|
Savage CEN diff Mod- (Jesus Built My Differential)
With all the Fluxes coming out, as well as BL conversions, I'd thought I'd do a quick how-to on the Cen diff mod for Savages. Nitro motors break the stockers easily enough, so well see how the new Flux diff hold up BL power!
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. The Flux does use a stronger ring gear than other Savages, but still shares the diff cup w/ 10x16mm bearings and the weaker spiders. Also, given the huge pinion gear on the Flux's motor, a drop in drive ratio would be welcome. The Cen diff does have fewer teeth, to gives a final drive ratio of 2.89 vs the savages' 3.31. You will need to adjust gearing of spur/pinion to give same FDR. EG: 2.89/3.31*(std pinion)= new pinion size needed 2.89/3.31*(20T)= ~17.5 -> 17T or 18T pinion needed. You can play with ratios easier w/ BrianG's Calc. Cen Diff parts, and comparison to Savage Pinion, Ring Gear, and Diff Output Cups of a Sav XL: http://i7.photobucket.com/albums/y25...ndiffparts.jpg Notice just how much larger the teeth are: http://i7.photobucket.com/albums/y25...f/IMG_6189.jpg 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. 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. I've seen others use a 1/8" (0.1250") drill bit to do this. I used a 3mm (0.1181") as I didn't want any slop. In the end I had to do a bit of filing to the hole to get the thru pin through easily, as well as the spider bevel gear to go on smoothly. In the end I would prolly just go w/ a 1/8" bit for simplicity. Also, the Savage output cups are not as hard as I expected, so a standard bit cut through it fine. Be sure to take your time and get the hole as straight as possible. File any edges so the spider gear slides on easily. http://i7.photobucket.com/albums/y25...f/IMG_6199.jpg Reassemble the diff with the new Savage cups as well as a rubber shielded 8x16mm bearing. Don't use the unshielded bearing Cen uses. Fill w/ your favorite oils. 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.) http://i7.photobucket.com/albums/y25...f/IMG_6202.jpg One Diff to Rule Them All: http://i7.photobucket.com/albums/y25...f/IMG_6205.jpg Not quite done! 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 Time to reinstall the drive pinion and diff, check mesh, then seal it up and go! http://i7.photobucket.com/albums/y25...f/IMG_6206.jpg Notes:
If you manage to destroy these diffs.... Jesus I don't know what you are doing. At least the parts are cheap! |
NICE! I want to know how this holds up long term. If it came out of a Genesis I would imagine a savage would have no business stripping them.
|
Very nice detailed writeup! I will be doing this on my flm savvy as I plan to run cen wheels/tires and they are heavy!
I am wondering if you think the x diff cases are strong enough? I looked into getting the flm cases, with towers and the lst shock kit. Not too impressed with the "small bore" x shocks.... If the pastic cases the x comes with are good I will keep them, as I really do not want to spend another 120 bucks if I do not have to. Wondering if they flex enough to cause mesh issues? With the larger teeth on the cen diffs the flex may not be a problem...? |
Great How-to, i vote for a sticky :)
are you dyslexic? (reading the title, "jesus built by differnetial" |
Make it a sticky! Great how-to!
|
As far as cases go.. I do know the flux had upgraded cases. I would try those first before the flm ones, unless you really wanted them. I think you lose the quick removal capability too (all iirc)
As far as the title....dammit... Did you read that thread where I proposed greater edit functions? Ya, this is why lol Its supposed to say Jesus Built My Differential My other alternate title was "or How I Learned to Stop Worrying and Love My Differential," but it didn't fit. :) I better go PM Brian... 0_o |
I will give the stock X cases a try first. Just ordered the flm towers and lst shock adapters from Mike...
