MonsterGT Clutch & Slipper 

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Section 2 - SLIPPER MOD


Section 1 - Tune your clutch

Issue 90 (May 2003)
Xtreme RC Cars

Jeff Eveleigh

Your clutch is one of your best friends. You could have that new 2.9 horsepower .28 mounted in your top-of-the-line chassis, but if your clutch doesn't transfer the power from your engine to your wheels, you won't be doing too much bragging. You've come to the right place to learn all you've ever wanted to know about clutches. How you should tune, adjust, and maintain your nitro vehicle's most prized possession is on this  page.

OK, here's the skinny on MGT clutch tuning - Quick MGT Clutch tuning from Chevy-SS - Stock Monster GT clutch works great. Works even better with tuning. Tuning the clutch simply means adjusting the spring tension or the weights of the shoes, thereby adjusting the point at which the shoes will engage. You don't want the clutch engaging just off idle, the engine is not making any power. You want it to rev up some before it engages, this will give you MUCH more power out of the hole. Mugen 1.1 springs work great. Additionally, you can lighten the shoes, as shown below;


Read all this below if you want to be a real expert on clutches...........

Clutch Shoes
Clutch shoes are the heart of the clutch and allow a lot of room for altering clutch performance. The mass, size, number, and installation can all change when and how hard a clutch engages.

A lighter clutch shoe will cause the clutch to engage at a higher RPM. Since your nitro engine is timed to produce its power at a high RPM range, the later your clutch engages and the more bottom end power your vehicle will have. Although light clutch shoes offer increased bottom end power, it makes your car harder to drive on low-traction surfaces. Basically, a lighter shoe makes the car feel like your engine is tuned with a slightly leaner bottom end, offering a harder acceleration out of the turn. This setting is preferred on high-traction surfaces and tight courses where quick acceleration is important.

The heavier your clutch shoes are, the earlier your clutch will engage. A clutch with a heavy shoe will have less power while in the low-RPM range, but your vehicle will be easier to drive. If you are racing on a low-traction surface with large, sweeping corners, a slightly heavier clutch shoe is for you.

You can alter the mass of your shoes on your own to change the timing of engagement. If you want your clutch to engage later, you can remove a bit of mass by removing some material. Depending on the clutch, you can either drill a hole in the top of the shoe, cut a small piece of material away from the trailing end of the shoe, or remove some material from the back of the shoe. You can't really add mass to a clutch shoe, so if you want your clutch to engage earlier than the stock clutch allows, you will have to turn to clutch springs (which will be explained next) to do your fine tuning. Don't go too crazy with the hobby knife; if you go too light, the car may be difficult to drive or the clutch might not engage at all. However, don't be afraid to experiment. Clutch shoes are relatively inexpensive, so a few cuts won't kill you while you are searching for that perfect clutch setup.


Another way to adjust your clutch engagement point is to alter the mounting point of the shoe and thus the leverage. Companies such as HPI and Traxxas offer a few clutch shoe mounting hole choices allowing clutch tuning without having to alter shoe mass or change clutch spring rates. When tuning with mounting holes, the closer the pin is to the center of the shoe, the later the clutch will engage since there is less leverage. Moving the mounting hole closer to the center has the same effect as removing mass from the shoe, but the mounting hole change will allow you to go back to your original setting, while mass removal will not without installing a new set of shoes.


The number of clutch shoes used can also alter clutch performance. Generally speaking, the more shoes you use, the more surface area your clutch will have, reducing slippage and making your clutch feel more consistent. Most manufacturers utilize a two-shoe clutch design while high-performance clutches (like the Monster GT) usually have three or four shoes.

What Does A Clutch Do?
The basic job of a clutch is to connect (and disconnect) your engine's output shaft to the transmission, and in turn, to the wheels of your car. The perfect clutch will both engage and disengage at just the right time to allow maximum power transfer, ease of driving, minimal slippage, and quick disengagement.

