Diff just doesn't wanna stop being gritty.

[Zedmaster]

I've been trying to rebuild my Team Car's diff for a little while here. It just seems gritty, and I haven't found any posts yet that have done the trick. I've tried tearing it down, washing everything in solvent, cleaning the outdrive hubs w/ a Q-tip... Relube, put back together according to the manual. Tried replacing the drive rings. Tried washing it all again, no dice.

Am I just overtightening it? I've got strong fingers, so it's possible. I'm not absolutely sure where the grittiness is even coming from, but it sort of seems like maybe its the drive rings sliding past the outdrive hubs. At this point I'm almost ready to just order a new diff gear and bearings if I can't get to the bottom of it.

My questions for the wise and mighty are:

• How do you know you've tightened the diff correctly other than the scant info in the old RC10 Team Car manual?
  I'm told the drive rings are the most common source of grittiness, but are there any other likely sources of grittiness?
  Any other suggestions for things to try before I just order more parts?

Thanks.

[RC10resto]

Did you replace the diff balls?

[RC104ever]

If you need to rebuild the diff, the TC3 rebuild kit parts fit perfectly.

[Eau Rouge]

A "gritty" diff comes form various things... mostly a work thrust bearing setup. The tiny balls and plates in the outdrive should be replaced every 3rd or 4th time you rebuild the diff, or immediately if it's a new to you gearbox. You can resurface the rings by hands sing the 400/600/800 wet/dry sandpaper on plate glass trick, but the balls should be replaced or at least cleaned thoroughly.

Diff rings also go bad. They can almost always be resurfaced, barring the worst scoring or gouging. Use the male diff outdrive and sand the rings smooth.

Diff balls should almost always be replaced with every rebuild. Use the cheap steel ones and replace them often. Ceramic and other fancty expensive balls are nice, but unless you are racing every week, you don't need to spend the money there. A jar of 100 3/32 or 1/8 diff balls would cost less than 12 ceramics.

Clean EVERYTHING with motor spray and dry it off well. I use a detail brush to make sure the parts are all free of dust and grit from the cleanings. I also inspect everything with a loop before it is reassembled. You can't see most of the stuff that will make a diff a mess.

I posted a lot of my diff rebuild techniques in a thread here a few years ago (SEARCH), and a similar tutorial on my Harper Sprint Car Blog here.



The best thing you can also do before you reassemble everything is to put it all down on a clean paper towel, then WASH YOUR HANDS. Dirty hands can ruin a perfectly good clean diff rebuild, and it's always helpful to start from a clean slate.



HTH,


doug

[Jay Dub]

As eau rouge said, the mostly likely culprit is the thrust bearing set up. However, I like the ceramic balls, and on e-bay, they are cheaper than the steel ones. I think the last set of 12 I bought was was around $4 USD plus shipping. So, I ordered enough for all my cars, and have yet to replace them. I don't have a link , so do a little searching and you should be able to find them. -Jeff

[Eau Rouge]

The ONLY problem with ceramics, is that when you rebuild the diff, you are less likely to throw out the diff balls because they are more expensive (usually $1 a ball). What kind of quality ceramic ball are you getting for $4 a pack? Anyway, if you are re-using ceramics, they need to EACH be individually cleaned before using them over again, which can be tedious and not usually 100% perfect.

Irrgang Racing Service sells packages of 100 diff balls in both 3/32" and 1/8" for $7.50. You won't ever have to worry about cleaning diff balls again. I'm still on a case of 3/32" balls from years ago.

I'm just sayin'.

[Zedmaster]

Lots of great replies!

I have not yet replaced the diff balls, nor have I replaced the thrust bearings. All I've actually replaced were the rings.

I will try looking at it with a loop, and I may try ordering the TC3 kit, that looks pretty good!

Thanks for the help so far!

[slotcarrod]

Do not waste money on diff balls just yet! 99.9% of the time it's in the thrust balls and those rings. Try flipping to the unused side of the thrust rings first and make sure you use black grease on them and stealth lube on the diff balls! If it's still gritty, only replace the thrust balls and thrust ball rings. BTW, you can flip the diff rings as well but you should not need diff balls!

[Zedmaster]

Do not waste money on diff balls just yet! 99.9% of the time it's in the thrust balls and those rings. Try flipping to the unused side of the thrust rings first and make sure you use black grease on them and stealth lube on the diff balls! If it's still gritty, only replace the thrust balls and thrust ball rings. BTW, you can flip the diff rings as well but you should not need diff balls!

Gonna try that this weekend!

[Zedmaster]

OK, I got new thrust balls, and a new thrust bolt at my LHS. Cleaned the whole thing up w/ motor spray. Put a dab of CA on some new diff rings and stuck 'em to the outdrives. Reassembled the whole thing with attention to cleanliness, and voila! it's still gritty.

I am now wondering seriously if I'm overtightening this thing, or if it's still just not clean enough! Other than feeling for the thrust spring bottoming out like the manual says, is there any other way to know it's tight enough? For example, how hard should it be to turn the outdrives? Once it's assembled and adjusted, should it be possible to hold the diff gear and slightly wiggle the outdrive hubs?

If I loosen this thing up a bit, it's smooth as butter, but it's also pretty easy to turn the outdrives, and I can very slightly wiggle the outdrives when I hold the diff gear (not a ton, but a little).

I dunno, thanks for all the help so far. Hopefully I'll stumble across the solution sooner or later!

Matt

[Charlie don't surf]

For the stealth differential you want to tighten the 5/64 adjuster screw until it is tightened all the way down ( without using both hands on a T handle driver ) then back the screw out 1/8 to 1/4 of a turn. Fine adjustments can be made from there if it is slipping with a hot modified motor. A correctly built differential will still be buttery smooth and easy to turn even when adjusted on the tight side. If you are using old or junk diff balls, or overtightening the diff after assembly you can dimple the balls or rings and always get that notchy feeling in your diff-

[Eau Rouge]

Honestly, there is no way I rebuild that diff and replace everything in it except the $1 diff balls. Seems like a perfectly good waste of time, actually.




Reg's way is a good way to tighten the diff, and I also like to use a tool for holding the diff outdrives to check tightness...



You should not be able to turn the center gear by hand when holding the outdrives stationary. Keep tightening the diff slightly until you just can't move the center gear. The method of tightening it all until it bottoms out locked and then loosening it up always scared me because of the pressure it puts on everything when it's all locked down initially. The method shown in the photo is how I set EVERY ball diff I build.

That tool above is from http://www.speedysracingparts.com, but you can use a needle nose pliers and some dexterity.

[Charlie don't surf]

I have a flexy plastic version of that diff tool, I hate the one I have- ( too much flex in the plates to set the diff ) I might just make one from carbon fiber after seeing the speedys

[Eau Rouge]

Speedy's is black G10, but you can do a lot with scrap CF bits.

[Zedmaster]

Thanks everyone, more to chew on!