i have to rebuild my f & r diffs because last week when i was running in my yard and after a few minutes it started sounding like it was reving to much for how fast i was going. so i thought maybe my slipper was a little loose, so i keep[ running then i notice i only have front wheel drive. then after about 2 minutes of that, no wheel drive!

oooohhhh boy, i took the front diff out and opened it up and it was trashed inside!! the 4 screws that hold the ring gear on the diff carrier all broke. the inside of the aluminum gearbox case was all grinded into the inside. the spider gears were all over, just a mess! so i might use the stock black plastic diff housings and order 2 new diff carriers and try to use the robinson racing gears i have for both diffs.

i would like to keep running blue aluminum diffs, because it wasnt the diff housing that went wrong.

when i do get my new diff carriers, i used robinson grease last time. should i keep using grease in the diff, or silicone diff oil/fluid?

well i got one of the diff carriers today. i put the gears in, the spider gears and when i go to put the robinson racing ring gear on, it dont fit flush on the diff carrier and the spider gears inside dont turn good. but when i use the traxxas ring gear it fits perfect and all the spider gears turn great. i might have to just use the stock traxxas ring gear. i mean its metal so im not afraid of it stripping out. i just want to use the robinson racing gears i have for the diffs. i still have the robinson racing pinion gears i can use. i dont know if i should just use the stock black plastic diff housings, or get new aluminum ones? i really want to stick with the blue aluminum diff housings! i just hope the 4 screws that hold the ring gear on dont break again!

ok, i found out why the robinson ring gear wouldn't go in the diff carrier. there is 4 little tabs on the diff carrier that stick up for the stock ring gear to lock into. well i just took my dremel and shaved them down. then the robinson gear fit flush. i also noticed if i tightened the 4 screws that hold the ring gear on the diff carrier tight as i could, the 2 output gears/shafts wouldnt turn smooth, or as easy as they should. so i tightened the 4 screws tight, then backed them off about 1/2 turn. so now they spin good. i can actually button this gearbox up and put it back on the truck. but i really want to get the blue aluminum diff cases. so i think im gonna wait until i can buy them.

these are the aluminum gear boxes im looking at-

http://www.ebay.com/itm/Integy-T-Max...item4843dc79df

but in the description it says dont fit the 4908 model, which i have. it says t maxx 3.3. i wonder if that really matters sinse im using traxxas cvd's, aluminum bulkheads? the other ones i had were by integy but had black screws. im afraid to buy these and they not work.

then i saw these-

http://www.gnchobbies.com/gear-boxblue-emx.html

these say will fit the t maxx 4908.

i found a few places i can get the integy blue aluminum gear boxes for the 4908 t maxx. they go for between $30.00-$34.00 each. i already have both the stock plastic gear boxes, but i want to stick with the aluminum ones.

any ideas or thoughts why this happened? i dont want it to happen again after im spending about $75.00 to fix this.

When your ring gear screws come loose that allows the spider gears room to play around and beat the crap out of each other.

the 4 screws that hold the ring gear on broke in half, not came loose. it happened in the rear first, then a couple minutes later the front. im trying to figure out why them 4 screws broke?

Were the diffs still full of grease when u opened them?

oh yea the grease was still in there good. i took my tranny and diffs to hobby town usa to have the guys there give me a hand assembling everything. everything was good when we put it together. plus i ran the truck with them diffs for over a half hour before this happened.

Strange.
I wonder if the wrong (weak) screws were used.
I tried grease once. It did not hold up so I went back to diff oil. Keep in mind diffs get hot. I think the oil helps dissipate the heat.

thats the only thing i can think of. because when i was at the hobby shop, we couldnt use the 4 screws that go on the stock traxxas ring gear because they stuck up to high on the robinson racing gear and rubbed the inside of the diff housing. so the guy at hobby town grabbed a pack of silver screws that had a flush head so they would sink down in the robinson racing ring gear. them screws were probably not made to hold up for that kind of stress. so the screws im using now are longer and hopefully stronger. well other than the screws breaking, the grease was good inside. i mean i was making high speed runs up and down my street for about 5-10 minutes before i started driving around the yard. then after like 2-4 minutes is when i noticed something wrong.

That makes more sense.
Just keep an eye on how hot the diffs get and if they start to get noisy open one up to make sure the grease is still ok.

yea its hard to hear when its running, but i can roll the truck when its off and listen. i mean i know everything was good before i went out to run that day. i mean there might of been some damage with them screws from another day i ran it and just didnt know. i haven't ran it much since i rebuilt everything.

ok, i got my other diff carrier today. i put the spider gears and the other gear in, put grease in then put the robinson racing ring gear on. now both brand new diff carriers are ready to go! i actually could get my truck back together if i used the stock diff housings i got. but i want to get the blue aluminum ones again i will try to order one this week, and hopefully get the other one in two weeks after that on my next check. its going to cost me around $65.00 for both. its kinda crazy when i have both stock plastic black diff housings setting here but, im picky with my blue parts!