Savage 6768 CD Parts build

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Savage 6768

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Have decided to build my own cd conversion from all my parts I have lying around. Picked up a onfa truggy roller real cheap with all the parts I needed ( motor mount and Diffs )
Started pulling everything apart and mocking up the motor mount to the savage tvp. Have had to make up a alloy block and mounting plate to get the motor set up in the middle of the tvp to get front and rear drive shalf to line up in a straight line to the diffs. So far all pretty good. Photos so far :)

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Savage 6768

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Got the motor mount bolted up to the tvp. Hit my first problem as using the standard flux hpi drive shaft from center diff so from the cd to rear diff is 120mm pin to pin and at first couldn't find a drive shaft :argh: so spent next hour going through all my spare parts and found a drive shaft from a hsp truggy ( result :woot: ) only problem the shaft is a bit on the small size only 4mm dia but will see how it goes.

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Jam Racing 1

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Man that is alot of motor to have hanging out in space with no support on the end, otherwise looks good.......
 
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Savage 6768

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Man that is alot of motor to have hanging out in space with no support on the end, otherwise looks good.......
Yeah just been looking at that. Doesn't seem to have any flex but I think I will have to make up some kind of support to go under the motor plus will help tie the tvps together.
 

Northernnightmare

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Looking good, is that a ofna motor too?

It do look big like that but thats a good thing ;)
 

xtremsavage

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Looks good. I can't fully remember off hand, been awhile since I've wrenched on the savvy or did any major research, but I'm thinkin the dogbones that go fron the diff to the axle will be the length you need. I'm pretty sure they are 123mm pin to pin. Just a suggestion.
 

olds97_lss

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Man that is alot of motor to have hanging out in space with no support on the end, otherwise looks good.......
It's surprising, but that's how many brushless motors are mounted. Like almost all the arrma vehicles, the e-revo as well. Just a couple 3mm bolts holding it on from the front. In some cases, 4mm bolts. After having the motor in your hand, it's hard to imagine that's all that holds them on.

My concern would be more the TVP itself flexing if the center diff mount isn't tied in to the other TVP as well. The TVP's will bend pretty easily in the open space with your hands. The ladder structure the truck has is what makes the TVP's strong.
 
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Savage 6768

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It's surprising, but that's how many brushless motors are mounted. Like almost all the arrma vehicles, the e-revo as well. Just a couple 3mm bolts holding it on from the front. In some cases, 4mm bolts. After having the motor in your hand, it's hard to imagine that's all that holds them on.

My concern would be more the TVP itself flexing if the center diff mount isn't tied in to the other TVP as well. The TVP's will bend pretty easily in the open space with your hands. The ladder structure the truck has is what makes the TVP's strong.
The whole motor mount is bolted to both tvps I have made it to fit by using alloy block and bolted to the top alloy plate ( sorry no photo ) but you can see the mounting hole in one of the previous photos
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Savage 6768

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Now just got to work out what weight oil or grease to run in the center diff ? ( any idea ) At the moment spur is 50t/ pinion 11t. Front and rear bullet proof diffs are filled with 30 weight oil and will be running 6s.
 
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Just been looking online at what oil everyone using in there center diff conversions and I am a bit confused :confused: . I see most use between 100k - 500k I gather that is weight not cst weight as 500k cst would work out to be 40 weight. Is that true ?
 

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Now just got to work out what weight oil or grease to run in the center diff ? ( any idea ) At the moment spur is 50t/ pinion 11t. Front and rear bullet proof diffs are filled with 30 weight oil and will be running 6s.
I'd say go with 75k or thicker. I also run thicker oil in the front diff as compared to the rear. I'd have to go back to my build thread to see what I filled my diffs with when I did my IRC build. Keep in mind, I'm also runnin nitro and not brushless.
 
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Savage 6768

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I'd say go with 75k or thicker. I also run thicker oil in the front diff as compared to the rear. I'd have to go back to my build thread to see what I filled my diffs with when I did my IRC build. Keep in mind, I'm also runnin nitro and not brushless.
Thanks for that. ha ha was just about to order some Traxxas 500k ( that would have been a mistake ) :oops:
 

xtremsavage

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Thanks for that. ha ha was just about to order some Traxxas 500k ( that would have been a mistake ) :oops:
You can use that, but it would give it an almost locked feel front to rear. Kinda like using the original center box and gear set-up. I've got a wide range of diff oil from 5k to 50k and one bottle of 100k.
 

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If your not sure what to go with, just make sure to buy from the same mfr if you get a few different weights as they vary quite a bit from one company to another. Sticking with one brand at least helps you be consistent when you go up or down in weight.

