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  1. #1
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    4x4 Diff oil changes. What can I expect for performance?

    I have just recently completely overhauled the diffs in my sons 4x4 vxl slash. I have gone with 30k front oil which is same spec as what's in the truck stock out of the box. That was just a clean out and oil change for maintenance purposes. It is a little heavier than traxxas 30k but probably negligible. The real difference is what I've done in the rear. It comes stock out of the box with grease in the rear diff. I have now cleaned it all out and changed it to 10k traxxas diff fluid. I realize it's a fairly lightweight oil but am wondering what may be the noticeable difference in performance from the stock rear diff grease. As well, I'm starting with 10k. I may change out the oil shortly and go to a higher weight oil or possibly have 30k front and 30k rear. I'm waiting for a set of tires to arrive (stripped out the hub, my fault for loose wheel nut) so I cant run the slash for a another few days. So hopefully some of you can shed some light on this. Running on asphalt and off road bashing.

  2. #2
    RC Qualifier Panther6834's Avatar
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    Quote Originally Posted by Buncha Blunts View Post
    I have just recently completely overhauled the diffs in my sons 4x4 vxl slash. I have gone with 30k front oil which is same spec as what's in the truck stock out of the box. That was just a clean out and oil change for maintenance purposes. It is a little heavier than traxxas 30k but probably negligible. The real difference is what I've done in the rear. It comes stock out of the box with grease in the rear diff. I have now cleaned it all out and changed it to 10k traxxas diff fluid. I realize it's a fairly lightweight oil but am wondering what may be the noticeable difference in performance from the stock rear diff grease. As well, I'm starting with 10k. I may change out the oil shortly and go to a higher weight oil or possibly have 30k front and 30k rear. I'm waiting for a set of tires to arrive (stripped out the hub, my fault for loose wheel nut) so I cant run the slash for a another few days. So hopefully some of you can shed some light on this. Running on asphalt and off road bashing.
    First, the heavier weight diff fluid should be in the rear. Think of using different weights to adjust the "slip" of the diff. By using such a lightweight fluid in the rear, you've, essentially, created a "fully open" diff. In the rear, what you want is something between "limited slip" and "locked". When I rebuilt the diffs in my Rusty (essentially, a Sl4sh with a shorter wheelbase), I put 15K in the front, 10K in the center (yes, I replaced the slipper, with the TRA 6780 HD Center Differential), and 80K in the rear. For another example, I recently did a lot of upgrades on my Losi Baja Rey, including replacing the plastic diff cups with the machined aluminum cups crib Exotek. For the BR, I went with 15K/15K/80K. Notice, in both, 80K was used in the rear. Some people will go 100K, or higher. For those who've replaced their slipper with a center diff, some people have been known to do the same thing (ie. using 80K, or higher, in the center diff).

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  3. #3
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    First off thanks for your response Panther! But I've got say I AM SO CONFUSED!!! if the rear "should" be thicker than why does Traxxas ship them stock out of the box with grease in the rear and 30k in the front. I thought by putting 10k in there I was making it thicker than what's stock. There are soooo many opinions on this and I cant really make heads or tails of any of it. I do realize that its trial and error. I run my slash on asphalt and in construction zones on hard pack and sometimes on loose gravel. Really multi use so I guess that is what I'd like to set it up for. A good all around diff lduid setup. My understanding is that if the rear diff fluid is too thick, it affects the steering and causes understeer. Man, I wish there was a good video I could watch about understanding rc diffs a bit more......

  4. #4
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    Most Traxxas 1/10 stock setups use 30k front, grease in the rear.

    I use 30K front, 10k rear, but read other setups using 50K front / 30K rear or 50/30 allround.

  5. #5
    RC Qualifier Panther6834's Avatar
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    Higher, or lower, in the rear will primarily depends on your use. Also, as I've always understood it, the grease in the stock rear is incredible thick...equivalent to 1M diff fluid.

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  6. #6
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    There's no right or wrong as far as diff setups go. If you have 30k in the front and 10K in the rear, it will make the truck act like it has front wheel drive with the front tires pulling harder than the rear. This will give you better steering in corners essentially pulling the truck around the turn. It will be less likely to wheelie with this type of setup.

    If you go in the opposite direction and put a heavier oil in the rear, it will tend to push to the outside of a corner giving you less steering and will be more prone to wheelie. It's all a matter of personal preference and how you want the truck to drive.

    When I was racing my truck at my local track or just bashing around the house , I went with the first type of setup with 30k in the front, anywhere from 60k to 100k in the center diff, and 10K in the rear. I don't like my truck to pull wheelies , and I like better steering.

