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Savage Diffs

guinnessdublin

Well-Known Member
Messages
324
Location
England
Have now gone through pretty much everything on truck apart from looking at my diffs, so decided to pull them apart. Looking at them apart from truck not being used for the last 15 yrs & when I last done them when being run regularly was agood 4/5 yrs. Totally forgot I replaced diff cups for metal when doing spider mod. Looking at them can’t see any real internal wear on cups or spider gears other then diff silicon missing, this was also not using any shims inside.
Replaced cup drive o rings & filled back up with diff silicon again hopefully good to go with no breakages later.
Was going to replace diff housing for up dated savage x design for ease of maintenance but due to having so many good spares & not having any real problems with them may hold off this to perhaps something breaks!
Are there better o rings/mod you can do to seal in silicon diff oil now & can anyone tell me the make of these diff cups please?
 

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Biddie_fiddler

Well-Known Member
HPISF Supporter
Messages
324
Location
Perth, WA
I'd also love someone else's opinion on diff sealing. If I leave my truck for about a week the diff fluid starts leaking out. I have put new o-rings in it to no avail 🙁
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
I haven't done anything special on my flux hp and X diffs. Both run the BP ring/pinion and HPI alloy cups. I do run 50K in them though, perhaps that's why I haven't had any leaking issues.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Interesting they have leaked out so quickly I have put 30k in mine, mainly because that’s what I had to hand.
What strength have you put in your diffs Biddle-fiddler?
Did wonder if as well as using paper gasket you could also use a right size o ring to make a seal?
 

Biddie_fiddler

Well-Known Member
HPISF Supporter
Messages
324
Location
Perth, WA
100k in mine 😂

I don't think the gasket is the issue with these diffs

Mine leaks where the drive cups come out (where the o-ring is supposed to seal it)

I'm going to order brand new diff bulkheads, and refill the diffs. I may be putting too much grease on the diff itself. Could be my issue 🤷‍♂️
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
When you fill them up do you just add enough to just cover spider gears?
Wonder if you could double up on o rings & use a shim to help push them down, then when it is all put back may help take up slop also?
 

mess1ah1

Active Member
Messages
87
Rebuild the diffs with new o-rings and use Team Associated Green Slime on the o-rings. That’ll help. Diffs are going to leak. All you can do is try to manage the amount and perform regular maintenance.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Point taken just my theory though is if all gears are meshed correctly the tighter it is surely is a positive thing & they would not have the scope to move as much?
 

Horatio

Member
Messages
37
Point taken just my theory though is if all gears are meshed correctly the tighter it is surely is a positive thing & they would not have the scope to move as much?
All the gears need to be meshed correctly anyway. Running the diff too tightly will definitely make matters worse and make the diff more likely to break/blow the seals.

Savage diffs are not great at sealing - there are numerous areas where they can and will leak, which at times feels like fighting a losing battle! 😂

Where the ring gear mounts to the diff cup, past the o-rings on each out drive - the odds are stacked against us! Then of course there is a tendancy for the screws that hold the ring gear into composite diff cups to back out with high torque motors.

My diffs are 16 years old and really need upgrading. Diff access isn't the easiest, so maintenance is a labour of love!

I'm thinking about upgrading to bullet proof diffs 9/29. Alloy diff cups. If they can handle brushless, they should be fine with my STS .30! 😁
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Yes have been thinking yes/no about upgrading to easy excess diff housing, just have 2/3 pairs of new old type still which was thinking be a waste to just bin but think I will just so I can inspect/maintain diffs easier!

What are the HPI composite bulk head set you can get from HPI benefit from having?
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
If i upgraded to the HPI Bullet proof 29t/9t bevel gear set apart from supposedly lasting longer would you actually notice any real difference in speed/acceleration then the stock 43/13t fitted, what’s your experience/views please?
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
If i upgraded to the HPI Bullet proof 29t/9t bevel gear set apart from supposedly lasting longer would you actually notice any real difference in speed/acceleration then the stock 43/13t fitted, what’s your experience/views please?
I think it would be a bit faster. About the same as dropping 1.5T on the spur:
ring/pinion difference: (43/13)-(29/9) =0.085
spur/bell difference: (48.53/18)-(47/18)=0.085

