MMM eating my diffs

[Vindex]

Hey guys just a noob here on the other side of the world

I've got my self a dual force Kyosho Gigacrusher and have put a MMM in it runs like a dream in till the front diff gave out the the rear followed suit

straight to the point any ideas for stronger diffs and any one out there running kyosho kit with suggestions

Cheers
Sam

[George16]

I have no problems with my ST RR diffs with the MMM/CC Neu on 5S. I shimmed the diffs and it helped a lot.

[brushlessboy16]

Sounds like the MMM is doing its job perfectly?





DOes the giga crusher use standard 8th scale differentials?

[simplechamp]

The GigaCrusher uses standard 1/8th buggy size diffs and has helical (spiral) cut gearing.

What part of the diffs are giving out? The crown gear and spur or the internal spider gears?

Might need to look into some shimming, otherwise since it uses standard 1/8th diffs try some diffs from another brand and see if they hold up better.

[magman]

Correct shimming seems to take care of a lot of diff probs.

[JThiessen]

Originally Posted by magman

Correct shimming seems to take care of a lot of diff probs.

So help him out - he stated he was somewhat new, and probably does not know anything about shimming diffs. I would be more beneficial to give a link to a thread on diff shimming, or at least a brief explanation of what you mean. Where to shim, where do you get "shims", how does one "measure" correct shimming versus "incorrect".

Now that I'm sliding my soapbox back in....I must humbly say that I also dont really know what to do for correct diff shimming.

[magman]

Originally Posted by JThiessen

So help him out - he stated he was somewhat new, and probably does not know anything about shimming diffs. I would be more beneficial to give a link to a thread on diff shimming, or at least a brief explanation of what you mean. Where to shim, where do you get "shims", how does one "measure" correct shimming versus "incorrect".

Now that I'm sliding my soapbox back in....I must humbly say that I also dont really know what to do for correct diff shimming.

I would have...except I had to leave for a bit....

I found this..http://www.rc411.com/pages/howto.php?howto=35&page=1

and these pages for parts: http://www.quicktechhobby.com/Car_Ac...s_for_cars.htm
http://www.rchobbies.com.au/store/in...ath=34_279_281

[lincpimp]

Diff shimming is quite easy, as long as you go in the correct order.

First you will need some shims, depending on what size the pinion shank is will determine what size internal diameter shim you need to correctly shim the pinion. For the diff itself, you can use shims that will fit between the bearings and the cup/crown gear. For diffs with fixed drive cups (most 1/8 scale) you may find it easier to get shims that are the same outside diameter as the bearings (most 1/8 scale stuff uses 8x16 bearings, so 18mm OD shims with 15mm id work ok) and you can shim between the outside of the bearings and the diff case/carrier.

1st step is to assemble the diff and pinion in the case and attempt to see if the pinion is engaging the crown gear (also called ring gear) properly. You can add shims between the pinion and the inner bearing to place the pinion closer to the diff cup. Basically what you want is complete engagement of the ring and pinion teeth. Then I like to install the cup or cvd to the pinion shank and check for play. You may need to add shims between the cvd/cup and the outer bearing. This will eliminate any "walking" of the pinion, and thus keep the ring and pinion teeth in correct alignment. Another plus is that the bearings will last longer. You want the pinion to spin freely, but not be able to push it in or out of the carrier.

2nd step is shimming the diff side to side. This is where most problems occur. If you are starting with new gears you want them reasonably tight, as they will wear in and loosen up over time. If you are starting with used gears you can set them looser, as they are already worn together.

Side note, always change both the ring and pinion out if either breaks, cause using a new gear with an old gear will not last very long, and usually ruins the new gear.

Basically all you do is add shims to one side or the other of the diff to move the crown gear side to side. Best to have clean gears with no grease on them. With new gears you may have a few tight spots as you rotate but the gears will wear in. Also when you shim the diff, make sure you have it shimmed so that it cannot move from side to side in the carrier, this will keep the mesh tight, and not allow any slop, which causes accelerated wear. So you may need to add shims to both sides of the diff, keep this in mind.

Now here is the tricky part. You need to "feel" the gear mesh when you add the shims to the diff. So it is best to get the diff simmed so that it does not move side to side in the carrier, and put all of those shims on the cup side of the diff. This will place the ring gear as far away from the pinion as it can get. You can then rotate the pinion and see if the mesh is smooth. If it is smooth then hold the diff outputs and turn the pinion back and forth to feel for slack. If you do not feel much slack you are good to go. If you do feel slack, move 1 shim from the cup side to the ring gear side and try again. Keep doing this till it feels good, then swap 1 more shim over. That should make it too tight to turn easily. If so, put that shim back on the cup side and you have a correctly shimmed diff. I say to do the last part as a double check on your "feel". If it is too tight you know it was just right, if it still turns smoothly you know you had it too loose.

If these are new gears you will likely have some spots that are a bit tight when you turn the pinion. It is always good to rotate the pinion at least 4 times during each step as you want to get a feel for the entire revolution of the ring gear. Also if you have new gears you may want to run them for a few packs, the pull them back out and see if they still feel smooth and the pinion does not have much play when you hold the diff outputs and try to turn the pinion. The gears will wear in, and you may need to adjust the shims on the diff to tighten them back up. This is where very thin shims come in handy, as you can make small adjustments. Keep the gears well greased, and you will get good life out of your ring and pinion gears.

