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Old 12-22-2007, 05:14 AM   #1
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Default mbx,mbx5r,mbx5t Leaky diffs

all mugen owners have you noticed oil does not stay in your diffs long ,,i have heard this and beleive its true because i pulled my diffs apart 4 weeks after rebuild and found them empty,,, now i beleive this is true and Amain and carolinas sell a slightly larger oring to combat this ,,,does anybody know what size these are and if there special o rings or just normal as i would like to buy from a oring ,bearing specialist shop as im in australia and have to pay heavy postge ,,,ANYONE KNOW SIZE ???????????
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Old 12-22-2007, 06:00 AM   #2
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This should be in the MBX5R thread. But then again, almost every losi driver likes to start a thread so why not...

The S5 o-rings are the ones you want on the the diff outdrives. Check you haven't stripped the threads in the diff cases, it's very easy to do. Use 2 gaskets between crown wheel and case. Don't run the small S3 o-rings on the cross shafts. Dont overfill the diff. Tighten using the star pattern.

I think that's all I can think of. I did have leaky diffs at first. The first two were because the guy who built my buggy before I owned it stripped the threads on the diff cases. I'm pulling my buggy down over the next two weeks so I'll be able to check the current diff status.

As for australian availability, any shop stocking mugen should be able to get them in. Which city are you in?
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Old 12-22-2007, 06:57 AM   #3
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Gen,

The Mugen diffs "can" leak in two places:

1] At the out-drive where the S5 o-ring seats
2] At the diff gasket

For the outdrives you need to use a good quality waterproof sythetic grease. Mugen Super Grease, Maxima sythetic grease or Mobil 1 sythetic grease all work well. You can get the Maxima grease from most motorcycle/ATV shops and the Mobil 1 grease is easily found in any auto parts store. Use the grease on the o-ring, on the shim and on the outdrive. Make sure you get grease in that groove on the outdrive. Don't be afraid to put on a lot of grease. The stock o-rings or slightly oversized o-rings both work well with the grease. I also sell the o-rings on my website. Since you're in Australia, I do all int'l orders via email as my cart doesn't support Int'l orders except for Canada, but shipping is cheap for just some o-rings.

On the gaskets, I've used both one or two gaskets on the diffs and it doesn't make a difference as mine never leaked. The two gaskets just feels smoother to me so why I use two gaskets now. But one gasket is fine too if you follow these steps. What I do is sand the diff cups smooth (tip from Chad Bradley when he ran for Mugen) to make sure they seat perfectly against the gears. It only takes about 20 seconds per diff cup and you only have to do it once, then the cups will last you gallons upon gallons. I use a 400, then 800 and then 1200 emery cloth paper. Just use a perfectly flat surface, lay down the paper and slide the cup around in a figure 8 pattern for a few seconds. Start with the 400 and work up to the 1200. Blow them off with compressed air to clean them. But the key to them not leaking here is to use longer screws. The 3x8mm flat head screws are way too short to get a good amount of torque on the gasket without the cup stripping out. Use 3x14mm flat heads and tighten in a star pattern.

If you do this to your diffs, they'll never leak.

Best regards,
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Old 12-22-2007, 09:26 AM   #4
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I am having the same trouble with my prospec and I am not real sure what to do. I have even put those bigger o rings in them and they still leak and no bolts are stripped so I give up I will just have to live with changing them every two weeks or so unless someone can tell me something that I have not already checked. I have a buddy that runs the mbx5r and his did the samething but then he bought those bigger o-rings and it didn't do it anymore
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Old 12-22-2007, 09:44 AM   #5
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use some 220 grit or higher sand paper and set it on a flat surface and sand the diff cup lightly. After that use the larger o-rings. I have done this and never leaked anymore.
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Old 12-22-2007, 09:47 AM   #6
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oops, didn't read all of Tony's post.
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Old 12-22-2007, 11:34 AM   #7
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I use slightly oversized orings from carolinas rc, along with some associated green slime for a lubricant, and then I use belray grease on my outdrives. With these 3 procedures taken my diffs stay pretty full. I dont sand the cups but I also double gasket my diffs but that is mainly for a smoother feel. Hope this helps.
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Old 12-22-2007, 04:57 PM   #8
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Which part of the diff cup are you guys sanding?
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Old 12-22-2007, 07:59 PM   #9
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Some folks take their diff cups and sand the flat side in which the ring gear is bolted to. You simply take a sheet of sand paper and lay it on a flat smooth surface, take your diff cup and sand the flat side by making passes on the sand paper in a figure eight motion. It is simple to do but I dont think it is necessary, the orings and the grease seem to be the key.
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Old 12-26-2007, 01:46 PM   #10
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Thanks Guys

