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Old 01-23-2015, 02:31 PM   #841
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Thanks for all the help. I will first try putting the bushings back and remove the bearings as that is what I did. Then I will try the shimming.
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Old 01-23-2015, 02:42 PM   #842
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Quote:
Originally Posted by Leester View Post
Here is a tip from one of the TRF drivers who made a comment to me about the new diff AND about substituting bearings for the kit supplied diff bushings.

"About the diff: I have read the comments about the diff on RC TECH and I'm really surprised so many people have this issue. For me the diff is fine and it leaks almost nothing. I use the Kyosho red o-ring as this is better for leaking but you need to be careful because after using it a few weeks the o-ring gets bigger so you need to shim out the outdrive again ( go from 0.3 to 0.2 or even 0.1mm ). Slime can also help and of course heavier diff oil helps as well. I use the standard diff bushing, if you use bearing the oil goes into the bearing and the diff is not free anymore."

Naznai is correct in his comments about compressing the o ring too much. The diff oil swells the o ring to a point where there is too much compression and it requires re-shimming to compensate for the swelling. goingtodirt, this is probably why your diff started to leak as the o ring began to swell. Looks like re-shimming might solve the problem. It's at least worth a try to see if it solves the problem.
I've also heard guys swapping out the kit supplied bushings that come with the diff with bearings. As you can see from the comment above, it's not the best choice for a free moving diff. I think Tamiya would have put bearings in this area if it was the best choice in their high end kit. It may also be the cause of a diff leak. If the diff oil can penetrate the bearing it will also seep through it and possibly be the cause of leaking.
So another words, as the o-ring swells, we need to use smaller shims / shim less?

Last edited by Raman; 01-23-2015 at 03:00 PM.
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Old 01-23-2015, 03:37 PM   #843
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Yes. Go from a .03mm thick shim to a .02 or possibly a .01mm shim and use the Kyosho red o ring. You might try to measure the thickness of a fresh o ring and that of a swollen o ring to determine the thickness of the shim more accurately.
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Old 01-23-2015, 03:54 PM   #844
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And you guys are talking about the shim inside the diff that pushes on the o-ring held down by the pin correct? Any part numbers for different size shims? I have shims for the king pins etc but not like the ones in the diff.
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Old 01-23-2015, 03:59 PM   #845
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Here is my set up sheet for our local track in anyone would like it. I consider it a med/high bite carpet, mid-size track (10 second laps). One of our local fast guys was turning 13.5 lap times with my 17.5. He liked my set-up.
TRF419_TQ Setup.pdf
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Old 01-23-2015, 10:20 PM   #846
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I forgot to mention I use bronze bushings in all my diffs, including Xrays.

This is important because shimming the outdrive means the shims will push against the bushing. If you used a bearing, the shims would have to push against the inner race of the bearing, not the outer, and that can not be guaranteed.

The shim inside the diff (under the sun gear) is there to provide the correct sun gear height hence engage the mesh correctly with the spider gears. It does help to put even pressure on the o-ring underneath as well, but the amount of pressure is decided by the outer shims, the outdrive ones, pushing against the bronze bushing.

The correct procedure to building a smooth leak free diff is to 1. shim the sun gear to achieve smooth mesh, 2. shim the outdrive to apply correct pressure on the o-ring and keep it leak free.

All those magic slime and grease and rubbish is just snake oil so to speak and good to bamboozle feeble minds who think there's some secret potion that guarantees eternal happiness. Any grease will do. I actually use a bit of the silicone oil I am going to fill the diff with, and that's it.

If you want to be super anal, you can use some graphite powder on the outer (outdrive/bronze bushing) shims, but that's not really necessary. Don't whatever you do use grease or oil, or you'll just collect dirt. Best leave it dry because the bushing is actually graphite bronze, so it's self lubricating (as are many bronze bushings used in similar applications in machinnery elsewhere).

If you are really anal and want to use graphite powder again you can buy lots of snake oil or if you're a normal person you can just rub a normal pencil lead (the softer the grade, the better - 2B for instance) on the bushing. It's the same thing.

One other thing I found was that the the spider gear shafts (I am talking about the individual metal/alloy upgrades) sometimes rub against the outdrive if the latter pokes too much through the sun gear face. I machine down a tiny fraction of the outdrive always to make sure this doesn't happen and check protrusion. Keep in mind that the shims under the sun gear might change the outdrive protrusion.

I also use shims under the spider gears (again this is to achieve the best mesh AND diminish friction) and I always sand smooth the back of all (sun and spider) gears.

