Good differential replacement

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h00vy

h00vy

Member
Messages
45
Location
Lancaster, PA
My truck sat for quite a while with a broken front differential. I finally had time to fix it (stripped pinion) and took it out for a drive. I had 1/2 a battery pack through it, and the rear differential went south. I figured it was the pinion again, so I ordered 'HPI 102692 Bulletproof Machined Differential Bevel Gear Set', just like I did for the front. I may have ordered an extra set too... Anyway, I removed the rear differential only to find that the gears were not stripped, but the differential housing split open in 4 places. I think the screws may have come loose holding it together, and it eventually exploded.

I can't seem to find a complete differential to purchase. Can I just purchase a Hot Racing housing, and move my spyder gears over? What is the best plan of action?

By the way, this truck has only ever been running on 4s, and never sees blacktop, except the last 1/2 battery, which may explain why it tore up on me.

Thanks,
 
If I use 'HPI Alloy Diff Case Savage X Ss', is it ok to reuse the spider gears? Or what do you think for simply eliminating the spider gears, and lock the axle?
 
You can reuse the spider gears.
Don't forget the shims.

Locking is possible. But only recommended for off-road use only. So you will be fine..
 
WP_20160926_20_11_23_Rich.jpg I inspected my differential a little closer tonight. Hmmm, I don't think I'll be reusing the spider gears. The one is chewed up pretty bad. Now I have to decide if I want to build a differential from scratch by using HPI 86827 & 86032, or lock it with Hot Racing's locker. I can't really find any reviews on the locker though. Any thoughts?
 
I wouldnt use any of those gears again actually, looks like it was not lubed and grit and all built up causing the diff cup to break.... build it all new and pack the differential with heavy grease, red hi temp stuff works well....
 
This was the first time I had the rear diff/bulkhead disassembled. Three of the four screw caps were snapped off that hold the differential together. It was really gritty, although now metal 'chips'. I'm not sure in what order things went bad, but there were quite a few things that were not right.
I'm going to rebuild the differential with new spyders, bevel gear, thick grease, upgrade to Boca bearings and put it back together. I already did all that to the front, except of grease inside the diff, I used Traxxas 30k oil. I'll either use the 50k grease, or the wheel bearing grease that I have.
 
When I rebuilt the front, I was amazes how much a difference 30k was then stock. Stock (or pre-rebuild) was very loose. That's why I was considering 50k for the rear.
 
If you go thicker on the rear diff you will have problems with steering.
The rear wheels will push harder resulting in udersteer.

But so does locking the rear axle only.. :) :)

My savage has 50K in front diff, 300K middle diff and 30Krear diff..
 
Does adding a middle diff to the Savage mainly keep it from doing wheelies as much? How else does it effect handling and traction?
 
Lots of Flux users do it to eliminate wheelies.
I did it to make my nitro handle better. Corners a lot better and I just had to try. The center diff came from an HPI Super 5SC and is a direct replacement. And I still have the mechanical brakes..


Only thing is you have to ee gear when you want to do this. I am at 17/43 now but it will go to 20/43 in a while.
 
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The way I'm shredding differentials, I wouldn't want another one to break! ;) I'm simply going to back down the punch control with the ESC to hopefully lengthen the life of the truck (until I can handle it better). I had backed it down a little bit already.

It already had the XL frame, and it pulls a wheelie pretty good. I can't imagine how undriveable it would be to have the short wheelbase and punch control at 100%. (I bought it very slightly used on the Bay, with some modifications done already)
 
Caretaker109 said:
Best thing you can do is upgrade to the BP gears, you have the HD gears i guess.
Click to expand...
From what I understand, and judging by the part numbers, the Flux HP already has the BP gears from stock? At least in the manual it gives #102692. That is the BP one, right?
 
Caretaker109 said:
102692 are the correct ones.
But what you showed us in the pic aren't the same.
Click to expand...
Seriously? How can you tell? Like I said before, I never had this particular one apart before, but I don't know what the previous owner did.

Regardless, I will be replacing all the gears and will be using #102692 BP gear, #86827 housing and #87193 internal gears. Hopefully that fixes it up.
 
