Nitroholic Posted June 1, 2013 Share Posted June 1, 2013 People do keep telling me that these things are able to handle brushless .... but once again, I find that isn;t the case! What am I doing wrong? One full pack and half a pack of 5S and the centre diff has melted. Literally! The spur side gear has failed bigtime, and as the thing ground to halt, I was greeted by the lovely sight of diff oil bubbling out of the case.... not had that before When I opened it up, it wasn;t just the end geart that had failed. The 4 spiders had pushed out of their tracks and the resulting friction had melted them in place...they are now permanently welded to the case and about 10' out of line. I am now looking for options. I need a setup that will last more than one session..... 1) another diff that won't fall apart 2) some help with a shim/setup that won't break 3) Should I just lock up the centre diff? It wheelies a lot and the front balloons....so perhaps the cure is to lock it up...or will it just blow the front or rear diff instead Quote Link to comment Share on other sites More sharing options...
DeadMeatUK Posted June 1, 2013 Share Posted June 1, 2013 Do you do a lot of WOT starts and hard braking? I'm still on my first set of diffs after 15 6s packs just rebuilt the rear and is showing signs of wear but still useable My centre diff is filled with 100k and does get warm (maybe from the spur/pinion mesh?) I am progressive with the throttle and avoid hard braking and its set at 30% Quote Link to comment Share on other sites More sharing options...
DeadMeatUK Posted June 1, 2013 Share Posted June 1, 2013 That's Ansmann standard diffs! Quote Link to comment Share on other sites More sharing options...
Mr. Doktor Posted June 1, 2013 Share Posted June 1, 2013 What diff oil do you use? I have been using the same diff in my savage, a hyper 7 center diff with a 46t spur gear with aluminum spiders for almost 2 years without a single failure. I use 50000or 100000 diff oil. You have to find what generates the heat either in or near the diff Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 1, 2013 Author Share Posted June 1, 2013 Diff is full of 60K ....and the heat was from the gears rubbing over each other I suspect. I don't do WOT starts, as doing that just puts it in it's roof. I get it rolling before I give it throttle. Braking is set at default, but I wasn;t doing a lot of hard braking. 1 Quote Link to comment Share on other sites More sharing options...
DeadMeatUK Posted June 1, 2013 Share Posted June 1, 2013 Sounds like you are doing everything right? Are you running larger wheels? Quote Link to comment Share on other sites More sharing options...
Mr. Doktor Posted June 1, 2013 Share Posted June 1, 2013 (edited) I ran wheels from lst 2 and I did not have any of these issues, wheels alone are not the cause. how tight are your gears shimmed? I shim all of 6 of mine to such point that I feel them spinning tooth by tooth over each other, but they still move freely without any friction or need of any force to turn the diff outdrives. do you have a build thread somewhere? Heat can be generated from old bearings, dogbones coming out of diff at angles, rubbing of diff against something etc... are the screws holding the spur to the diff case tight? Edited June 1, 2013 by Mr. Doktor Quote Link to comment Share on other sites More sharing options...
GorillaZilla Posted June 1, 2013 Share Posted June 1, 2013 (edited) Have you checked to see if the side of spur gear isnt rubbing against the center chassis brace that is under the Center diff mount? I found the Hyper 7 spider diff for some reason could slide some way backwards and forwards, and the spur could grind at the center chassis brace when it slid to the extreme towards the spur end. I had to secure the bearing at the Non spur gear end of the diff with a screw through a pre existing hole in the plastic half of the center diff mount to keep it clear. I thought it might have only been the case with the RC monster motor mount, but perhaps it extends to the ansmann style mount too? Edited June 1, 2013 by GorillaZilla Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 1, 2013 Author Share Posted June 1, 2013 Wheels are stock Hyper ST ones....so I know it's not them. I had tried addin and extra shim under either end gear...and that made no difference. I then tried putting an extra shim under each of hte 4 spiders gears. That seemed to work OK on 4S, but has failed badly on 5S. I couldn;t add any extra shims under the end gears as the pins would not go in. Screws holding spur to diff case were done up firmly. Bearings on the diff were brand new, and the angles for dogbones etc. were stock, so really should not be an issue. I did have some issues with the spur rubbing to start with, but they were solved before I ran the car. I made sure everything riolled freely and did not rub before I bolted the motor on. I will check to make sure nothing has moved etc. I'll also check for for/aft movement. Gut instinct says it's the internal gears failing that is the root cause....with the heat as an after effect. Pics a bit blurry....but here's the gear from the spur end... Quote Link to comment Share on other sites More sharing options...
