Trf502x Diff Build Problems

[Tweaky]

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

[stefke]

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.

[Chris]

Originally Posted by Tweaky

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

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

[stefke]

Originally Posted by Tweaky

Hi

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.

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.

[kidcongo]

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

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

[Airwave]

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

Could be a lead for you too...

[Airwave]

Originally Posted by kidcongo

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

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

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

[kidcongo]

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

[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.

[Oval/offroadracer43]

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.

[Airwave]

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!

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...

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!!! 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...

[Aussie Top Force]

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.

[Airwave]

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...

[kidcongo]

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.