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Old 04-05-2012, 04:44 AM   #706
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What size are the diff balls? They look tiny. You would be better off just changing to Kimbrough spurs that also take 1/8 ceramic diff balls. Do that and you'll have no more problems.
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Old 04-05-2012, 05:33 AM   #707
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Quote:
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What size are the diff balls? They look tiny. You would be better off just changing to Kimbrough spurs that also take 1/8 ceramic diff balls. Do that and you'll have no more problems.
They are 1/8 balls. They start off as a tight fit (they are even tighter now!)
You can see in pics how they have elongated (melted) the spur holes.
That's why they now look undersize.

My logic is these parts normally last well. For some reason sometimes they are destroyed like this in minutes (seconds?) I suspect I'm doing something wrong in assembly.

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Old 04-05-2012, 06:29 AM   #708
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I have never seen anything like that before in any class. Have you tried a different diff ball?

That is a TON of heat buildup to do that kind of damage to the dif.; What is your track like? How tight is/was the dif set too? Are you using grease? Have you tried a different diff ball?
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Old 04-05-2012, 08:29 AM   #709
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Three options:

- The diff is to loose.
- Diff balls are to small
- The spur gear holes aren't 1/8"

In the last case, I guess the spur is made for TC cars and the holes are bigger because in TC's they use screws to mount the spur.

Go with Kimbrough spurs and 1/8" carbide or ceramic diff balls, tighten the diff as it should be and you will have a long lasting diff.
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Old 04-05-2012, 09:28 AM   #710
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Hiya!

Ima almost certain it's cos your diff is too loose.

What's happening is that the spur is spinning out on the outdrives. My guess would be that the diff was loosened to make the car easier to drive (cos maybe the motor was too hot? or tires not grippy enuff?).
Throw the spur away, reusing it will cause another stipped diff. the holes that you think are still ok, are not. From the looks of the pics, it looks like plastic has been melted out of the spur.

Most pan car drivers will also advocate ceramic balls... I do!

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What am I doing wrong? Every so often after a diff rebuild I damage my spur as per photos. Tends to happen fast, ie during first run.
I always use 3racing spurs. Steel balls used for this build. They usually last well. Last spur probably did 10-15 runs before motor moved after a big bump and it got chewed by the pinion. The ball holes still looked OK.







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Old 04-05-2012, 10:30 AM   #711
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Quote:
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What am I doing wrong? Every so often after a diff rebuild I damage my spur as per photos. Tends to happen fast, ie during first run.
I always use 3racing spurs. Steel balls used for this build. They usually last well. Last spur probably did 10-15 runs before motor moved after a big bump and it got chewed by the pinion. The ball holes still looked OK.







Are those the proper sized balls? Looks like they are too small and or your diff is not properly working and overheating.
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Old 04-05-2012, 11:01 AM   #712
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use only one track(circle) with balls not two like you did. And fill all holes with balls. Succes
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Old 04-05-2012, 11:09 AM   #713
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That doesn't matter, the outside row is fully filled. It would be an idea to fill out the inner row entirely too but it is not what caused the problem.

Like I said... If the spur holes are correct, the diff balls are correct, it was a loose diff. Nothing more and nothing less.

The diff on a pancar is not a tuning option but something that needs the same adjustment every time. Unlike a TC where you can use the ball diff as a "sort of" slipper unit. On a pncar you can't. Adjust it the right way and use grip options like giving less gas or different tires...
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Old 04-05-2012, 01:27 PM   #714
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Since your the expert joost i don`t dare to disagree, But i just want to share my experience and hopefully it will help oneother. Running 1/12 i had the same problem when i used 2 tracks with balls on the spur. When i changed to one track > problem solved. Could be that its caused by the way the diff rings are pressed to the balls. It seemed in my case that only one row/cirkel with balls got the pressure from the diffrings wich caused the second row to slip and heat up. Well any way lots of advise i see.

i would say try it and see if it helps you like it helped me.

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Old 04-05-2012, 01:58 PM   #715
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You can hear if the diff is slipping so it is realy easy to know what is going on.

Like most said, fill the outer holes and no slipping diff and the diff should be fine. Kimbrough are the only spurs i use and in my opinion the standard for pancar spurs.

Flat diffrings is also very important in a diff. Yesterday i rebuild my diff and used new D-rings. They were wobbly out of the package. No sanding would remedy that. From now on only IRS diffrings for me.
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Old 04-05-2012, 02:10 PM   #716
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Djiewie: It is common, in particular in modified 1/12 & Pro10, that people fill both rows with diffballs so that the power of the motor is transfered better to the diff. In that case you should fill them all up or just the outer row. So you were not so wrong in that way that the inner row was half filled.

Like Alexander (2wdrive) said. Make sure the diffrings are FLAT! IRS rings are by far the best choice in combination with Kimbrough spurs and for most racers ceramic diffballs. Sand the diffrings flat with 600 sandpaper, that should do the trick just fine. Don't polish the diffrings to a mirror shine, that will geve the rings less grip on te diffballs and will cause the diff to slip also.

Also, don't use too much diffgrease. Over-greasing the diff won't make it better but only worse...

@MrChodes: I hope all these tips will help you on your way to running more than a couple of minutes with your diff...
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Old 04-05-2012, 08:16 PM   #717
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Thanks very much. I've been a lurker here for a while, was hoping to get input from you experienced people. Read everything twice and saved to a text file...

Will fill all holes in future (if using both rows)

Interesting regarding wobbly diff plates out of the bag. I bought a used Rebel 12th scale recently, mainly for the spares. There is an unopened bag of 10 IRS diff rings

If I could trouble you for 1 more piece of advice - ballpark life expectancy of ceramic balls ?
When I put the diff together properly I'll get 10-15 runs before holes in the spur are big enough for the balls to be noticeably loose. I usually replace everything then. (probably pull apart, clean and re assemble 2-3 times during that time)
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Old 04-05-2012, 09:15 PM   #718
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Normally I race more than a season with a set of ceramic diff balls so with a proper working diff they should last a very long time.

Keep in mind that even when you are using IRS diffrings, you still have to sand them flat (on both sides!!!)
I only use the light weight diffrings from IRS with only the outer row filled with diffballs and it works great.

Before you put in the diffballs, try to put some diffgrease in the palm of your hand en gently rub the diffballs through the grease. Put the balls in the spur gear after that. That amount of diffgrease should be enough.
If I look at the pictures of your particular spurgear and the amount of grease that is present. I would use about the amount that is left in two or three holes.
The more grease is in you diff, the more dirt and debris will come in the diff causing the diff to fail.
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Old 04-05-2012, 09:49 PM   #719
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Thanks again Joost.
Wow - surprised at the longevity of the ceramic balls.

I did use more grease than usual for the damaged spur in photos. Still learning.
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Old 04-06-2012, 12:14 AM   #720
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@MrChodes....We all are
Still learning tricks and i have been running RC cars from 85

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