I had a look on ebay, seems like some of the diffs have different cases. The GST look to have plastic cases, while the nemisis have al cases. Are the diffs inside any different? Do they both have the al cups? And I also looked for the crosspins for the spider gears...are they really that expensive!!!??? |
Quote:
|
I happened to find an ad on RCU with a bunch of GST diff parts if anyone is thinking about doing this.
http://www.rcuniverse.com/market/item.cfm?itemId=486907 |
Quote:
|
I have also done this mod, for my brushless XL (neu 1515 1y 4s) So far the only thing I have found to be a problem is this. I used the drive cup that came stock with my cen gen diffs. After getting the pinion shimmed correctly it left very little of the pinion shaft sticking out of the savage bulk heads. It was causing the set screw in the drive cup to not fully seat on the flat on the pinion shaft. This caused my setscrew to come loose. So to fix that I grounf off a small amount of the end of the drive cup so that more of the drive cup fits on the shaft. Cant test this mod yet as there is about 10 inches of snow on the ground again. Global warming I sure.
|
Any reason you used the Cen drive cup? I used the oem Savage drive cup and there was room for the whole setscrew to contact the pinion.
FWIW: The F Cen diffs come with diff cups. The rears come w/ cvds. I had only rears. |
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......... |
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.
|
Silly q, where can I get these cen parts online? Already hearing stories of Flux diffs giving up!
|
Quote:
You can get them on ebay but I've seen them at online hobby shops but don't recall which ones. |
Quote:
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:
Good write up Finnster - hopefully I wont ever have to read it in more detail!!!:smile: |
Quote:
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:
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.
|
Cen diff review in Flux:
http://www.savage-central.com/module...=703271#703271 |
OH Noes!!!!!!
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:
|
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. |
Finn- I thought you went the way of the dinosaurs. Good to see you post, I hope life is going well for you.
My builds are going slow but plodding along. Peace brotha! |
hi finnster. the questions are for anyone who can answer too :) or add specs/pics
yes it may be to extend obsolete. but dont some people still upgrade to cen diffs ? the ring gear only has 26t vs27t so aren't these a bigger size/another pitch ? about those CEn input pinions, they surely lok like another type of teeth than their ring gear as well. am not too fond of their ring and pinion gear anyway.. i think the main idea/wish, was to have that CEN diff case fit onto savage ring gears. wondering if those cen cross pins would fit as well. as i have the savage diff, old and new(BP), they both have this alu alloy grey diff case, and actually i saw a broken one by foty. the CEN case seems better simply cos of easy of access when having two 'endbells', we could use xray m2.5x14mm pins in the 10t spiders, and much easier to shim the diff (rather than 'emptying the whole diff cup to shim the 10t spider gear inside the cup). the case itself looks stronger than the savage aloy diff cups. as per your answer, that ain't gonna happen then. but will the cross pins fit a savage diff then ? probably not ? so the cen spider gears are lesswide and taller than savage gears ? the 'diff cup' = diff output cup/out drive right, (cute kid has many names?) to use savage diff output instead or CEN, is this becoz the CEN outdrive is 8mm ID and not 9/11mm? is it a rumour or true that hot bodies d8 spider gears are harder than savage spider gears ? they look just the same. do anyone know what buggy spiders gears would be a preferred upgrade ? i have a mutilator diff, that i got an alu (novaRC) cup for, and had to drill a set screw hole to fit the pin inside the spider in the cup. the orig. plastic cup had this. the savage diff aloy cup is rounded off such way that there really isnt room for a set screw hole (would weaken cup alot). is novarc closed btw? can anyone recommend an upgrade diff cup for savage ? ill try make some comparison pics of savage dif parts and ofna/hobao mutilator diff, perhaps theres some interesting to conclude, perhaps not.. |
I dont think anyone messes with the Cen gears anymore.
|
Hot bodies is the best option. Related links.
http://www.rc-monster.com/forum/showthread.php?t=29094 http://www.rc-monster.com/forum/showthread.php?t=29113 |
| All times are GMT -4. The time now is 05:24 PM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2025, vBulletin Solutions Inc.