Talking Hydraulic Clutches With Silver Sport Transmissions

In terms of performance and reliability, it’s no secret that automatic transmissions have evolved exponentially over the years. In many ways, they’ve surpassed their manually shifted brethren. However, it is also equally true that many individuals still like to get that adrenaline rush of banging through the gears and enjoying the feeling of being connected to the car beyond sliding a shifter into Drive. As with the automatic, the manual boxes have also evolved, and the efficiency of function has equally improved. If you’re a traditional muscle car or street rod fan and prefer a manual shift, then you’re probably familiar with the heavier feel some mechanical clutches deliver – and some prefer that feel. However, the benefits of a modern transmission coupled with a hydraulic-clutch system far outweigh an old-school mechanical setup.

Hydraulic clutch

Part of the installation process also involves what is called the Bearing Cushion Measurement. The Concentric Slave Cylinder (throwout bearing) is designed to be compressed more than ½-inch by the pressure plate fingers when at rest. The CSC needs a minimum of 1/8-inch “cushion” beyond that to allow for clutch-disc wear and expansion from heat. Clutch slippage will result if the CSC bottoms out and is partially depressing the pressure plate fingers at rest. The acceptable range for the CSC cushion is between 1/8-inch (0.125-inch) and 3/8-inch (0.375-inch). If your cushion measurement is outside of this range, you will need a spacer(s) to adjust the position of the CSC.

If you’re basking in the warmth of being a traditionalist or are knee-deep into a nut and bolt restoration that requires a mechanical clutch and OEM transmission, an upgrade probably isn’t in your vocabulary. However, if you’re the type of individual that likes to stretch your vehicle’s legs, a modern hydraulic-clutch upgrade is clearly an option. As with things that require change, there are always pros and cons to take into consideration. To clear up some of the confusion, we reached out to the folks at Silver Sport Transmissions (SST) to get some advice.

In the SST catalog, you can find a wide range of transmission packages that have been designed to work with most car brands. Some of the more popular offerings are the TREMEC TKO, the T-56 LS/Magnum, and the all-new TKX. But, the SST systems encompass a wider palette of shifting options. While we will use the modern boxes to illustrate some of the procedures, it is worth keeping in mind that if you don’t want to swap out your existing old-school four-speed, you can nudge it into the 21st century by replacing the mechanical clutch with its modern hydraulic counterpart — a Concentric Slave Cylinder — more commonly referred to as a hydraulic throwout bearing.

Installation of the Concentric Slave Cylinder is the next step in the process. This procedure will vary, depending on which type of transmission you’re working with, whom it was purchased from, and if you’re converting it over from a mechanical clutch system. If you have a TKO from another TREMEC supplier, you will need to be particularly careful because it requires the removal of the front bearing retainer so it can be swapped with a custom SST bearing retainer. Failure to follow these instructions can cause the input shaft to fall out, which would allow the roller bearings to fall into the case, which would require disassembly of the entire unit. If you’re working with an RS, T56, Magnum, or T45RS, your bearing retainer is only used as a mount for the CSC. It is completely external to the transmission and does not contain the input shaft bearing or oil seal.

Fluid-Driven Separation

The cost of doing one of these upgrades is always a factor to take into consideration. A full swap will place you at a much higher price point. However, the mechanical-to-hydraulic switch, while still requiring an initial investment upfront, is actually cost-effective. We asked Jeff Kaufman of SST for his input on the nuances of such an upgrade. He notes, “The only perceived downside is the initial cost, but there are far more plusses that negate that initial cost.”

So, the logical question is, why make the switch? Let’s look at what you have with a mechanical system. By virtue of its design, with regular use, mechanical systems require periodic adjustments as the clutch wears down. Also, all the hardware utilized (linkages) takes up more space. Another consideration includes the deterioration of those linkage pieces that wear with time, causing actuation to get loose.

With the assistance of the folks at SST, planning what to install will require very little homework as to what will be best suited for a given application. The biggest mistake to avoid is the idea of piecing together a hydraulic system from a variety of different manufacturers. This can be quite problematic because every component needs to be mechanically matched in order to work properly. A company like SST offers a selection of kits that they’ve designed and tested for a wide range of vehicles.

If running a three-finger clutch (Borg and Beck) it is highly recommended you change this style pressure plate to a diaphragm-style unit when using a hydraulic throwout bearing. You should also remove the clutch pedal over-center spring if your vehicle is equipped with one. Failure to remove the over-center spring could result in the spring holding the clutch pedal down during normal operation. It will also hold the pedal down while performing the bleeding operation. An over-center spring is not recommended for use with a diaphragm-style pressure plate.

