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Towing on All Fours

Discussion in 'Gen 2 Prius Main Forum' started by Cephyr13, Jan 13, 2016.

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  1. Cephyr13

    Cephyr13 New Member

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    In the User Manual, it states explicitly that a Prius cannot be towed with all four wheels on the ground, because it will break the transmission's sun gear. In other words, when the vehicle is NOT turned on, it can't be towed or it will break the transmission.

    But what if the car is turned on while towing it?

    This is how I tow my current vehicle, because I got tired of replacing my rack and pinion once a year. I don't see why it wouldn't work with a Prius.

    The only problem I can see is if the car stalls out. If stalls out, the transmission would instantly break, it seems. But that's a little confusing to me, because what if I'm driving the Prius and the car dies? Wouldn't that instantly break the transmission? Doesn't seem like any manufacturer would be so careless as to design a car that will destroy it's transmission if it dies while driving it.

    Anyone have any input on this?

    (SIDE NOTE: No one makes tow bar brackets for a Prius, so I'd have to custom make those, unfortunately.)

    Thanks.
     
  2. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Logic says that if you turn it on (ready), it should run the engine to burn down the charge on the battery. So logically, you should be able to do this. Of course the car will incur the mileage from the tow.

    May I ask why you need to tow it?

    Disclaimer: I'm not an expert on this and any advice I give is just speculation from my feeble brain.
     
  3. tanglefoot

    tanglefoot Whee!

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    I think this can only be done at low speeds and for very short durations (i.e. down a neighborhood street). When the car is in "ready" mode and the shifter is in "N", MG2 [Correction...MG1 is the one in danger of overspeeding--thanks for the reminders] is still directly connected to the front differential. If the car passes the 41 mph threshold, it will spin MG1 at faster than its design speed. I believe keeping the car in "ready" mode and in "N" for long periods can also damage the HV battery, by allowing it to discharge past its designed minimum charge state.

    "Stalling out", or the car falling out of "ready" mode, is very unlikely and probably not an issue in itself.

    I suppose towing it with the shifter in "D" would remedy the MG2 overspeeding and traction pack issues, but it could cause other ones, one of which being that the car will try to push you around a bit when stopped.

    I think it's best not to make a habit of moving it, wheels down, unless it's a very short, very low-speed relocation (to the other side of the workshop, etc).
     
    #3 tanglefoot, Jan 13, 2016
    Last edited: Jan 13, 2016
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  4. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    I agree that the car would have to be put in either "D" or "B". "B" might be the better choice. I really don't know. I also agree that "N" would not be a wise choice.
     
  5. 48mpg

    48mpg Member

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    just buy a used car dolly for $500 and do it right, the repairs to the prius will be much and you will not have to remove the bumper to attach it to your tow vehicle or get a Saturn that can be towed with all 4 wheels on the ground with no mod's
     
  6. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    If the front wheels turn, they will generate electricity. Where are you planning on putting it?
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    ^ Not if the car's in Neutral?

    Still, this seems like a bad idea, not understanding why it's imperative, would take another approach, any approach: that gets the front wheels off the ground.
     
  8. Cephyr13

    Cephyr13 New Member

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    I deliver vehicles around the U.S. I tow my car behind those vehicles, then drive my vehicle back home or to the next vehicle that needs to be delivered.

    I've used a tow dolly, but it's a big pain. I have to put a tow hitch on my car to tow the tow dolly back home after I drop off a vehicle. So it's 500 lbs of extra weight I'm towing around, on top of the 300+ pounds that my special hitches weight which are in my car. The goal is weight reduction and reduction of headaches...and tow dollies are annoying. My tow dolly got stolen many years ago, and now that I'm in a house, I have no where to put the tow dolly. My driveway is steep and right next to a major street, so having a tow dolly would be a huge hassle and a little bit dangerous. Not an option I care to use.

    Also, I wouldn't have to remove the bumper to tow the car. There are hidden hitches that attache to the front subframe and have two small tubes that come up to the front grill. Then you take two tow bar brackets and insert them in those tubes and lock them in place (or remove them when you're done towing). These brackets are where you mount your tow bar. That's pretty similar to the system I have on my car now, except my tubes are under the bumper and come up in front of it. I'd have to make a custom hidden hitch for a Prius, though, since no one manufacturers tow bar brackets for it. That one issue alone may cause me to go with a different car. It'll be a pain building a custom hitch. A big pain.
     
  9. Cephyr13

    Cephyr13 New Member

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    I still don't understand what will happen if I put the car in neutral while it's running and tow it. Can anyone shed some light on that?

    Thanks. And thanks for the replies thus far, too.

