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Old 02-27-2008, 10:32 AM   #16
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I don't own a mugen, but the great tips posted by Tony should be able to be applied to just about any other car. I really like the tip about sanding the mating surfaces. Even if you use two gaskets, tightening down something that mates imperfectly can cause a very slight twist. While this may never mean anything I think that the 20 seconds this would take would be a worthwhile step considering what we all pay for these cars and how much money is spent on racing every week. Plus, less oil on the chassis will always be a good thing IMHO.
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Old 02-27-2008, 12:55 PM   #17
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I have moved the issue to the MBX5R thread to keep the number of threads low, and to share this with the people on the 5R thread.

Thanks a lot for your quick and helpful answers guys!

Originally Posted by imaxx21 View Post
machined screws..3x14
Originally Posted by ezveedub View Post
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.
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,

Originally Posted by TonysScrews View Post

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,

Last edited by Starter box; 02-27-2008 at 03:32 PM.
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Old 02-27-2008, 07:48 PM   #18
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The diff cup should not buldge. If it does, then perhaps there is either fluid behind the screw, it went in on an angle or teh cups were not drilled/molded properly. Best bet is to run a 2.5mm drill bit down there (3/32" bit will do). Use a cordless drill an just run it in at a very gentle, slow speed.

Best regards,
Tony P.

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