is a whole in the casing that is used in other models for a solenoid that allow engage disengage the 4wd by the driver so i put a screw to permanently keep the transmission in a 2wd mode until i will receive the new chain from Japan. the car drive fine for now, no more banging an knocking...
will update after installing the new chain.

[Kurtanius21]

That's interesting to see. You mind taken some extra pictures of reassembly and the finished project? Your extra experience assembling the wildly inconvenient previa would be nice to add to the knowledge base here. I am particularly interested in vibrations once you reinstalled everything. Lots of shafts and potential for driveline vibrations when reinstalling everything. Good luck with your project!

[shoo]

hi, it is all assembled now, so there is nothing really to see, i will try to document it better once i will replace the new chain and will try to show the screw that holds the fork
and no, no vibrations at all. i didn't do it myself i took it to Toyota mechanic here in Israel and these guys...i noticed that even when they ate dismounting a wheel for whatever reason, they mark the bolts to reinstall it at the very same way....so i imagine that they have marked everything prior to removing any shaft.