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Old 08-27-2007, 04:06 AM   #1
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Default TRF415 REAR DIFF

Can someone help me, I have broken 3 rear diffs in 4 meetings(front diff is fine). The diff basically welds itself together. I have tighten the diff until you can just move the diff pulley by hand, I also tried the diff a little looser but running a 4.5 novak all it does is slip, can someone solve my problem. Am I doing something wrong?

P.S. berfore some ask the GTB novak is only set at 40% throttle.
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Old 08-27-2007, 07:50 AM   #2
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Default 415 diff melting

Your problem is not the rpm, but the torque that the 4.5 produces. The 4.5's torque is probably equal to that of a 5 or 6 turn brushed motor, and the composite diffs simply can't handle that. Because they are plastic, the plastic bends under high torque and the diff slips.

If you want to keep running the 4.5, I would do the following:
1) tighten the diff until you can't turn the spur by hand at all,
2) see if someone makes an aluminum rear diff for the 415
3) turn the punch on the speedo to the lowest settings
4) dial in negative throttle exponential on your radio (slow acceleration.)

Or you could get a 10.5 or a 7.5 motor which has much less torque.

These should solve your problem.
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Old 08-27-2007, 08:41 AM   #3
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Try this: http://www.precisionrc.com/nv/car/pr...oduct_id=52985

It's bullet proof and I order stuff there all the time.

Good luck and Happy Racing!
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Old 08-27-2007, 10:21 AM   #4
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look near the end of the 415 thread, the team guys are building 16 ball diffs. the instructions are there.
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Old 08-27-2007, 07:32 PM   #5
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First of all a 4.5 is about equal to a good 8 turn, and second, a Tamiya diff built properly can handle a 3.5 with 6 cells no problem. You said you tighten it until the pulley just slips, this is too loose. Put it in the car and tighten it until you cannot turn the spur gear at all when holding both rear wheels. If that doesn't fix it than your doing something else wrong.
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Old 08-27-2007, 10:40 PM   #6
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Quote:
Originally Posted by patrick View Post
First of all a 4.5 is about equal to a good 8 turn, and second, a Tamiya diff built properly can handle a 3.5 with 6 cells no problem. You said you tighten it until the pulley just slips, this is too loose. Put it in the car and tighten it until you cannot turn the spur gear at all when holding both rear wheels. If that doesn't fix it than your doing something else wrong.
sorry to butt in.. how much force should be? and let's say i can't turn the spur gear by holding two rear wheels so its okay now but what if the balldiff is not free?(if i will rotate only one wheel to test the freeness of the diff)....
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Old 08-28-2007, 08:02 AM   #7
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Well if built correctly, the diff should not slip but still turn freely.
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Old 08-28-2007, 08:15 AM   #8
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need a lot of experience in this case of trouble
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Old 08-28-2007, 09:05 AM   #9
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Default couple of things

Patrick: The 4.5 is equal to an 8 turn in rpm, not so much in torque. Brushless motors have gobs of torque. The watt value of the 4.5 is 530watts (per novak), the watt value of a 10turn single is about 270 watts (per rcca), and 8 turn would be about 350watts. The brushless has about 50% more torque.

After tightening the diff, the problem left could be the composite diffs. Under pressure, they can bend and warp and let the diff slip. The diff slips, heats up, and melts the diff halves.

Are the guys you are talking about running composite diffs, or aluminum diffs?
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Old 08-28-2007, 10:29 AM   #10
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16skyline--- best advice for building the 415 diff is to take your time and use new parts each time you build a diff, especially if you are using the composite outdrives. If you are using the aluminum outdrives then you can replace on a less frequent basis.

Use Associated Black grease for the thrust and Assoc. Red label diff grease for the ball lube. My personal order is as follows

Black grease packed into the thrust
Place diff screw into thrust making sure the cone side of the brass insert is facing inside, the the diff screw head is against the flat machined side.
Place a thin coating of the Red label on the diff outdrive
Place diffring on outdrive (sidenote here at Tamiya Nats last week I saw a batch of bad diff rings. I had to go through 5-6 plates to find 2 good ones for a couple of our local drivers)
Place a small drop of Red label in each diff hole
Use Carbide or ceramic only balls placing one in the Red laber in each hole
place bearing in recessed outdrive place spacer and second bearing on second outdrive
Bring the entire assembly of outdrives, diff pulley together
Before you place the diff spring into the outdrive pre-set the spring by squeezing it with a pair of needle nose pliers.
Place retainer and nut into outdrive
Slowly tighten until there is light tension on the diff screw. I then use a dremel set onto lowest setting to start break-in for 15s. Put the dremel in one outdrive and hold the other.
Another half turn on the diff and 15sec with the dremel
You should be just about tight now continue until you get to full tight and then back off 1/4 turn
Your diff should be set just right you might have to loosen or tighten based on your personal settings.
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