Trf502x Diff Build Problems

[taomo]

Originally Posted by Aussie Top Force

I built the diffs first time out as per instructions, after the first run the diffs felt rough, upon inspection the ceramic grease had contaminated the ball diff grease. See how you go. I just built a DB02 for one of my kids to race. It has exactly the same diffs. They feel great and nice and smooth after the build, as did the 502X. I have used ball diff grease on the bevel gears this time. If they get rough, it is definitely poor quality diff balls.

As you are using Ceramic balls I'd be interested in hearing about how the diffs perform after a few runs.

I will build the diffs with the new balls (ceramic in rear and tungsten in front) next week. I will post how the diffs perform after a few runs (if there are no problems with the weather) ;-)
My original diffs (balls are steel made), after 2 month approx., now get rough. Time to change it!
Hope I can use the #53970 and will fit it correctly.
For now I will not use the #50880 spare parts, simply I will turn the original ones.

Best regards

[DaveG28]

Interesting, I use the ceramic grease in there too, may try a change!

[kidcongo]

Hate to say it, but the original Tamiya steel balls are junk. They were gritty after one race day. I put ceramics in both ends of my 502X and no problems since. I've had them in one year, and rebuilt them once, but did not need new balls, just a cleaning and new grease. No problems since I upgraded!

[Aussie Top Force]

Originally Posted by kidcongo

Hate to say it, but the original Tamiya steel balls are junk. They were gritty after one race day. I put ceramics in both ends of my 502X and no problems since. I've had them in one year, and rebuilt them once, but did not need new balls, just a cleaning and new grease. No problems since I upgraded!

Yes I would have to agree. My standard built diffs are now in Aussie "rough as guts mate", even after a strip down and rebuild, using same parts.

Thus time to order some new balls and rings for the 502X. My 201 has had many more runs and the diff is still very acceptable. Wonder why the 502X got such a bad set of balls?

[djmcnz]

I still use 1 or 2 steel balls in my diffs (12 and occasionally 6 o'clock) with the remainder being tungsten carbide... ages ago I recall reading (can't find it now) that this was a good way to stop the plates fouling.

I've always done this, my plates don't foul but is it necessary?

NB - the steel balls remain round - I suspect this is because the load on them is negligible.

[taomo]

Those who have changed the diff balls, what grease did you use?
Because first 2 days the diffs became a little gritty, I rebuild the rear one but changing the original Tamiya grease to a 3Racing grease (in the 3/32 balls). I must say that, today (after two months approx. running), the rear diff works a lot better than the front one (both are gritty but the front is worse).


Best Regards

[kidcongo]

as long as it is silicone grease on the balls I think your are OK. I have used Kyosho clear silicone grease and tamiya silicone, and cant say I notice a difference. The reason it is silicone grease is that silicone grease has very low "shear strength". This means that the grease will squeeze out of the way and allow direct contact between the diff balls and the pressure plate, causing the balls to "roll" so the diff does not slip. At the same time the grease lubricates the surfaces where the balls roll inside the plastic cage of the nylon diff gear where the pressure is not a great, preventing wear of the nylon part.

For the diff's small 'thrust' bearing you are only interested in having minimal friction so they use AW or Black grease, which is a grease containing molybdenum or aluminum particles that has a very high shear strength. In other words it doesn't smear out of the way under pressure. Moly type "black" grease is what you see in high pressure applications like a tractor-trailer 5th wheel plate.

In your ball diff, you never want the balls to slip, you want them to roll along the plate. If you use normal grease, black grease, or ceramic grease that is not for diff plates, you essentially make everything way too slippery, and the diff balls will not function like the planetary gears they mimic in a standard gear diff. They will slide along the plate, which puts flat spots on them and makes the diff feel "gritty" before it's time.

If you look at the steel balls from the "gritty" diff they are typically covered with a multitude of microscopic flat spots.

[taomo]

Hi,

I am rebuilding diffs and, when I open the front gear box, I don't like what I see: There is dust inside as you can see in photos (in only 2 months running...).
Anyone know any tip to make it waterproof?
Ball diff ring gear and bevel pinion gear are a little damaged but are still usable. Nevertheless I am changing it to the new ones included in the 502x upgrade kit.

Best regards

[kidcongo]

The durango outdrive boots fit the tamiya outdrives perfectly and prevent dirt and dust from getting into the diff through the slot in the outdrive.