    Also, towing it in D seems like it'd have charging issues with the battery getting too much charge on it, even if it were doing everything it could to expend the extra energy. B mode would help, but still shouldn't be able to expend that much constant energy going to the battery, I'd imagine. Neutral seems like the only option, but I'm guessing it won't work either.
     
  10. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    I don't know about the 41mph threshold thing that tanglefoot spoke of but, I do know that "N" does not allow for charging of the HV battery. If you leave it on, the car will slowly drain the HV battery and you theoretically could drain it lower than its threshold for starting the car. That's the danger. Idk how long this would take but it would depend on the charge state of your battery when you put it in "N".

    As for D and B, if the battery gets too much charge on it, it will "waste" the extra electricity by spinning the ICE. To my knowledge, the gas is cut off but the MG spins it to burn off excess electricity. I'm confident the system could burn enough energy to protect your battery but again, I'm no expert. B mode seems more ideal for this but it will also put more drag on the car making it harder to tow.

    Unfortunately, I don't have a great solution for you and you would kind of be a guinea pig if you listened to me.
     
  11. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    #11 usnavystgc, Jan 13, 2016
    Last edited: Jan 13, 2016
  12. tanglefoot

    tanglefoot Whee!

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    The car can manage its own charge level in D or B...as usnavy mentioned, it'll just waste it off when the traction pack reaches 80%.

    In N, though, it's my understanding that the car will not maintain the charge level in the traction pack, and it will just discharge past its design minimum (40%) until incurs damage and or isn't able to start the engine, as navy mentioned. At this point, it will need to be grid-recharged.

    Under normal operation, the engine must spin up as the car increases speed (at the 41 mph threshold), otherwise MG1 (not 2--my mistake) will overspeed. If the car is shifted into N when the engine is not running, it is my understanding that the engine will not spin up to protect MG1. If shifted into N when the engine is running, I believe it will protect MG1 but I don't know if it will continue to do so for the entire trip.

    From what I've learned, flat towing it is not a good idea at all. If you do, use D or B, but you really should choose a different car to flat-tow. It's Prius-abuse.
     
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    I think just taking a Prius thru a tow-along car wash in neutral has run the battery down dangerously?
     
  14. tvpierce

    tvpierce Senior Member

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    According to Mr. Einstein, 'Energy cannot be created or destroyed, it can only be changed from one form to another.'

    So I pose this question... because I don't know the answer: Excess electricity that gets "wasted" would have to go somewhere. Heat? If so, that's a lot of heat.
     
  15. tanglefoot

    tanglefoot Whee!

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    Yes, heat is the end result. The Prius restricts the valves in the gasoline engine and then spins it with MG1 in order to dissipate excess charge. This results in a fair amount of heat being released to the atmosphere, but nothing like the regenerative braking of railroad locomotives being dissipated through ventilated, resistive grids in the roof.
     
  16. valde3

    valde3 Senior Member

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    If you need to tow Prius with all front tyres on ground best way is to turn Prius on (acc or ready) put it into neutral and remove PCON MTR relay from under hood fuse box then engage E-brake and turn the Prius off (you need to turn E-brake on other vise Prius won’t shut down with that relay removed and you need to turn Prius off other vice battery will discharge). After that you can just take the E-brake off and flat tow it.

    Towing this way is safe up to 42MPH and maybe safe up to about 60MPH.
     
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  17. Cephyr13

    Cephyr13 New Member

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    Wow, that's a lot of trouble to tow the car. I may have to get a different tow vehicle. Mines an old '91 Taurus SHO, and they tend to be very expensive to maintain. I've had several of them, but they're too expensive for me now. Gotta get something more reliable and economical for my tow vehicle. Maybe I'll get a Prius just for an Uber vehicle instead of using it as my tow vehicle, too.

    Thanks for all the replies. Much appreciated.
     
  18. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I don't think this is very safe because the motor generators in the transaxle will continue to produce substantial electricity at 42 mph which is not being usefully absorbed anywhere. This might cause excessive voltage to develop and create a short in a stator winding.

    The OP is not talking about towing a car for only 5 miles - he may be towing it 2,500 miles. The Prius definitely cannot be towed with the front wheels on the ground for such a distance without substantial risk of drivetrain damage.

    I suggest the OP get a vehicle with a manual transmission if he wants to tow it for such long distances. Jeep Wranglers are popular for this purpose because the transfer case can be put into N to totally disengage the drivetrain from the wheels. Or, look at the RVers who tow little vehicles behind the large RV to see what vehicles are commonly used.
     
    #18 Patrick Wong, Jan 15, 2016
    Last edited: Jan 15, 2016