In effect, shimming the spider gears should actually be done before the two steps I mentioned above to make sure they engage the entire length of their teeth with the sun gears. This will then decide how much you need to shim the sun gears for correct depth mesh and that will decide how much you need to shim the outdrive for pressure. It's a lot of trial and error, and assembling and taking apart the diff to get it right but you end up with a long lasting, smooth, reliable, leak free diff.

Last check is for lateral play. With the diff assembled and all shimmed (no oil in) I check that the outdrives can not move in/out much if at all whilst making sure they're free to rotate. This play if it does exist might be between the sun gear pin and the bottom of its channel in the gear of it might be the whole cluster moving side-to-side through the diff. You don't want that. Work out where the play is and shim accordingly.

Not using the spider gear shims can be costly as one member at my club found out recently when one of his brand new spider gears fused to the shaft (he claims he's very experienced).

And finally, run in your diff, preferably not in the car. I load it in my lathe with one outdrive captive in the chuck and run it at various speeds, whilst applying some load by hand to the free outdrive. Vary the load and your hand will feel the diff working, if it's notchy, where is the point where it fully engages (any diff oil has a point where it locks the diff solid) and so on. This is a way of testing diff oils as well. I run diffs in using kit oils which I don't use for racing. I use Asso oils for racing simply because that is what I can get locally in any density I want. I don't know if they're the best or not and I don't care. they work for me.

After a few minutes, I take the whole thing apart, wash it clean and put it back together with my choice of oil.

If you made it through the whole post, congrats, maybe you don't have ADD just yet!
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Last edited by niznai; 01-24-2015 at 08:59 AM.
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Old 01-23-2015, 10:42 PM   #847
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Very insightful write up Niznai, greatly appreciated!

My diff never leaked out of the outdrives, I'm using the red o-rings from the kit and a very little amount of 100K diff oil for sealing instead of grease/slime. Stock 900# Tamiya oil in the diff. Where the diff halves meet, some oil escaped and lightly coated the pulley. I have cleaned it as much as possible and re tightened the screws as evenly as possible. Doesn't look like any more oil has leaked out but it is hard to tell when there is already a light coating on the pulley from before. I guess I will know for sure when I receive my new esc so I can run the car.
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Old 01-23-2015, 11:03 PM   #848
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Comes with doing millions of diffs, there's no insight, just be methodical and chase out the gremlins trying to understand what is going on rather than follow a quick formula (use this or that miracle ointment).

The centrifugal force will throw out the oil no matter what but that doesn't mean the diff has to leak. The gaskets in the kits are very good, but you need to be careful not to damage them when taking out the cutout holes or whatnot. I soak mine in a bit of oil to make them a bit more flexible and like I said before, I sand the mating faces of the diff halves. Be realistic, these are not swiss watches we're playing with here. They're a cheap (expensive) toy car in a kit. There are imperfections and such. Take a good look and you'll see. Sometimes the gasket is not pressed enough because the diff halves can not come close enough to each other to press it. Look and decide how much you need to sand. I've seen this even on Xray diffs which I rate as amongst the best as far as quality of execution goes. Functional quality is different, but even there the Xray is up there at the top (there's always room for improvement).
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Old 01-24-2015, 07:16 AM   #849
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I'm thinking of getting this car as there's a good deal on it at the moment and it's the cheapest of what I consider the top cars.

How are people finding it in general? Would you recommend it?

I race indoors so need something that doesn't fall apart when you look at it! Are there any known weak points? What spares are recommended?

I've heard it's remarkably similar to the Yokomo, do setups carry over well?

Thanks.
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Old 01-24-2015, 08:19 AM   #850
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Quote:
Originally Posted by daveaustin5 View Post
I'm thinking of getting this car as there's a good deal on it at the moment and it's the cheapest of what I consider the top cars.

How are people finding it in general? Would you recommend it?

I race indoors so need something that doesn't fall apart when you look at it! Are there any known weak points? What spares are recommended?

I've heard it's remarkably similar to the Yokomo, do setups carry over well?

Thanks.
I have all kinds of spares i will sell you . I bought a bunch and it never breaks. Seriously the only spare part you need is the c-hub.

Many folks at our track have both the BD7 and the 419. They are very similar they tell me.

You will love the car.
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Old 01-24-2015, 09:07 AM   #851
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The one constant weak point of Tamiya cars be they TRF or other is soft hingepins. They bend easily and you can't straighten them. I buy spring or tool steel in 3mm rods and cut my own hingepins. These will outlast the cars.

Also, the tie rods are some sort of hardened aluminium which breaks easily. I replace these when they break with titanium items, I prefer Lunsford.

Other than that, all parts are on par with other manufacturers, maybe a bit more fragile than Xray plastics, but not a real worry. Don't crash. Have some arms, hub carriers, C hubs on hand and the usual consumables.
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Old 01-24-2015, 12:09 PM   #852
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Quote:
Originally Posted by daveaustin5 View Post
I'm thinking of getting this car as there's a good deal on it at the moment and it's the cheapest of what I consider the top cars.

