Hyper ST centre diff.....again....

[DreXeL]

That's a shame, I was sure that was your issue.

I think you should try some really thick oil, like 500k.

Edited June 2, 2013 by DreXeL

[Mr. Doktor]

his problem is not related to diff oil in any way, not even 500k will help. These diffs are capable of any brushless power in any 1/8th scale truck. my truck weighed 15lbs at the porkiest of times and I had a more powerful motor and I did not have any of his issues

what spur do you have? maybe you have a bad spur gear, 

by the look of the bevel gear in the picture above I think that it is not close to the 4 spider gears. As if the spur gear was badly machined and it is deeper in area where the bevel gear sits on the diff outdrive pin , which means it is off centered, simply not close enough to the 4 spider gears. I think the teeth of the gear in the photo are not in full contact with the spider gears

[Nitroholic]

Well..I have another diff cobbled together to try.

 

Now...I had no more Hyper diff gears spare ...but I did have some Savage ones. These are deeper than Hyper ones by around 0.5mm each...so you normally can't use them..but I found with just one gear ( at the spur gear end) It actually fitted up quite snugly. It turns smoothly and there is absolutely no play at all.

 

Now...I didn't expect it to fit and rotate...as that is quite a bit ofr space to take up. I know with a pair of these at either end, the diff locks up solid...but hey...it worked!

 

I certainly couldn't have taken up that much slack with shims either.

 

It's had a gentle drive round the garden to check it rolls smoothly and doesn't appear to have any issues. Tomorrow, I will charge up the batteries and see what happens!

[Mr. Doktor]

savage gears are made of steel, they will outlast anything made of aluminum, hope they will work! Strange that your issues are bound to the center diff exclusively, that neither front nor rear diff has had similar problems. I think your spur gear might be the root of all problems by creating too wide gear mesh between the bevel gear on the spur side and the 4 spiders. But these thicker spider gears from savage seem to just compensate it by being more robust and thus eliminating the excessive play. Good luck with your diff eater tomorrow 

[Nitroholic]

That's my hope

[SmugR]

How did you get on with this in the end? I`ve just had a similar center diff failure, but only on 4s, the planet gears are now welded into the diff case. 

[Nickarla]

As above. Great thread. Great advice. No conclusion.

[Fly In My Soup]

Hey dudes...just caught up on this thread..... So NH....are you running the same ratio in all three diff's?

 

Edit..... I just checked the date of this thread.... Lol

[capri-boy]

[Nickarla]

But still useful and relevant, lol.

[Nitroholic]

For those wondering how this ended.....

 

The ESC went up in flames, and I ended up selling on the truck without an ESC as I was pretty much stuck for cash to replace it short term, and had not enjoyed the brushless overkill experience as much as I thought I would. Motor and ESC never got so much as warm and the gearing was not extreme. Odd really. Was running it on a BMX track...it went over a couple of humps, and drifted off into some long grass. Stopped. Picked it out....dropped it back on track...hit the trigger...and up she went.

 

The centre diff didn't give me any further problems after I fitted the HPI diff internals. But...to be fair...I only ran it a few times before I died a fiery death for no clear reason. The HPI gear was thicker, which took up the gap better than a shim. I probably would have tried an ally diff case next as well as they hold dimensions better under load.

 

All 3 diffs were running he same ratios. Only the centre misbehaved

[Jumper]

i have destroyed one of these and i run 500k oil and that worked better, still gets really hot though. 

[Nickarla]

I’ve just started my Hyper ST switch from getting fed up with my FTX diffs breaking, lol.

[Nickarla]

I have a voucher for Modelsport and was looking at getting the HobbyWing Max6 rather than the Max8 for this car as the price is very similar but it would run cooler and will be more flexible with motor options. Would this likely cause more diff issues or would it not make any difference if the battery cells are kept the same (no way I would go 8s...yet ? )

[Nickarla]

On 02/01/2019 at 18:01, Nitroholic said:

The centre diff didn't give me any further problems after I fitted the HPI diff internals.

 

Do you know which part this HPI diff is? The only one I could find is this but it doesn't say which material it is and I dont remember the ST diffs this shape (although its been a while since Ive looked).

 

https://www.modelsport.co.uk/hpi-bevel-gear-set-gear-diff-/rc-car-products/15799

[Nitroholic]

Just a bog stock HPI Savage diff gear. The front/back gears are identical in tooth count to the Hobao ones, and fit right into the diff case. They are slightly thicker, and tightened up the slack I had, forcing the gears together and stopping the teeth tearing up.

 

[Nickarla]

I've taken a look at my centre diff today and found that I need to top up with oil. What oil rating did you use?

Also, how can you tell if the gears need shimming? To look at the diffs you need to open it up which gives you no way of telling how tight or loose they are.

[Nitroholic]

I used 100K in the centre diff.

 

Shimming for me was about feel. Feeling for any slack or play, adding a thin shim...checking again... and when it starts to get tight...backing off a bit.

 

[Nickarla]

Ok thanks. I bought my ST used and they diffs are in perfect condition. The previous owner did put 1 shim in both gears so I will leave it at that.

 

Ive been looking online and most people are using a 7f, 10c, 3r oil which makes no sense to me as others like you use 100k...which is a big difference to 10, lol.

 

[Nitroholic]

7/10/3 was the setup I used in a Hyper 7 nitro. It worked well.

 

I preferred the almost locked even transfer of power 100K gave me. Otherwise it would pick up the front wheels under power, and spin away all the power to the fronts. I wanted some give...so did not lock the centre diff...but wanted to keep drive to all wheels all the time.

 

Nitro wheelies a lot less, and the more even split gave a better feel

[Nickarla]

Just to confirm that Im not missing something (Ive not needed to consider oils before), are we walking 7k, 10k, 3k? 

 

What did you use in the front and rear diffs and do you think 100k for the centre is a good starting point or would it be better to start lower, say 50k, to see whether my driving style needs to go higher or lower?

[Nitroholic]

Probably good to start with 50K and see what it did....If you really want to dial it in, you will need to have a selection of oils

[Nickarla]

Awesome, thanks. Ill get some ordered. 

Do I keep the front and rear 7k and 3k or do they increase because the centre increases?

[Kukynas]

17 minutes ago, Nickarla said:

Just to confirm that Im not missing something (Ive not needed to consider oils before), are we walking 7k, 10k, 3k? 

 

What did you use in the front and rear diffs and do you think 100k for the centre is a good starting point or would it be better to start lower, say 50k, to see whether my driving style needs to go higher or lower?

your 7K/10K/3K figures are in "wt" , if you will be buying oil in "cst" rating as commonly used in EU you need to multiply it by 10 as mentioned in below guide

https://www.msuk-forum.co.uk/forums/topic/225333-silicone-oil-guide/

 

your diffs should have 6 shims, 4x for smaller and 2x for bigger gear, follow the instruction manual for exact sizes, if it's the same as SSTE (should be) you can change 4x smaller shim as per my below post

https://www.msuk-forum.co.uk/forums/topic/232542-hobao-hyper-sste-rolling-chassis-build/?do=findComment&comment=2454698

 

[Nickarla]

So the 7k/10k/3k is really meaning 70k/100k/30k but in cst? Im confused now. The way Nitroholic put it made me think that the Hyper 7 nitro was 7k/10k/3k cst and in the ST the centre was 100k cst.

 

I'll open the diffs up and compare to the manual a bit later/tomorrow.

Just checked the diffs. All washers are present and correct.

Edited March 25, 2019 by Nickarla