I'm probably a retard for asking this V. FWD?

Discussion in 'OT Driven' started by Blip, Feb 9, 2007.

  1. Blip

    Blip Active Member

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    If you jack up the front end of a FWD car, specifically a 1999 Toyota Corolla, should both wheels be turning at the same speed?:hsugh:

    I'm trying to diagnose a front end noise on my wife's car, thought it was bad wheel bearings, but they turned out to be okay. I had the front of the car up on stands running in D :noes: so I could check for the noise and noticed that the driver's side wheel (the side where the snoise is coming from) was turning a LOT slower than the passenger side. :ugh2:

    Normal?
     
  2. deusexaethera

    deusexaethera OT Supporter

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    Like any axle with a differential between the two wheels, the speed of each wheel depends on the difference in the amount of drag between the two wheels. In your case, two factors come into play:

    1. Your car has floating brake calipers, which means that only one pad on each caliper will get pulled away from the rotor when you take your foot off the brake. As such, there could be slightly different amounts of drag being applied to each brake rotor, resulting in faster rotation of the wheel with less drag.

    2. Being a seven year old car, and given that people don't drive in the exact middle of the street, it's unlikely that the wheel bearings on both hubs have the exact same amount of wear. Unevenly-worn bearings will also cause a difference in drag between the two wheels.

    The things I'd do as preventative maintenance are:

    1. Take the brake rotors off and sand them with rough-grit sandpaper. Check the pads to make sure they're worn more/less evenly on both sides.

    2. Drop the axles, replace the CV joint boots, and regrease the CV joints.

    3. Check the service manual and find out if the differential has its own oil, or if it uses the transmission oil. If it uses its own oil, change it.
     
  3. P07r0457

    P07r0457 New Member

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    ugh deuse being a dumbfuck again.

    99 corolla has an open-diff transaxel. So yes one wheel will turn slower than the other.

    And don't run the car on stands... not safe.
     
  4. Vicious-S

    Vicious-S New Member

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    open diff. read: one tire fire.
     
  5. 4W4K3

    4W4K3 New Member

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    :mamoru: Revving 2-3K RPM's, stands shoot out, car flies through wall. I can picture it now!

    Or worse you are bent down in front with a buddy in the seat, stands shoot out...and you are now a pancake :noes:
     
  6. Blip

    Blip Active Member

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    Cool, thanks!

    Running car + stands = not safe. 10-4. It was only idling though and both tires were off, so if it did fall it wouldn't go so far....I hope.:noes:
     
  7. Blip

    Blip Active Member

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    :noes:I know it's not safe, but I'm not shooting for the Darwin award. Car was only idling, chocked rear wheels, parking brake on, and both tires were off, so no rolling if it fell.

    If I do get squashed I will post pics!:rofl: If I can.:eek4:
     
  8. alltracman78

    alltracman78 New Member

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    And why exactly would the stands shoot out?
    From growing legs?

    You guys are jumping at shadows.....
    As long as the stands are 4 leg and secure, there is absolutely no reason not to run the car.
    Now I would reccomend having the E brake pulled, and not revving the shit out of the engine.
     
  9. P07r0457

    P07r0457 New Member

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    just starting the engine can rock the car.... bottom line, it's not safe!
     
  10. deusexaethera

    deusexaethera OT Supporter

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    Ugh, Jollyogre being a belligerent asshole again.

    I know his car has uneven-length driveaxles coming off the differential, but as long as the wheels are the same weight (thus requiring the same force to spin them) and as long as both driveaxles have the same number of CV joints (McP strut, multilink, and double-wishbone suspended cars always have two CVs per axle, yeah?) then under ideal conditions the amount of friction would be the same on each side, and the differential would have no reason to split power unevenly when the wheels are hanging in the air (or rolling in a straight line).

    That said, I did list a number of reasons why the drag on each axle would be unequal, so the end result is the same as what he observes.

