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Rear Diff problems - What really is the deal?

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BlueRidge1

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OK, my rear diff went last weekend. I've been doing a pile of google searches and it appears to be a fairly common thing. After all, you can't buy a bevel gear set to save your frickin life right now, so what's that say?

Anyway, I'm wondering what root cause is on this. In my case, the first thing I saw was 4 loose screws on the diff casing. So obviously this led to the bevel destruction. Then I see everyone talking about the 4 spider dif mod. Well, it won't do a dang thing if the screws back out.

What are you guys seeing? Screws backing out? Or just plain destruction in general?

If it's mostly the screws, I'll find some longer ones and use locktite. If not, I'll spring for the 4 diff mod while I'm in there.
 
Plain old destruction was my culprit. Too much picco power! The shaft holding the spiders ate into the diff case and I think that is what did my gears in, bad allingment causes excess wear. Did not observe any screws backing out, There are upgraded cases though, out of alloy for ouch, $50. I just put a plastic case back in mine ($6?). Great upgrade, truck isn't nearly as squirly as it was before the 4 spi and diff oil!!

Good luck, My LHS has gears on their shelves right now I think.
 
Mine was total destruction, very similar to unsavagable's, none of my screws were loose, the spider shaft twisted in to the plastic cup ripping the inside of the cup apart, the bearing disintigrated, and all the gears were missing teeth. I was only using the stock .25 in mine, no real powerhouse. It happened on the tenth tank with mine.

You can also use the ofna gear set since the HPI ones are non-existent. My problem though has been finding replacement cups. They are selling for $15 to $20 plus $5 shipping on ebay, and its only a $6 list price, because they know no one has them.

I think the plastic they are using for the cups is very weak, I am considering getting a set of the 7075 aluminum cups from maximizer. They are a bit pricey though at about $50 each.
 
Well what are the chances of this happening if the 4 spider mod isn't performed?

Could it be the result of to much fluid or too heavy?
 
Originally posted by killahbz
Well what are the chances of this happening if the 4 spider mod isn't performed?

Could it be the result of to much fluid or too heavy?
Click to expand...

Well as NCNitro mentioned he toasted his diff and that was with the stock engine! Just imagine what could happen if you put a Wasp or something similar into the Savage without doing the diff mod. You would probably be replacing them each time you went out!

You will know when you blow a diff. Your Savage won't be able to climb squat! Below is a picture of NCNitro's Savage after we found out he blew a diff. Notice the front tires ballooning. :)

61broken_diff-med.jpg
 
Thanks guys. Based on this info, I will spring for the 4 spider mod while I'm in there.

Anyone have Ofna part numbers to substitute for Savage rear diff gears? Are they an exact match? Strength?
 
If they had any kind of customer service I would try, I have tried on several occasions to contact them, waited on hold for 50 min, left my number twice, still no call back, I'm getting totally blown off by them.

I need to email their sorry asses the pics.
 
with the problem with the diff case i wonder why noone hase made an aluminum one
 
actually there a lot of people that believe that the diff problems are related to the way the savage's brakes are set up(& just about every rc) having you're brakes too tight or applied too hard puts a lot of stress on the bevel & ring gear you have to remember that when you apply the brakes it is the bevel & ring gears slowing the truck as opposed to a car's brakes slowing via the axle. If you are able to flip your truck on it's lid when applying your brakes they are probably too tight .I've got mine set up to stop the vehicle in a reasonable distance without locking up. I went 8 gallons with out a diff failure and I do run my truck hard. Just mine a a few others 2 cents.
 
where would a guy get those metal spools? does anybody have a link? thanks i'm in the same boat . my diff is shot.
 
Waybad... Good point. I'm sure tight brakes are a reason for many failures. At the same time, however, I think that HPI may have an issue with their bevel gears. The scaricity of the bevel gear set is incredible. They are in at Tower finally: http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXDLD4&P=Z.


Crash... I don't have a link right off hand but just make sure you are going to stay off the pavement with a spool. Your diff output cups will take a real beatin otherwise. I chose to give the 4 spider gear mod with 3000 wt (in rear) silicone a try.
 

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