Interior diff shim?

JKLNHYDE

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157
So after two hours on a brand new diff, they chipped again for the third time!!bad word After the second time I replaced the cups with Nova cups, I shimmed the unit so there was what I felt to be an extremely smooth mesh, used 10,000 weight silicone diff fluid, but they stripped again. None of the small bevels were damaged, just the large ones. So after some :thinking: about how things move inside the cup I'm leaning to believe that there can still be some shimming to be had but on the inside of the cup to raise the large bevel gear slightly to take up just a little more slop. After putting it together dry, it seemd to be even smoother than without the shim. The picture shows what I'm referring to, I put 1 BRP shim behind the pin. It effectively raised the bevel slightly to improve the mesh. My question is can someone tell me why this is a bad idea? I'm tired of going through bevel gear sets.

The truck is a stock X with the 4.1, running a 15T CB and a 47 spur. I am running 25% fuel too. Before it stripped, she ran like a monster so I'm curious if I need to change the CB to something a little taller to relieve some torque on the diff... Thoughts?
 

frddyj

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boston
we can solve this.

lets back up a little.

1. just to be sure, your -internal- diff gears are stripping? is that right?
2. can you take a pic of exactly how you have the internals set up?
3. I'm looking to see if you installed the blocks that go behind the smaller spider gears inside the diff when you installed.

....

br used 16 shims when he built his nova-cup b.p. diffs. i found the shims, but still have yet to build the diffs https://www.hpisavageforum.com/forums/showthread.php?t=16716
 

frddyj

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boston
and no, you wont "need" to change your clutch bell but might want to kick it up to a 17 for more speed, but that will be up to you.
 

JKLNHYDE

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157
FRDDYJ,
Thanks for your interest on this! To answer your questions:

1.) Yes, these are the internal 4 bevel gears inside the cup.
2.) I will put up a picture of how I'm installing the internals at lunchtime.
3.) You mention blocks behind the smaller gears? My cups did not come with any blocks. If I'm tracking with where you're going on this, are they blocks that go under the shafts in the channel the shaft rides in to prevent it from moving up and down? In my cups, the channels the small gear's shafts ride in, two go all the way to the bottom of the diff cup, and two only go halfway. Does it matter which channel the first shaft and small gears go into? I would think the full channel because it will allow the gears to mesh tighter but my thought process could be wrong.

I did contemplate shimming behind each small bevel gear to decrease side to side movement but again, I'm not sure how tight this should feel once it's all together. I assume the shims you're suggesting go inside the diff to tighten the small gears up?

Thanks for your help!
 

JKLNHYDE

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Messages
157
So after much research, I am struggling to find that 4x10x.15 shim. I did find some alternatives though..Finding a 4mm ID is tough with a .1 thickness...

I like this kit because it's got a variety of thicknesses. .1, .2, and .3 and there are 10 of each size.
http://www.amainhobbies.com/product_info.php/cPath/1_25_1460_133/products_id/4066/n/Kyosho-4x6mm-Shim-Set-10

I also like this kit because it provides the slightly larger surface area because they are 10's...
http://www.amainhobbies.com/product_info.php/cPath/1_24_121/products_id/35551/n/Racers-Edge-5x10x02mm-Clutch-Shim-Kit

This kit has three thicknesses as well but I can't tell what the OD is...ID fits at 4mm.
http://www.amainhobbies.com/product_info.php/cPath/1_25_1464_1146/products_id/139955/n/Tamiya-4mm-Differential-Shim-Set

And these would be perfect if they came in .1 thickness instead of .3 :(
http://www.amainhobbies.com/product_info.php/cPath/1576_699/products_id/176906/n/Team-Durango-4x8x03mm-Shim-Set-10
 

JKLNHYDE

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Messages
157
Here's the pics of the assembly process I have been doing...














Hope this shows what you're looking for...Thanks!

Scott
 

frddyj

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boston
ok. first off, here are your shims https://store.vgracing.com/robitronic/r27001-washer-4x10x0-15mm.html

here are the "blocks" i was referring to; they go on the cross-shaft between the spider gear and the diff case to keep the gear mesh right.

They wont fit into the Nova cup so you have to use the 4x10x.15 to shim. B/r did it and it took him a rediculous amount of shims to get the fit right. i'll ask him to chime in here for ya.

 
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Bankrupter

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4,792
OK whats the issue ? I have and run Nova hellfire cups with the BP diffs. Fred PM-ed me to look at this thread. Each cup took 18 shims when I did it to get it all to the proper internal mesh. Total of 32 shims all together for the two diffs. All the pics are in my gallery.

When its finished you want the top gear flush with the diff...



You shim the spiders in to get the proper mesh
these two showing 8 shims ....



All 16 shims + the two for the sun gears ..



They work nice if you take your time and check all meshes inside the bulk as well ....
Shim the bearings out into the bulks.. don't force them in like a noob, now that you have invested this much time and money .... ( Not that you will but, 16mm shims don't belong in a diff housing and most just don't know... )



GL ... Need anything else PM me and Ill post it here ...
 
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JKLNHYDE

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157
Thanks for the great pics and explanation Bankrupter. I just ordered the shims so they should be here in a week or so. The only other question I would have is which way does the first set of spiders go in? Does it go in the half channel or the full channel? Thanks for the assistance on this!
 

Bankrupter

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4,792
Thanks for the great pics and explanation Bankrupter. I just ordered the shims so they should be here in a week or so. The only other question I would have is which way does the first set of spiders go in? Does it go in the half channel or the full channel? Thanks for the assistance on this!
uht oh... what Nova cup is that ? I am using hellfire cup so I can use two full size bearings and get rid of that one that blows up all the time. I think we jumped the gun and were thinking your doing the same mod. Is that a Nova savage cup?

