cumminspower5.9

My Feedback: (4)

So attached I have a picture of the problem area I am seeing in my Flux XS. This is the rear diff issue I was talking about. The circled drive cup has too much slop, and this in return moves the smaller bevel gear from the main bevel gear in the diff. I don't know what to do with it, whether to shim it or what. And I believe this is also what caused the bigger bevel gear to chip a tooth causing some serious issues, i.e no rear drive.

futureboy1969

ok..common prob. I just went through this on my Losi 8T rear diff... U need to make sure ur bearing r in great shape first. any wooble out of them and no matter how well u shim the diff u can strip those gears !! I went the hole 9 yard on mine..New diff case, new bearing, gear set, and shim that ring gear, it's ok if it feels a little notchy or stiff wen u spin them.they will break in... the whooble in my bearings was the real problem with it, I found out. I use to just clean bearing and reuse um..but now i check for how worn out they r too...hope that helps

cumminspower5.9

My Feedback: (4)

Well is seems like the whole drive cup assembly moves up and down too far. I don't see how a bad bearing would cause vertical slop in it. I will pull the diff apart again and see about the bearings. Ill possibly take pics if i need more help or info.  Thanks.

echthelion

you talking about the id say 1.5mm of play the cup has

Foxy

Does sound like a bearing the way you describe it.

You say vertically? Does the drive cup go actually up and down when pulled, or do you mean it moves in and out affecting the mesh of the ring and pinion? In any case, if the latter, then it may not even be an issue, since it looks like the diff pinion is supposed to float. If it is in fact attached to the drive cup in a more permanent way than appears by the pic you posted, then it may an issue which would indeed need shimming. Unless something has been left out of that manual image showing how the bevel gear circled is held to the drive cup, then it appears that shimming wouldn't do anything anyway (since it's floating, its not attached). Hope you see what I mean.

cumminspower5.9

My Feedback: (4)

When pushed orpulled, the drive cup will move in either direction the arrows are pointing. The bevel gear that connects to the drive cup sits in a pin that goes thru the shaft of the drive cup. When the rear diff turns, it hits the smaller bevel gear and pushes both the small bevel gear and drive cup up and away from the diff, causing the loss of RWD. I just don't get why it does, do Ihave to throw a bunch of washers between the pin and drive cup to stop it from pushing up?

Foxy

That seems to be the way its designed. Double check you shouldn't be looking elsewhere for this problem, cos this doesn't look like something that has changed with use, it was like that or it wasn't, the design of the fixing method of that bevel gear hasn't changed during your ownership of the truck, and I'm assumig this hasn't always been a problem? Have the gears themselves changed dimensions to cause this from wear? You sure the bearing's ok? You can shim behind the pin, must be worth a try, but consider why it is needed now and wasn't before.

echthelion

mine moves to but ive never loss RWD

cumminspower5.9

My Feedback: (4)

Yea never been a problem till I took it to the BMX track. Everything is stock, never replaced anyhting. Took the diff out to inspect why I lost RWD, only culprit I thought was a chipped tooth on the large bevel gear. But apparently that isn't the issue. I'll have to take it back apart, and put it back together exactly according to the manual. I may have put a washer in the wrong spot inside the diff case, but that would have nothing to do with the drive cup in front of the diff. what a headache. or maybe i can shim the dogbone coming out of the transmission to keep the diff cup in place and not slide forward. idk. this is going to take some time to figure out, diagnose and fix. as soon as I can pull it apart, I will post up the issue and my fix, incase of people in the future having the same issue. thanks for the help so far guys

cumminspower5.9

My Feedback: (4)

Well, pulled it apart again last night. There is a nice shiny spot on the large bevel gear where the smaller bevel gear was grinding on the top, but no damage to the actual teeth. I threw some shims behind the pin on the drive cup. I might have to put a spacer or two on the drive cup coming out of the tranny to push the dogbone into the drive cup to the rear so it stays pushed into the diff.  I don't see how this thing would even acquire movement over time. there is no wear, and nothing to break to let it move. it's stupid lol

SLAYERDUDE

Shimming the diffs should eliminate any movement in the pinion gear, here's my shimming guide for an 1/8 Savage but it should work the same.
Besides doing it the way I show, (not sure if I've updated that thread) you should center the pinion in the teeth of the ring gear by shimming the pinion first by either installing shims on the pinion before sliding it into the housing, or by putting shims behind the inner bearing inside the diff case to push the pinion towards the diff, then shim the sides of the diff to get all the slop out then remove a shim so there's the least amount of play.
The grease on the gears will take up the extra minute bit of slop, this is how a 1:1 diff is shimmed.
(Shimming tight and "letting it wear in" as Futureboy said isn't the correct way to do it, you will be putting extra stress on the bearings at that point)

http://www.savage-central.com/module...wtopic&t=93602

cumminspower5.9

My Feedback: (4)

Slayerdude, it seems the issue isn't witht he differential at all. It seems to be with the drive cup play that spins the rear diff. There is too much play so when I hit the throttle, the diff spins and pushes the drive cup away from the larger bevel gear.