DreXeL Posted June 1, 2013 Share Posted June 1, 2013 (edited) I think I remember reading that you replaced one of the front or rear diffs with a Hyper 7 one? If that's the case then there is your problem, the Hyper ST and Hyper 7 diffs have different ring/pinion ratios, if you have an ST diff at one end and a Hyper 7 diff at the other then your centre diff is working over time. It's quite a big difference too, when I swapped my ST diffs for 7 diffs I had to drop my motor pinion by 4 teeth to get the motor temps back into sensible realms. BTW I've never had any issues with my standard non-spider diff, I run a Castle 1515 on 5S and I've never even shimmed my centre diff, and I've had zero problems with it. Edited June 1, 2013 by DreXeL Quote Link to comment Share on other sites More sharing options...
smiithy1 Posted June 1, 2013 Share Posted June 1, 2013 hay fella i had the same problem when i done my hon nor blew 8 diffs in total same as yours twisted the cases and jamed the gear i upgraded mine to a spider diff as they have 2 extra planet gears just one shim under every gear fill with 50k oil and jobs sorted been cool ever since like as it has a cnc case to so stops all flex and the extra gears must take the load better they not so much eigher look on ebay as bytime ya buy a few new diffs and the upgrade the internal gears therse the price of the spider diff much better for brushless like Quote Link to comment Share on other sites More sharing options...
PurcyP Posted June 1, 2013 Share Posted June 1, 2013 If you keep blowing diffs you need spider gears Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 1, 2013 Author Share Posted June 1, 2013 I think I remember reading that you replaced one of the front or rear diffs with a Hyper 7 one? If that's the case then there is your problem, the Hyper ST and Hyper 7 diffs have different ring/pinion ratios, if you have an ST diff at one end and a Hyper 7 diff at the other then your centre diff is working over time. It's quite a big difference too, when I swapped my ST diffs for 7 diffs I had to drop my motor pinion by 4 teeth to get the motor temps back into sensible realms. BTW I've never had any issues with my standard non-spider diff, always run 5s with a Castle 1515 and I've never even shimmed it. Interesting.... I was told the things were the same....but I will strip the front and rear and check that out tomorrow. If there is a difference, then that would explain the problem and a cure is simple. Spider gears are the next thing to try....but I don;t have the funds right now, which is a pain. I've also been looking at alternatives in terms of diff cases. I have a spare alloy Savage diff case, which I could adapt if I grind off around 1mm and then fit some Hyper internals...but that's a ball-ache to do. Has to be accurate, and the shimming has to be right too. Will look at all this again tomorrow Quote Link to comment Share on other sites More sharing options...
DreXeL Posted June 1, 2013 Share Posted June 1, 2013 (edited) Interesting.... I was told the things were the same....but I will strip the front and rear and check that out tomorrow. If there is a difference, then that would explain the problem and a cure is simple. Nope, different ratios. http://www.msuk-forum.co.uk/topic/164933-correct-spider-diffs/http://www.rc-monster.com/forum/showpost.php?p=193027&postcount=14 When I stripped a ring gear on my ST diff I swapped to Hyper 7 diffs as they are cheaper and easier to come by than ST diffs (I got two brand new complete diffs and pinions from an eBay chop shop for the same money as it would have cost for an ST ring and pinion gear, which weren't in stock anywhere anyway) and I was amazed at how much they raised the overall gearing. Edited June 1, 2013 by DreXeL Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 1, 2013 Author Share Posted June 1, 2013 I used a complete assembly diff case/diff/etc so I just bolted that on. Soo the ring/pinion gears would mesh just fine...just I potentially have different ratios front rear as the other diff I left alone. As you said...if the ratios front/rear are different, then that would put a horrid strain on the centre diff as it would bias power to the lower geared end. In myu case...I think it's the rear that is H7 .... which would biase power to the lower geared front diff Quote Link to comment Share on other sites More sharing options...
DreXeL Posted June 1, 2013 Share Posted June 1, 2013 Yep, I bet a pound to a penny that is your problem Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 1, 2013 Author Share Posted June 1, 2013 Been doing some checking...and the ring gears are actually the same tooth count....though not the same shape. The pinions are different...hence the different tooth shape on the H7 to mesh. So as I bolted on a complete assembly off a 7....thats 13T pinion. the other one would be stock St, so thats a couple of teeth lower. Pretty sure I got a good H7 pinion...or else I will pinch one off the Rally Hyper for testing. It'll either work...or I'll be needing yet another diff....... Quote Link to comment Share on other sites More sharing options...
