Diff questions

[lincpimp]

Ok, so most here have seen my 8s 14xl powered savage. Completely stock so far. All I have upgraded is the center driveshafts, went to the heavy duty hpi cvds.

Now I just blew out the front diff, a 2 spider unit. I have a 4 spider in the rear, with a stock plastic case. Should I buy the flm 7075 diff cups, or the complete hybrid bulks? I like plastic stuff, as it is cheap to replace!

Any ideas or info is handy, as I do not have much experiece with the savage. I really like the truck, and it seems very sturdy so far.

Also , any info on diff shimming? I am sure that if I go with the hybrid bulks, shimming will be necessary. What about with the stock bulks/cases and the flm diff cups? Any links to shims will also be appreciated!

Sav diffs suffer same prob as T or EMaxx - the plastic lets the diff twist slightly under load and this lets ring and pinion pull away from each other and eventually strip or blow out.

Usual solution is same - stiffen assembly so it cant twist under load. Alum diff cup, metal diff case and eventually metal bulks. I upgraded my 4.6SS to Nova 7075 diff cups, gpm alum diff cases and alum bulks. Sav diff cup may not be as critical as in a TEMaxx where the 2mm screws just cant handle the shear load, but I went ahead and changed anyway. No more diff trouble with the stock 4.6, a 27Picco or Axial 32, but nitro doesn't have that instaneous BL torque either. Here's a shim reference-

http://savage-central.com/modules.ph...wtopic&t=55122

[JERRY2KONE]

I am sure that you know my thoughts on the matter linc, but I always say go for the gusto and build it to last. If you want something that will not break then get rid of the plastic weak point that is giving you trouble and put some metal beef in that thing. You love the raw power of your toys, thats why you always put those gigantic motors in them. So you either need to improve the material integrity or lower your power plant.

[lincpimp]

Duster - Many thanks for the info. I bought a pair of flm 7075 diff cups from Mike last night, so I will give them a try. I will also shim the diffs in the stock cases and see how they do.

Jerry - I know, go big or stay home! If I do buy the hybrid bulks, they will go on the flm tranny forward, as I am running cen genesis wheels/tires and those things are heavy! I am sure that the stock diff housings will not hold up to that!

I am using this savage to figure out the strong and weak points so that I can upgrade the other savage. The other truck will be heavier, so it needs strong parts!

In my experience with my big and heavy extended savage aluminum diff cups, with shims and 4 gear diff takes care of the problem. My savage wouldnt handle my axial .32 I ran in it for two years without the upgrades.

I now have been running my savage with a 7XL and 4s and sometimes 5s lipo and the diffs are holding up fine even with the slipper tighten all the way with a metal spur gear. In two years of racing and bashing I only blew the front diff out once with my setup, and that was because I had the throttle pegged and ran into a nasty wall at high speeds. Gotta let go of the throttle when your going to run your front wheel into something hard & fast

I also recommend locking the tranny in second gear, it wont take long before you to break some tranny gears when that sudden power from a brushless motor slams the tranny when shifting from 1st to 2nd.

When the tranny is locked in second and the diffs are shimmed & aluminum diff cups the savage drivetrain is easily as strong as any buggy / truggy that I have used in my experience.

[Serum]

The cheapest available option to beef up the savage diffs is to buy a set of GPM housings, and the new HPI diffcases. (i don't know if you've got the savage x or the normal savage? the diffcases that HPI produces are from molded aluminum, and they come with steel inserts. The GPM house eliminates flex, so the ringgear/pinion won't strip, and the aluminum HPI housings with the steel inserts prevent the cross-pins to eat their way through.

Another good upgrade would be to make the output side of the ringgear (which normally uses a 10X16 bearing) 8mm, so you can use a larger bearing (8X16, which can hold a lot more than the 10X16)

[Serum]

@paralyzed; my best guess is that they where a tad too tight, i never had issues with the pinion bearings.

[_paralyzed_]

I run in pretty fine dirt, that may have been the culprit. The bearings went out on me 2 or 3 times, when I put the boca bearings in I actually put a hose clamp around the input side of the diff case. For whatever reason its been holding.