SLAYERDUDE

A diff consists of a ring and pinion (and spiders inside), the larger "bevel gear" as HPI calls it is your ring gear, the smaller bevel gear is the pinion.
Your pinion gear should not be able to move in and out, this jakks up the mesh between the ring and pinion, which needs to stay constant or else it will destroy the gears.
The drive cup attatches to the pinion gear, and if both are moving in and out your gear mesh isn't staying close like it should, think of it as you motor moving back and forth while you drive - your spur and pinion would strip if allowed to do this.
I've never seen an XS but it should be similar to an 1/8 Savage, you may need to shim on the outside of the pinion as well to keep it from moving further in than it should, but you should first shim the diff regardless.

EDIT - Oh... I just looked at your pic and I see the pinion gear just slides on the drive cup shaft... that's kinda lame.
You may be able to put shims behind the pin inside the diff to set the mesh between the ring and pinion, check the slop, then install shims on the outside before installing the cup shaft to tighten things up.
Or as I said earlier, put shims in the case behind the outer race of the bearings, whichever is easier to find shims for.

cumminspower5.9

My Feedback: (4)

Yea I was looking and it's the same as the 1/8 Savage. I got the terminology now lol. But I don't get how all of a sudden the drive cup has all the slop and now the pinion misses the ring gear. All bearings are ok, I can tell you that. When I have more time (possibly this weekend) I will rebuild the diff per say. I won't replace any parts, just clean, inspect, and put back together like the stock form. Make sure all washers/shims are in the correct places, and do the same witht he pinion/drivecup. I'll go by you post on savage-central as much as possible. And I'll look at the front diff too cause they should be exactly the same. Or maybe I'll switch and see if the rear diff, pinion and drive cup do the same thing in the front. Thanks Slayerdude. I'll let you know what I find out.

Foxy

Bingo. Welcome to the thread. lol.

Shimming the ring gear like we do in most cars, won't help him I don't think. Something has worn, something not easily noticed, but you're right, it is a lame way to attach a diff pinion.

cumminspower5.9

My Feedback: (4)

Your damn right something not easily noticed Foxy lol. This is a headache. I can only shim the pinion so much, remember it has to be able to sit in the pin. I put a few shims between the pin and the inner bearing on the drive cup, but I don't know if it was enough. A test will tell, which I will do that today.

echthelion

hmm how much do you have? mine has just about 1.5mm of movment

cumminspower5.9

My Feedback: (4)

Mine has got to be atleast 3mm or more. I don't have a picture though. It's enough to where the pinion doesn't mesh with the ring anymore.

echthelion

any chance its the bulkhead/gear box maybe one of the 4 pieces broke and its allowing alittle play or one of the like 8 screws/nuts came lose

cumminspower5.9

My Feedback: (4)

No, because if the gearbox case was loose, it would not allow that much play cause the case would be spread apart. Something tells me shimming between the cup and the pin will do the trick. I just have to see how much I can do. Or add more spacers in the tranny output drive cup to push the dogbone tight against the diff cup.

echthelion

ahh i was just thinking if you say all the gears are fine it would be a bearing or the case itself to allow 3mm of play

cumminspower5.9

My Feedback: (4)

Well the bearings are fine, all screws are tight, nothing I have checked leads to the cause of the slop. I mean it happened when I was driving. And I would hit the throttle and boom, no RWD. I was like ***? Since then it hasn't run right.

echthelion

i'd say you sir are in a conundrum

the pin itself should keep the pinion from backing off that far

you could do 3 things

1# take apart the front and compare them and hope you find the problem

2# buy a complete case with diff off a ebay chopshop

3# curse alot and then do option 1 or 2

cumminspower5.9

My Feedback: (4)

This is quite the conundrum. I've done option 3 several times lol. I think the best thing to do is compare the front and rear diffs, figure out what's missing/broke, and replace or repair as necessary.

cumminspower5.9

My Feedback: (4)

Well, I finally got it all back together with almost no slop (maybe 1/2mm) I had to use some other shims that I had to dig thru a coffee can full of washers to find at my dads. finally got it tho. Now I'm just missing a whole tooth on the ring gear, but it still grabs, just not sure how it will grab under power of the lipo.