“There are a lot of companies out there that use aftermarket parts,” says Jeff. “There is a difference between those and original equipment parts (OEM). With OEM parts, there is a whole lot more engineering behind them for long term use. The company that makes our bearings is an OEM tier-1 supplier to a number of automobile manufacturers. These bearings are the same-quality bearings that you will find in a brand-new Camaro. Their OEM validation is 10 years or 150,000 miles before you should expect any need for service, so our bearings are made to last within those parameters. The bearing itself is actually rated at 300,000 miles or one million strokes. That is the testing and validation on the bearings that we use.”

The Heart Of The System

Buying a kit that has been pre-packaged is a sensible approach because all the leg work has been done for you. With the SST kits, Jeff points out, “The appeal of our hydraulic-clutch systems is the firewall mount. In order for them to work, you have to have a small master cylinder. The concept of it is exactly the same as brakes. The small master cylinder on the firewall pushes fluid through a hydraulic line to a hydraulic bearing, making it expand, and that is what pushes the clutch finger to release the clutch. A Camaro firewall is going to be different than a Corvette firewall, so we have engineered individual firewall mounts that are specific to a given car that allow it to be mounted at a proper angle and location. We do this so someone doesn’t have to mess around to find the correct pushrod angle and where to mount the master cylinder.”

He further adds, “Older cars with mechanical clutches have a rod attached to the clutch pedal that goes through the firewall. They are set at a particular angle. That is what we duplicate with our firewall mount. That mount will maintain the pedal ratio and a straight push into the master cylinder. You can’t have the rod going into the master cylinder off-center, because it will score the internal bore. As long as the owner maintains a straight push of around a 6:1 pedal ratio, then the pedal will be nice and soft with that straight push into the master cylinder.”

On a car originally equipped with a manual transmission, you’ll need to locate the clutch-pushrod hole. On a factory automatic car, this may be a hole with a rubber grommet or a small sheetmetal cover. Some vehicles may not have a factory hole in the firewall at all, but there should be a spot that is contoured for a hole. If you don’t have an existing hole, you’ll need to cut a 1-inch hole in the factory spot on the firewall.

The correct installation of the master cylinder is critical for a properly functioning system. The pushrod has to be centered in the firewall hole and point toward and reaches the clutch pedal attachment point. It has to move in a straight line and will not tolerate a side load, which will cause excessive wear and lead to premature failure. The firewall pictured is of a first-gen Camaro and shows the metal plate that would need to be removed.

Are there any downsides to a hydraulic system? We’ve mentioned the perceived up-front cost is actually a non-issue when factored with the longevity of the system, however, hydraulic systems aren’t bulletproof – nothing ever is. Maintaining a proper fluid level in the reservoir and keeping the system leak-free are key factors with a hydraulic system because it allows the clutch to self-adjust. Outside of that, it is maintenance-free.

Jeff does point out, “Typically, we don’t see any failures, but when we do, it usually occurs from the beginning, when there is a very specific set of procedures to have the bearing operate in a defined distance behind the clutch fingers. If a person skips those steps or doesn’t read the directions — or makes assumptions and the bearing is outside of that functioning range and it overextends — that’s when it can blow apart. If the directions are followed, there won’t be any issues.

Most guys we work with don’t do this every day, so they aren’t going to have an understanding of the nuances of these systems. If something is unclear, we have dedicated tech support. Jeff also points out that if you have a vehicle that is not a mainstream brand or model, SST has you covered as well. “We have a universal kit where you can adjust the pushrod length and the pushrod angle on the master cylinder, so it can be more universal.”

hydraulic clutch

Bleeding the system will be required and is a two-person operation. You must use DOT 4 brake fluid as the CSC units are not compatible with DOT 5 fluid, and will be damaged as a result. SST’s instructions outline the steps to follow, which are very similar to bleeding a brake system. Another option for bleeding the system is to use a vacuum bleeder.

Doing the swap to a hydraulic clutch system isn’t very difficult, and is in many ways a cost-effective upgrade that will add enjoyment to your driving experience. The task can typically be accomplished in a day, with a few simple hand tools. ONce completed, you’ll be bangin’ gears in no time, and staving-off leg cramps from holding the pedal while in traffic. What’s not to like?

Article Sources

About the author

John Machaqueiro

John has been immersed in the car hobby since his teenage years. A fan of endurance racing, and muscle cars, those interests have evolved into a journalism career that has allowed him to photograph and write about them.
Read My Articles

Hot Rods and Muscle Cars in your inbox.

Build your own custom newsletter with the content you love from Street Muscle, directly to your inbox, absolutely FREE!

Free WordPress Themes
Street Muscle NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Street Muscle - The Ultimate Muscle Car Magazine

We'll send you the most interesting Street Muscle articles, news, car features, and videos every week.

Street Muscle - The Ultimate Muscle Car Magazine

Street Muscle NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...



Classic Ford Performance

Drag Racing

Classic Chevy Magazine

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Classic Ford Performance
  • Drag Racing
  • Classic Chevy Magazine

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Thank you for your subscription.

Street Muscle - The Ultimate Muscle Car Magazine

Thank you for your subscription.

Thank you for your subscription.

Loading