What did you do to your HPI Savage today?

Biddie_fiddler

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Direct from Freudenberg Sealing Technologies (FST) themselves- a manufacturer of O’Rings:
“Generally silicone o-rings don’t go well in silicone oils, Nitrile should be good with silicone oils. If they are in fact using silicone o-rings in silicone oils, there maybe some additive that is being used that requires the silicone o-rings that we don’t know of. Silicone can take high temperatures and has a long life, but they are not a very good dynamic seal due to low abrasion resistance. They would be okay in a static application though”

I don’t know why, but silicone orings have very poor chemical resistance to silicone based oils. Every site that labels chemical resistance for their silicone orings all state this.

I’m not gonna lie, I feel like this is done on purpose so replacement parts are required more often. You seen the price for replacement orings?!
from Australia’s FST branch, they’re 23c each (and this is for low quantities)! From the hobby store it costs $16 for 8. WTF!!!
I bought 20 orings for $10 today
10 6x2mm and 10 6x2.5mm. Gonna see if I can squeeze the 2.5mm in the diffs xD
 

lokky

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241
I cant say I have any major issues with silicone o-rings in diffs, but would be good to hear if nitrile fair any better. If you know the o-ring size then there are plenty of alternative cost effective suppliers rather than the OEM supplier. I tried some thicker diameter o-rings in a diff recently and they affected the mesh with increased friction.
 

lokky

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Question is are silicone o-rings pure silicone or compounded with other elastomers to improve shear resistance and tensile strength.

You never really know the full spec.
 

xtremsavage

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@xtremsavage do you happen to know what material they are?

I'm buying some nitrile ORings from an O'Ring supplier we use at work. After talking to their team they are very puzzled as to why silicone O'Rings are used with silicone lubricants. Not a good mix - same can be said for silicone O'Rings used in shocks. what a dumb design.

The O'Ring supplier said that the silicone O'Rings may have some additive in them to prevent wear.

Either way, if these nitrile ones go well. I'll consider doing a bulk order and selling some as wee kits. Turns out 6x2mm O'Rings are quite common!

Not sure. But like I said, mine haven't leaked since I rebuilt them 5-6+ yrs ago. And my garage sees temps in the 110-120° degree range during the summer and 30-40° degree temps in the 3-4 months short winter season. And with the hotter temps in my garage, every liquid becomes a little thinner.

Oh, and I also didn't use the HPI gasket either. I used the Mugen gasket instead.
 

Biddie_fiddler

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Went to reddit for the answer. Here is it, and yes I do remember this from chemistry and first year of uni 😂
5C984D27-079D-4DD4-8A0E-637425AABC24.png
 

lokky

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241
The way I read and try to understand the above is that silicone is not generally recommended for o-rings used in dynamic applications, I don't see or read evidence that there is any significant chemical incompatibility with silicone shock oil. You then have to consider whether the diff o-ring is under significant dynamic stress. I think issues with leaking diffs maybe due to manufacturing tolerances in diff cups and o-rings (how many brand new cars have you seen with leaking diffs), along with compression set and wear over time (how many used and stored cars have you seen with leaking diffs). Only a scientific experiment with controls could prove any difference in performance of silicone vs nitrile in diffs using shock oil, but there arent any as far as I know. Alternative is to get some nitrile o-rings, fit them say in the front diff, fit new silicone o-rings to same size spec in rear diff, then run them in car for x hours. Swap the front diff o-rings to new silicone and rear to new nitrile and repeat and assume any results are reproducible and robust. Leaking is as much likely from the gasket seal and gasket material and thickness can vary, as well as how tight the screws remain during use. Leakage rate is also dependant on the viscosity of the silicone oil, in experience using above 20K reduces it. Different shock oils may have different additives/impurities, which may have a chemical reaction with silicone, as I am not sure that the shock oil is 100% silicone. I'll get some nitrile o-rings for the next time I rebuild some diffs and will see if they show any benefits over silicone. The more evidence the better.
 

Biddie_fiddler

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Ever notice a silicone oring go hard after some time in a diff or shock? It’s because the silicone is being sucked out of the oring and into the oil. Just science 🧑‍🔬

but they are clearly the standard in the industry and there has to be a reason why 🤷‍♂️
 

lokky

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241
Osmosis is it, unfortunately not seen any shrivelled hard o-rings in diff or shocks, usually the o-ring in the shock cap seal gets stretched due to over-tightening the cap and not experienced any leaking issues with the o-ring seal on the shock shaft. The diff o-rings always appear fine from what I remember after stripping a diff, even if it has leaked. Most new rtr cars don't come with silicone diff oil, usually grease, or do they now?
 