DreXeL Posted June 1, 2013 Share Posted June 1, 2013 (edited) Yep, same tooth count but cut differently to mesh with the 11t pinion of the ST. I don't *think* the ST ring gear will mesh correctly with the H7 pinion, but I've not tried it. Edited June 1, 2013 by DreXeL Quote Link to comment Share on other sites More sharing options...
Mr. Doktor Posted June 2, 2013 Share Posted June 2, 2013 so you had pinions of different tooth count? both 11t and 13t at the same time??? Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 2, 2013 Author Share Posted June 2, 2013 Right .... just completed the stripdown... Front diff. Stock Hyper ST. 11T pinion, 43T ring gear. Rear diff....I had to replace the diff case as the bearing was loose on the pinion side....so I bought a complet unit fro E-Bay. It said for Hyper 7/7.5 and ST...... so I assumed it was all OK. I checked the ring gear and counted 43T ..... but yes. As Drexel guessed....13T pinion!!!!!! Good spot. Never knew they managed 2 pinion sizes but never imagined they would fit on the same tooth count of ring gear. When you hold the two together, the ST one has a larger diameter. The Hyper rally has been raided for it's rear diff which I had on the same oil as teh ST front, along with it's pinion. I also pinched it's centre diff and replaced it's oil with 60k. Now to test run it and see what gives. MUST be better with the front and back end on the same gearing I suspect the lower geared front must have been taking more power than the rear, made worse by the front end lifting. Must have been shock loading the diff every time the fronts landed again and friction forced them to slow down. Just as well I didn;t lock up the diff.....as that would have got even more interesting Quote Link to comment Share on other sites More sharing options...
PRAETORIAN Posted June 2, 2013 Share Posted June 2, 2013 Never mix your diffs and pinions on the ST mate. You either need to run ST diff with ST pinion, or H7 diff with H7 pinion. Otherwise you are in for trouble. Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 2, 2013 Author Share Posted June 2, 2013 Never mix your diffs and pinions on the ST mate. You either need to run ST diff with ST pinion, or H7 diff with H7 pinion. Otherwise you are in for trouble. I was running ST diff with ST pinion AND H7 diff with H7 pinion! Centre diff would have been happier I reckon if I ran the same both ends though. I had ST front H7 rear. Quote Link to comment Share on other sites More sharing options...
PRAETORIAN Posted June 2, 2013 Share Posted June 2, 2013 I was running ST diff with ST pinion AND H7 diff with H7 pinion! Centre diff would have been happier I reckon if I ran the same both ends though. I had ST front H7 rear. Admittedly I don't think I have ever run that combination, so I am not sure if it will be that causing your problem or not. I have had two ST Pro brushless cars and never had issues. That said I was only running 3-4S so there was less stress on the drive train. However, given the torque in a lot of brushless motors these days, I would also look into your throttle and brake settings as well as the gearing. It could be that torque spikes when you punch the throttle, or use the brakes are over stressing the drive train. Quote Link to comment Share on other sites More sharing options...
DreXeL Posted June 2, 2013 Share Posted June 2, 2013 Right .... just completed the stripdown... Front diff. Stock Hyper ST. 11T pinion, 43T ring gear. Rear diff....I had to replace the diff case as the bearing was loose on the pinion side....so I bought a complet unit fro E-Bay. It said for Hyper 7/7.5 and ST...... so I assumed it was all OK. I checked the ring gear and counted 43T ..... but yes. As Drexel guessed....13T pinion!!!!!! Good spot. Never knew they managed 2 pinion sizes but never imagined they would fit on the same tooth count of ring gear. When you hold the two together, the ST one has a larger diameter. The Hyper rally has been raided for it's rear diff which I had on the same oil as teh ST front, along with it's pinion. I also pinched it's centre diff and replaced it's oil with 60k. Now to test run it and see what gives. MUST be better with the front and back end on the same gearing I suspect the lower geared front must have been taking more power than the rear, made worse by the front end lifting. Must have been shock loading the diff every time the fronts landed again and friction forced them to slow down. Just as well I didn;t lock up the diff.....as that would have got even more interesting I reckon you won't have any more centre diff problems now Handling must have been 'interesting' with that setup Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted June 2, 2013 Author Share Posted June 2, 2013 Nope. Another centre diff has gone to the great scrapyard in the sky. Got 2 packs through it this time, but as soon as I gave it some serious stick on pack 2, the thing let go again. Stopped as soon as I heard the sound of slipping cogs...and sure enough, the teeth on the spur side gear are starting to round. Will slap a servicable gear back in and return it to the nitro car I borrowed it out of. Need to find another solution for this. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.