I try to stick with mugen now that OFNA isn't available. I use mugen 50k wt in front/rear diffs. Could probably use higher, but that's all I had on hand the last time. I probably should have used 75k or 100k. With that in mind, guessing I'd want even thicker for the center if/when I go that route.
 
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Savage 6768

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Getting closer to completing. Gave the motor mount plates and tvps a coat of paint. Also made up some battery mount brackets going to be using some Redcat Xbe battery trays. Also sorted out motor esc combo I am using the hobbywing 2250kv motor and the esc is the redcat rtr 150amp esc which is also a hobbywing. Still haven't decided on what oil or grease to use in the cd but looks like it will be 100k - 150k when I fine some. I know its probably an old mod but might try the silicone putty ear plug method ?
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xtremsavage

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I know its probably an old mod but might try the silicone putty ear plug method ?

What do you mean silicone putty ear plug method? Never heard of that, but been out the RC game for awhile.
 

olds97_lss

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With that (silly putty or earplugs) you will lose the lubrication the oil will give you. With all the brushless stuff around these days, you can get some seriously thick oil, 1M weight... that has to be like tar.

I just ordered a center diff trans from rc4me and I intend on starting with 100k associated oil in it. I also ordered 200k just in case. I have 50k mugen oil which I use for front/rear diffs, but I don't think it's nearly thick enough for a center diff in a MT. It was fine in a 1/8th buggy with smaller tires, but guessing I'd get a lot of front wheel unloading if I ran that in a center on the savage. It will suck though as replacing the oil means tearing down the trans... really hoping 100k is good. lol
 
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Savage 6768

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I know its probably an old mod but might try the silicone putty ear plug method ?

What do you mean silicone putty ear plug method? Never heard of that, but been out the RC game for awhile.
Basically instead of filling the cd with oil just jam the silicone ear plugs into the diff it acts like a locker but still has some diff action. I have heard of some guys have been using it there 8s xmax. They been using the Macks silicone putty ear plugs.
 
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Savage 6768

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With that (silly putty or earplugs) you will lose the lubrication the oil will give you. With all the brushless stuff around these days, you can get some seriously thick oil, 1M weight... that has to be like tar.

I just ordered a center diff trans from rc4me and I intend on starting with 100k associated oil in it. I also ordered 200k just in case. I have 50k mugen oil which I use for front/rear diffs, but I don't think it's nearly thick enough for a center diff in a MT. It was fine in a 1/8th buggy with smaller tires, but guessing I'd get a lot of front wheel unloading if I ran that in a center on the savage. It will suck though as replacing the oil means tearing down the trans... really hoping 100k is good. lol
That's what I was worried about. I can get hold of some 1 mill associated oil so might also try that too. Apparently if you put some diff oil in the diff with the silicone ear plugs that helps with the lubrication
 
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Actually... no, it's associateds 200,000cst oil. Will probably show up and be watery shock oil or like my 10k wt ofna oil and I wasted $15 on the 100k/200k cst oil. The 200k was ASC5461.

https://www.teamassociated.com/parts/fluids/diff_fluid/

Got it on ebay though.
That's the problem with everyone saying they run 100k -200k. Like you said every manufacture seems to use different measurements
( Weight vs CST ) Good luck with the new CD, cant wait to hear what you think about
 

olds97_lss

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Well, I'll let you know what the associated 100k/200k look like when they show up. All I really have to compare to is some old OFNA 5K (I think) and mugen #50000 oil. I use the mugen now for my front/rear diffs, which is like honey coming out of the bottle. But once I put tires on, they spin pretty easily. With the diff in hand, turning the output cups feels like concrete. Funny how a little leverage makes it seem ok. I get decent power to the ground when one tire is in the air, but it's by no means "heavy" as far as I can tell, which is why I was trying to find a 100k equivalent.
 

xtremsavage

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I suggest trying to stick with Mugen for your diff oils. They are pretty dead on with their oils when they are tested for viscosity. Same goes for their shock oil. Which both are measured by wt instead of cst, I believe. I read an article that was posted on here yrs ago about shock oil comparisons (manufacturer to manufacturer and # wt viscosity test and its equivalent to cst #). I think it even had diff oil on there too. I do remember about Mugen bein 99% spot on on the test #s and HPI shock oil was right along side Mugen.
 

xtremsavage

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Also, another trick when building your diffs that I learned from a racer is to coat the O-rings with a extremely heavier oil than what you use to fill the diff or something specifically made to coat them to help seal around them better. I've rebuilt diffs and used brand new O-rings only to have them leak before I even installed them. I also use Mugen diff gaskets cuz they seal alot better for some reason.
 
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