Biddie_fiddler

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Some center diffs come with silicone oil in them, just bought an arrma center diff for the alza center diff conversion. Came with 100k silicone oil in it.
I'm gonna be stripping it and putting a much higher weight into it, I'll check what material those are made of. They might not be silicone.

You are right tho, now that I think of it. Diffs usually come with grease in them and not silicone oil 🤔
 

lokky

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241
Other problem is overfilling the diff with oil, I try not to go above the cross pin level. Too much and it will forced out. I think I put 500k last time into centre alza diff and seemed to keep front down more.
 

guinnessdublin

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Thought I would use Moogocows idea he used on jazzing up his TVPs by covering with carbon fibre & freshen up my now off white dish wheels with still good dirt bone tyres on!
 

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mrmiro

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I sent it a little to hard. popped a wheelie, next thing she was cartwheeling. Minor repairs.
 

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olds97_lss

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Having them up like that kind of kills the LCG the TVP's give you. Probably better off at least making it wider from front to back so you don't have to stack them. Will lower the COG a bit.

Looks nice though. Did you make the TVP's? Alza center kit or did you make that too?
 

Goose1072

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Having them up like that kind of kills the LCG the TVP's give you. Probably better off at least making it wider from front to back so you don't have to stack them. Will lower the COG a bit.

Looks nice though. Did you make the TVP's? Alza center kit or did you make that too?
Those are not the batteries I will be using with this truck, the only ones I had at the moment. I just ordered some hard case batteries, 6s and 8s single battery. LCG is pretty good the weight on the truck is perfectly balanced, I am also using rear Baja wheels so the truck is extra wide.

The TVP's are custom and had them made a long time ago when the truck was gas, came with the rear drive shaft since its custom. The center is Alza and wish I had made this change years ago, so much better tahn the stock tranny.
 

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carldav

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Used a custom lower arm hinge pin braces (+13mm offset) and Tekno Truggy universal driveshafts:
 

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Seanthemechanic

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I found a brand new body on eBay so I threw that on and also a set of DirtBonz!
 

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olds97_lss

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I found a brand new body on eBay so I threw that on and also a set of DirtBonz!
I have that one on my flux HP. Got it on ebay a couple years ago. Isn't too dinged up yet.

If I drove the savage much, I'd replace it with a probodyrc one. But I haven't driven that thing in over a year. Thought about taking it out a couple days again with my stampede, but went with the outcast instead.
 

Seanthemechanic

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I’ll be nervous to wreck this body! I think I’ll leave it as a shelf body. Who knows when I’ll be able to get another one. I was thinking about getting an outcast. How’s it holding up for you?
 

olds97_lss

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I’ll be nervous to wreck this body! I think I’ll leave it as a shelf body. Who knows when I’ll be able to get another one. I was thinking about getting an outcast. How’s it holding up for you?
After doubling the cost in upgrades... it's doing fine. ;)

Really, M2C chassis, towers, rear tower brace, any alloy chassis braces, aftermarket servo, RPM front bumper, t-bone rear bumper/skid/wheelie bar and some TLC with the diffs, it's pretty good.

If you don't launch it like I do, you may not need all of that, but if you do, then you do or you end up replacing broken stuff a lot more often, which adds up.

I've made it 4 pretty harsh bash sessions as of late with minimal damage. Broken wing mount, body mount, shock ends and one axle carrier. I launch this thing pretty good though and a wreck at 50mph from 15 feet in the air... nothing will survive that more than once.

This was my last bash and I was pretty easy on it:

I'll guarantee you my savage wouldn't have driven away from some of those awful landings. I've bashed it at that place a couple times and it doesn't end well. Something on it always gets mangled and I don't drive it nearly as hard.
 

Seanthemechanic

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After doubling the cost in upgrades... it's doing fine. ;)

Really, M2C chassis, towers, rear tower brace, any alloy chassis braces, aftermarket servo, RPM front bumper, t-bone rear bumper/skid/wheelie bar and some TLC with the diffs, it's pretty good.

If you don't launch it like I do, you may not need all of that, but if you do, then you do or you end up replacing broken stuff a lot more often, which adds up.

I've made it 4 pretty harsh bash sessions as of late with minimal damage. Broken wing mount, body mount, shock ends and one axle carrier. I launch this thing pretty good though and a wreck at 50mph from 15 feet in the air... nothing will survive that more than once.

This was my last bash and I was pretty easy on it:

I'll guarantee you my savage wouldn't have driven away from some of those awful landings. I've bashed it at that place a couple times and it doesn't end well. Something on it always gets mangled and I don't drive it nearly as hard.
Yeah you take bashing to a whole other level! That’s insane! I’ve seen some of your videos and you’re nuts man lol. I found a used one locally with a few “upgrades” I think I’m going to scoop it up. It’s in great shape
 

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