    As usual, your answer jumps straight from the apparent cause (open diff) to the apparent effect (one wheel spinning faster) without including any information as to WHY it actually works that way. Will you ever learn?
     
  11. deusexaethera

    deusexaethera OT Supporter

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    Open diffs don't automatically equal uneven torque split. For reasons I don't understand (probably something to do with the spring tension of each driveaxle), torque steer is caused by uneven-length driveshafts. My Passat has an open diff and even length axles, and it can peel out in a perfectly-straight line with both of my hands casually resting in my lap.
     
  12. P07r0457

    P07r0457 New Member

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    Brake pads arn't the cause.... Take the calipers off and you'll still have only one wheel spinning (or at least one faster than the other)
     
  13. 4W4K3

    4W4K3 New Member

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    Jack up your car and then go sit in it. Start it up and rev it a few times. It can move around, even if the e-brake is pulled. Bad jack placement, vibrations, weak lift points, etc. It's just dangerous. 99% of the time nothing will happen, but I don't want to be the guy with my car through my wall so I don't mess around.

    It's not like they are bolted to the ground, although that would be cool. We had a guy in December who had a car run off the rack, slam him through the wall clear to the next room. DEAD! Not even funny. Car should never be running while on the rack, or jacked up. That is like a one in a million chance...but he is still dead.
     
  14. deusexaethera

    deusexaethera OT Supporter

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    Of course dragging brakes can cause one wheel to spin slower, though that may not be the case for this guy. You don't actually know why one wheel tends to spin faster with his kind of transaxle, do you?
     
  15. P07r0457

    P07r0457 New Member

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    open-diff transaxels are mostly the same... and brakes arn't the cause.

    as I have said before, take the calipers off and they still spin at different speeds. That clearly proves you wrong. Now run along.
     
  16. alltracman78

    alltracman78 New Member

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    Oh really?
    Out of curiosity then, how do you do a trans flush?
    Or a caster check on the alignment rack?
    Or diagnose a driveline noise?

    No matter how secure a car is on a lift or jackstands, it will ALWAYS be able to move a bit.
    Ever try to loosen frozen toe arm nuts without rocking the car at all?
    There is a HUGE difference between the car being able to rock slightly and being on the edge of falling off.....

    I'm not recommending throwing your car on stands on a hilly gravel driveway...
    But if you are on a flat hard surface and the jackstands are placed securely, other than having a rusted chassis it won't just randomly fall off. Period.
    You have 2000+ lbs pushing down on 8 legs, via a rail, in 2 V type shapes. Simply physics tells us it isn't going to slide uphill, even if the engine is running rough.
    It also isn't going to slide backwards [assuming the Ebrake is pulled and works of course].
    Nor will the 4 leg jackstand just tip over on it's own. You would need a pretty hefty force, like another car, or a football lineman, to move it. ;)

    There is absolutely nothing wrong with being safe.
    But there's no need to be a grandma.....
     
  17. P07r0457

    P07r0457 New Member

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    ya rly.
    I don't need the vechile on stands to flush the trans. Get a machine that goes in-line with the trans cooler. Don't ever have to take the vehicle off the ground.
    Alignment rack is different. Those are very secure. I couldn't push a vehicle off one of those. However I bet I could push a vehicle off of basic home-style stands. Apples and oranges.
    Do what you can without stands, but if you need it running with the wheels off the ground I'd probably recommend a real mechanic's lift.
     
  18. alltracman78

    alltracman78 New Member

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    That's what we use. ;)
    Flush works best with the wheels spinning...
    ya rly.

    He stated "car should never be running, while on the rack or jacked up. My reply was aimed at that.... Though maybe you couldn't read it?
    BUT, I bet I could pull a vehicle off an arm lift[mechanics lift] no matter how well it's on there. ;) THAT'S sure as hell an apple to an apple. NOTHING is secure if you are doing your best to remove it from where it's secured to. Running or not.
    My point isn't that you can't possibly knock a car off jackstands even if it's securely on there.
    My point is that a car will NOT fall off properly set up jackstands unless there is outside help. Like a dumbass trying to push it off....
    Your engine running is NOT going to cause it to fall.


