MonsterGT MGT-RPM Knuck Mod 

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TheDude, TD Racing
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MGT-RPM Knuck Mod

April 27, 2012 - READ THIS FIRST! All the stuff below is old, out-dated info. I am leaving it here so that folks can see what we did a few years back. This mod worked real well - but THESE KITS ARE NOT FOR SALE ANY MORE!!!

However, if you want to upgrade to larger 8mm stub axles, then I will bore out YOUR RPM knucks (to utilize 8x16x5 bearings) for free. Please note: there is no way to utilize the larger pillow balls. The larger pillow balls require custom hand-made Delrin (plastic) retainers, and I do not have the machine set up any more to make them.


OK, myself and TheDude have been working on a knuckle solution. Some of our original work started as a mod using TTR knuckles. Read about the TTR knuckle mod here. Well, we had a few problems with knuckle breakage in the rear of the MGT. The TTR plastic is just a little too brittle and breaks. In the front, however, the TTR knuckles work great! So, we've been arduously examining other alternatives and have come up with a solution using RPM knuckles.

The modeled upgrade looks REAL GOOD. Here are some details and pics of the assembly and it's components...

Benefits of this system include:

bulletutilizes HPI 8mm buggy stub axles, which are virtually indestructible
bulletuses standard (every LHS carries these) 8x16x5 wheel bearings (inner & outer), last much longer than small MGT bearings
bulletRPM knucks can be used on all four corners
bulletyou can use stock a-arms, as well as RPM arms; your choice
bulletuse 17mm* or 23mm wheel hexes, as needed, very easy to swap
bulletRPM knuckles are extremely tough, using flexible plastic**
bulletRPM knuckles are exact same geometry as stock MGT knuckles
bullethuge, lightweight pillow balls will not pull out on impact (stock balls often do!)
bulletlarge pillow balls allow you to Dremel knuckles out for steering mod (your option)

NOTE: this setup does NOT work with stock MGT 14mm hexes!
*NOTE #2: some 17mm adapters may slightly hit the Delrin retainers, so I advise using 2mm offset 17mm adapters if you want 17mm adapters.
**NOTE #3: these modded knucks are NOT covered under RPM's lifetime warranty.

As of today (3/31/07), I (Chevy-SS) have decided NOT to sell this kit. It's just way too labor-intensive to produce.

Here's what the MGT-RPM Knuck Mod kit will contain:

  1. Five modded knuckles (one for a spare, just in case)
  2. Four HPI 8mm stub axles
  3. Four 3x17 pins to secure 17mm or 23mm wheel adapter of your choice (wheel adapters NOT supplied)
  4. Four 5mm set screws (to hold the wheel adapter pins)
  5. Eight 8x16x5 rubber sealed bearings
  6. Ten (two for spares) custom machined Delrin pillow ball retainers
  7. Eight lightweight pillow balls


Installation of the MGT-RPM Knuck Mod:

The knucks go on pretty easy, however, you need to do two things:
1) Drill out the a-arms for the larger pillow ball shafts, and,
2) Grind the front knuckles for extra steering.

The a-arm holes need to be drilled out to accept the larger pillow ball shafts, however, the a-arms themselves remain at the stock length. I used a 13/64" drill bit to enlarge the holes. Don't go too deep. WHEN DRILLING - BE CAREFUL, AS THE DRILL WILL WANT TO PULL ITSELF INTO THE HOLE, AND IF YOU GO TOO DEEP YOU RUIN THE A-ARM!!!!!!!!

The Delrin retainers can be adjusted with a large screwdriver, or you can simply use a quarter or other large coin. I recommend you re-check adjustment after running for a while. When removing and re-installing the retainers, take your time to make sure the threads align properly!

You will need to Dremel a little bit of the front knuckles. Do it slowly and carefully. Get it so that the pillow ball shaft lies at about the same angle as the knuckle arm.

The knucks will need some grinding for maximum steering -

Yeah, I know this doesn't look pretty, but it works just fine. I leave the final grinding in your own capable hands.

That's it, you only need to do this to the front knuckles. The rears should have enough for the up/down movement, but it's always good to check and make sure. It's real easy to clearance as necessary.

Just take your time and don't grind too much! I'm sure you can do a prettier job than me, hahaha.............


Now adjust toe and camber as usual.



Pics of the knuckle mod -

*NOTE #2: some 17mm adapters may slightly hit the Delrin retainers, so (to avoid this) I advise using 2mm offset 17mm adapters if you want 17mm adapters.

I don't think I've ever heard of anyone actually BREAKING a RPM knuckle. RPM uses a proprietary plastic which is very strong and flexible. Unfortunately, the flexing sometimes allows the small, stock pillow balls to pull out. But the huge TTR balls won't pull out, that's for sure..........These modded knuckles are awesome.

The front knucks needed quite a bit of Dremeling to get "maximum" steering.

STEPS TO CREATE THE MOD - There's more to this mod than meets the eye. Here's a short summary of what needed to be done:

  1. Bore out stock pillow ball holes for oversize pillow balls, precisely locating the new balls
  2. Tap the new pillow ball holes
  3. De-burr and smooth the new pillow ball holes for smooth operation
  4. Bore out 15mm bearing pockets to 16mm, for inner and outer, precisely (and I mean, it had to be PERFECT) locating holes for depth and alignment
  5. Turn down (on lathe) 5/8" Delrin rod and hand-fabricate new pillow ball retainers, one at a time, holding tolerances within .002"
  6. Test fit each and every piece by hand to ensure optimum fit

Note on JIGS

I made jigs to hold knuckles at various stages. I made them out of plywood, as you're only milling plastic, so a super-strong metal jig is not necessary. I used a jig for reaming and tapping the pillow ball holes.

For drilling out the bearing pockets I used a piece of 2"x4" wood and drilled a 3/4" hole in it, then held the knuck (with my fingers) over the hole. The 3/4" hole was so the .528" guide pin would have a spot to go into.

Note on tap in pic above: it is NOT the stock 15mm thread. The stock thread is 15.0x1.0

The machining process is slow and laborious. Everything needs to be pretty damn accurate and it takes time to set up (and switch) the tooling and the jigs. The Delrin retainers are all lathe-cut by hand and we can only make about a dozen per hour, so this is not a high-quantity production line..................Another option may be to take some stock 15mm aluminum retainers and use a Ball End Mill to hollow them out a bit, then just thread the knuckle appropriately. I didn't want the pillow ball contacting metal, so I used Delrin plastic.



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Last  update on: 4/19/12.