Trf502x Diff Build Problems
 

Hi

Is it me or is this diff in the 502 pants! I've spent hours stripping, measuring, changing balls, changing plates, polishing etc but i can't seem to get a nice graunch free diff. It only seems to be the last bit of nip on the screw to stop the diff slipping which seems to really bind it up. Never had this problem with any other diff.

I'm heading to the conclusion that its the thrust race balls jamming in the outdrive as the races have no grove in them for the balls to run in.

What do you all think ?


Thanks
Paul

The 502 diffs are fine if you pay attention to the following :

- DITCH THE KIT DIFF BALLS !!! They are worthless. I still believe it's a disgrace that Tamiya includes such sub-standard parts in such an expensive kit. Tungsten or ceramic balls are available from TRF or other brands. I prefer Tungsten myself.

- Do not use the Tamiya ball diff grease. It hasn't changed since the 90'ies so it is too thin for present day power levells. There are several aftermarked alternatives

-If applying grease to the diff gears, be sure this grease cannot enter the diffs. so use grease very sparsely on the gears or don't use any grease at all.

- be sure to precompress the diff spring before building the diffs

- I believe tamiya suggests in its manual to use anti-wear grease on the thrust bearing. Use a good ceramic or graphite grease instead.

I have the same problem, that's why i prefer the TRF511.

AE uses this thrust bearing system for over 20 years, so I doubt this is the problem. If anything : i think it's the diff spring that causes your problem.

The 502 diffs are normal, predicatable and just fine if you ditch the stock balls and get the upgrade. Personally, I really like the Tamiya AW grease and find it still very smooth when I rebuild (not that often since I went ceramic). Ceramic is a bit more finnicky than tungsten as it will slip easier. If you look at the crap ball that tamiya supplied with this kit, they probably have very minute flat spots all over them. The good news is the sealing surfaces on the 502X gearbox covers will keep all the grit out of your diffs if you take the time to seal the slots in the outdrives, which extend into the gearbox. I use Durango outdrive boots and they work fine on the tamiya outdrive.

A good set of balls is the key to success :thumbsup:

you can see the out-drive boots in this pic.

http://i1177.photobucket.com/albums/...X/P1170994.jpg

Since a use a TOP thrustbearing I have much smoother diff in my 502x...

Could be a lead for you too...

Meaning you are building your diff with AW-grease on the main plates??? Or only on thrust balls?

No....AW only in the thrust bearing, never on the plates

If the 502x has ball-diffs I assume I know why your having problems.
Best thing to do is buy tugsten carbide balls and re-break in the diff.
My diffs have always remained smooth using the tugsten balls.

Maybe you have hearded about the slipper problem...

I think 90% of diff problems come from this problem. Let me explain...

First, I built my differentials just like in the manual, and after 3 qualifications, my car was crying, really, making a strange noise when it attacked the jumps! :cry:

So I disassembled my diffs and discovered that the black grease came in contact with the main plates, crap! :( Then I re-built them with a TOP thrustbearing and a few black grease... They seemed perfect, the car was easy, but the differentials went crunchy in the afternoon... :eh?:

I disassembled my diffs again and discover huge marks on the plates, just as the diff has slipped a lot!!! Very strange because I setup the transmission very precisely (slipper + diffs) many times while the race and it seemed ok...

I've discussed a lot with other Tamiya drivers and it seems that the motor heat is making the center cell very hot, and the slipper is tightening itself while the run!!! :o:o:o So be careful, if you set your slipper, think about the fact that it will be tighter while the run and it could cause damage to your ball differentials...

Too Much heat?

I've run my 502X in 36 degree Celsius heat for race meet. The diffs don't make noise and the slipper works! Motor is a 6.5 turn reedy.

The diffs don't feel as smooth as the 201X but performance does not seem to be the issue. I'm going to replace the kit balls with ceramic versions in the near future and new rings.

Seriously, I did setup the slipper before the race then race indoor for 7 minutes and recheck the slipper at the end, it was was tighter than before the race! and my LRP motor was about 70°C...

Is there a chance your slipper pads are contaminated? Also if the slipper is too loose it will heat up the pads more than usual, which may cause the slipper itself to change it's properties.

That's my next hypothesis... I'm waiting on new pads to change them for the next race...

If you have one diff with ceramic balls and the other with tungsten balls, which of the two you will put in the front and which in the rear (TRF502X in outdoor track and no astro)?

Another question: in the original kit, there is a ceramic ball grease. It is usable or it is better to use another?


Best regards

Diff ball grease is usually a clear silicone for the pressure plates and black grease for the thrust bearing. If you are talking about the white Tamiya Ceramic grease, I wouldn't use that on the diff balls.

IMO, I would run the ceramic diff in the back, because that diif is usually run looser, and more prone to slippage. which will put flat spots on metal balls.

Hi,

this is the Tamiya Ceramic Grease included in the original 502x kit (see the attached file).

Do not know if it will be good to use or better use another:confused:
Has anyone ever used?

Thanks for the advice :)


Best Regards

Don't use the ceramic grease on the gears in the gear boxes. Due to the high speed and the bevel gears it gets into the ball diff and contaminates it! Thus just use ball diff grease on the bevel gears. Thus, no contamination of greases. The AW grease works fine in the thrust race assembly though.

Its not that the ceramic grease is poor quality, it was designed for gears and not ball diffs. I use the Ceramic grease on the gears in the 201 and it is fine. In the 201 it can't contaminate the diff.

Hi,

ok! I have never used the tamiya ceramic grease (it's brand new). I have ball diff grease in gears. I will only use the ball diff grease in the new ceramic and tungsten diff balls and AW grease in the thrust tungsten new balls if this is the correct way.


Best regards!

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! :D
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

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

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?

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.

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

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.

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

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
http://i1177.photobucket.com/albums/...X/P1170994.jpg[/QUOTE]

Thanks for the tip. I will buy it!

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.

link to follow

Lets try that link again:

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

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

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

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.

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

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

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.

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.