Its my nap time now.. Ill hit this thread when I get home from work 2 mor..
 

Bankrupter

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4,792
OK if it's the hellfire cup what are you referring to when you say...

Does it go in the half channel or the full channel?

First one should go all the way down but my 4 "channels" were the same. My cross pins float they don't bottom out on anything..

 
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JKLNHYDE

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Messages
157
Maybe it's a sublte design change they made...I don't think mine ride on the half channel either but thought I would ask. I just need to wait for the shims to get here and I can put this thing back together. I guess I have tme to break her down and give it a good cleaning...Thanks for all your assistance thusfar. I'll keep you posted as I begin putting it back together.
 

JKLNHYDE

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Messages
157
It's hard to show in the pics I took but the grooves the small spider gear shafts slide down into are two different lengths. Two go all the way to the base of the diff cup, and two only go half way. I don't think my shaft rides on the lip but I would have to check when I get back home. I think it floats high enough to be a non-issue.
 

JoeGuam

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893
Location
Virginia
:smiliejam: Scott just forget about it. Just use one or the two BP diff and FLM bulkheads I sold you and be done with the headache.
 

JKLNHYDE

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Messages
157
:smiliejam: Scott just forget about it. Just use one or the two BP diff and FLM bulkheads I sold you and be done with the headache.
I am trying to avoid putting those into my Basher right now...I'm starting to look for a nice mill for the XL...As strong as those are, I want to learn the process as I go too! I actually had the XL rear setup in my truck until my parts showed up but I ended up replacing mine.
 

frddyj

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ok i just checked my nova hellfire cups, & yeah, all 4 grooves for the rods are milled all the way down.

you should prob be ok tho caz the hellfire and savage cups are almost identical with the exception that the hellfire cup takes 2 same bearings.

let us know how you make out when your shims arrive
 

what the FLUX

is goin' on around here!
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325
Location
Victoria, Australia
I've got the Nova hellfire cups also. I think the reason two grooves that go to the bottom of the cups, is so you can fit the pins in the outdrives. Like bank said the cross pins just float.

BTW, I only need a very small amount of basklash on the pinion, correct?
 

JKLNHYDE

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Messages
157
So as you can read above I ordered these shims from VG Racing on the 20th of September and they are still not here yet!!! bad word If I could have found them elsewhere, I would have cancelled this order. I have sent a few emails to VG Racing and all I get back is "Keep waiting, we mailed them First Class on 21 Sept." :blahblah: Just resend the damned order already...

Sorry, I had to vent....
 

frddyj

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Location
boston
In my cups, the channels the small gear's shafts ride in, two go all the way to the bottom of the diff cup, and two only go halfway. Does it matter which channel the first shaft and small gears go into? I would think the full channel because it will allow the gears to mesh tighter but my thought process could be wrong.
Maybe it's a sublte design change they made...I don't think mine ride on the half channel either but thought I would ask..
OK if it's the hellfire cup what are you referring to when you say...

Does it go in the half channel or the full channel?

First one should go all the way down but my 4 "channels" were the same. My cross pins float they don't bottom out on anything..



Alright, i finished my Nova-Hellfire Cup, bullet-proof, boca diffs last night and now i know what your talking about.

On my cups, 2 of the grooves are milled all the way to the bottom of the cup and 2 are not (like jek's). All 4 of banks are milled all the way to the bottom & i wonder if this is what is causing the difference in my shimming:


my diffs only took 2 shims/spider gear for a total of 8/diff (only 1/2 of what bank's used) also, i used hellfire spiders & suns where bank used some savage internals that he already had (don't know where the difference in tolerance lies but my diffs locked up tight with 4 shims/spider).


bump for jeck's info on this mod
 

JKLNHYDE

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Messages
157
As shown below in Bankrupter's photo, this is how I shimmed my diffs. I can't remember exactly how many shims I used but I think I was 12 to get the top sun gear to sit flush with the top of the cup and mesh perfect with the outer gear and the pin.

And I'm happy to say, I have not had any issues with it up to this point. Looks to be holding up well.


 

mothman

Member
Messages
23
As shown below in Bankrupter's photo, this is how I shimmed my diffs. I can't remember exactly how many shims I used but I think I was 12 to get the top sun gear to sit flush with the top of the cup and mesh perfect with the outer gear and the pin.

And I'm happy to say, I have not had any issues with it up to this point. Looks to be holding up well.



Sorry guys, as english is not my first language, can you please elaborate what does sit flush means? does it mean that the top sun gear sits a little bit lower in the diff cup just like in the pic?
 

frddyj

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Sorry guys, as english is not my first language, can you please elaborate what does sit flush means? does it mean that the top sun gear sits a little bit lower in the diff cup just like in the pic?
if the sun gear were "flush" it would be even with the 2 outer edges. but yeah, it sits a bit lower in the pic. mine is the same way. flush made the gears bind.
 

2QIK4U

Member
Messages
7
Ok.....chance to laugh at the newby.....when I put shims on the bevel gear, the pins wont go through drive shafts. The cup is wider than the bearing and 2 x shimms where the shaft goes through. With shims on the bevels mesh heaps better but I cant get pins through diff shaft.
Do I need to machine diff casing/hats down?
Cheers
 

olds97_lss

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Dekalb, IL 60115
You should be able to add shims to the spider gears and that will push them in which will take up any extra slop that the sun gear shims your trying to use are taking up.
 
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