RC-Monster Forums - Savage CEN diff Mod- (Jesus Built My Differential)

RC-Monster Forums (https://www.rc-monster.com/forum/index.php)

- HPI Savage (https://www.rc-monster.com/forum/forumdisplay.php?f=30)

- - Savage CEN diff Mod- (Jesus Built My Differential) (https://www.rc-monster.com/forum/showthread.php?t=18933)

Quote:

Originally Posted by fastbaja5b (Post 264141)

Silly q, where can I get these cen parts online? Already hearing stories of Flux diffs giving up!

You can get them on ebay but I've seen them at online hobby shops but don't recall which ones.

Quote:

Originally Posted by 93firebird (Post 264111)

Owning a Cen genesis and another Cen product, I'm not quite sure why you chose their diffs for the project. Just look on RCU and you will see all the problems ppl have with them.

I think the cen diff issues all stem from the **** house cen diff housing. The plastic savage cases seem to be strong enough to hold them together. I have been running the cen diffs in my brushless savage on 6s and 80mm medusa (R.I.P) and have sheared a drive pin holding the drive cup to the tranny but the diffs are fine.

I would also recommend the X casings for this mod. Bearing sizes would be different for the flux but i'm sure it could still be done.

Quote:

Originally Posted by fastbaja5b (Post 264141)

Already hearing stories of Flux diffs giving up!

How many have you heard of?

Good write up Finnster - hopefully I wont ever have to read it in more detail!!!:smile:

Quote:

Originally Posted by MTBikerTim (Post 264149)

The Cen diff case is really crappy. Like an emaxx design, but only one sm screw a flimsy collar. The rest is squeezed by the bulkheads. If they are stripping in Cens, well, I wouldn't necc translate that to Savs.

The savage design is 100X better and easier to access and maintain as well. I have the XL (same as X) so well see how it goes. It was my understanding that the Flux has more reinforced bulkheads, so hopefully even stronger, but time will tell.

I didn't trash the pinion or ring gear, but the spiders in mine hopelessly detonated. This was w/ a nitro even at that.

Quote:

Originally Posted by doo540 (Post 264042)

I liked the way the Cen cups look alot better then the oem Savage cups. I figured I paid for them might as well use them. haha I think there are going to be alot of unhappy Flux owners out there when their diffs start breaking. Did you get this mod from RCbasher? http://www.rcbasher.com/savcendiffs.html
Or did they steal it from you? Either way it works, I just hope it works all summer long. I plan on doing some 6s neu 1515 1.5d testing this spring just to see how high and far a Savage can jump. My neighbors have a pool.........

No, I have seen that write up before, as well as a few others. I'm not sure who first did it. I felt that:
A.) Not everyone here, as well as new Flux owners may not have seen it
B.) Some write-ups lacked a few details and hints that made a couple parts a bit confusing or not as easy as could be. I wanted to write a further detailed review that answered a few questions I had and offered a few hints to make things smoother.

I agree, your write up was much better, just wondered if two great minds were thinking alike, and it appears they were.

I managed to break a pinion!!!!

http://i7.photobucket.com/albums/y25...f/IMG_6357.jpg

The issue was the way I shimmed the diff. It was tight, but I had too many shims on the pinion, and more should have been on the diff to bring the ring gear in. It looks like the pinion was riding high on the ring gear and actually rubbing the case a bit. The teeth broke right off. What you can see the way it broke was the pinion is cast metal. A machined part would be even nicer.

I backed off 0.3mm on the pinion, and will add more shims to the bearing sides on the diff and try it again. BTW, you def need shims somewhere around the bearings as they float a bit on the diff cases. You don't want side to side movement on the diff. I am putting 8mm shims on the ends itself. Its more of a PITA as you have to take the diff apart to take the drive cups and bearing off, but its a better way to go once its adjusted properly. I would only fill the diff w/ oil once you've got all the shimming just right. You don't want to dump oil every time you need to add a shim to get the mesh right.

Finn, I've been looking at the Cen machined steel upgrades for the ring and pinion. Take a look, what do you think? Different ratios but they are a drop in fit. I wonder if they would be tougher?
http://www.cenracingdirect.com/index...OD&ProdID=1289

http://www.cenracingdirect.com/index...OD&ProdID=1288

nice find electric eel, gear ratio would be 3.45 to 1 with the gears you have listed.
What were you searching under to be able to find those gears? They are going to work great in my savage5T that I'm building.

A guy at my bashing place was running them in his Genesis or 7.7 or whatever the truck is called. He had dropped in a 90 size nitro motor and was having all kinds of problems.
I think I'll get a set and try them in the Flux.

I saw those before, but they looked like the normal sized teeth. At that point I figure what's the adv of doing this mod, other than the better spider gears? For all that you could prolly find normal truggy diffs that would do better than the Cen HD stuff. I thought I had read Kyosho diffs were super stong, as well as X2. No idea how hard they would be to fit.

I got the diffs fixed today and we're back in action. Feels a bit smoother than before too. :) The breakage was def user error on my part. I did open the rears and they are shimmed just fine. I left those as was.

I'm gonna start on this asap. But I have no idea where to get the parts, I wished I could just find a set of drop in diffs that would work.

very interesting thread, and yes i know its old :no: old is still great

i hope anyone can answer some of these questions and/or provide pics of the parts.