So like having an 18T bell and going from a 48.53T spur to a 47T spur. I know 48.53T doesn't exist, was just adjusting it until the math lined up.
 

guinnessdublin

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Messages
324
Location
England
Okay thanks for info very interesting, although of all the years of having savage & racing at weekends can’t recall a problem/fail with diff using the 43/13t set up. Having said that I did early on do the 4 spider mod & upgrade to metal diff cups which I guess helped greatly! 👍🏻
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
Okay thanks for info very interesting, although of all the years of having savage & racing at weekends can’t recall a problem/fail with diff using the 43/13t set up. Having said that I did early on do the 4 spider mod & upgrade to metal diff cups which I guess helped greatly! 👍🏻
I had issues with them quite a bit until I got the machined ring gear (vs the sintered) and used alloy diff cases (the large box the entire diff goes in) and shimming for good gear mesh. That was with the older style pre-X diff cases. Then they held up ok unless that bearing blew out, then it would take the tips off the gears usually before I caught the problem.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Done a fuel tank today to test out my newly filled diffs & what a difference. Before when diffs were void of any diff oil & running somewhat dry, what I was finding when running in new engine was I would have liked idle speed higher but had to balance it slightly otherwise it would start making the truck move forward.
Today what I found was I could have idle set higher to aid smoother running & found this would not move wheels like it was doing prior to rebuild of diffs, this may also be down also to new broken in engine starting to settle down some more I don’t know?
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
Yeah, I don't see how diff fluid would change your experience with truck movement, unless you now have binding you didn't have before. Would make more sense that your engine is starting to calm down a bit and stabilize. Either way, sounds like your on the way to having fun instead of headaches!
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Yes engine is miles better running now my only concern is idle is not what I call a constant rpm it does still seem to fluctuate very slightly (May try a new g/plug next time) engine temp was around 167 at one point & if I Richen up HSN anymore it will unscrew from brass barrel.
My theory with diff oil was now it is in diffs its acting as some sort of friction for movement in drive train to have to fight against it?
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
167 is cold. You should probably lean it out some to get it up above 200F.

When driving in a straight line, the diff oil has no impact on anything. Diff oil only affects things when your turning and the left/right wheels aren't spinning the same speed.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Okay thanks for info, what I should of said also was when I noticed wheels moving this was with truck raised off floor!
Sorry typo meant 267f not 167f reading, when does it get dangerous to engine life?
 

olds97_lss

Well-Known Member
Messages
2,475
Location
Dekalb, IL 60115
Okay thanks for info, what I should of said also was when I noticed wheels moving this was with truck raised off floor!
Sorry typo meant 267f not 167f reading, when does it get dangerous to engine life?
When you stop seeing a decent amount of smoke and get a lean bog when you give it throttle usually. I know some have had good performance beyond 300F, but any engine I've had seemed to run well between 240F and 275F. Some run on the lower end of that, some on the higher end. Usually when any engine I have gets up to 280F, it performs bad, sounds bad and smoke is minimal.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Currently have loads of smoke all through throttle & isn’t bogging at any point, will keep an eye on temp specially when I start using it with body shell on! 👍🏻
 

Horatio

Member
Messages
37
If i upgraded to the HPI Bullet proof 29t/9t bevel gear set apart from supposedly lasting longer would you actually notice any real difference in speed/acceleration then the stock 43/13t fitted, what’s your experience/views please?
The 29/9 are engineered with fewer but bigger teeth. For this reason, they are better able to cope with the much higher torque from brushless motors etc. Thus, they are a bullet proof option for nitro users wanting to upgrade.

The ratio between them 29/9 vs 43/13 is slightly different, so both ends of the truck need to be converted at the same time.

29/9 = 3.22
43/13 = 3.3

The 29/9 option would give slightly higher top speed / less acceleration for any given clutch bell spur compared to 43/13, but it wouldn't be perceivable.
 

guinnessdublin

Well-Known Member
Messages
324
Location
England
Okay thanks for input, think I will stay with original 43/13 as now have 2/3 sets kicking around & have never had one break/fail on me!
 
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