The stock clutch that is coupled with any vehicle usually works perfectly, if the rest of the components are still untouched, and performance modifications are left alone. Chances are, if you are reading this article, one of the vehicles sitting amongst your collection has, or had, a clutch issue at one point in its life. Maybe it's due to added power, the way you drive, or simply because it's finally warn out. If it hasn't started slipping yet, eventually, a replacement clutch, upgraded or not, will have to be installed.
Let's just assume that your ride, for the purposes of GM High-Tech Performance, is not stock. That high-performance ride of yours sounds similar to a top-fuel dragster (at least you think so), and consequently, the windows are surely rolled down when cruising around town, creating a custom eight cylinder symphony for your listening pleasure. One time, sitting in rush hour traffic, a sneaky smell wafts its way into your left nostril, and it doesn't smell like raw, unfiltered exhaust. BAM! It hits you. During all of the stop and go rush hour rubbernecking nonsense, you've finally noticed that your clutch is slipping, and it's emitting a putrid scent while doing so. Has it started slipping because you've been dragging your left foot?
Alternatively, at the track, the tree turns green, and like a finely orchestrated and synchronized dance move (…not the sprinkler) the left foot slides rearward, while the right one smashes oh so carefully into that throttle. BAM! You should've cleared 60-feet by now, but instead, you're wondering what that smell is, and that maybe it's time to kick that ill performing stock single disc to the curb, in favor of a beefy twin disc.
Okay, okay. Enough with the scenarios. The clutch is worn out, and it needs to be replaced with an adequate version, single or twin, that's able to hold up to whatever abuse you intend to punish it with. On the contrary, a full race-spec clutch is not the answer for a heads and cam 5th-Gen. Or, is it? Where do you begin? The RAM Clutches team has provided some valuable insight, and graciously provided some pointers with pictures. You see, increased horsepower is often assumed to be the only factor, when in fact, multiple factors are in play. We'll address those “other factors” that impose additional loads on the clutch and transmission, which are gearing, tire selection, and power adders. Finally, we'll take a look at signs of wear, to determine how the clutch beneath your body was lost, in order to find the best replacement.
Tips, with the help of the RAM Clutches team:
If you run a higher gear ratio (lower numerically) it will severely overload the system, meaning your clutch and transmission. For example, a 3.55:1 rear gear will introduce a significantly greater load on the clutch than a 4.10:1. If you've messed with the gearing in your chariot, make sure that you're not going to prematurely wear down your clutch. If it's already slipping, and you know the ratio has changed from stock, the answer is an improved clutch.
If you run a drag radial, the car will have a tendency to hook the tires rather than spin them. As a result, it too will impose a greater load on the clutch system. Leaving the line on sticky (thanks to a good burnout) tires instantly puts tons (literally) of increased stress through your entire setup. Think of the induced load like a shockwave from an explosion. It's going to go from that engine, all of the way to the tires (clutch in-between), before you get that perfect launch. Even if you're not an eight-second regular, swapping on those stickies may be of concern for your clutch down the road.
Q: Given the amount of bluing on the friction pads of this clutch plate, is it completely toasted? Can it ever give service again?
A: The outer area of the pad has more blue than the inside, indicating that the pressure ring has warped. This disc could not be used on a new plate, and would result in uneven contact on the friction surface
Q: Also, how much bluing can the friction pad take?
A: While it’s difficult to predict, it most likely has to do with how much glazing or hot spotting the pressure ring has on it.
Q: Does the pressure plate blue before the friction pad, or versa visa?
A: Usually, the ring will hot spot, or smear, around the same time.
Adding nitrous, a blower, or a turbocharger (or two) to your beast will impose an instant load on the clutch system. Once that stock clutch wears out quickly, make sure to always select an aftermarket clutch system with a higher horsepower rating, than your current power level, or your anticipated level. Selecting a clutch system that is under rated ensures premature wear, and is obviously why your stock clutch won't last.
Larger diameter clutches or clutches with more aggressive friction materials, (higher coefficient of friction) for example, like metallic materials, will address increased loads better. Alternatively, stepping up from a single disc to a dual disc setup will also help to address those increased loads.
If street time is limited and track time becomes the priority, it would be advisable to select a dual-disc clutch at the onset. Dual disc setups will transmit higher torque loads more efficiently, helping to dissipate the heat, and will function properly, for a longer timeframe.
Not to point fingers, but simple driving habit changes can prolong clutch life, while halting premature wear. Take a look at these three tips on how to avoid clutch troubles at the drag strip, from the professionals at RAM Automotive Company:
First, disable the traction control to eliminate the risk of introducing extreme loads to the clutch system, inadvertently. Some traction control systems apply the brakes, while others use rapid ignition retardation that affects the clutch.
Second, remember to select a low gear. Even professional racers have launched in second and third gears, all stressing the transmission and clutch.
Third, ensure the rear tires are positioned in the water. As you exit the water, depress the clutch pedal before they reach dry track surface. Following this advice avoids transmitting stressful, and severely damaging, loads through the clutch system and drivetrain. Speaking of stressful loads, let's look at signs of wear, in a Q and A between the pros at RAM Clutches, in the pictures below:
Q: This 10.5-inch clutch is pretty hammered, so what went wrong?
A: Possibly, a single disc unit was selected, but more clutch was needed. Driver error could also be to blame. However, there could’ve been installation issues. If the fingers of the clutch are shiny or worn, the release bearing could have been adjusted too close to the fingers, and as the clutch wore in, the bearing unloaded the clutch.
Q: Do the oblong marks on the clutch fingers, where they made contact with the bearing, appear normal?
A: The wear on the tips is fairly normal, and if there were a lot of flat spotting, it would indicate the bearing is riding the fingers from maladjustment, or from the driver ridding the pedal.
Q: What is the most important precaution, to ensure this misalignment is avoided?
A: Concerning mechanical/cable release vehicles, having the bearing adjusted too close to the fingers initially, when the wear occurs, the bearing will end up ridding the fingers and unload or slip the clutch. On hydraulic setups, too much preload on the bearing may cause it to bottom out rearward and unload the clutch.
Q: Why is there fabric caught between the fingers and the cover body? Presumably, the black dust conveys something ominous?
A: Simply, this is caused by the severe wear that has taken the friction material right down to the fiber and it has gathered around the fingers.
Q: Is this a single 9.5-inch that was subjected to forces better suited for a 10.5-inch? Are there any other symptoms (smell, audible, visual—maybe lots of black dust) that should have alerted the user that things weren’t well in the clutch department?
A: The smell of the unit for sure, the driver may have even been getting some black dust out of the bell housing. The parts tell the same story, and this setup must have been slipping almost non-stop. The driver needed more clutch.
Q: So this single setup is very much warn, and here’s the reverse side, but when you said, “The driver needed more clutch,” do you mean he needed a dual-disc or are there other alternatives you have in mind?
A: I was thinking of a dual disc or if the vehicle is more of a racecar, perhaps a proper racing clutch.
Q: Do these pictures of the fingers of this clutch suggest an overly close bearing?
A: Notice the flat spotting. Normally, the finger would be rounded off along the contour of the lever tip. Potentially, it could be just from a constant riding of the pedal by the driver. Poor adjustment is a common mistake that individuals make when installing a clutch. If you do not leave bearing clearance, as the disc wears, the fingers move back or get taller, and can ultimately bottom out of the bearing, and cause it to unload the clutch.