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Old 05-19-2008, 01:18 AM   #1
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Default Mugen MBX5R rear end breaking loose, Help Pls!

Hi all,

I have a MBX5R with a v-spec and am having problems controlling the car. It just doesn't feel planted around corners. I am racing on a loose dirt tract but other car seem more planted I just keep spinning out when trying to push the speed.

-I have 5k,7k,1k Diff oils. Front to rear.
-Sway bars loose at the grub screws.
-Only a little amount of droop wound out. (grub screws only just poking through)
-90% steering EPA using Futaba 3PM.
-Proline crimefights about to change to Medial Pro Pulsar
-400wt shock oil all round
-2.75 rear toe
-all wheels fairly straight facing

What can I do to make the buggy more planted around the corners?
I also don't seem to have much on power steering but that could be because of the rear breaking loose.

The buggy setup is pretty much as the stock sheet required as its only new..

Thankyou all, I will make any changes sugested and or give any other info that could be important..

thankyou!
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Old 05-19-2008, 02:47 AM   #2
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-Check your brakes so that they don't drag.
-Try lowering the rear droop
-Lower the rear ride height to around 24-25mm
-Use 5000 diff oil in the center
-Check your diffs if they bind
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Old 05-19-2008, 02:54 AM   #3
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longer rear link in the suspension. i have mine set in the middle far inside on the shock tower.
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Old 05-19-2008, 03:31 AM   #4
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Quote:
Originally Posted by vti-chris View Post
-Check your brakes so that they don't drag.
-Try lowering the rear droop
-Lower the rear ride height to around 24-25mm
-Use 5000 diff oil in the center
-Check your diffs if they bind
-so lowering the rear droop you mean take less droop. as in screw the grub screw in more?
-I will check my ride height cheers. this isn;t the same as droop is it? i am guessing droop is control by the grub screw and ride height by the shock spacers. correct?
-I will try the different oil too
-diff binding? how is this checked?

do you guys have your EPA for steering set to max just below the wheels going to bind on the suspension?

thankyou
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Old 05-19-2008, 03:32 AM   #5
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Originally Posted by mugenlife View Post
longer rear link in the suspension. i have mine set in the middle far inside on the shock tower.
thankyou. once i change the link position do i make the rod longer or do i allow it to pull the wheel over?
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Old 05-19-2008, 04:00 AM   #6
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You will have to reset the camber after changing the link position.
The droop is altered by the screws on the A-arms.Less droop=turn in the screws.
Ride height is controlled by the shock-spring preload-spacers.
Remove the wheels and grap the wheel hexs(17mm) and turn them.You should be able to turn them and not feeling any grnding of the gears in the diffs.
It's better to check them from their outdrive cups but you will have to remove them from the cases to do so.(More work...)
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Old 05-19-2008, 04:20 AM   #7
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thankyou, i will check and do these things...

another quick question. In the manual is said only to use shims between the flywheel collect and front engine bearing to space out the flywheel and for clearance for the clutch bell which mine was fine so i didn't use them.

is this a problem? will the collet when tightened bind on the front bearing?
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Old 05-19-2008, 01:39 PM   #8
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Spacers are used behind the collet so the flywheel doesn't bind on the engine. The rest are for setting the CB endplay with the CB bearings. They can't be too tight and also not too loose either.
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Old 05-19-2008, 04:29 PM   #9
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thankyou, i understand that. what i was asking is if i don't need to space the flywheel (which i didn't) and i don't use shims behind the collet will the collet then bind to the front engine bearing when the flywheel is tightened? and is this a problem?