Hmmm.. After looking at the pic on a bigger screen you do have the BP gear...
But I think they are the sintered and not the machined. Machined are a lot stronger.. Machined are black and sintered metal color..
The parts you will be using are going to fix all the problems you might have had. :)


And don't forget top shim them properly and check the bulkheads, they might have some flex.. And replace all bearings just to be sure..
 
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Ya, I ran into a shimming issue the first time. I got it shimmed where I felt comfortable, then I disassembled it to insert the pin, reassembled it and locked the screws down. And when I tightened the screws, it shortened up the diff and had too much play. So I had to disassemble it again to add a shim.
The first diff rebuild took about 2 evenings (including help from my 3year old) But assembling and shimming/installing the next one should take half the time.
 
Yep, that is a (rookie:) :) ) mistake... Just use 2 of the screws and tighten them to make sure this doesn't happen again. :) Then add the shims and take it apart again. Don't forget to add the gasket to the ring gear.. Or you will tighten it too much for the spidergears.
 
Thanks for the tip! I should be getting the parts this week yet, and they're calling for rain on Saturday, so I may be stuck inside. Perfect timing to work on it!
 
I know this is an old thread, but do you have to use threadlocker on the diff case screws? Nobody local has the green. Only red and blue. I haven't even taken it apart because I don't have that to put the screws back properly. Currently waiting on a drive gear and wanted to take care of some other maintenance while waiting impatiently. hehehe
 
Awesome. One last thing if I may..... when I read that i am to "pack with grease" is that literal? Or do I just apply a generous amount? Sorry if this sounds stupid, but I am new to all of the maintenance with these fantastic machines. I would like to keep it running for a long time. Would also really love to purchase a used nitro savage to replace my t-maxx at some point when I have alittle to spend. Can't get enough of these savages
 
derikmills said:
Awesome. One last thing if I may..... when I read that i am to "pack with grease" is that literal? Or do I just apply a generous amount? Sorry if this sounds stupid, but I am new to all of the maintenance with these fantastic machines. I would like to keep it running for a long time. Would also really love to purchase a used nitro savage to replace my t-maxx at some point when I have alittle to spend. Can't get enough of these savages
Click to expand...

I pack the inside of the differential with heavy red grease to slow down the diff action, and use a light coat of white lithium on the ring gear prior to installing the diff assembly into the bulkhead...

you only need the blue locktite when using the alloy diff cup also which are highly recommended due to them holding the internal gears more precisely aligned..

a couple of pics of your setup may help to determine what you have.....
 
Well I am at work now and I already put it all back together. I do have the alloy case and I used blue threadlocker on the screws. I packed them with Lucas oil red n tacky. Will be getting my drive gear on Thursday. Should I put a light coating of lithium grease from a tube on them or spray from a can? I have both on hand. Got my diffs and shocks done, just need the transmission done and I'm finally ready to have some fun again.
 
I'm debating on this as a last resort. Mine keep breaking on the pavement with street tires. But I keeps rebuilding with all used parts so that don't help. Pricey but worth it if it's a final fix. May do a new bulkhead to be safe!!!!
 

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Hello Everyone! Hoovy, what a member mentioned before about the screws getting out because of the differential oil entering the screw holes is quite true, I realised that happening to mine as well when I started putting my hands on every single part of the RC. Try to use either a strong thread lock glue, just a small from at the edge of the screw that will be guided all the way to it as you place it. To be honest I have my Savage with the simple differentials and I run with a LRP .32. I never had any Kind of damage. I recently got my Flux that I run on 6S and I never had any problem as well. In what type of terrain are you running your car??? How often do you replace the oils and which one are you using???
 
I've been out of the RC truck world for several months now as I try to get my (real) truck on the road after rebuilding the diesel in it.... Now that it's getting colder outside, I hope to have more time to fix the truck again. I will certainly pay more attention to the differential as I'm assembling it, and probably use some thread locker on the screws, and double check for some oil in the threads.
I've been flying my quads the last while, but my larger one jus bit the dust. Hopefully next spring I can buy a good quad. My luck has been a lot better with quads then driving my truck....
 
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