Will attempt to get hold of the o-rings and grease and slime hopefully will cure my only niggle with the mbx5r
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Old 12-26-2007, 04:06 PM   #11
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Here is a link to the Mobil 1 synthetic grease:

Mobil_1_Synthetic_Grease

Here is the Maxima grease:

Maxima waterproof grease
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Old 02-26-2008, 08:24 PM   #12
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Tony, Thanks a lot for your tips!

I noticed one problem with my 5R diffs though:

I use 3x12mm screws to tighten down the spur gear/bevel gears on the diff cases. However, I noticed on one diff case today, that on the outside of the diff case the longer screws are causing bulges. I believe as soon as a screw gets into the case slightly off the 90 degree angle, it causes the case to bulge. Any thoughts on this? I might want to go one step back to 3x10mm?

Best regards,
Frank

Quote:
Originally Posted by TonysScrews View Post
Gen,

The Mugen diffs "can" leak in two places:

1] At the out-drive where the S5 o-ring seats
2] At the diff gasket

For the outdrives you need to use a good quality waterproof sythetic grease. Mugen Super Grease, Maxima sythetic grease or Mobil 1 sythetic grease all work well. You can get the Maxima grease from most motorcycle/ATV shops and the Mobil 1 grease is easily found in any auto parts store. Use the grease on the o-ring, on the shim and on the outdrive. Make sure you get grease in that groove on the outdrive. Don't be afraid to put on a lot of grease. The stock o-rings or slightly oversized o-rings both work well with the grease. I also sell the o-rings on my website. Since you're in Australia, I do all int'l orders via email as my cart doesn't support Int'l orders except for Canada, but shipping is cheap for just some o-rings.

On the gaskets, I've used both one or two gaskets on the diffs and it doesn't make a difference as mine never leaked. The two gaskets just feels smoother to me so why I use two gaskets now. But one gasket is fine too if you follow these steps. What I do is sand the diff cups smooth (tip from Chad Bradley when he ran for Mugen) to make sure they seat perfectly against the gears. It only takes about 20 seconds per diff cup and you only have to do it once, then the cups will last you gallons upon gallons. I use a 400, then 800 and then 1200 emery cloth paper. Just use a perfectly flat surface, lay down the paper and slide the cup around in a figure 8 pattern for a few seconds. Start with the 400 and work up to the 1200. Blow them off with compressed air to clean them. But the key to them not leaking here is to use longer screws. The 3x8mm flat head screws are way too short to get a good amount of torque on the gasket without the cup stripping out. Use 3x14mm flat heads and tighten in a star pattern.

If you do this to your diffs, they'll never leak.

Best regards,
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Old 02-26-2008, 09:10 PM   #13
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Quote:
Originally Posted by Starter box View Post
Tony, Thanks a lot for your tips!

I noticed one problem with my 5R diffs though:

I use 3x12mm screws to tighten down the spur gear/bevel gears on the diff cases. However, I noticed on one diff case today, that on the outside of the diff case the longer screws are causing bulges. I believe as soon as a screw gets into the case slightly off the 90 degree angle, it causes the case to bulge. Any thoughts on this? I might want to go one step back to 3x10mm?

Best regards,
Frank
Are you using machine threaded screws or coarse threaded. I have the machine threaded screws and have no issues. I believe I used the longest possible, either 12 or 15mm long.
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Old 02-26-2008, 09:51 PM   #14
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machined screws..3x14
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Old 02-27-2008, 08:59 AM   #15
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Hey guys... I have the Mobil 1 Synthetic grease in syringes, that the Caster team guys are using (same as the Mugen guys).


www.casterracingusa.com should have them but it's not on the new website yet. But right now I can get them if anyone wants one....
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