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Old 05-19-2008, 06:12 PM   #10
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Something else you could check would be to check the internal diff pins(one that are inside the diff cup going through the outdrive shaft holding the larger internal gear. I had one break and it make the rear break loose extremely easy(snapped loose mid turn out). I would also go to 2000 in the rear diff fluid.
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Old 05-19-2008, 06:39 PM   #11
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You can't bind up the front bearing unless your flywheel goes deeper over the collet. I have always used at least the thinest spacer for this, it helps to keep the dirt away from the front bearing seal. Also like to have the spur gear riding closer to the bell but not touching, this helps with bearing life in the bell.
as for your spinning out issues be sure your shocks do not bind or any of the suspension components forthat matter , Mugens are known for killer rear traction so you must be over looking something simple?
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Old 05-19-2008, 08:30 PM   #12
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First off make sure you did not build the diffs with the small S3 orings behind the 4 small gears in the diffs. Then try 3 degrees rear toe in, 5k rear diff oil, if you do not need a lot of punch to clear jumps right out of corners on your track, 5k center diff oil should also help but you will lose a fair amount of punch. Run the lower hinge pin hole in the rear hub and run the link long. All of these should help. You can also space your rear hubs forward to get more traction. I also run 350 rear shock oil.
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Old 05-20-2008, 07:34 AM   #13
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Quote:
Originally Posted by windellmc View Post
First off make sure you did not build the diffs with the small S3 orings behind the 4 small gears in the diffs. Then try 3 degrees rear toe in, 5k rear diff oil, if you do not need a lot of punch to clear jumps right out of corners on your track, 5k center diff oil should also help but you will lose a fair amount of punch. Run the lower hinge pin hole in the rear hub and run the link long. All of these should help. You can also space your rear hubs forward to get more traction. I also run 350 rear shock oil.
+1 on virtually all of this.

I'm not sure about 3 degrees of toe though. It DOES make the rear more planted, but it also makes it harder to recover if you get sideways.

Also... smaller rear swaybar will give you more cornering bite in the rear... if you already have the smallest rear bar, you can go bigger on the front bar to take some traction away from the front, which essentially does the same thing to balance the handling.

Mugen swaybars are nice too... adjustable... if you loosed the set screws on the bar ends and slide them OUT, it is like going down in bar size... slide them in is like going up in bar size. (don't forget to re-tighten them!)

Get a camber gauge and be sure to set them all even. The mugen seems to like a lot of camber- we used to run about 3.5 degrees, which is a LOT. Start with at least about 2 degrees, but don't overdo it! (3.5 wouldn't work well with Crimefighters due to the flat tire profile!) If you can get your hands on a Hudy setup station (a little pricey, but worth it!) you can also set front toe. Try about 1 degree OUT per side... if the car turns in TOO abruptly, reduce it to half a degree per side. You could also set it with graph paper, a protractor, and just some flat plates of metal or plastic with a hole for the hub and the same distance from the hole to the end as you have from the hole to the center of the tire tread on your wheels. A camber gauge is available for about $10 or so... but that Hudy station that sets toe is over $100... nice, but you can go the cheap route with graph paper and protractor if you are on a budget!

Leaning your shocks in at the top will give more cornering bite too... but also makes the car get upset over bumps easier. EVERYTHING is a tradeoff.

7k in the center diff like you have makes the car very aggressive. Going down to 5k will calm it down. 5k front 5k center 2k or 3k rear is a good starting point. 5-7-1 like you have is a great setup... for an experienced driver that LIKES a car to be loose and aggressive! The center diff in this case is probably more of your problem than the rear... try 5 and see if it doesn't calm things down significantly.

Make ONE CHANGE AT A TIME and note the results, then continue from there. It is a painstaking process to set a car up for your preferences, and since every driver is different, what works for one may not be a good setup for another.


And just a word of caution: The Mugen is THE most planted, stable, forgiving, easy-to-drive car made... and it is tough as nails! Don't even think about changing cars if you think that one is too loose. Just work with the setup to get it where you want it to be.
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Last edited by DOMIT; 05-20-2008 at 07:47 AM.
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Old 05-20-2008, 04:42 PM   #14
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great reply DOMIT, thankyou!

I am going to try again this weekend as i went through the setup lastnight and i had stuffed up a fair few things. has the wrong spaces on the arms and tooo long a wheel base etc...

going thicker oil in the rear diff make it steer less or more? i will do the center first but i keep hearing different stories relating to changing the rear..

cheers!
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Old 05-20-2008, 05:46 PM   #15
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Another thing, check your centre diff, i had the outdrive bind up in the spur gear, and ive heard of it happening to other drivers aswell.
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