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Old 09-03-2009, 07:10 PM   #1
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Default DIFF ADJUSTMENTS?

ran a TC3 around the track and in the sharp corners it wanted to do a 360 and did, even at low throttle and compound on the tires

someone suggested the front diffs were too lose so I tightend'em and it made a diffrence..ok, should the front /rear diffs be adjusted the same ? also whats the meaning of a "locked diff, that mean the adjust screw is turned in all the way so the tires will barely move? if so why?
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Old 09-03-2009, 08:36 PM   #2
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You can lock by doing that, which isn't very good as the diff screw may snap after awhile. The alternative solution is to use a spool instead.
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Old 09-03-2009, 09:18 PM   #3
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You can lock by doing that, which isn't very good as the diff screw may snap after awhile. The alternative solution is to use a spool instead.
ya might wanna enlighten me re car terms, not too familiar yet why lock? spool?
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Old 09-03-2009, 11:29 PM   #4
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Old 09-04-2009, 12:15 AM   #5
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Originally Posted by drive2survive View Post
ya might wanna enlighten me re car terms, not too familiar yet why lock? spool?
To answer your question, a spool is not a diff at all. It simply locks the wheels left & right. This is what you typically see when racing on a large asphalt track. If everyone else at your track is running a front spool, you should probably invest in one as well...

On a very tight asphalt course, a front diff will probably be better. Typically you run the front diff a little tighter than the rear. If your rear diff is too tight, your car can get very loose when mash on the throttle. Readjust your rear diff to be as loose as possible without slipping. Then make your front diff a little tighter than that.
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Old 09-12-2009, 07:13 PM   #6
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To answer your question, a spool is not a diff at all. It simply locks the wheels left & right. This is what you typically see when racing on a large asphalt track. If everyone else at your track is running a front spool, you should probably invest in one as well...

On a very tight asphalt course, a front diff will probably be better. Typically you run the front diff a little tighter than the rear. If your rear diff is too tight, your car can get very loose when mash on the throttle. Readjust your rear diff to be as loose as possible without slipping. Then make your front diff a little tighter than that.
does that diff adjust apply to belt drive like a HPI sprint?
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Old 09-13-2009, 01:06 AM   #7
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My experience is with a TRF415-MSX. This is a dual belt drive touring car. I believe the principal applies to all cars though...
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Old 09-13-2009, 03:49 AM   #8
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May not be a diff issue. You may have too much front grip relative to the rear.
When my local track gets gooped, we have to compensate for the extra steering.

Is it off power and when neutral throttle as well ? Or just on power ?
A spool will help pull the car out of the corners better,but tend to under steer into turns .(this can be tuned out)
A rear diff too tight will cause the rear to power slide on exit too.

Approach one of the better drivers at your track and get them to check it for you.
Most will be happy to help and experienced eyes will find problems faster.

I solved a similar problem with a Losi Type R that did a similar thing....
I traded it in on an Xray. Best thing I ever did.

Fleet.
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Old 09-13-2009, 12:36 PM   #9
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The one part of kit building and car adjustment which I find most difficult and where I often find peoples advice confusing is diff building and adjusting.

As far as I know there is no diff tightness gauge, or little marks to line up or a clear procedure to test tightness.

Obviously a diff is too lose if you can easily move the pulley, while holding the out drives from moving. It is obviously too tight if the diff acts like spool or when you turn one wheel/out drive and the wheel/out drive on the other side seems to bind or the ball diff feels gritty.

I have seen two methods of testing. One is to raise the whole car up turn both wheels (on the end of the car you are testing) in the same direction and make sure you can hear/feel the motor rotate as yo urotate the wheels, if motors magnetic resistence to turning is sufficent to makr the diff slip then it is too loose.
The other method is to do the same but have the wheels on the opposite end actually contacting the surface and then see if rotating the rear two wheels will cause the wheels on the other end to rotate or will the friction from the contact with the surface hold the other ends wheels sufficiently to cause the diff to slip.

The idea is too loosen the diff until it just barely passes one of the above tests.

Note: I think it is also the case that diffs loosen themselves over time particualrly newly rebulit ones and thus need to be readjusted after the first run or two.

The other related question that I hear differing answers too is; how much diff lube to use. The most common opinion I think is that less is better and as long as each ball is covered the amount of lube is sufficent.

I have the feeling that this is one of the areas that the top pros have down pat or have their own methods and that their own techniques or rules of thumb, which are not necessarily part of our common knowledge pool.
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Old 09-13-2009, 01:25 PM   #10
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On the same subject. How would a Front Spool act in a TC3? Pros/Con's?? VTA on carpet. since a oneway is not a option anymore
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Old 09-13-2009, 01:53 PM   #11
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On the same subject. How would a Front Spool act in a TC3? Pros/Con's?? VTA on carpet. since a oneway is not a option anymore

What a spool does is make the front of the car push coming into a corner. Since both tires will spin at the same speed, and the inner tire is on a smaller diameter circle during the corning, one of the tires must slip. This makes the car push on entry.

However, when your car starts to accelerate out of the corner, both wheels, will receive the same amount of power, allowing the front end to pull the car thru the corner, and accelerate harder. With a diff the inner wheel (it has less weight on it), will get more power then the outer wheel, causing slower acceleration, and wheel spin.

I dont know if I would run a spool on carpet. They are used more in low traction conditions. Another problem with a spool is they are hard on the outdrives, and dogbones.

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Old 09-13-2009, 02:18 PM   #12
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If you are setting the TC3 diffs per the instructions try loosening the rear another 1/8th or 1/4 turn. I thought the settings in the instructions were a little tight.

On an HPI Pro 4 i've found that a fairly loose rear dif allows me to flow through tight turns.

Hope that helps.
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Old 09-13-2009, 02:20 PM   #13
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tire wear too
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