Anyone having Savage diff problems?
 

I haven't had too many problems with my savage diffs but I decided to beef them up anyway. Seeing as though some people here are going to be running 1521s I can see a need for stronger diffs. I haven't actually run these yet so I don't know how well the hold up but I have never heard of anyone who has done this mod break them.

http://lh3.google.co.uk/MTBikerTim/R...0/IMG_0878.JPG

Basically they are Cen GST diffs with savage output shafts. They fit almost perfectly. You can see in the picture the savage diff teeth (on left) look tiny. The pinion needs to be shimmed out by a little over a mm and the drive pin holes in the output shafts need to be enlarged to 3mm and that's about it. The drive cup on the pinion also needs to be secured by a grub screw too instead of the savage screw in pin. The other benefit of this mod is that the bearings on the outputs are larger on the Cen diff and are less prone to failing like they do on the stock diffs. These diffs are also really cheap on ebay.

That is a great mod. Those CEN rings look beefy! I am going to run my diffs until they cash out then I may have to give this a try. I am hoping the FLM Hybrids will help keep them alive for a while due to their rigidity.

If your diffs are shimmed and in the flm hybrids I doubt you will ever have a problem. I was thinking about the hybrids or these and these were a lot cheaper. Also I like the easy access plastic housings.

Ya, I agree about the shimming. I ended up adding shims after I had pretty much built my whole truck. There was just too much slop in them...

It's funny that the Cen diffs have less side to side slop then the stock ones. My stock diffs have 2 shims in them to stop the diff moving sisde to side. The cen diffs did not need any.

Thats a great tip on the difs. I like it. :yes: Cheap and effective. Do you know the gear ratio on the CEN difs? I know they use some funky tooth counts in their buggy and truggy. The Buggy is something like a 9T pinion and 26T ring gear. Are these the same gears? If so I have a couple of those diffs sitting here in my CEN parts bin as spares from my buggy tht I never needed. If they are the same, I might just do this mod. I think the CEN buggy difs are Mod1.5 gears rather than the standard mod1.

I had issues with my Savage X difs at first. I had the plastic cups from the box, I kept cracking the cup not breaking the gears. After tearing up a few sets of those rather quickly I upgraded to the aluminum cup in the rear and shimmed it up properly and I never had another issue. The front dif is still the stocker wth the plastic cup and I never had an issue so its still running. I have the aluminum cup for it sitting here in a box along with a full set of gears and pinion for it but I am not going to replace it untill it breaks. I also bought aluminum bulk/gearbox for the rear but again I have been waiting to see if I needed it before installing it. I didnt want to just fill the truck with aluminum just for the hell of it. And so far I havent needed it.
Of course I'm not running a 1521 either. Just a little 1940. :whistle:

I forgot to mention the diff ratios. Yes they do change quite a bit after doing this. The diff ratio is 26 and 9 so they are probably the same diffs as the buggy. You could check by looking at the part numbers in the manuals for the gst and buggy.

After doing this mod I now have 2 spare diffs so it will be interesting to see if the stock diffs in my nitro die before these. Personally my bet is on the bearings in the stockers to be the first thing to go.

the main problem with the savage diffs is that there is flex in the plastic housings. I can imagine the larger teeth to hold up better in these plastic housings.

I have run the stock diffs, the ones with the steel inserts and the aluminum cups, with a 1521 for a while now. They are bullet proof! No problems even with running larger, gear destroying tires like Big Joes and Jumbo Kongs. Innovative-RC is coming out with an alloy easy access diff case with larger bearings that should even solve the small bearing problem.

Nice I didn't know that. That sounds awesome. Innovative make some awesome gear so these should be great.

Do youknow anythimg about the timing on these? The access part is nice, but with bigger brgs, you shouldn't need to access it much anymore!


Serum is right on - flex is the biggest prob with stock setup, 27picco was enough to destroy rear diff regularly til upgraded with alum cup, alum diff cases and bulks. I used some prem brgs (boca) and they've been fine so far.

The last time i heard was that he canceled the plan since it cost too much for the machining. Not sure if he changed his mind..

You can simple machine the ringgear down to 8mm od instead of the usual 10, that removes one weak bearing. the 16X8X5 hold up fine.

hi

those cen diffs look nice for sure.


the 'old school' usual mods i and many others did to the savage diffs were the following.

- use a kyosho IF103 cup instead of the normal 'plastic' cup. so you can mount a 16x8x5mm bearing there.

http://62.2.107.106/~beat/images/17-...mn06_(153).jpg

- trim the ringgear so you can use a 16x8x5mm bearing there too. like serum said above.

http://62.2.107.106/~beat/images/17-...mn06_(150).jpg

- inside the cup trim the pins down a bit and use the little plates (here shown in a alu cup). works well in the plastic cup.

http://62.2.107.106/~beat/images/20-06-04/aludiff8.jpg

four years later hpi did the same principle to their 'new' savage x diffs.

http://62.2.107.106/~beat/images/17-...mn06_(109).jpg

- to take the stress from the inner bearings you can mount two additional bearings 21x12x5mm on the diff

http://62.2.107.106/~beat/images/17-...mn06_(135).jpg
http://62.2.107.106/~beat/images/17-...umn06_(91).jpg

- trim the bulks

http://62.2.107.106/~beat/images/17-...umn06_(89).jpg

http://62.2.107.106/~beat/images/17-...umn06_(97).jpg


diffs modded like this and shimmed properly hold up pretty good. of course all of this can be done the alu parts (cup, bulk etc).
i know this is all very old news but it fits to the topic here. maybe some 'new' the savage stuff havn't seen this before.

bye
rhylsadar

yeah, thanks for sharing Rhylsader;

the next to weakest link in the savage diffs are the internal gears, but if these are shimmed proper they are pretty tough too. that and the 2.5 hardened pin that tend to break every now and then, or eat their way through the output cups.

Don't know if you noticed this, but HPI is now actually selling a heavy duty gear option..

Poor guys.. instead of including it in their kit, you can buy diffs that meet the standard..

yep.
i guess the new hardened gears are hpi no 86922.

greets
rhyls

Ring gear is hardened and the carbide bits cost more than I want to spend. I don't need/use carbide bits in the gunsmithing I do (competitve rifles mostly), the metal I work is not that hard. If I had carbide tooling, I would've have tried it already - I know of a few from Sav Central who've done it and it seems to fix the prob.

This thread is has got some great ideas in it. I wonder why HPI doesn't make the ring gear and case use the biggerbearings in the first place.

because the material is hardened it can happen that the thin collar (1mm thick) snaps right off. It would be VERY easy for Jamie at Fastlane to adjust the bearingholes on the savage diffs so it would fit larger bearings. I'll discuss this with him.

Now, there's one heck of an idea!!!

I took the nitro savage out racing on the weekend and you know what happened? The bloody diff bearings have gone already in the rear diff (stock savage diffs). I broke a rear dog bone snapped a LST shock shaft and have blown the rear diff bearings :diablo:. Who said nitro motors don't have enough power? I only put new bearings on those diffs just before Christmas and they have seen less then 4L of fuel. The bearings are definitely the biggest problem with the savage diffs.