Most people only think of clutch characteristics with regards to engaging and overlook the important task of disengaging. If your clutch doesn't disengage properly, you could get "run-on" into a turn, a situation that occurs when a clutch doesn't disengage when the throttle is released, forcing the vehicle to carry too much speed into a turn. At low RPM, your clutch should disengage to allow your vehicle to slow down or come to a complete stop without stalling your engine.

Clutches work by following one of the simplest laws of physics. Once an engine reaches a certain RPM, the centrifugal force subjected onto the clutch shoes overcome the holding power of the clutch springs and the shoes are forced outwards against the walls of the clutch bell. The friction between the clutch shoes and the clutch bell causes the clutch bell to rotate at the same rate as the engine's crankshaft and spin the vehicle's transmission and wheels.

Clutch Springs
Just like the mass of a clutch shoe can alter when a clutch engages, the rate of a clutch spring can affect engagement to the same degree. A heavier clutch spring does exactly the opposite of a heavy clutch shoe. Heavy clutch springs cause the clutch to engage later and deeper into the power band of the engine. This makes for a "snappy" feel on the bottom end but makes the car harder to drive, especially on low-traction surfaces. A heavy clutch spring makes your car accelerate very quickly, but it is not always the best setting for drivers with a heavy throttle finger. One of the main advantages to heavier clutch springs are that they allow a slightly higher idle to be set since the clutch won't engage until a higher RPM. A slightly higher idle will make your engine more reliable while at a standstill, like during pit stops or at the start of a race.

Soft clutch springs work the same way as a heavy clutch shoe in that your clutch will engage early, offering less bottom end power but making the car easier to drive on low-traction surfaces.

Clutch springs can be very temperamental and require continuous attention to ensure they are working properly. A broken clutch spring will end your race in a second since a broken spring will not allow the clutch to disengage, causing your engine to "flame out" every time you stop your car or slow it down through a low-speed turn. You should also replace your clutch springs on a normal basis to make sure they haven't weakened with age. A once-firm spring could become softer as it gets older, which would alter the clutch settings that may have worked well in the beginning.

There are a couple of signs to look for that may tip you off that you are having clutch spring problems. If your wheels rotate as soon as your engine starts, your springs are either too soft, worn out, or one or more of the clutch springs are broken (It could also be melted clutch shoes or seized clutch bearings.) The same problem is responsible for a car that cannot remain stationary while the wheels are on the ground (assuming the engine's idle is set properly). If this happens, you should immediately remove your clutch assembly and examine it closer for damage or wear.

Wave of the Future?
Clutch shoes CNC-machined out of aluminum seem to be one of the hottest items in the nitro scene lately. Why is that? Maybe it has to do with the fact that they last exceptionally longer then conventional shoes. It may also be that they offer consistent performance without the worry of melting. Or it could be the reduced mass and stronger engagement. The one thing that it definitely isn't is the increased cost of use and the excessive wear on clutch bells, but if all-out performance is what you are looking for, I guess this doesn't matter much.

If the extra money required for the initial investment and the increased wear on your clutch bell are not issues, then you may be in the market for aluminum clutch shoes. Money aside, the increased performance of an aluminum clutch shoe seems like it is the way to go. A longer-lasting shoe, more consistent performance, and a harder grab make aluminum the wave of the future for competitive nitro racing.

GET THE SHAFT! SG or Pilot that is...
The vehicle that your engine and clutch are to be installed in usually determines whether you should install an SG or pilot shaft, but generally speaking, both types will work in any car with the proper additional parts. There is an argument that an SG shaft will run truer as compared to a separate pilot shaft since the clutch shaft is one piece along with the crank shaft, but for the majority of users, the differences are so minimal that no noticeable performance would be lost or gained with either setup.

Regardless of the type of shaft you are using, it is very important that the pilot shaft or clutch nut is secure. Use blue thread-locking compound (There is never a reason to use permanent-red thread lock in this hobby.) and a strong twist of your wrench to ensure all of your clutch bits stay where they belong.