I have no problems with gritty diffs since I switched to ceramic and started using the Durango outdrive boots. When I open up my gear cases the diffs are totally clean - no dust or grit

See below
[/QUOTE]

[taomo]

Thanks for the tip. I will buy it!

[kidcongo]

Ok,

You can get them at A-Main hobbies etc.

The TRF 502X outdrives have a design flaw in that the slots in the oudrives extend into the gearboxes allowing dirt and dust to pass through the outdrive into the gearbox. What the Durango boots do is seal the slots so they are not open. They fit perfectly into the space between the plastic gearbox housing and the metal outdrive without disassembling the gearbox. It's a bit tricky when they are new.

A tip: The durango rubber is very durable, but can rip as you pull them over the "dog-bone" end of the outdrive. To install put the rubber outdrive boot onto a set of thin needle-nose pliers to expand the boot and allow you to slip the dog-bone end throught the hole.

The boots don't really wear-out on the in-board, and I have never had to replace them. They keep the grease in too. I tried the Durango boots as well on the outboard (wheel-side) but they did get torn and were more of a problem there. I also put these boots on my center drive-shaft just because.

Anyways.....buy a few sets (I think they are cheap) so you have spares.

[kidcongo]

link to follow

[kidcongo]

Lets try that link again:

http://www.amainhobbies.com/product_...ive-Boot-Set-2

[taomo]

Thanks kidcongo!
I will buy it this week, no doubt

[kidcongo]

No problem,

Keep that needle-nose plier trick in mind. It makes it easy and the hole is very small that the assembly has to pass through

[djmcnz]

I use the same boots and can recommend them. Agree with the above re: installation - you do need some careful force. Lube the dogbones before you start and turn the boots inside out are my additional recommendations.

[Chris]

I use heat shrink tube to cover the slot (inside the case)

Originally Posted by taomo

Hi,

I am rebuilding diffs and, when I open the front gear box, I don't like what I see: There is dust inside as you can see in photos (in only 2 months running...).
Anyone know any tip to make it waterproof?
Ball diff ring gear and bevel pinion gear are a little damaged but are still usable. Nevertheless I am changing it to the new ones included in the 502x upgrade kit.

Best regards

[taomo]

Hi,

This morning I went to the local track to prove the new diffs and durango boots. After 5 batteries running, the results are (1 battery is about 22minutes):

1-Both diffs are perfectly new as if I had not went to the track today. I know it is too early to give a verdict but I have good feelings.
2-Ceramic balls diff (in rear) is tighter than tungsten balls diff (front). Tungsten balls diff is smooth than the ceramic one.
I would have to adjust them better.
3-As you can see in pictures, the Durango Driveshaft Boot Outdrive (#TD310022) fits perfectly like as if it had been designed for the 502x. I used the pliers you can see in pictures and it helps a lot (good tip!). Nevertheless, after 5 minutes running I see that they were coming out. Every 5~10 minutes I had to stop to put it in the right place. At the end of the morning, 2 boots were damaged.

People who use the Durango boots have this problem? What do you do to prevent this problem? Chris tip (heat shrink tube) seems that can help.


Best regards

[djmcnz]

Originally Posted by taomo

People who use the Durango boots have this problem? What do you do to prevent this problem? Chris tip (heat shrink tube) seems that can help.

Thanks for the report, it's good to read these experiences.

I use the Durango boots on my 511 which is a different design. I just use them to keep the drive cups (outdrives) clean, not the diff because the 511 doesn't have the slot problem.

Mine don't get torn because they don't contact the bulkhead.

However they still can move down and I use a little bit of threadlock inside the boot, on the drive shaft, to stop them slipping. Put threadlock on the shaft and squeeze the boot onto it. Works great.

[kidcongo]

Hey Taomo,

Sorry, forgot another detail until you mentioned it. Yes the Durango boots slide down. You need to use a small amount of CA glue on the narrow part of the boot to fix the boot to the drive shaft. After the boot it attached put a little more CA that will form a ridge the boot will not slide over. The boots have been in place on my car so long that I forgot all about that detail that I figured out early on.

Glue the boot to the shaft, not the out-drive.


I also checked my boots and they do extend all the way into the gearbox and don't catch on anything. I think your boots are being torn as they slide off the outdrive. Mine go right into the gearbox without issue, and like I have said, they've been there over a year with weekly racing for the most part.