Shims are available in various thicknesses, OFNA has a great selection, as does HPI. If they offer 2 different thicknesses of shims it may be wise to get both, as that will give you some options.

[J57ltr]

Originally Posted by lincpimp

Diff shimming is quite easy, as long as you go in the correct order.

First you will need some shims, depending on what size the pinion shank is will determine what size internal diameter shim you need to correctly shim the pinion. For the diff itself, you can use shims that will fit between the bearings and the cup/crown gear. For diffs with fixed drive cups (most 1/8 scale) you may find it easier to get shims that are the same outside diameter as the bearings (most 1/8 scale stuff uses 8x16 bearings, so 18mm OD shims with 15mm id work ok) and you can shim between the outside of the bearings and the diff case/carrier.

1st step is to assemble the diff and pinion in the case and attempt to see if the pinion is engaging the crown gear (also called ring gear) properly. You can add shims between the pinion and the inner bearing to place the pinion closer to the diff cup. Basically what you want is complete engagement of the ring and pinion teeth. Then I like to install the cup or cvd to the pinion shank and check for play. You may need to add shims between the cvd/cup and the outer bearing. This will eliminate any "walking" of the pinion, and thus keep the ring and pinion teeth in correct alignment. Another plus is that the bearings will last longer. You want the pinion to spin freely, but not be able to push it in or out of the carrier.

2nd step is shimming the diff side to side. This is where most problems occur. If you are starting with new gears you want them reasonably tight, as they will wear in and loosen up over time. If you are starting with used gears you can set them looser, as they are already worn together.

Side note, always change both the ring and pinion out if either breaks, cause using a new gear with an old gear will not last very long, and usually ruins the new gear.

Basically all you do is add shims to one side or the other of the diff to move the crown gear side to side. Best to have clean gears with no grease on them. With new gears you may have a few tight spots as you rotate but the gears will wear in. Also when you shim the diff, make sure you have it shimmed so that it cannot move from side to side in the carrier, this will keep the mesh tight, and not allow any slop, which causes accelerated wear. So you may need to add shims to both sides of the diff, keep this in mind.

Now here is the tricky part. You need to "feel" the gear mesh when you add the shims to the diff. So it is best to get the diff simmed so that it does not move side to side in the carrier, and put all of those shims on the cup side of the diff. This will place the ring gear as far away from the pinion as it can get. You can then rotate the pinion and see if the mesh is smooth. If it is smooth then hold the diff outputs and turn the pinion back and forth to feel for slack. If you do not feel much slack you are good to go. If you do feel slack, move 1 shim from the cup side to the ring gear side and try again. Keep doing this till it feels good, then swap 1 more shim over. That should make it too tight to turn easily. If so, put that shim back on the cup side and you have a correctly shimmed diff. I say to do the last part as a double check on your "feel". If it is too tight you know it was just right, if it still turns smoothly you know you had it too loose.

If these are new gears you will likely have some spots that are a bit tight when you turn the pinion. It is always good to rotate the pinion at least 4 times during each step as you want to get a feel for the entire revolution of the ring gear. Also if you have new gears you may want to run them for a few packs, the pull them back out and see if they still feel smooth and the pinion does not have much play when you hold the diff outputs and try to turn the pinion. The gears will wear in, and you may need to adjust the shims on the diff to tighten them back up. This is where very thin shims come in handy, as you can make small adjustments. Keep the gears well greased, and you will get good life out of your ring and pinion gears.

Shims are available in various thicknesses, OFNA has a great selection, as does HPI. If they offer 2 different thicknesses of shims it may be wise to get both, as that will give you some options.

Thank you! Since I am used to 1:1 cars I have shimmed a few diffs in my time. When I started noticing some of the higher powered buggys blowing gears right away I started asking about shimming diffs. Most of the answers I got was to only shim the pinion which I thought was stupid since they both have to mesh correctly with each other.

Jeff

[magman]

Man linc...beats the explanation I found...well done!

Your explanation should be used as a sticky

[JThiessen]

Originally Posted by magman

Man linc...beats the explanation I found...well done!

Your explanation should be used as a sticky

I vote for that too! Thanks linc, and you too Magman for the linK! The part I could never figure out was how to take care of rotational slop.

[magman]

sent a pm to Brian to see if he will add linc's description as a sticky!

As a matter of fact, I am going to print out a copy to have on hand and give to my friends

[jpoprock]

Linc's post does indeed rule. But I wish it had PICTURES! i've seen some various threads here and there with pictures, but they always seem out of date. I would do it per Linc's instructions, with pix, for my Losi XXL Diff (with HD Cup), but I'm not yet sure if I have all the proper shims! And, I've never done it to this diff... so I may not be the best guy to do it! LOL!.

[jpoprock]

I'm not sure if this is "taboo", but here is basically what Linc is talking about it.. only with pix. It's from the LSTForum, and specifically how to shim an LST2 diff. The XXL diff's are exactly the same except I believe they have the better HD cup in them and use a slightly beefier ring and pinion gear. But I can't confirm that.

http://hdrcvideos.com/forums/viewtopic.php?f=18&t=15378

[Bondonutz]

All the gears between LST1,Aftershock,Ram,LST2,XXL all have the same gears.

The XXL comes with the HD cups with the metal pin inserts, none of the others do.