RC10Talk - The Net's Largest Vintage R/C Community

I am having trouble with the stealth's differential on Project X. When I run for a minute, it seems like the differential screw comes undone or loose, makes an extremely loud noise, and stays still. So I tightened the screw again. Ran it for a minute, then the same thing happened.

Is this a sign of the differential needing a rebuild, and if so, can somebody spoon feed me the part #s for the rebuild?

Thanks!

sounds like you may need a new lock nut and you have the diff in backwards so when you drive it, it loosens up

bearrickster wrote:sounds like you may need a new lock nut and you have the diff in backwards so when you drive it, it loosens up

I do believe you are right. Upon closer inspection, the screw head is on the Left hand side of the diff instead of the right hand side like labeled in the manual. I also notice that the t-nut is loose as well. I will have to take it apart tomorrow and switch it around.

Should I just rebuild it while I am at it?

that depends on kow it looks? if its ok just grease it up.

As long as you weren't just hammering on the throttle while it was slipping you should be good with a new T-nut (for some reason that makes me laugh) and a regrease. A rebuild kit is only a few dollars so it couldn't hurt.

ASC3926 is a rebuild kit for the TC3, that should work on your rc10. I could be mistaken, it's been a long time since I have needed to rebuild my diff, I usually just regrease.

If you are looking at it from the back, The T-nut should be on the left and the adjustment should be on the right.

bearrickster wrote:that depends on kow it looks? if its ok just grease it up.

What does a bad ball diff look like? I'm serious, I don't know. I have a ball diff in my old Monster Beetle and one in the RC10T I am rebuilding.

I replaced the balls in the Beetle's Thorp diff only because I thought I should...this was the last kit I had when I was a kid and I don't recall being a maintenance freak when I was 12 years old.

First off it should feel very smooth when you hold one wheel and turn the other. If it is not, a rebuild is called for. The balls are hard to tell by the eye unless they have slipped very badly. Flat spots can be hard to determine. I use ceramic balls from Acer Racing and they are very durable (as in 5700kv brushless for a year in my T4 and still perfect). The diff rings usually have a mark from the balls, but a groove is a sign for replacement. There are ways to smooth them out but as cheap as they are I would just replace them. Make sure the diff gear holds the balls fairly well with some diff lube. The holes can elongate over time and make for a sloppy fit.

diff balls are pretty cheap anyhow, about $8 if you want to get fancy and use Ceramic.
http://www.amainhobbies.com/index.php/cPath/1_24_1560/n/RC-Cars-Trucks-Option-Parts-Differential-Balls/filter_mfr/209

They do cost a little more but not too bad IMO. The greatly reduced rebuilds makes up for it and then some in my mind.

CamplinP wrote:If you are looking at it from the back, The T-nut should be on the left and the adjustment should be on the right.

Yeah, it's definitely set up back wards. I'll switch around tonight and check if it needs rebuilding. Thanks everyone again!

If it doesnt turn smooth after swapping it around i would flip around the idler gear to,Unless its new too.When using the same gears just replaceing the diff balls and rings always replace in same direction as come out the trans or get binding issues.Don

CamplinP wrote:First off it should feel very smooth when you hold one wheel and turn the other. If it is not, a rebuild is called for. The balls are hard to tell by the eye unless they have slipped very badly. Flat spots can be hard to determine. I use ceramic balls from Acer Racing and they are very durable (as in 5700kv brushless for a year in my T4 and still perfect). The diff rings usually have a mark from the balls, but a groove is a sign for replacement. There are ways to smooth them out but as cheap as they are I would just replace them. Make sure the diff gear holds the balls fairly well with some diff lube. The holes can elongate over time and make for a sloppy fit.

Thanks for the tips regarding a bad diff...just what I thought it would be. I wasn't sure if there were less obvious signs to look out for.

When I redo my diffs I get 400 and 800 grit sand paper and set it on a flat surface. Decide what side of the diff ring is least hurt, and sand it putting even pressure on it and use a figure 8 pattern on the sandpaper. Use the 400 grit till the marks in the rings are gone then graduate to the 800. I do this even with the new rings. They are not perfectly flat, and the sanding action gives the balls tooth to grip to, allowing a looser diff with no slippage. Lasts longer that way as well.

If you have carbide or ceramic balls, they will not need to be replaced, unless they are obviously damaged. Sand the thrust bearing washers using the same method above and replace the thrust balls. They do not last too long, and often if you think your diff is crunchy, many times it is the thrust bearing and not the main diff balls. Always use a new locknut and be sure (like Rick said) that it goes in the gearbox correctly.

Black grease on the thrust bearing, clear grease on the diff. Don't overdo it with the lube, you don't want it flinging out and fouling your gears.

Do not overtighten the diff upon reassembly. Tighten it a little, then spin it. Tighten it till it is almost impossible to turn the diff gear in your fingers with the outdrive cups locked. I used this method in my 91 RC10 that I ran last year at the vonats. I haven't touched it since with exception of minor adjustments.

Brandon built the diff in my 09 VONATS team car, I haven't had to rebuild it yet. His method works