Quote:

Originally Posted by Finnster (Post 263834)

The diff mod has several advantages, the biggest of all being a huge and rugged diff. Not only are the teeth really, really meaty in the Cen pinion and ring gears, but the spider gears are also larger and a stronger steel than the Savage diffs. Also, the diff uses 8x16mm bearings throughout, so more reliable bearings as well.

>> do anyone know the mod size of the teeth on the CEN diff, being 26t it must be another pitch than stock savage (43t or 29t). theres a load of teeth info, ust wondering if anyone knew.

Cen Diff parts, and comparison to Savage Pinion, Ring Gear, and Diff Output Cups of a Sav XL:

>> can anyone provide comparison pics/weights of the CEN vs spider diff:
- 10t vs 8t spider gears
- 20t vs 14t spider gears

>>what screw (8) sizes are needed to clamp together the CEN diff parts, do CEN have a kit for this? and does this work with a stock savage flux diff, meaning only the clamping/center part (diff case/cup?) of the CEN diff used with stock savage diff parts ?

>>does the savage diff output drive shaft cup need shimming when used with CEN spider gears, and CEN 3mm shaft pins etc.?

The Mod is fairly straight forward. The Cen diff is a std 1/8th size. The Savage output cups do need to replace the Cen output cups.

>>why is that ? dogbone ball sizes ? what are the size of the CEn diff output shaft-drive cup ?

The holes are centered properly, so the only real work need is to increase the thru hole for the drive pins from 2.5mm to 3.0mm.

Note: Not pictured but later installed are Cen Cross Pins. These are optional and not required, but are one more bit for strength, as well as less oil needed to fill.)

>>will these work with stock savage spider gears ?

One Diff to Rule Them All:

http://i7.photobucket.com/albums/y25...f/IMG_6205.jpg

Remember that the Cen ring gear is smaller than the Savage's. Therefore the drive pinion will have to reach further in the diff case to mesh with the diff. You will need several 8mm shims to do this. I used a total of 2.3mm worth of shims to get the proper mesh. YMMV.
http://i7.photobucket.com/albums/y25...f/IMG_6213.jpg

>> whats ymmv ?
>>whats the reason to clamp up the pinion in a vice for shimming ? did you drill it or sand it ? How many flats do the CEN input pinion have ? it doesnt use a step screw like m5x3mm, but a m5 grub/set screw ?
[*]I used hot glue to plug the hole in the Cen pinion. Not sure this is necessary. as the drive cup is closed.

>>so you filled the hole in the pinion with hot glue, what does this exactly do ?

Notes:

One diff I had came with hex screws and grease, another with oil and phillips head screws (these were loose.) Otherwise they were the same. WTH?

>>what diff ? the CEN or the savage diff ?
The Cen Drive Pinion is held by a 5mm setscrew, rather than a 5mm drivepin like stock. Easiest way to get the pinion back in is to just pull the stocker straight out the diff case, leaving the drive cup on the center dogbone. Then just push the new pinion straight thru onto the drive cup, making sure to align the flat spot on the pinion for the set screw. Discard drive pin.

>>what does above mean, unless using some cvd condom or cvd cover ? easiest way to get pinion back in thru the bearings ?
The Cen gears are very, very hard. I easily drilled thru the 4 Savage output cups with the same bit w/ little wear. I needed to enlarge a hole on the spider gear brace for the cross pin to align properly, and it was a major PITA. It took forever and it dulled the bit. The cen gears are really really hard.

>>that sounds great! i like how the cen diffs use back plates for the small spider gears, rounded and decreasing te diff volume, making the grease not accumulate in the corners. Though a wrecked diff might act suicidal when little space it to throw away the 'baby teeth'. So I would like to know how to replace a savage diff cup with a CEN diff cup/center clamp piece.

If you manage to destroy these diffs.... Jesus I don't know what you are doing. At least the parts are cheap!

>>a little royalty is not too much to ask for anyone. Holy diffs, they rise again after 3 days no ? (lol)
can anyone show a pic of comparison of the savage cup (any kind) and the CEn diff cup/clamp piece?
sorry for quoting the wrong way, dunno how to quote right, a tip would be nice if applicable. Please post links to other threads of CEN difs /savage converted diffs if you know some good ones :)

First time back in forever and I happened to see this. Try to answer some ?'s you have.

It should be noted that this mod is basically obsolete ever since HPI came out with thier bulletproof diff set a couple years ago. This was done to replace the old savage diffs which broke fairly easy. I think the HPI's diff are better as the ring and pinion are machined rather than cast metal like the CENs. The CENs were better than the OLD savage diffs since the teeth were so large, but the newer HPI diffs have the same size teeth, but in machined steel for ultimate strength.

That way, all this modding is not needed, the parts drop right in and easy to find.

If you really want to continue, I'll answer what I remem, but its been a while.

-Only the savage diff cups are used. The Cen ring gear only fits on the cen diff body and vice versa. You go one way or the other, can't mix and match unfortunately. The HPI diff cups are needed as the Xl and Flux had larger dogbones

-The screws were 3x10mm or 3x12mm. No kit needed, just regular pan head screws

-thought I had pix of the spiders in the OP, guess not. No idea on weights, but performance difference would be negligable. Think the CEN spiders are stronger, but not really worth the effort anymore. The HPI spiders look like any truggy spider you would see. I'm sure there are truggy spiders that could replace the HPI spiders if you really had a problem, but likely not needed.