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Horrible noise coming from my HPI Trophy Truggy Flux

10K views 13 replies 6 participants last post by  Bloodbath 
#1 · (Edited)
Hey guys,

Recently I took my truggy out for a normal off-road run, nothing too bad but there was a couple of flips that landed fairly hard.
Towards the end, when I was about to stop and leave, I noticed a really bad churning noise. It sounded as if some gear was grinded or as if something that was out of place. I'm an amateur RC hobbyist so I didn't have a clue as to what was actually going wrong.

I stopped the car, opened up the lid and had a quick look, but everything seemed to be OK except a dog bone that had been slightly more bent(it was bent before). I first thought, I thought the dog bone might have been loose so I replaced it and had another go. The sound started again and I noticed it accelerated no where near the rate it used to before. I also noticed once it hit the (new) top-speed of about 6-7km/h, the abnormal noise would stop. So I figured it must have something to do with the gears.

The issue's been bothering me a lot, and I really want to get this truggy up and running again.

Would you guys have any clues as to what would be going on or any advice to fix the issue? Any help help would be greatly appreciated and if you want to see it, I can upload a video tomorrow.

Thanks!
 
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#3 ·
I am thinking pretty much the same as above...I would be pulling out the diffs one by one, check, repair and re-oil.

A bent dogbone could mean that a diff pinion has been smashed into the crown wheel of the unit and damaged it, it could also be the internal gears(planetary gears) within the main diff unit itself....these are not hard to work on, but to save any confusion, lay the parts out in the same pattern as they are in the model, this way you will know where everything goes when putting back together

Is the motor getting really hot? the limited speed and grinding noise could also be that....loosen the screws that hold the motor in alignment with the main spur gear, remove the motor pinion and then hook the battery up....try to spin the motor up, because it is not engaged with the drive train, you should only hear it.....

While the motor is free, try to turn the drive train by hand, it may also give you a clue as to where the problem is

With the dog bones out, you can spin each diff separately....this will also help to identify any binding or damage that may have occurred
 
#4 ·
Lift the front end and hold the wheels, and roll the rear wheels along the floor and listen for the noise

Lift the rear end and hold the wheels, and roll the front wheels along the floor and listen for the noise.

Noise at test 1 and not test 2, is rear diff

Noise at test 2 and not test 1, is front diff

Noise with both tests, center diff or motor

Do the tests with the car together and it will help you narrow it down to which area it is before you star pulling things apart if your not confident working on it.
 
#5 ·
Firstly, thanks a lot for your replies!

Secondly, I'm very sorry for such a late reply. I have been busy with exams and projects at uni, and finally got my holidays now! :D

I made an attempt today at having a look at the truggy, and after doing the suggested tests, it seems that the problem is with the central diff. I checked the engine and it revs perfectly when free.

I started opening up the central diff and I noticed that the oil has turned ink black. I assumed that was a bad thing, and decided not to proceed any further, till I get some new diff oil. But I just discovered there are a few different types of diff oil after looking it up.

I was wondering which diff oil would be the best balance for this truggy...as I have no clue. From what I saw #10000 seems to be in the middle of the range. Would this be okay?

Thanks!
 
#6 ·
Centre diff for a Flux version you could easily drop 50 000wt in and get a good result, the heavier oil will help to transfer power to both front and rear diffs for a more even power balance

Before dropping in new oil, check the condition of the internal gears, if they are damaged, you will need to replace them as well, also check the bearings for wear
 
#8 ·
I personally think 30 000 will be a bit light, and would be asking them to bring in a heavier oil....alternately, give a few Aussie stores a call....I know there are shops that stock 300 000wt and 500 000wt oils as a standard stock line here in Brisbane

Where are you located...someone may be able to suggest a LHS or more local then Brisbane
 
#10 ·
I think I have fixed that problem...I'm assuming it just needed an oil change.

But a new problem has come up...The grub screw holding the pinion gear keeps coming loose constantly. I have tried applying blue thread locker, but had no luck :/

I'm thinking about putting a bit of thread locker tape. Although I'm not sure if its a good idea for when I want to take it out?

Thanks!
 
#12 ·
Grab a new set screw...the bottom is supposed to be tapered, but after being spun they flatten off...

Once you have the new set screw, apply a small amount of loctite, tighten into position and allow a good few hours to set

Loctite is just another form of glue and needs to set to achieve full strength
 
#13 ·
That's good advice Towie, buying bulk bags of 3, 4 and 5mm set screws was probably one of the most useful things I have in the spares box.

Nothing more frustrating than a rounded set screw when trying to get a pinion off as well! Prevention is better than cure..
 
#14 · (Edited)
By the sounds of it I have exactly the same issue with mine. Just happened yesterday at the beginning of what would have been an awesome bashing session dammit! Tonight or tomorrow I am going to strip down the centre diff and find out what is wrong with it. Strange thing is I opened it up out in the field and everything seemed to be in place and functioning except the oil was black.

Let me know if you fix yours dude and I will let you know when I find out what is causing the issue with mine. Oh Yeah and I'm in Perth to. I find Perth RC ok for parts but recently went to HobbyTech International in O'connor and was impressed by the volume of parts they were holding, just thought I would mentioned that, good luck.
 
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