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Old 03-09-2010, 02:08 AM   #1
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Questions?? Deformed differential spring makes the diff feel uneven and not smooth

Many touring cars use a spring in the differential, to produce tension and friction between the plates and the balls. The problem is that after a few rebuilds, the diff seems to have uneven tension - if you rotate one outdrive 360 degrees you can feel that it is lighter or tighter around the cirlce. My guess is that the spring is bent or deformed, and it needs to be replaced. Sometimes even new springs are slightly bent. If you look closely, you can see that the top and bottom sides are not parallel to each other. This makes even a diff with brand new balls, plates and outdrives, not work smoothly.

Have you noticed all that, or is it just my impression? Do you have any tips? The only way I can fix this, is by trying new springs until I find one that sits straight and properly inside the outdrive. Maybe there is another way.. Hope to hear everybody's ideas.

Thanks
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Old 03-09-2010, 02:59 AM   #2
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Try lookin at the losi XXXS diff set up
doesn't use a spring,it uses beveled spring washers , so never had that prob always silky smooth (aslong as it's clean an good diff balls an plates used)
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Old 03-09-2010, 02:59 AM   #3
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There is one thing you can do... change to a TOP Photon!

It has belleville washers instead of a coil spring, and the diff is super-smooth.
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Old 03-09-2010, 03:10 AM   #4
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also a good idea to always polish/sandpaper the diff plates to take out high spots. Springs also deform if you over tighten them.
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Old 03-09-2010, 03:18 AM   #5
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yes xray use a cone or spring washer in their diffs and are really smooth, no high spots.
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Old 03-09-2010, 03:37 AM   #6
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There's plenty of other cars that use Belleville washers (Kawada, Avid, etc), even Tamiya uses those in the low end cars with the Manta Ray or TA03 balldiff, but it's not really necessary to change the diff setup.

If you're not happy with your diff and you're positive it's because the spring is not square, you can "machine" it square on a grinder. That's what I do, anyway. Take your time and check your progress as you go. Keep the spring square (perpendicular to the grinding wheel) and try to follow the same face as you grind away, don't change the angle of the spring to the grinding wheel as you grind. Use the lateral face of the wheel too, that is perfectly flat and should result in a smooth, flat face on the spring ends.
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Old 03-09-2010, 04:01 AM   #7
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the best diff is the yokomo bd5, no slip and ultra smooth, it uses a spring...
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Old 03-09-2010, 04:16 AM   #8
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Quote:
Originally Posted by gameover View Post
the best diff is the yokomo bd5, no slip and ultra smooth, it uses a spring...
Idd, no way that a small spring that doesnt have the ends exactly parallel and is 4mm in diameter can put that much uneven force on a diff so you can feel it.
In my old BD, the diffs are also with a spring and they are smooth as hell, even after 2-3 years.

My experience in 1/12th when you feel the diff going smooth for part of a cycle is that the thrust bearing isnt perfectly centered. this causes one of the plates of the bearing to bind against the centering screw (only for a moment cause when its positioned out of center and you make a circle there's 1 moment it binds against the screw which is in the center).

So you prolly have a problem in the thrust bearing area of the diff.
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Old 03-09-2010, 04:46 AM   #9
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Thank you all for your replies.

I'll do some tests on my diff, based on your feedback. Hope to get consistent performance from it, since it is such an important part of a touring setup.
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Old 03-09-2010, 07:49 PM   #10
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I have been in this hobby for many years, and I never had diff spring problem. I had more problems with those cone washer for diff spring. They go flat after a few months, break, or do not have the same tension after a few weeks.

Quante has the right idea. Check thrust washers & balls. Also check diff rings and balls.
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Old 03-10-2010, 01:50 AM   #11
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Yes, Quante's post is interesting, I had never thought of that.

For pancar diffs, I've found that even the nut on the right hub, which puts the diff together, is very important. Sometimes nylon nuts are not prefectly straight and make the diff bind. Now I use an aluminum nut on my pancar diff. It goes in straight and puts an even pressure on the cone washers, and this makes the diff work really smooth.

As far as touring car diffs with a spring setup, I use thin steel washers between the nut and the right outdrive, and between the spring and the left outdrive. This is because the outdrives are made of delrin, which, like any plastic, is not hard enough to withstand the pressure. So, if I don't use washers, the nut on the right side and the spring on the left tend to "dig" into the outdrive material. This makes the assembly tweaked and the diff feels terrible.
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Old 03-10-2010, 02:37 AM   #12
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Quote:
Originally Posted by billtc3 View Post
This is because the outdrives are made of delrin, which, like any plastic, is not hard enough to withstand the pressure.
For this reason I prefer aluminium (or steel) outdrives - they tend to build a much better diff.
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