How are people finding it in general? Would you recommend it?

I race indoors so need something that doesn't fall apart when you look at it! Are there any known weak points? What spares are recommended?

I've heard it's remarkably similar to the Yokomo, do setups carry over well?

Thanks.
Yeah, I run my TRF 419 with the BD7 2015 Setup, check this out:

http://www.petitrc.com/reglages/tami...Setup20150121/

This is by the way the Best Setup I ever drive on a Tamiya TRF
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Old 01-24-2015, 03:37 PM   #853
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Thanks guys
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Old 01-24-2015, 06:07 PM   #854
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Quote:
Originally Posted by Simmi View Post
Yeah, I run my TRF 419 with the BD7 2015 Setup, check this out:

http://www.petitrc.com/reglages/tami...Setup20150121/

This is by the way the Best Setup I ever drive on a Tamiya TRF
seriously ?
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Old 01-25-2015, 12:46 AM   #855
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Quote:
Originally Posted by niznai View Post
I forgot to mention I use bronze bushings in all my diffs, including Xrays.

This is important because shimming the outdrive means the shims will push against the bushing. If you used a bearing, the shims would have to push against the inner race of the bearing, not the outer, and that can not be guaranteed.

The shim inside the diff (under the sun gear) is there to provide the correct sun gear height hence engage the mesh correctly with the spider gears. It does help to put even pressure on the o-ring underneath as well, but the amount of pressure is decided by the outer shims, the outdrive ones, pushing against the bronze bushing.

The correct procedure to building a smooth leak free diff is to 1. shim the sun gear to achieve smooth mesh, 2. shim the outdrive to apply correct pressure on the o-ring and keep it leak free.

All those magic slime and grease and rubbish is just snake oil so to speak and good to bamboozle feeble minds who think there's some secret potion that guarantees eternal happiness. Any grease will do. I actually use a bit of the silicone oil I am going to fill the diff with, and that's it.

If you want to be super anal, you can use some graphite powder on the outer (outdrive/bronze bushing) shims, but that's not really necessary. Don't whatever you do use grease or oil, or you'll just collect dirt. Best leave it dry because the bushing is actually graphite bronze, so it's self lubricating (as are many bronze bushings used in similar applications in machinnery elsewhere).

If you are really anal and want to use graphite powder again you can buy lots of snake oil or if you're a normal person you can just rub a normal pencil lead (the softer the grade, the better - 2B for instance) on the bushing. It's the same thing.

One other thing I found was that the the spider gear shafts (I am talking about the individual metal/alloy upgrades) sometimes rub against the outdrive if the latter pokes too much through the sun gear face. I machine down a tiny fraction of the outdrive always to make sure this doesn't happen and check protrusion. Keep in mind that the shims under the sun gear might change the outdrive protrusion.

I also use shims under the spider gears (again this is to achieve the best mesh AND diminish friction) and I always sand smooth the back of all (sun and spider) gears.

In effect, shimming the spider gears should actually be done before the two steps I mentioned above to make sure they engage the entire length of their teeth with the sun gears. This will then decide how much you need to shim the sun gears for correct depth mesh and that will decide how much you need to shim the outdrive for pressure. It's a lot of trial and error, and assembling and taking apart the diff to get it right but you end up with a long lasting, smooth, reliable, leak free diff.

Last check is for lateral play. With the diff assembled and all shimmed (no oil in) I check that the outdrives can not move in/out much if at all whilst making sure they're free to rotate. This play if it does exist might be between the sun gear pin and the bottom of its channel in the gear of it might be the whole cluster moving side-to-side through the diff. You don't want that. Work out where the play is and shim accordingly.

Not using the spider gear shims can be costly as one member at my club found out recently when one of his brand new spider gears fused to the shaft (he claims he's very experienced).

And finally, run in your diff, preferably not in the car. I load it in my lathe with one outdrive captive in the chuck and run it at various speeds, whilst applying some load by hand to the free outdrive. Vary the load and your hand will feel the diff working, if it's notchy, where is the point where it fully engages (any diff oil has a point where it locks the diff solid) and so on. This is a way of testing diff oils as well. I run diffs in using kit oils which I don't use for racing. I use Asso oils for racing simply because that is what I can get locally in any density I want. I don't know if they're the best or not and I don't care. they work for me.

After a few minutes, I take the whole thing apart, wash it clean and put it back together with my choice of oil.

If you made it through the whole post, congrats, maybe you don't have ADD just yet!
I'd love to know where you put bronze bushings in Xray diffs....
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