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Toyota 4WD systems explained

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  • ccco1ccco1 Posts: 9
    Rav4's with 2wd, only drive the front wheels. So, a simple way to check for 4wd is: crawl under the rear of the Rav and look for a rear differential with a drive line running to it from the front.
  • wwestwwest Posts: 10,706
    I'm sure someone will tell me if I'm wrong...

    The Sequoia has two modes in which all four wheels are driven. The first of these, which I prefer to call AWD, does NOT lock ANY diff'l.

    This AWD (full-time) mode uses an open center diff'l so that all four wheels are driven when on reasonably good traction surfaces. If any wheel(s) should begin to slip then the brake on that wheel or wheels is moderately applied so that engine torque continues to be apportioned equally, in a rough sense.

    In "true" 4WD it is my understanding that the center diff'l is locked and therefore all the cautions and warnings apply.
  • gkatz1gkatz1 Posts: 296
    But, where talking about binding that occurs while going from 2WD to 4WD. Between the time the button is pressed and the system actually engages is when you have to be careful because the center diff doesn't work.
  • wwestwwest Posts: 10,706
    The statement is literally" bumping while the 4WD is on".

    The earlier post was regarding the system in transition, this, #1289, was simply "on".

    I take that to mean either there is a failure as a result of earlier incidents or the vehicle is being driven on a high traction surface in a turn. Either of my Jeeps would bust knuckles (Ouch, Damn!)in the latter case.
  • Great posts in this board. I'm trying to diagnose a frustrating driveline thump in the rear end of my 99 LC w/ 60k miles. It typically occurs as the rear end settles after braking or in any situation where the rear settles from a high position as opposed to the rear squatting under weight or compression from a bump. The local dealer says that it is a function of the slip yoke in the drive line found on LCs and new 4WD 4Runners being packed with too much grease. The grease was drained and the problem went away but quickly returned so I'm unsure that's it. It feels as if slack it being taken up and creating the thump somehow between the transfer case and the rear end. Looking for anybody with similar experiences before another trip to the dealer. Thanks.
  • I disagree this is caused by too much grease in the slip yoke on the rear shaft. Malarky. Within a hundred yards of driving, the excess grease is pushed out the ends of the splines as normal.

    It's most likely to be too little or too infrequent greasing of the rear shaft, but that does not seem to be the case here. You don't mention miles or history on your truck. My second suspicion is that you've not done frequent enough tire rotations and one or more tires are a different circumference. Before getting into any elaborate mechanical issues, consider replacing the tires if they justify it. Otherwise, very exactingly measure each tire in turn and see if you find a circumference difference. Run a tape measure around the center of the tread and record it to the 16th of an inch.

    What can happen is the center, rear or front (or all three) diffs end up with the gears coming under a slight amount of pressure as you come to rest. It's held this way until the instant you let off, then the gears gently rotate relative to one another (from 'drive' faces touching to 'coast' faces touching or the opposite) when engine torque moves them.

    Anyhow, getting technical here, but measure your tires and also be sure they're all properly inflated.

    IdahoDoug
  • I own an 03 4Runner, and it has the driveline thump described by himcdonough. It most often occurs when getting underway after stopping, but can also occur just before the vechile comes to a complete stop. Here are some facts:

     - The thump went away after I had the drive shafts lubed by the dealer. It returned in about 4000 miles. I'll have them do it again at the next oil change.

     - The thump will never occur if I shift from drive --> neutral --> drive while stopped.

     - My 4Runner has the adjustable air suspension in the rear. When raising and lowering the vehicle, it sometimes makes a popping sound. I suspect that this is due to the extension/retraction of the driveshaft as the vehile is raised/lowered. This did not happen in the roughly 4000 mile period after I had the drive shafts lubed. Therefore, I believe the 'thump' and the 'pop' have the same root cause.
  • I have a 99 TLC with 60k miles and it has the exact thump you describe. I think I called it a clunk so if you search the postings for clunk you will find several posts on the Toyota Land Cruiser board. My thump also goes away when put in neutral after stopping and doesn't happen at all if I stop slowly/gradually. My Toyota dealer called it normal which pissed me off... I would like to hear of any fix you come across with your research so please keep posting.

    I was thinking about getting new shocks as I've heard that the stock ones can go bad at around 60k, depends on driving.

