Differential Dimensions?

Hi all,

I'm sick of shattering differentials in my E-Savage (the actual production one, not a GP->E conversion), so I'm trying to see if I can shoehorn some other production differential into the E's case. Some of the folks on E-Savage.com have used the pinions from the Maxx trucks, and drilled out the bevel gear and case to 6mm to support that. I tried it, but the hub on the main bevel gear shattered while I was drilling out the hole. In addition, I keep shattering the internal bevel gears inside the diff cup, so switching to the Maxx pinions won't really help me on that score.

The E-Savage differential is the same size as the MT2 differential, which is quite a bit smaller (depth wise) than the Maxx differentials. I'm hoping that people can chime in with the dimensions of their trucks' diffs; I need to know the diameter of the main bevel gear, the diameter of the diff cup, and the depth from bearing to bearing (outside to outside) to see if anything else will fit inside the E-Savage case.

If anybody is willing to help me with this, I would appreciate it. Trucks that have occurred to me as possible donors include the CRT.5, Lightning series, and 8ights... but I'm willing to hear (read?) anything you've got.

Thanks!

[BrianG]

What exactly are you shattering? I mean during normal use, not when you are trying to drill them.

And no, I can't help you with the dimensions - I'm just curious why you need to mod the diffs...

Everything in this picture:

http://www3.towerhobbies.com/cgi-bin...?&I=LXPCY0&P=7

The smaller bevel gears are the ones that shatter, while the pinions will break off at the hole in the shaft. HPI has some new, hardened pinions, and I haven't broken one of those yet - today was my fourth broken differential, two deaths by pinion and two deaths by bevel gear.

All this from a Feigao 9L.

[BrianG]

Wow, that does suck! Are you using a plastic or metal cup? Maybe the plastic cup is flexing and causing the small gears to "skip"? I take it that a "real" savage diff won't fit in there?

Right now I'm using the stock plastic cup. I just discovered these:

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=014

So I may order one of those and see if it helps.

I haven't tried stuffing a GP Savage diff into the housing, but I'm willing to bet large amounts of money that it won't fit - a Maxx diff is too big, and the GP Savage one looks even bigger from the pictures that I've seen.

The gears are shattering cause they're hardened. You have to use tungsten carbide bits on hardened steel. TRX spyders (without shaft) are T and E Maxxes diff weakest part. RRP stuff is weaker yet (heat treating is not the best).

I've had decent luck with FLM diff cup upgrade - you get a new ring modded to use 3mm vs the 2mm stock screws and a better arrangement for the spyder cross shaft - its kinda keyed into a slot in the FLM alum diff cup so its less prone to move and bust spyders. The other thing needed are alum diff cases - even the 4 screw cases from 3.3 will not be strong enough to resist flexing that lets R&P pull just enough apart to start stripping teeth. Buy the cheapest alum diff cases you can find and a set of alum diff collars too.

The alum diff cases and the flm diff cup will last for a while - stronger than stock. The next step up is to HB diffs in flm hybrids or UE 6 or 8 sypder diffs. I've been thru this all this with small block to big block swap on Tmaxx.

Ah, that explains the shattering while drilling. I thought it might have been because I have cheap drill bits.

Unless I misunderstood, your other recommendations are for Maxx trucks, right? I may tuck those away in case I get sick of replacing diffs on my E-Savage and buy one of the new E-Maxx trucks instead. :-)

Originally Posted by BrianG

Wow, that does suck! Are you using a plastic or metal cup? Maybe the plastic cup is flexing and causing the small gears to "skip"? I take it that a "real" savage diff won't fit in there?

Prob is the plastic diff cases have only 2 screws and they are at the front of the case. Torque reaction flexes everything and the R&P pull apart and "skip" or strip - mine would tear out 3 or 4 teeth at a time. The 3.3 cases added 2 screws at the pinion end, but they're still plastic cases. Its takes strengethening the assembly to put an end to diff probs or at least make diff probs less than an every run occurence.

Once I upgraded to a alum diff cup - flm or maximizer, then the stripping started. Up to that point I was shearing all 4 2mm screws that hold teh ring on the cup. Got old in a hurry!

Sav won't come close without a lot of work.

My bad!! My dumb a** didn't notice you're having prob with a E-Savage!! So sorry.....

Have you checked sav central to see if this is discussed over there??

Nope, I hadn't checked Savage Central - so I just ran over there and checked out their E-Savage forum. It's pretty small, and no new information that I haven't already seen or experience via E-Savage.com. :-) Thanks for the pointer, though - I didn't even know that Savage Central existed; how sad is that?

FLM does show diff cups for your E-Sav and they mention a full diff upgrade that uses the nitro Sav diffs, so there is help out there. I did not see much over at Sav Central either - I'm registered over there, but they can be pretty snooty so I don't spend much time there anymore.

It would be nice to find some info on what others are doing about the probs you're having. Check some of the big boards out too like Radio Control Zone and RC Universe.

I'm always amazed at what I can find using a search engine!!

Where did you see the FLM diff cups? Their E-Savage product page only lists extended TVPs:

http://www.fastlanemachine.com/Publi...3/Default.aspx

I know about their GP Savage conversion that uses the E-Savage transmission; a couple of people over on E-Savage.com have that conversion and like it. That's available on addicted2rc.com:

http://www.addicted2rc.com/E_Savage.html

If I'm going to convert a GP Savage, though, I'm just going to get the new conversion package that has been discussed on this site extensively already.

As for other sites, every time I search for E-Savage info on anything other than E-Savage.com, I tend to find people who haven't really upgraded the truck. I think that's actually a good thing - the truck doesn't seem to be able to handle upgraded power, but is a tough and speedy little thing with the stock motors. In retrospect I probably shouldn't have installed the brushless and instead just gone to 7 cell NiMh's and been done with it. People break the driveshafts a lot, but I fixed that by mating Tamiya TNX MIP CVD dogbones with MIP Maxx axles. Some people break the center shafts, but I fixed that by designing a custom extended set of TVPs, and using the UE titanium dogbones front and rear. I've also melted three spur gears, so I drilled out an Integy steel GP Savage spur and use that instead. I guess the only weak links that are left are the diffs, hence my problems.

Is it too much to ask to have a truck that can run brushless and not break anything unless I smack it into a tree?

Unfortunately, you're right - I went to addictedtorc's site and saw the cups when I clicked on products for E-Savage. I assumed they were for the E-Savage, but now I see they're not direct replacements.

If the MT-2 pieces fit, then these guys sell a alum diff cup -

http://www.novarcproducts.com/diffcups.html

Sounds like if you're sticking with BL, you don't have many choices to solve your diff probs.

The best thing I've done so far for my E-Savage is to drill out the diff spur and cup and use the 6mm revo bevel gears. It takes some work, but it's worth it. Then you can use trx outdrives, which are also stronger. I have yet to break one of the 6mm bevels, but we'll see how long the HPI spiders hold up now. The diff is a lot tighter than it was stock, and sort off.. crunchy ? Does not seem to affect performance other than adding a bit of limited slip effect.

J.