so i recently put a hyper .21 in my race savy, yes a .21, and i blew my rear diff. when i first bought the truck it had a mach 427 and it blew the front diff, and while replacing it i decided just to switch to x bulkheads. and now i blew the rear diff. is this common, do they just need to be shimmed perfect, what do you guys think about the cen diff mod. Ani input will be helpfull.
savage diff
- Thread starter p3-28revo
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- hpi monster truck savage
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Lessen
Super Awesome!
Supporter
From what I've read about Savages, it seems aluminum diff cups are one of there very few upgrades needed right out of the box.
Scrogg
Hardcore RCTalk User
CEN diff mod is unnecessary and changes the gear ratios, adds a ton of horsepower robbing rotating mass to the driveline.
it is a simple matter of shimming. It took me a while to get it down myself.
i can take a plastic savage diff cup in a stock plastic gearbox, shim everything properly and it will snap dogbones all day long without damaging the ring and pinion or the bevel gears. I have ran some high power mills with no diff problems.
Another thing that helps big time is to use silicone on the bottom of the gearboxes where they join with the skidplates. Dirt sneaks in ther overtime if you don't.
Shim the ring gear to be as tight as possible against the pinion and still spin freely. if it has one little spot that you feel friction while turning the differential by hand, don't sweat it. They'll wear in to each other nicely. Setting ring and pinion mesh is just like setting the spur mesh, just a tick tighter though.
Don't use too many shims, alot of people make the mistake of adding more shims than necessary. Too many shims causes premature bearing failure, which leads to ring and pinion damage.
The al. cups do help but are not necessary.
it is a simple matter of shimming. It took me a while to get it down myself.
i can take a plastic savage diff cup in a stock plastic gearbox, shim everything properly and it will snap dogbones all day long without damaging the ring and pinion or the bevel gears. I have ran some high power mills with no diff problems.
Another thing that helps big time is to use silicone on the bottom of the gearboxes where they join with the skidplates. Dirt sneaks in ther overtime if you don't.
Shim the ring gear to be as tight as possible against the pinion and still spin freely. if it has one little spot that you feel friction while turning the differential by hand, don't sweat it. They'll wear in to each other nicely. Setting ring and pinion mesh is just like setting the spur mesh, just a tick tighter though.
Don't use too many shims, alot of people make the mistake of adding more shims than necessary. Too many shims causes premature bearing failure, which leads to ring and pinion damage.
The al. cups do help but are not necessary.
Last edited:
Lessen
Super Awesome!
Supporter
Yeah, Scrogg is right. Definately a shimming issue.
Well, with stock plastic diff housings, I found it impossible to shim anything. They fit so snug side to side that I couldn't put any shims in without putting excess stress on the bearings.
With that in mind, I have converted one diff in an old savage to having stock internals (4 spider version), but an alloy diff case. This allowed me to shim properly since they have a bit of extra slop.
There is more than one benifit of running alloy cases.
1st and perhaps most important, the shimming is allowed and you can get your gear lash perfect. Takes time and effort, but is worth it.
2nd is that the case doesn't wear/flex/warp and cause gear lash changes over time.
3rd, it case is less likely to warp due to high powered engines or low gearing.
4th, you have alloy threads holding your skidplate on and half your shock tower.
The only drawbacks I've come accross is the cost, $30 a piece for the cases and that you can't use XL or X diff output drive cups. They are too big to fit either aftermarket cases I've used (dynamite and Hot Racing).
I recently blew both diffs in a new to me savage. I have no idea how much fuel was ran through them, but I do know the owner I got it from doesn't understand landing on power is bad. So, they gave out pretty quickly after I aquired the truck.
I bought two new XL diffs off ebay and 2 new alloy Hot Racing diff cases from LiquidRC. That's how I know the XL diff output shafts are too large to work. I had to use the ones from my blown diffs instead.
Considering the one I did in my old savage now has a new owner and I know at least 6+ gallons of use has gone through it, that the alloy cases really do help the life of the diff ring/pinion gears. The gears still look like new in his and he just recently blew the front diff that I didn't replace with an alloy case.
Now my truck should be bullet proof as far as the diffs are concerned, but considering snow is on it's way, traction will be minimal. But rest assured I'll find out the life next season.
Geez... sorry for the rambling.
With that in mind, I have converted one diff in an old savage to having stock internals (4 spider version), but an alloy diff case. This allowed me to shim properly since they have a bit of extra slop.
There is more than one benifit of running alloy cases.
1st and perhaps most important, the shimming is allowed and you can get your gear lash perfect. Takes time and effort, but is worth it.
2nd is that the case doesn't wear/flex/warp and cause gear lash changes over time.
3rd, it case is less likely to warp due to high powered engines or low gearing.
4th, you have alloy threads holding your skidplate on and half your shock tower.
The only drawbacks I've come accross is the cost, $30 a piece for the cases and that you can't use XL or X diff output drive cups. They are too big to fit either aftermarket cases I've used (dynamite and Hot Racing).
I recently blew both diffs in a new to me savage. I have no idea how much fuel was ran through them, but I do know the owner I got it from doesn't understand landing on power is bad. So, they gave out pretty quickly after I aquired the truck.
I bought two new XL diffs off ebay and 2 new alloy Hot Racing diff cases from LiquidRC. That's how I know the XL diff output shafts are too large to work. I had to use the ones from my blown diffs instead.
Considering the one I did in my old savage now has a new owner and I know at least 6+ gallons of use has gone through it, that the alloy cases really do help the life of the diff ring/pinion gears. The gears still look like new in his and he just recently blew the front diff that I didn't replace with an alloy case.
Now my truck should be bullet proof as far as the diffs are concerned, but considering snow is on it's way, traction will be minimal. But rest assured I'll find out the life next season.
Geez... sorry for the rambling.
Scrogg
Hardcore RCTalk User
The plastic cups usually only take one shim.
I totally agree with you on the al. cups olds97ss. They do allow for more room and last longer with proper maintenance.
I say just hit E-Bay...you can find these kind of deals all day long.
http://cgi.ebay.com/Savage-X-SS-Dif...14&_trkparms=72:1205|66:2|65:12|39:1|240:1318
Just check the shimming on them. HPI was not shimming them right on the first X versions. The newer versions seem to be shimmed perfectly.
I totally agree with you on the al. cups olds97ss. They do allow for more room and last longer with proper maintenance.
I say just hit E-Bay...you can find these kind of deals all day long.
http://cgi.ebay.com/Savage-X-SS-Dif...14&_trkparms=72:1205|66:2|65:12|39:1|240:1318
Just check the shimming on them. HPI was not shimming them right on the first X versions. The newer versions seem to be shimmed perfectly.
- Thread starter
- #9
well i just took another look at it and the bearing on the diff blew. Thinking about the last one that blew last summer, the bearing on the diff was also the cause. I didn't build these the guy a bought the truck from did so i dont know how there shimmed but is blowing a diff bearing normal, caused from to much abuse, or just the shims.
Which bearing? On the diff or the pinion? Regardless... No. I've had bearings last many many gallons. Like the ones in my aftershock diffs and the rear diff in the savage I put an alloy case in. My aftershock diffs are 10+ gallons old and still feel good.
Well, they could be going bad because of time, neglect or too tight of shimming. When you replace them, just make sure the diff spins freely after shimming and putting the case together. Having side load on bearings chews them up more quickly.
Scrogg
Hardcore RCTalk User
Olds nailed the bearing thing dead on. I replace the two bearings on the diff outdrives every two gallons. They develop slop around that mark, you are gambling with a Ring and pinion after that.
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