Diff Question

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Monkey Wrench

My last words will likely be, Crap that didn't wo
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I recently broke the front diff in my Revo down because I thought I may have blown it out due to the left front wheel spinning freely (turned out the wheel nut had backed itself out a bit and the axle pin slid out, so much for checking the obvious first, huh?)

Anyhow, as I had some RD Logics aluminum diff cups, I decided to rebuild it and use the RD cup versus the stocker. The diff gasket was shreaded, so rather than have to buy a new diff set for the gasket, I decided to use RTV sealant.

Here's my issue. I put the pinion and spider gears in, filled the diff cup with 7K fluid then added the other pinion and crown gears. Once I tightened the bolts that hold the crown gear to the cup, the diff acted as if it were locked. It took a fair amount of effort to spin one side while holding the other still. If I loosened the crown gear bolts a bit, it was easier to spin one side. I went ahead and tightened them down to the point where, if I slide a hex wrench through each yoke hole on the outdrives, I could counter-spin them. The dff felt a little "choppy", but I racked that up to the fluid getting worked in around the spiders and internal pinions. I did not shim the diff as it didn't need it (no measurable play with the internal pinions).

I installed the diff back into the Revo, went out and ran it and it seems to be working alright, although I can hear a bit of clicking from the truck when I jump on the throttle. It also seems as if I've lost a bit of the high end speed, but that may be as a result of my mill finally going in the crapper. I changed the tranny gears out from close-ratio to standard-ratio and am going to be changing the CB from 16T to 15T but keep the 36T spur.

So, in regards to the front diff, does it seem normal to be that tight on a rebuild? I'm fairly certain I put 7K fluid in it the first time, but don't recall it being that tough to spin. Does anyone else use the RD cups (or aluminum cups) and have the same results?

I hope this makes sense, but if I need to clarify something, let me know.

Thanks!
 
Did you fill the cup completely up or just to the top of the pins on the spider gears?
 
Just a bit over the spider gear pins, but not quite all the way to the top. You think too much? Never thought of that.
 
Just curious, Did you allow the RTV sealant to dry prior to fully tightening down the crown gear? I have thought about using that as well as a last measurement. I have never used the RD cups before so I am not sure about your issue.
 
I let it set-up for about two minutes then attached the crown. One of the fellas I raced with about two Sunday's ago suggested it when I mentioned my front diff was leaking. He said that's all he does now to seal his diff's. I also heard from the LHS that the diff gaskets from a Jato work as well, but I cannot verify that. I may stop by and see if he has any and try that.
 
I know the gasket is thin but is it possible that it's just thick enough to give the right amount of space between the diff halves so you can tighten it down and still spin freely?
 
I have spare diff from my LST to try this on. I will se eif I tighten all the way down with ni gasket, will it bind? I will let you know. We are talking about a small space. It could be the culprit but I will have to see for myself. Anyone have a REVO diff to try it out on?
 
if memory serves me right there are no shims inside the Revo diff. This would lead me to believe that the gasket provides the clearance needed so when tightened it's not binding up. Also why so light on the fluid? Stock is 30,000, I would think it would allow too much power to the front and make you very loose off, as well as major ballooning. As far as level, I think Xray and Mugen are now saying 70% full.
 
I know the gasket is thin but is it possible that it's just thick enough to give the right amount of space between the diff halves so you can tighten it down and still spin freely?

Good point! Never thought of that, but I figure I have a heavier bead of RTV in there versus the stock gasket, BUT, I may not have waited long enough for the RTV to set-up and it could've compressed itself out of there. Good idea, SMaxxin, never considered that.

Also why so light on the fluid? Stock is 30,000, I would think it would allow too much power to the front and make you very loose off, as well as major ballooning. As far as level, I think Xray and Mugen are now saying 70% full.

Not sure, just wanted to feel pretty, I guess! The front tires do balloon like crazy, so I probably will add a heavier fluid. Suggestions? May go 50K front, 70K rear.



EDIT: Stopped by the LHS durnig lunch and picked up a couple Jato diff gasket sets (only $1.00 a piece) and I'll give the one up front a whirl. The gaskets do look exactly like the Revo gaskets.
 
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Well, the culprit is the aluminum diff cup itself. Installed the new gasket, added 30K fluid and got the same results.

Decided to try using the stock cup and it's as smooth as silk!

Only thing I can think of is the aluminum cup is warped or something.

Oh well, live and learn!
 
You said you bought a couple of gaskets right? Try two... The aluminum cup may be countersunk a bit more. It's worth a shot if you still have it apart.

I made the mistake of leaving the gasket out of my savage once... I couldn't even hardly turn the diff. Fortunately I spun it before installing it. I would have been pissed to blow a brand new diff.
 
I recall hearing problems with the RD dif cups many moons ago, don't remember what it was but everyone switched back to the stockers. 30K front and 50K rear for me with the TM
 
Sorry for changing the subject MW but I like you so I'll do it anyway. Don't get excited, I don't like you like SD does.

I have been trying to pat attention to what diff/ shock oils everyone is using because my suspension tuning skills or non existent, what weight oils come stock?
 
I recall hearing problems with the RD dif cups many moons ago, don't remember what it was but everyone switched back to the stockers.

Well, thanks for the tip, Mr. Johnny-Come-Lately! May have wanted to share that earlier before I shitcanned a bunch of diff fluid trying it out! Then again, you are the same guy that failed to tell me what the marshalling pylons were for to begin with, so you're par for the course! May you judo-chop yourself in the balls someday!

Don't get excited, I don't like you like SD does.

Hey, I don't like the way SD likes me! He's been talking about moving to Massachusetts for some reason...

Like you, I have no real suspension tuning skills. I put 30K fluid in the front and will put 60K in the rear and see what results.
 
I thought they were cracking at the screw hole or something, not the problem you mentioned, though, in reality it may have been from that. Glad I could help, now come on back down from Brokeback before you and SD get Buttbroke!!
 
HA HA HA HA...funny guy........NOT!

Anyhow, went ahead and dug the rear diff out. Broke it apart and it was dry as a bone! Spiders and internal pinions looked good, so, replaced the pinion gaskets, gave everything a thorough WD-40 bath, added 60K fluid and attached the crown gear. As I'm setting the diff into the diff case and greasing the crown gear, I noticed there's a wave in the crown gear. Spin it around and few more times and sure enough, a definite wave. Tighten the four bolts holding the gear to the cup, same thing. Spray the grease off and, son-of-a-biscuit-eater, one half of the gear had been worn down! Obviously, dumb-ass me clearly did not make sure the crown was bolted to the cup squarely when I changed diff oils last time. Explains why it was bone dry as well!

Ah! I'm just glad I noticed before I had the whole thing back together! Hi-ho, hi-ho, off to the LHS I go!
 
Sell what, my Revo? Nah, I love this thing to much! I just need to make sure I install the crown gear nice and evenly when I replace it! It wearing out was a direct result of my own stupidity! Fact is, the rear end was operating fine! I never notice and performace lag from the uneven stripping! Kudos to the Revo, she just kept on trucking!
 
I was just giving you a hard time. I've contemplated getting rid of my savage because of my revo... but I just can't part with something that gave me that many good memories. Besides, I just got it to the point that I like to drive it just as much as my revo.
 
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