Shimming diffs question...
 

Is there a way to tell if you shimmed your diffs properly without driving your truck(MBX6T). Is it like checking gear mesh? Can I have the top gear cover off to check the mesh? or does that not work?

I remove the assembly from the car. hold the diff in place and rock the pinion/driveshaft back and forth.

It should tick back and forth like the clutch bell and center diff deos.

So I just set it by feel.

Thank you, thats what i thought.

Yes but in an mbx6t you want it tight. Not so tight that its binding but I set it to as close to no play as possible without binding. For some reason in that truggy if you don't do it tight you get excessive wear on the pinion gear.

How many shims are you using? I just did my rear (Thats where i was having issues) and I had 1 on each side, but I took one off of one side and now have 2 on one side and none on the other. Its not tight, but it seems that there is no play and is very smooth. Gonna inspect the front...

make sure you have 2 on the ring side

This is quoted from Jonathen Bell in the ZO1T section he helped me out the same principles apply for shimming diffs.

(Make sure the bearings in the housing that the pinion gear rides in rotate freely. Place your shims on the pinion gear and install into the housing. Now while pushing in on the pinion install the driveshaft/cup. Make sure to push in on the pinion while tightening down the set screw. When done corrcectly there should be NO in and out movement in the pinion gear.
Ring gear;
I start by taking the diff cup and place it face down on about 1000 grit sandpaper and work it in figure 8 patterns. This will ensure that any high spots or imperfections from molding are taken out and you have a square surface for the ring gear to sit on. Next I usually replace the screws that hold on the ring gear with some that are about 3mm or so longer. This will allow a little more gripping power for the screws. When bolting on the ring gear I will use a power driver with an adjustable chuck, this way i get the same amount of torque on each screw when there tight and it doesn't allow the ring gear to be lower on one side then the other. If so this is the tight spot on one side and loose on the other when you rotate the diff. If everything is perfectly square the ring gear will have the same mesh all the way around the gear as it rotates. This helps because you can get a more consistent mesh and it's not to far away from the pinion where its smooth and notchy on the other side. After doing this I will test fit the diff into the housing and check side to side play. Im not really worried about mesh at this time but just adding enough shims to make sure there is NO side to side moving in the housing. When checking this make sure you install the diff cover and tighten down a couple screws that hold it on. If not you may get false readings. It's kind of a buger taking it on and off but trust me having it shimmed correctly will reward you in the long run. Once there is no side to side movement, now you have established how many shims you need. You will now need to reposition the shims on each side to adjust the mesh. Take a couple shims off the other side and place them onto the ring gear side and reassemble. Now with the cover installed hold the ring gear and try to turn the pinion left then right and see if the pinion has any space between changing directions. If your holding the ring gear and you can move the pinion left and right without the ring gear turning take out a shim on the other side and put it on the ring gear side. Repeat this until there is no movement in the pinion without the ring gear moving, also known as zero backlash. The last step is to ALWAYS use and high quality grease on the gears. I like to use mobile 1 synthetic. I like to take the grease and load it into an old shock oil container. Then I will put it on and rotate the ring gear as i'm going it to get a "bead" all the way around the gear. The grease is very important it is the cooling system for your gears to prevent premature failure. After one race weekend I will disassemble and check to see if all my settings are still correct and if nothing changes you should be good for several weekends of racing with no problems. I know it's long but I have had great success using this method over the past couple of years. I had 3-4 different trucks with helical cut gears by different manufactuers and I can't remember the last time I striped a ring and pinion and I race almost every weekend. Hope this helps.)

Again this is from Jonathen Bell it helped me. figured I would pass it along.

great advice above post..
 

It's worth it to check it and re check it. I like to put a thin shim on the diff gear side, but underneath the bearing. this moves the bearing out so the outside shims aren't needed. the mugen it tight in the first place, and this helps make it more precise. He's right push the crown gear all the way in while tightening the set screw. Hold the shaft and tic the diff back and forth with the cover off. Loc tight it and use sealed bearings so you don't mess with it too often. Once it's right, with new parts it will run free after running. If it is still tight then get back in there and free it up.

One diff has just 1 on the ring gear side. The other has 2 on the ring gear side. It all depends on the diff plastic casting, as well as the diff. I check it before each race day to see if it gets worse. If I had to change it from the last race I check that diff after the first qualifyer. A spare pinion gear is something I always have on hand with these trucks. So far I haven't needed, but I had it get loose on my Mbx5t. The 6t I got is still pretty new.

nice article! :nod:;)

dont just put them in on each side because you have them. like zero said the best way to check is to have the assy put together off of the chassy and turn it upside down, hold onto the center shaft dog bone and check the play/mesh between the pinion and ring gear. use a small amount of grease on the ring gear and use the shims to mesh correctly. on most 6t's i've found 1 shim on the ring side after breakin ,a second one on the ring side but its best to check this yourself. you'll know right away when its too tight when you check the mesh. and there's a thread for the mugen 6t already where you can ask questions and find some good info.

this helps i ges ill try 2 on one side. ;) i dont thank it will work but ill try it.

One thing
 

Sometimes when you put the bulkhead cover on and tighten up everything it can close the gap too much, so make sure and check it after the car is built...It never hurts to take the cover back off...

thats is exactly what I experienced. You need to balance the shim correctly for a tight fit.

I hold the pinion by the rubberboot on the cvd and then try to move the ringgear back and forth. Also lube you ringgear and pinion with Mobil1 oil or AE blackgrease. Running them dry causes more heat and the the plastic will flex/expand more then which is bad for the mesh.

I broke my mbx6 in with 1 shim and it's still going strong with 1 shim and no backshlash.