Hi

Ive been racing down my local track now for a month, all of a sudden last weekend my car was making a funy sound when i reved the engine. Then it stopped moving. Took it apart and found the centre diff had siezed and the gear melted into the diff case. So i got another one, tested it and it seemed ok. Didnt run it for long, then took it out last night and the diff went again. Any1 got any ideas. Ive just ordered a spider diff thinking that this would be better and maybe solve the problem, but there quite expensive and was wondering if anyone may have another ideas i could try first.

Haven't seen anybody say they have had any problems with the center diff. No issues with mine.

What kinda fluid are you puttin in there?

if your putting a spider diff in there i recomend using this oil in it thats what im using seems to be fine and if your running a rtr i would recomend chaning out the grese to the diff oils instead i run in my hyper st a 7k front 10k center and 5k rear but will be swaping to 3k rear but thats a pretty good set up and you will notice alot more performance out of your truggy if you haven't swaped out the grease yet all you have to do is open the diff spray it with wd-40 clean it all out get as much grease out as you can and fill with oil works alottt better
http://www.amainhobbies.com/product_...ducts_id/14084

Did ya shim it correctely.?

My center diff probably has over 20 gallons, and its like new when I open it up.

Tho my rear diff is starting to click a bit, should tear that off before the next time I run I guess...

sorry for the late reply. It was all fine at first, i had run it in, run it through one race event, then i put a .28 xz engine with a jp4 pipe in and it all went pear shaped. I was running 7,10,3 which i was told down the hobby shop was the best setup. Ive tried another diff since then and would you believe its happened again. Its getin a it expensive now!!. I check the dif and the rubber selas are fine.. Someone has told me it could have something to do with the mesh from the flywheen and the diff. I done a paper test and it shredded the paper. Is this the problem.

If it shreaded the papaer i would say ur on the tight side.....but i dont see how mesh would affect the bevel's.......any pics of the messed up cases and gears ?

whats breaking the acutal diff inside or the crown gear that meshes too the clutch bell?

i would be hardpressed if the Spur was failing....and he said it was the spyder's already.

sounds like you have too much diff action! try upping the fluid weight in the center

more then 10K is gonna make that thing real Darty and want to wheelie on small bumps...its not the oil he's using...something else is goin on i think.

When you take the center diff apart............is there fluid i it? Do you see diff fluid sprayed around the center diff? On the inside of your body do you see a line of fluid up over the diff? Wondering if it leaks out and running it dry is not a good thing? Do you have any pics of the damage?

i too went through all 3 diffs already after about 5 gallons, here's the best solutions i've found so far:

1. be sure to fill the diff only to the tops cross pins. if they are overfilled the heat expands the oil and they leak. under filled the inertia pushes all the oil to the outside and some teeth are dry and heat up too, melting the case.
2. when you set the internal mesh of the gears make sure it has a bit of buzz when you turn it, if they are smooth there may be too much play and they will strip. use shims if too loose or ofna gaskets if too tight.
3. ebay has many chop shops for hyper parts, you can find whole diffs with crown gears for $15, hyper 7, 8, 8.5, hyper st, duratrax raze all use the same diffs.
4. open up your diffs at least once per gallon and at least look inside to make sure theres enough oil in there, they do run dry once in a while if the small orings tear a bit.


i've run the diffs in my buggy like this for well over 10 gallons, back from when it was a hyper 7 pbs. when i built the st i used what was provided in the kit expecting it to be good. was for a while. my new sets of diffs are shimmed properly and were set to "buzz" a bit when new. hope this helps, the hyper st is a very good race truggy, hate to see one not finish a main it was probably leading in.[)]