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    Quote Originally Posted by Panther6834 View Post
    Higher, or lower, in the rear will primarily depends on your use. Also, as I've always understood it, the grease in the stock rear is incredible thick...equivalent to 1M diff fluid.
    The grease they use in the rear is not thick.
    Don't know for sure, but I thought it's <10k.

  8. #8
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    Quote Originally Posted by StijnH View Post
    The grease they use in the rear is not thick.
    Don't know for sure, but I thought it's <10k.
    Definately not very thick. just swapped it out yesterday. consistency of standard grease. Much more loose than the front diff.

  9. #9
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    It is trial and error. I keep the stock 30,000 in the front differential of my trucks. I used to put 100,000 in the rear. Years ago I switched from 100,000 to 500,000 in the rear! I like the performance that I get from that setup so I continue to use it
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  10. #10
    RC Qualifier Panther6834's Avatar
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    Quote Originally Posted by Buncha Blunts View Post
    Definately not very thick. just swapped it out yesterday. consistency of standard grease. Much more loose than the front diff.
    I'm wondering if the grease used in the Slash's rear is different than that used in the Rusty. The Rusty had "thick sludge" in there, and it was far thicker than the 80K diff fluid I replaced it with. Let's just say, it was so thick, I had trouble completely cleaning the diff' gears, so I just bought new gears.

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  11. #11
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    Quote Originally Posted by Panther6834 View Post
    I'm wondering if the grease used in the Slash's rear is different than that used in the Rusty. The Rusty had "thick sludge" in there, and it was far thicker than the 80K diff fluid I replaced it with. Let's just say, it was so thick, I had trouble completely cleaning the diff' gears, so I just bought new gears.

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    Its possible i guess. I took mine out and soaked them in mineral sprits. They were clean spic and span in minutes

  12. #12
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    Quote Originally Posted by Panther6834 View Post
    I'm wondering if the grease used in the Slash's rear is different than that used in the Rusty. The Rusty had "thick sludge" in there, and it was far thicker than the 80K diff fluid I replaced it with. Let's just say, it was so thick, I had trouble completely cleaning the diff' gears, so I just bought new gears.

    ~ More peace, love, laughter & kindness would make the world a MUCH better place
    Its possible i guess. I took mine out and soaked them in mineral sprits. They were clean spic and span in minutes

  13. #13
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    Quote Originally Posted by MaXDee View Post
    There's no right or wrong as far as diff setups go. If you have 30k in the front and 10K in the rear, it will make the truck act like it has front wheel drive with the front tires pulling harder than the rear. This will give you better steering in corners essentially pulling the truck around the turn. It will be less likely to wheelie with this type of setup.

    If you go in the opposite direction and put a heavier oil in the rear, it will tend to push to the outside of a corner giving you less steering and will be more prone to wheelie. It's all a matter of personal preference and how you want the truck to drive.

    When I was racing my truck at my local track or just bashing around the house , I went with the first type of setup with 30k in the front, anywhere from 60k to 100k in the center diff, and 10K in the rear. I don't like my truck to pull wheelies , and I like better steering.

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    I agree with this post, always use lighter diff oil for rear diff to get better steering and faster turns.


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  14. #14
    RC Qualifier Panther6834's Avatar
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    Quote Originally Posted by alexsasax View Post
    I agree with this post, always use lighter diff oil for rear diff to get better steering and faster turns.


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    NOT always true. It depends on the vehicle type, the intended use of the vehicle, and the configuration of said vehicle. A vehicle with 4-wheel independent suspension will use different diff fluid weights than a vehicle with front & rear axles, which will, again, be different than a vehicle with IFS & rear axle. Also, a bashing vehicle will use different front vs rear diff fluid weight biases than a racing vehicle (and, even that will depend on whether it's an on-road, or off-road racer).

    I'll use the Vaterra Twin Hammers, and Losi Baja/Rock Rey, as a perfect example. For all three of these vehicles, you NEED to have a higher rear diff fluid weight. If the front had a higher did fluid weight than the rear, you would actually be making the steering WORSE and SLOWER. You would also cause the vehicle to be more susceptible to rolling over. Having a much higher did fluid weight in the rear provides better rear-wheel traction, gives the vehicle more stability (especially in turns), and makes the vehicle less likely to roll over.

    Front vs rear diff fluid weight bias is no more "set in stone" than, say, selecting tire compounds, or shock oil weights. For example, using race tracks, in regards to tire compounds, as well as shock oil weights, depending on the conditions (loose, packed, dry, wet, etc), and track compound (clay, dirt, carpet, etc), you might want the same compound front/rear, for others you might need a slightly softer compound up front, and, for others, you might need a slightly softer compound in the rear.

