MonsterGT Tranny & Diffs 

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TRANNY - The MGT tranny is fairly solid. The first thing you GOTTA do for racing is the FOC (forward only conversion). This removes a lot of weight from then truck.  It also removes a lot of rotating mass, which will help the engine spool up faster. When you do the FOC, carefully check to make sure all the gears line up perfectly. My FOC kit came with instructions that WERE NOT correct. This means the spacers would have ended up in the wrong spots and the gears would not be 100% aligned. Pics of correct FOC install here

The only thing you really gotta do for the tranny is check it once in a while. Tranny bearings will wear out. When that happens, something will probably break.

Tranny Shift Point - This really needs to be adjusted for racing. With high-revving engine, set mine it  to shift at higher rpm. Most tracks will have some sections with a tight corner and then a short run-up to the next jump. If you are still in second gear, then you will have a hard time accelerating and hitting the jump at the proper speed. You want your truck to be in first gear for those situations.

Alternatively, some guys actually disable first gear and race their truck in second gear only. This is good if you have an engine that produces tons of low-rpm torque, but not much high-rpm horsepower. Experiment to see which works best for you. You can experiment easily just by adjusting shift point screw.

See the screw below circled in red? Make sure they are tight! Use threadlocker too.

Check your CVD's for wear, both on the tranny and on the wheel axles. Look close on the pic below and you can see on mine that it is worn. Drivetrain slop increases the slamming effect when you make rapid transitions from full speed to braking, or from jumping, which means that your tranny and diffs take a beating.

LOOK at this pic (from STC007) below and you can see some incredible (but typical) wear. This is the kind of slop that will really start to tear up your tranny and diffs. Every time you start/stop or land a big jump, the slack in these loose joints gets taken up with a jolt, which is transferred to gears in the tranny and diffs. This is the biggest cause of tranny/diff failure, IMHO.



DIFF setup - For longer diff life, do the "quick and easy shim" below.

DIFF SETUP with Shims (by 1100SHOTS)

OK, here's a really cool mod from 1100SHOTS from the Monster GT forum. All of the following below text (in green italics) is from 1100SHOTS.

Click to view full size image If you find ANY flattened, chipped, or worn thin gear teeth on your pinion gear then JUNK IT! It is not uncommon to replace just the pinion gear. If your diffs make an occasional "popping" noise, chances are the ring gear is ok. If you have lost all drive from a diff, you may have stripped the internal gears, or the external (big) ring gear. Check them all.
Click to view full size image This pic shows the gear engagement between the pinion, and ring gears. This is a STOCK diff. As you can see, there is room for improvement with simple modifications, and some shimming. Having the gears line up, for 100% teeth mesh is essential for longevity.
Click to view full size image This is another view of stock diff with gears not engaging fully.


Quick & Easy Diff Shim

The ring/pinion mesh takes a helluva beating, as all the stresses of acceleration and deceleration are absorbed by one or two tiny teeth.

Virtually all of us have heard the dreaded diff clicking sound. Thatís the sound you hear when your ring/pinion mesh has basically been ground away. Chances are good, when you remove the diff housing and take it apart, you will see metal shavings inside. That metal used to be part of the ring and pinion gears.

Hereís a very easy and quick way to shim the pinion gear. This moves the pinion gear further into the ring gear for a more positive mesh. The goal with this mod is to eliminate all the slop, but NOT make it so tight that it binds.


Shim washers:

Step 8 assumes you have used two shim washers, totaling about .016 thickness. If you have used only one washer, then you would shorten drive cup accordingly.

I (Chevy-SS) also use the GPM case tighteners (see pic just below the shims pics).


Here are the shims you need to move the pinion out:

These are the 8 x 10 x .02 shims. Here's a link to order them from Tower:

These are only $2.89 for a whole pack.


Many times, Tower is out of the above shims. If that's the case, then you can use these shims instead:

These are $4.79 for a pack.


NOTE from Chevy-SS: I think 1100SHOTS and I both agree that the main problem area in the diffs in the ring/pinion mesh. Simply do that mod to your diffs and they should last a good, long time..

GPM case tighteners


GPM Aluminum Diff Cases (pics below) -  These are some stout looking pieces. Here's a link to order them:

They were thinking when they made these diff cases. Allowing for three bearings on the pinion gears shaft...there's the beef. The pic above shows 3 shims installed behind the pinion gears teeth. GPM diff cases more accurately locate the diff in between the case halves, so the diff does not move side to side in the cases. NICE! Also, the pinion gear meshes with the ring gear much better than stock, it takes 3 shims, instead of 4 or 5 to achieve 100% gear mesh.


Marking the case half with an "X" to help ease of re-assembly. This helps you get the ring gear on the right side, so your front and rear wheels rotate the same directions (yeah, I did that, lol). Just remember you always want the ring gear on the same side for all diffs.

DIFF Fluid - Here's a quote from RC Car Action magazine, Jan. '05 issue, page 46,
"This tip comes directly from Team Associated/Thunder Tiger driver Richard Saxton. You can tune the MGT's sealed differentials by using silicone diff fluid of different viscosities. To improve steering, fill the rear diff with 5,000 to 10,000WT diff fluid. Before you add the fluid, you'll need to get rid of the factory grease that's packed into the diff. Fill the clean diff with fluid and seal it. You can leave the front diff alone or fill it with 1,000WT diff fluid. Either way, your truck will have more steering." NOTE FROM CHEVY-SS; I don't really understand this, as typically you want heavier diff lube in front. Personally, for racing, I would try 10,000 in front and 5,000 in rear, but you will really need to experiment with this to find best setting for your truck and/or track conditions.


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Last  update on: 4/19/12.