Clutch Bells
When choosing a clutch bell, the most important variable is the number of teeth on it. You need a clutch bell that will offer the desired gear ratio. You should consider a few other performance characteristics of clutch bells. The best clutch bell designs are made of hardened and also have cooling holes to help dissipate heat and reduce mass. It is important to have a light clutch bell so it can accelerate and decelerate quickly as the clutch assembly does its job. Another area of the clutch bell vital to importance is the bearing mount, type and size. The best style of bearing to use is the ball bearing, and the larger they are, the better.


The mass of your flywheel plays a role in acceleration and idling characteristics. Generally speaking, a low-mass flywheel will allow your engine to be more agile in that it can accelerate and decelerate more quickly. This helps to increase acceleration on the track and makes your vehicle more responsive. A heavy flywheel causes your engine to lose some responsiveness but makes your idle more reliable because of the increased momentum. A heavy flywheel will also make your car less erratic while accelerating and easier to drive.

Some flywheels are vented or have a small fan machined into them. A vented flywheel serves two purposes: it reduces mass by removing material from within the flywheel and it also increases the flow of air across the engine's crankcase to help cooling. You probably won't notice a major difference after installing a vented flywheel, but the theory is there and should offer a slight increase in performance.

The type of material and the way your flywheel is manufactured are important. Most RTR or kit-style flywheels are made from cast aluminum. This type of manufacturing produces a weak flywheel. Flywheels don't really need to be strong themselves, but the clutch shoe pins that are press-fitted into them should be secure. A machined flywheel will offer a much more secure set of clutch shoe pins as compared to a cast flywheel, so if you are stuck with cast, once your pocketbook allows it, upgrade to a machined one.

Other than normal wear and tear on your clutch parts, the only other way to damage a clutch (as in melt the shoes) is by remaining on the throttle when the wheels can't rotate. This is a problem that many beginners have when their vehicle is stuck up against a wall and they continue applying throttle. If your engine is rotating at a high RPM and your wheels and transmission cannot rotate, then the friction between the clutch shoes and clutch bell will turn into heat and melt the shoes. If your vehicle is ever stuck in a position where the wheels cannot rotate, get off the throttle until your car is back in the position where the wheels can rotate freely, and you'll help to keep your clutch in top condition.

Clutch Bell Bearings
There are two main types of clutch bearings. There are caged roller bearings and sealed ball bearings. Caged roller bearings will work, but the nature of their design makes them less reliable since they can melt and their tolerances are much lower, causing excessive slop. Your best bet is to use a high-quality set of sealed ball bearings, and size does matter. The larger the bearing, the better. Some clutches use a 5 mm x 8 mm bearing while most high performance clutches use a larger 5 mm x 10 mm. The thicker races and larger balls of the bigger bearings make them much more reliable, and reliability is a major issue when it comes to clutch bearings. Outside of your engine, the clutch bearings spin at the highest RPM of any area on the car, and they are also subjected to the most heat. For this reason, it is important to use high-quality, large bearings and replace them on a regular basis to ensure they are in good shape. A damaged clutch bearing will usually mean that the clutch will lock up, and if you bring your vehicle to a complete stop, your engine will stall.


Clutch Maintenance
Maintaining your clutch is rather easy, as long as you do it on a regular basis. First, completely disassemble your clutch and examine the parts. Replace any parts that are excessively worn, like clutch shoes, springs, bearings, and the clutch bell. Sometimes you can clean up some of the existing parts. Clutch bells, for example, can be brought back to life by using some very fine sandpaper to clean away any built-up crap from the clutch shoe contact area. You can remove the glaze on the contact patch of the clutch shoe as well with some very fine sandpaper. A good cleaning is in order as well. Remove all of the built-up carbon and debris by spraying every part of the clutch with contact cleaner.