    A "real mechanics lift" is always safer than jackstands.
    But not many people [outside of techs] have acess to one.
    Jackstands WILL do in a pinch as long as they are properly set up.
     
  19. P07r0457

    P07r0457 New Member

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    Personally, I would never trust jackstands for that. Just putting some torque on a prybar last weekend to change my breakpads had the vehicle rocking back-and-forth. I would never crawl under it while that was going on -- or the engine running (or stand in front of it, for that matter). So say what you will, do what you want; I am known as a risk-taker and I wouldn't do it.
     
  20. alltracman78

    alltracman78 New Member

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    Dude, the vehicle will easily rock on a lift too....
    Breaking loose caliper bracket bolts
    Loosening rear toe adjusting arm nuts

    I've climbed onto my engine with the car on stands and it doesn't budge.
    Same goes for loosening the same bolts/nuts.
    Cars actually move less on jackstands than on lifts. [2 rear wheels on the ground provide greater stability].
    I still prefer lifts, but the point remains.

    What kind of jackstands are you using?
    If they're uneven, or the ground is uneven, or you have them supporting the wrong thing all could cause it to rock.
    But rocking isn't necessarily dangerous.
    Remember, you have the entire weight of the car pushing DOWN on the stands, holding the car on them. Any stands I've seen are at least to some extent angled down to a center point. So all the weight is concentrated at this center point. So in order for the vehicle to fall off, it either needs to slide backwards off the stands, slide forewards off the stand, slide sideways UP the angle off the stand, or have the stand fall over. None of which are really possible to happen AS LONG AS THE STANDS/CAR ARE SETUP CORRECTLY.
    It takes ALOT to slide a car when the wheels arent what is supporting it.
     
  21. deusexaethera

    deusexaethera OT Supporter

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    Why, Jolly. Why. You refuse to answer this simple question. I think you don't really know why; I think you noticed this same thing yourself a few years ago, and asked around, and got the same answer you're giving this guy now: "They just do that." The guy would be better off without that answer because he would at least have the motivation to find out why they do that.
     
  22. P07r0457

    P07r0457 New Member

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    So instead of admiting you're wrong you just try to change the subject???

    You mislead people. I didn't. I wouldn't be able to tell you the *exact* reason... Although I know that brakes are not the primary cause.
     
  23. 4W4K3

    4W4K3 New Member

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    Only reason we need the car running while in the air is during the alignment process for a short period of time. parking brake is on and wheels are blocked. You'd have to intentionally do something wrong to drive it off the rack. I don't think we've ever had a problem on the alignment racks, always the oil change/tire swap racks...because the "lower" techs work there and are less safety conscious, plus the racks are just less robust and not as safe IMHO.

    We don't do engine work or electrical work, so there really is no need to have the car running while in the air. We recommend it to a specialty shop for advanced work. We JUST started tranny service, and soon will begin state inspections. Lots of training in the near future...ugh.
     
  24. Eclipsed830

    Eclipsed830 Active Member

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    Fucking floor that shit and see what you can get the speedo upto while the wheels are off the ground :bowdown:
     
  25. Vicious-S

    Vicious-S New Member

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    holy shit. the answer is open diff. its just how they work. they have a combination of spider gears that allows the wheel that loses traction first to get most of the power. so one wheel will spin faster. in the case of both wheels in the air, its whichever wheel feels like spinning first. you can grab the wheel thats spinning, and it will make the other wheel spin.

    note: you shouldn't really try grabbing a spinning wheel... or should you?

    deus: you overthink this shit way too much.

    as for running a car on stands... use common sense. its that easy.
     

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