90 series vibration

[wisey Lurker Find all posts View Profile Close wisey]

Hi There, new to this site. Looking for a mechanic in nth Bris, (kallangur) I have just developed bad vibrations under load (New 1.5 ton van) arround 2000-2200 rpm in 4th and 5th. Have a TD with Iron man shocks/springs 2" standard lift and maxix AT tyres.
Have done 2 wheel balances, tail shaft balance and 2 mechanics including scifleet still no luck. Any help appreciated.

[fridayman Senior Member Find all posts View Profile Close fridayman]

There is a very good chance that it could be the rear UJ on the rear propshaft. Replacing th UJ cured a similar vibration for me (even though I could feel no play in the UJ by hand).

[wisey Lurker Find all posts View Profile Close wisey]

Thanks Fridayman, I'll give it a go

[wisey Lurker Find all posts View Profile Close wisey]

Hi there, just an update.
After lengthening and balance of the rear drive shaft, no improvement. Went to mechanic and replaced d-rubbers on swaybar and gearbox mount. No improvement. Decide to pull off front drive shaft myself and found I cound not drive with the rear wheels unless I lock the transfer case. This leads me to the conclusion that the 90 series is a front wheel drive car only. It runs great now without the front drive shaft and rear wheel drive. Lots more power and better fuel economy.
Getting the uni-joints done on the front as they don't move much in travel so have developed flat spots on each one. I have spoken to a drive line specialest who tells me you can do a mod in the tranfer case to allow rear whell drive and replace the front hubs with manual ones.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Hi Wisey,
Thanks for updating the thread. So just to get this straight, has removing the front drive shaft cured the vibrations?

Also, FYI, the Prado is not front wheel drive, it's full time 4WD. In standard H mode the centre transfer acts as diff to mechanically distribute power to the front and rear diffs. The moment you remove either drive shaft the vehicle will not move - because the transfer will send power to the shaft with least resistance. When you engage HL (LOCKED CENTRE), both drive shafts will spin 50/50.

As for modifying the transfer case; I'm sure it's possible, and I've heard quite a few people say it's possible, but I have yet to see anyone actually perform this on the Prado transfer case. Most assumed they could use kits marketed for the 80 series or 4runners, but I believe this is mistaken, as this transfer has different internals.

[wisey Lurker Find all posts View Profile Close wisey]

Hi Glen_ep,

Thanks for the knowledge. Yes confirmed the vibration is gone, however it will be intresting to see what it is like with the new uni-joints/balanced shaft. Hopefully next week if the wife allows more expense. Will also enquire more re transfer mod.
As per the no drive, why would the drive go to least resistance? If one wheel was off the ground, say on the front but the other was wedged in a rut, wouldn't this extra power give wind up and damage the diff? I would have thought if one diff had least resistance, power would go to the wheels with drive?
(sorry, i'm no mechanic.....as it proberly shows)
Further to this have you looked at any powerups? (chips) Have just bought new caravan and fuel went from around 13l/100km to 20 trying to keep around 100km/hr.
Looked at a couple but manufactures are claiming up to 25%power but only 3% fuel reduction.

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Hey Wisey, think of your driveline like plumbing set up in a H pattern (sideways), this is much like the setup of your driveline, the centre pipe, is the transfercase and driveshafts, and the top pipe is your front diff, and at the end of the pipe is the wheels, same gose for the bottom pipe just that it is for the rear, if you block one of the pipes, the water will still flow out, at the least point of resistance, now back to the vehicle, it is like this to allow you to turn into corners, otherwise you pretty much go straight ahead, you will not get wind up, because inside the diff are what is called spider gears, this allows the different wheel speeds (like when you turn a corner, as the outside wheel will turn quicker than the inside one), hence the name differential. you will only get wind up in the transfer case IF you have it locked (as stated on the lever - 4HL and 4LL, 4HL is 4wd Hi range Locked, and $ll is $wd Low Range Locked), and you drive it on a hard surface like the road, as soon as you try to turn a corner, the different difference between the front and rear wheels will not be allowed by the transfercase (and think of the transfercase as a 3rd diff). If you were to drive in a straight line on a hard surface with the transfercase locked you will not get wind up, nor will it cause any damage to it, (handy for the boat ramp if you have a big boat), but as soon as you try to turn a corner, this is when wind up will occur, and then you are putting the transfer case under alot of stress because you dont have that differential action happening, this is when your doing damage.
Now this is why people like diff locks, because it locks either the front diff or rear diff or both diffs.