[lincpimp]

Serum, thanks for the info. Where would I get gpm housings?

Are the flm hybrid bulks any good? Most of their stuff looks well made, and those are 60 each, and cover the diff cases and bulkheads in one shot. They appear to be cheaper than the other options I have seen, such as just the bulks for 40 bucks a pair.

I got mine in Hong Kong. I don't have the link on this PC, but when I get home I'll post it. I think its RCX - found it, these are the ones I used -

http://www.rcxshop.com/product_info.php?products_id=364

I've had decent service from them on several orders over several years. Be sure they have you zip code (that order took 9 weeks, lol!!)!!!

Have looked into upgrading brg size too as Serum mentions, but would need to buy some carbide tooling for my lathe to make that happen (ring gear is hardened) and so far at least for nitro, it hasn't proved to be a problem.


From HK, alum cases and and bulks are about $50 for each end. I don't have any experience with the flm pieces, but those may be just as good.

[Dafni]

Originally Posted by lincpimp

Are the flm hybrid bulks any good? Most of their stuff looks well made, and those are 60 each, and cover the diff cases and bulkheads in one shot. They appear to be cheaper than the other options I have seen, such as just the bulks for 40 bucks a pair.

They are good, but heavy. If you don't mind the extra weight, go for them.

[rhylsadar]

hi

there are different stages of upgrading savage diffs. practically most the savage diff problems were solved years ago.

one thing is to insert those little sliding blocks in the normal housings. by now some years later that hpi has done that on their own with the x ss you may just use their cups. however imo the old mod with the sliding blocks in high quality cups like maximizer is still tougher.

next step is the bigger bearings serum already mentioned. 8*16mm on the cup and on the 43t. if you stay with plastic cups you can use the kyosho IF103 that already has a steel output that uses a 8*16mm bearing. by now one can use the new hardened ringgear and pinion.

next step is adding two more bearings into the bulks that will take part of the load.

this all works well with plastic bulks etc. of course it can all be done with aluminum parts too.

i could show you pics of all those mods but sadly our private server is down since a few days. i guess i have linked those pics before in this forum.

but here is a old link that shows most of what i mentioned. its german but you may see some things in the pics.
http://www.nitro-mods-shop.com/SB/index2.htm

the problem with the gpm housings is that they are cut the wrong way. so you have to assemble the diff inside the housings if you are using the mod wiht the two additional bearings in the bulks. so using the normal plastic housings is easier with this mod.

regardless of what mods you do on the diffs the most important thing probably is a correct shimming. not to hard and not to loose.

and yeah of course the nightmare heavy tires you use do not help preventing diff damages.

bye
rhylsadar

[Serum]

@rhylsader;

the problem with the kyosho cups or the HB C8019 is that you need to use the unneeded expensive blocks from nitromods. (which wasn't his idea in the first place btw, he simple stole it and hit the market with it) the aluminum HPI cup covers this problem in an even better way. I use shims inside the diffs a thin layer of springsteel sheet. (which probably isn't needed with the 'new' HPI diffs)

And i don't use the paper gasket either, i use blue loctite. It seals it up very good, and it tightens up even better.

The GPM housings are available on ebay. The bulkless of FLM is a tad too heavy for my likings. I want to put mine on a diet once i've got my things up and running.

[lincpimp]

Ok, so the Gpm are lighter than the flm. I really like the flm quality, are the gpm parts comparable? I will most likely buy the flm parts for my flm tanny forward build, and keep the stock plastic bulks for the basher. I know that the heavier truck will be much harder on diffs.

One the subject of ring and pinion sets, are the savage ss metal cased diffs good enough, or should I upgrade them too? Is there an upgraded ring and pinion available, or will a std buggy diff gear set (ofna, etc) fit? The ofna diffs use the 6x16 bearings, so that would be a way to upgrade?

I will try the flm 7075 cups in the basher and see how they do with the stock plastic bulks. I do have a set of the hardened hb internals, will they fit?