    My best recommendation is to test different configurations (higher in front, higher in rear, equal front/rear), as well as different diff fluid weights, and find what works best for your vehicle, your style of driving, and where you're driving it. I realize that could mean disassembling, cleaning, refilling, and reassembling multiple times...but, in the end, you'll have a vehicle tuned specifically to 'you'.

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  15. #15
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    Quote Originally Posted by Panther6834 View Post
    My best recommendation is to test different configurations (higher in front, higher in rear, equal front/rear), as well as different diff fluid weights, and find what works best for your vehicle, your style of driving, and where you're driving it. I realize that could mean disassembling, cleaning, refilling, and reassembling multiple times...but, in the end, you'll have a vehicle tuned specifically to 'you'.
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  16. #16
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    Quote Originally Posted by Panther6834 View Post
    NOT always true. It depends on the vehicle type, the intended use of the vehicle, and the configuration of said vehicle. A vehicle with 4-wheel independent suspension will use different diff fluid weights than a vehicle with front & rear axles, which will, again, be different than a vehicle with IFS & rear axle. Also, a bashing vehicle will use different front vs rear diff fluid weight biases than a racing vehicle (and, even that will depend on whether it's an on-road, or off-road racer).

    I'll use the Vaterra Twin Hammers, and Losi Baja/Rock Rey, as a perfect example. For all three of these vehicles, you NEED to have a higher rear diff fluid weight. If the front had a higher did fluid weight than the rear, you would actually be making the steering WORSE and SLOWER. You would also cause the vehicle to be more susceptible to rolling over. Having a much higher did fluid weight in the rear provides better rear-wheel traction, gives the vehicle more stability (especially in turns), and makes the vehicle less likely to roll over.

    Front vs rear diff fluid weight bias is no more "set in stone" than, say, selecting tire compounds, or shock oil weights. For example, using race tracks, in regards to tire compounds, as well as shock oil weights, depending on the conditions (loose, packed, dry, wet, etc), and track compound (clay, dirt, carpet, etc), you might want the same compound front/rear, for others you might need a slightly softer compound up front, and, for others, you might need a slightly softer compound in the rear.

    My best recommendation is to test different configurations (higher in front, higher in rear, equal front/rear), as well as different diff fluid weights, and find what works best for your vehicle, your style of driving, and where you're driving it. I realize that could mean disassembling, cleaning, refilling, and reassembling multiple times...but, in the end, you'll have a vehicle tuned specifically to 'you'.

    ~ More peace, love, laughter & kindness would make the world a MUCH better place
    I really respect your opinion but we are talking about independent suspension
    TH have locked rear diff as I remember, sold it long time ago. Nothing to compare with Slash 4x4.
    Agree, tuning for your driving style is most important.


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  17. #17
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    Iím a 2wd guy. So when I got a Slash 4x4 I was a bit lost about how to set it up.
    My driving style is throw it into the corner and break the back end loose.
    I read a bit. I decided to stick with 30k in the front and go 50k in the rear. Something to try.
    I want those back wheels to break traction and spin evenly as I drift the corner exit.
    The truck pushed a ton on cornering when I first started, keep in mind Iím new to 4x4.
    With practice, as Iíve become more comfortable with the truck set up this way.
    Now that I know the braking ability, and how to throw the 4x4 into the corner, itís better.
    Iím driving it like a 2wd so the more locked rear diff really helps me in that driving style.
    Next rebuild Iíll probably switch it up, and see the results, and if I like them.
    I only had to buy one extra weight of fluid to have options to try. 30/50, 50/30.
    Bottom line is, thereís good advice above for both options. Try things. Find what you like.

  18. #18
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    Quote Originally Posted by Panther6834 View Post
    Higher, or lower, in the rear will primarily depends on your use. Also, as I've always understood it, the grease in the stock rear is incredible thick...equivalent to 1M diff fluid.

    ~ More peace, love, laughter & kindness would make the world a MUCH better place
    Actually acording to traxxas on chat I was just told today that 10k is thicker tan the grease and it would make the diff more locked than the grease

  19. #19
    RC Qualifier Panther6834's Avatar
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    Quote Originally Posted by papaford1963 View Post
    Actually acording to traxxas on chat I was just told today that 10k is thicker tan the grease and it would make the diff more locked than the grease
    And sometimes, that's what is wanted/needed. As I explained (if you read my long post), different constitutions, different purposes, different vehicle types, etc, can require different setups. Sometimes the front needs heavier diff fluid, sometimes the rear needs heavier, and sometimes they need to be equal. There is NO "one right answer".

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