    Interesting post by Doug, I will check my tires but they are the same age and the tread looks similar... I would like to get new tires though.
  • Many Sequoia's and Tundra's have the same issue new. What seems to fix it is adding grease in the slip joint on the drive shaft. I had posted in Sequioa problems the "fix" from another website. Part of normal maintenance in manual is to grease the fittings at every oil change. My thump has not returned since.
  • Believe me I have greased the shaft and it still thumps... The curious thing to me is the fact that it doesn't do it if you pop it in neutral, I wonder if the shaft has a worn zone and when you stop it compresses beyond the worn area then when you go it pops back down... I don't know. I would buy a new shaft if I was confidant it would fix it.
  • pokypoky Posts: 2
    I am trying to decide to purchase a new 2003 or 2004 rav4, are there 'enough' differences to purchase the 2004?
  • wwestwwest Posts: 10,706
    If the 04 AWD system has been upgraded in the manner of the HL and RX then the 04 is certainly a better value.
  • vodgutvodgut Posts: 162
    I think they also went from a 2.0 to 2.4 liter engine for 2004, so it's more powerful. I think they made other improvements, too.
  • albivalbiv Posts: 35
    I too had the thump on my '03. Started at about 1500 miles. I lubed the driveshafts and the thump's gone. Interesting that they required grease after only 1500 miles. I have almost 4000 miles on it now and no thump.
  • Idaho - My LC has 62k on it but only the last 3k or so are mine. The tires are pretty new with some of the nubbies still on them and they were rotated at about 59k. Measuring sounds like an interesting idea that I could try as the "drive" and "coast" scenario seems to fit. I haven't tried shifting to neutral either, perhaps in the morning. I like the greasing idea as it's simple but it seems to conflict with the dealers notion to drain the excess out. I suppose on the next oil change I'll have them go over the entire drive line and grease it. I can't lie, it's getting annoying as I don't expect a vehicle of this calibre to have this glitch. Thanks for the posts.
  • My 1992 4Runner V6 (302,000 kms) seems to be in 4WD and it will not disengage.

    I put it in 4WD a couple of weeks ago for the 1st time this winter, and just noticed from the 'hum'/ vibration, that I believe it's still in 4WD.

    Questions:
    - with the age of the vehicle, I don't want to spend lots of money on it. Do you believe this problem could likely be fixed for minimal $$$?

    - I just had my brakes done (new pads, rotors, etc), would this have affected anything?

    - also, my rear antilock brake light has been on for a number of months as well...is this related?....what is the problem here?...

    Please help me !
  • wwestwwest Posts: 10,706
    Different size tires on front vs rear?

    Even worn on one end vs the other?

    Try backing up slowly and then slip the transmission into neutral while still moving slowly. If that doesn't work try the same thing forward.

    My 92 Jeep starting doing that with new tires on the rear and 20K wear on the fronts, The above procedure solved the problem each time.

    Oh, just thought.

    The anti-lock indication could be for the same reason, different rotation rates, continually, front vs rear would put the anti-lock ECU out of service.
  • Same tires I've had on for years, both 31".

    ...but I will give your suggestion a try...will let you know...tks !
  • We have a 2002 and a 2004. Definitely get the 2004. More power that is noticeable, ABS, traction control (or something like that),tire pressure monitors, "better" inside colors, wheel mounted radio controls, variable intermittent wipers, many a few more differences between the 02s and 04s. Also we paid almost $500 less for the 04. Remember I'm comparing 02s with 04s. However I bet you could get a great deal on leftover 03s.
  • It's called axle windup. It is a symptom of solid rear axle vehicles. That is why the slip yoke is there to release the wind up pressure.

    The slip yoke requires regular lubing. The thump indicates the slip yoke is not lubed or is otherwise sticking.
    Mechanically it doesn't hurt anything except your ears maybe.

    The reason it doesn't do it in Neutral is because you are not creating the drive stress on the driveshaft to create enough axle wind up in the first place.

    I would also double check your suspension - that a spring or shock bolt is not loose.

    Of course it could be something else but that is the absolute most common source of the noise as has been described.
    It is very easy to create that thump in any solid rear axle vehicle, new or used. Come to a fast stop and keep your foot on the brake. When you let go of the brake, thump. The wind up is released.
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