flmrustler25

Hi guys, its been a while since I have been on here and since then I have purchased a Savage Flux. For some reason the rear diff keeps breaking one large bevel gear and one small bevel gear along with the pin that holds the large bevel gear in place. I have rebuilt it at least 4 times now while the front diff is totally fine still. The washer under the large bevel gear is getting a little bent up from the pin always breaking. Could that be my problem? Also I put it together without a diff case washer about twice (because the one I had got messed up) but that didnt seem to affect it at all. Sometimes I will get several batteries through it before the diff blows but one time I didnt get more than 5 mins and it broke. If anyone has any advice please let me know, I am about to loose my mind with this thing.

BigTb17

HPI now offers a "bulletproof" diff for the Savage Flux. There are many positive reports about its performance from people who have switched to it. Keep in mind, it's a slightly different ratio than the stock diff, so if you upgrade you should do both the front and the back.

Are you running 6S?

rcslsafut

they have had a real problem with this !!!!!!!!
they make a "bullet proof" diff,i dont know if thats the one you are buying?
there has been several threds on this subject.
i know it is critical that u set it up properly.
prob have better luck with this one in the hpi monster truck section!
thats what i can help with. sorry dont know more.

BigTb17

Oops. Just realized from your picture that you are breaking the internal gears, not the main diff gears. I don't know of an upgrade for those. Are you filling the diff with any type of diff fluid?

BigTb17

There looks to be some heat bluing on the gears and pins. They could be overheating and getting brittle. Lack of lubrication could cause this, as well as extended "one wheel peel". Basically allowing one wheel to spin very quickly while the other either doesn't spin, or spins very little. This causes the internal gears to spin very quickly, which can over heat them (particularly if the diff isn't filled with fluid).

If something is too tight, or out of alignment it could be causing excess friction and heat.

flmrustler25

Yes, I have been using the standard green diff grease that is recommended in the manual

flmrustler25

I use a whole tube of HPI diff grease every time I rebuild them

also I am running it on 6s, I dont do anything too crazy, mostly on road and grass with the occasional backflip (which I know its not good for it but it should definately take more punishment than what I have been giving it)

t9dragon

My Feedback: (11)

I am not sure what manual you are looking at but mine says the the Z164 Heavy Weight Grease (#30000/Gear Diff).

flmrustler25

Yup, that's what I have been using, Z164. The tubes are small so it is really easy to use the whole thing on one diff rebuild.

monsterbrad

I did this to my LST a long time ago and never had any issues it may work with your problem.
Fill the rear diff with 5000 silicone and the front with 7 or 10000 that will do a better job of cooling those spider gears you are blowing up all the time.
Also 6S is a crazy amount of power and you will break things that is for sure

Brainanator

My Feedback: (1)

does the savage flux have sealed diffs?

thzero

Yes just like all the other Savage Xs. And yes you can run diff oil in them instead of grease.

Redvanmafia

think about how much power is going to thoes tiny gears, metal or not there gonna break, Get titanium gears if you dont want them to break, untill then they'll keep breaking

scarletboa

My Feedback: (1)

just get a new diff case and be sure to lube up the gears nicely with the grease. if you can, try getting an extra tube or use some automotive grease along with the grease it comes with. i'm guessing your problem is from a warped diff case.

Brainanator

My Feedback: (1)

Thank you.

Redvanmafia

Grease isn't gonna magically stop your metal gears from breaking, if your metal gears are breaking already whats grease gonna do?, lubricate till they break again, Its got a slipper clutch use it

rclugnut10

My Feedback: (1)

about the HPI grease they don't come with that stock, its a black greese, i can't see the green stuff being very good in a diff or a whole tube doing the job either, its very sticky but it doesn't seem to like to goop and fill in holes and i can see it getting flug off the gears and sticking to the sides of the diff case as opposed to onto the moving gears where it needs to be and in any high powered RC you're diff is gunna get a ton of work this would cause lots of heat in there and then poof goes your gears, i'd also check your diff bearings excess heat could cause issues with those and they could be adding to the problem
i'd in the future use black grease or some diffs spefic silocone grease

the lug

Redvanmafia

i don't understand the grease theory, is it going to take force off the gears in a magical way? if your running huge power grease or not the same force is being put to the gears

BigTb17

I noticed what looked like discoloration from excess heat on the gears and pins. When metal overheats it can change its properties, making it more brittle. No lubrication at all where those gears ride on the pins will greatly increase friction, and therefore, heat. Considering the speed and force these diffs are subjected to, heat can build up very quickly.

Grease lubricates and reduces friction, which helps a lot. Filling the diff with silicone fluid goes a step further. Rather than simply being a small coating of lubrication (which can wear off or be flung off) it will flow in and around parts as they spin, increasing the lubrication. Because it can move around and there is more of it, it also adds a cooling affect. That is why it protects the gears.

I'm not saying for sure that's the problem, but that's why people are mentioning it.

flmrustler25

Thanks for all the helpful replies. I am going to try the slilicone, does anybody have a link to some good stuff. Also I dont understand why a new diff case would help, there doesnt appear to be any wear on it. Someone eariler mentioned titanium gears, where can I get those, I was not aware that they made them in titanium.

monsterbrad

the diff case can get warped from the heat.
You MUST lube the internals with silicone diff oil and grease the gears (ring and pinion)
Try this with there new diffs and new diff cases and let us know what happens
this is the area that most people do not realize the abuse that it takes its crazy stress from the power of todays brushless systems and new batteries.
Instant torque and those standing backflips thats the major stressor there
anybody that knows drag cars knows that a good gear set up is crucial its the same with these high power trucks and cars.
That is why 1/8 scale buggies have spiral cut gears that have to be set up correctly

scarletboa

My Feedback: (1)

a higher weight oil will also slow down the internal gears, further reducing heat.

rclugnut10

My Feedback: (1)

in short yes but what the high weight oil does is really prevent the gears from moving as fast because it is so sticky and thick so it doesn't like to move or let anything around it move, this lack of motion causes the friction, but any weight oil properly filled assuming its the correct oil will do the job

if its a plastic case i'd say deff a new case but since its Al i wouldn't worry too much just because they're pretty beefy units and aren't subject to flexing unlike plastic cups which do flex and cause issues with the gears.

the lug

thzero

It's a Flux, I hope that it didn't ship with plastic diff cases. Contact HPI and see what they will do for you; they may replace the diff gears. You definetly want to replace the diff gears with the upgraded
p/ 102692 MACHINED BULLETPROOF DIFF BEVEL GEAR 29T/9T SET for the Flux. Depending on when you bought it, lot #, etc. HPI might send you a set as a replacement.

Then grab some silicon diff oil (not shock oil) such as http://myatomic.com/catalog/viewsku?...f_oil_10000cps. I'd probably start with 10k from 15k rear, but you may want to go up from there. Go over to the diff the HPI Monster Truck forum here and do some searches on diff oil and you can read about what various people are doing. Some folks have gone as high as 100k in both diffs, which I think is a bit excessive, but there is no right answer and requires a bit of experimentation.

monsterbrad

Just remember that the higher the numder fluid in the front will make it turn harder and act more like a posi.
Also if you put super thick stuff in the rear it will push like crazy.
WHen the fluids are fresh you will notice this but as they break down it won't be as noticeable.
I have 7000 in the back of my LST and 10000 in the front but its over 5 years since I have changed it and its pretty thin now but the diffs are still going strong.