When it comes to things like the clutch springs, you are generally better to just replace them. Clutch springs only cost a few dollars and begin to weaken as soon as you start using them. Fresh springs will ensure that they don't become too soft or break during use. Ball bearings fall into the same sort of category as clutch springs. You are usually best to replace them if they seem worn at all, since the stresses on clutch bearings are so huge. If you decide that it isn't time to replace your bearings, you can simply clean them with contact cleaner and relubricate them. Be careful not to use too much oil or too light of an oil that could leak from the ball bearing and onto the clutch shoe, causing slippage between the shoes and bell.


Shimming And End Play
Don't just slap your clutch parts onto the shaft and install the retaining screw. Take some time to properly shim your clutch for maximum performance. You don't want your clutch end play to be too tight and binding, but you don't want excessive slop either. You ultimately want the least amount of end play while still maintaining a tight fit. This means that you should be able to move your clutch bell forward and back slightly, maybe the thickness of two pieces of paper. It is also wise to install a shim both before and after your clutch bell and bearing are installed.

This ensures that the shield and outer race of the bearing will not rub against the clutch nut or screw head, which could cause excessive drag and heat.

Screws Or E-Clips?
It is common for clutch bell assemblies to be retained onto the pilot shaft with either an e-clip or a screw. Wherever possible, it is better to use a screw with some blue thread-locking compound to hold your clutch together. If you have no choice and you must use an e-clip for the assembly, then apply a small drop of thread lock or silicone on the E-clip to prevent it from rotating or popping off of the shaft.


There you have it: all you've ever wanted to know about clutches. Tune your clutch to drive the car the way you want it driven, and keep this piece of machinery in top shape, and your super power plant will push your high-end chassis around the track for hours with no trouble at all.

Note from Chevy-SS: This clutch tuning page is "borrowed" from the Xtreme RC Cars folks and is a great reason to subscribe to their mag (I do)!


Section 2 - SLIPPER MOD

NOTE FROM Chevy-SS: In my opinion, it is best to simply tighten the slipper (pegs or washers, no matter) all the way down and then just drive a little easier. I use this rubber washer mod shown here, but I run it tightened right up.

From 10Kman at Monster GT Forum:
After recently frying another set of slipper pegs, and paying 10 bucks for a replacement set of them, plus 3 bucks for a new spur, my dad and I came to the conclusion that the slipper peg system is just not working out. I showed him the Strobe setup, but for the price, it just doesn't seem worthwhile.  So, my dad had the idea to just put some rubber washers between the slipper "pads" and the spur gear itself. And, we found out, that it worked like a charm.

Specifics of the "mod"....

Go to Lowe's/Sears/Home Depot, look for the rubber washers that are 7/8" outside diameter, 3/8" inside diameter, and 1/16" thick. Lowe's has them for about 50 cents.

Basically, the mod is very simple. Take a spur gear, take out all of those worthless slipper pegs and put them in your spare parts bin. The washers go between the silver slipper pad and the spur gear itself. The inner washer will fit over the collet and center itself, the outer one will need you to center it, but it isn't a huge deal if it's off, because it's going to be smaller than the silver slipper pad anyway.

Some notes:

I had it "almost tight", it had some room to tighten down a little more, but I left it where it was.

Wheels stayed down for the most part, but would still give me wheelies if I really nailed it. I'm sure if I cranked it down all the way tight, wheelies would increase.

Truck has a well-tuned Mach .26 in it, so I'm not dealing with the stocker .21.

Also, I have a set of fiber washers (Sears), same size as the rubber ones, but I didn't try them out. I'm pretty sure they'd work as well. The rubber ones after one quart of fuel showed no huge signs of wearing. You'll notice that the rubber ones sorta smash into the holes on the spur gear, and hold them in place for the most part, but we did see some slippage marks around the washer, so it was doing what it was supposed to do. And, if it doesn't slip, the rubber washer will sorta "flex", and produce the same result.

So, I'm pretty much sold on the 50 cent washer idea. Those pegs are just not workin' out, and the Strobe is just too expensive for what you are getting.

Good luck, if anyone tries any other washers, post results. If I get around to the fiber ones I'll post a follow-up.



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Last  update on: 4/19/12.