Please explain a Locked Diff
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  1. #1
    R/C Apprentice Baz345 is on a distinguished road Baz345's Avatar
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    Cool Please explain a Locked Diff

    I've been thinking about the whole concept of locking my diff on my 2wd slash but I don't actually understand the purpose, pros and cons of having a locked diff and if it would suit me or not. A detailed explanation would be greatly appreciated, cheers.
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    R/C God matt_971 is on a distinguished road
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    basically it means both wheels will turn the same amount no matter what. Hence the locked bit. It is good for getting power down. It is REALLY bad for steering. You will most likely loose all steering while you have power on and have bugger all when no power is applied.

    I'm not 100% familiar with the slash but a MUCH MUCH better option is a high viscosity diff oil. Say up around 50,000 or so. It will act like a locker but still has enough give so you have steering when you need it.

    Locked diffs are really only used in something you want to get power down in a straight line. Not recommended on a normal bashing car though.
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    Yeah there good in straight lines not turning

    Put some heavy diff oil in there instead as mentioned above

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    R/C Guru Peachey is on a distinguished road
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    if you want it to act like a locker you will need at least 100k, if not 500k if you want it to be tight. iv tried a fair few, i just put 500k in my merv, maybe that was a bad idea, it just wants to flick around now so im going to go back to 120k in the rear of the merv and 50k in front. gives me just enough side ways action with decent control and power. for my 1/10 BB revo im going to put the 500k in the rear next time i get the rear end apart and see how that goes.

  6. #5
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    As others have mentioned, locking the diff will cause the steering to become awful both on and off the power...you havent mentioned the reason behind locking the diff?

    With a normal gear diff, the Planetary gears (also known as sun gears and bevel gears) allow the inside axle to decrease in speed and the outside wheel speed to increase during a turn, this prevents the wheels skipping and helps to prevent traction loss on one or both wheels. The diff will have grease inside to lubricate the gears, and helps to prevent premature wear and gear failure.
    The advantage of a geared diff or Open Centre Diff...easier turns.

    With a Locked Diff, the planetary gears are removed and replaced with a solid block that joins the 2 axles inside the diff casing, when travelling straight the axles both rotate at the same speed, when you begin to turn, the inside wheel will begin to loose traction, while the outside wheel continues at the normal speed, this causes an Under Steer effect and makes turning harder, and with less traction at the rear wheels can cause instability and as a result, both wheels end up spinning as you apply more power and crank the steering over even harder to bring the front of the model around.

    The third and better option is to use a heavy weight oil in the diff, this slows the action of the planetary gears in much the same way as a Floating Rear in a normal car does, these diffs in cars with increased horsepower were trialed and very successful when first used, but with many people not understanding the requirements of the diff, they became less effective when incorrectly serviced, and maintained.

    To get the best advantage of the diff, a heavy weight oil is used to restrict the ease of the planetary gears to do their job, slowing the rate that the gears can rotate causes a slower transfer and causes traction to be applied more evenly across both wheels while preventing the inside wheel loosing traction and as a result makes the model turn in and remain stable.

    Diff oil weights begin around 1000wt and up to 500 000wt. The heavier you go with the oil, the more restriction it causes, 5000wt in the rear will be virtually normal, where 100 000wt will be almost locked.

    As long as the diff in your model can be sealed, you can use the oil filling method. Make sure all your seals are undamaged and correctly positioned. Clean all the old grease out of the diff, and reassemble the unit, then fill the diff to the cross pins that hold the gears, insert the last gear and close the unit up.
    Refit into your gearbox and you are done.

    Caution needed, with a heavier weight oil, your diff will have similar characteristics of a Locker, and may become a little tail happy causing you to have huge amounts of fun going sideways.

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    R/C Apprentice Baz345 is on a distinguished road Baz345's Avatar
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    Hmm I see. Thank you all for explaining as I'm still learning . I was never intending to lock my diff but just learn more about it incase I wanted to at some point. So what are the main reasons for locking your diff?
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    Locking the diff keeps both rear axles spinning at the same speed constantly, better for inline speed...it does however raise the chances of the truck going sideways a lot easier if the tyres break traction.
    Lockers are perfect for Drag cars, and launching in a striaght line, also good for crawlers, even if one wheel looses traction, the other is still spinning and should bite in.

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    R/C God schmarkoDave is on a distinguished road schmarkoDave's Avatar
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    Also good for drifting, where you specifically want to be sideways.
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    I was gona say Wat u said Pete just cbf off my fone lol

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    As said above drag racing, crawling and some drifting is all they're good for.
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  12. #11
    R/C Apprentice asc is on a distinguished road
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    A lot of onroad cars run very thick diff oil (50,000 - 200,000). Also 8th scale onroad run a fully locked rear spool and one way front (essentially locked on power). This is fine with heaps of grip but might be a bit strange in an offroad car for reasons stated above.

  13. #12
    R/C Apprentice Baz345 is on a distinguished road Baz345's Avatar
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    Ah k, yeah I just like bashing offroad and taking it out the front for some road driving. I guess I don't need to lock my diff, just had to ask because I though it gave you more power and traction(similar to tighten slipper clutch I though). Cheers guys.
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    If you want a good explanation of diffs watch the below. No I'm not pulling the p!ss (you'll know what I mean if you watch it ), you can skip to about 1:40 if you want to.

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  15. #14
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    Thanks Chris, I looked for that video but couldnt find it....one of the best descriptive vids on the subject.


    Cheers
    Pete

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