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> Centerforce Dual Friction Clutch - Clutch Basics
post Aug 6 2010, 06:35 PM
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When The Horsepower Count Goes Up You'll Need Some Extra Driveline Clout. A Centerforce Clutch May Be The Answer.
From the August, 2010 issue of Popular Hot Rodding
By Jim McGowan
Photography by Jim McGowan

Here are the components of the Centerforce Dual Friction clutch assembly. The disc and pressure plate come as a matched pair. Always install a new throwout bearing. We're also are using a Centerforce clutch alignment tool (PN 53010).

Chatter, slipping, limited or no adjustment, catastrophic failure, and heavy pedal pressure are the most common reasons to upgrade your clutch, but sometimes the simplest reason is a technological upgrade for comfort. Older OEM finger clutches have been used with most three- and four-speed standard shift cars for decades. These old heavy-duty clutches sound cool, but have you ever driven one in stop-and-go traffic? Not fun, unless you have a hydraulically powered left leg. This '70 Judge had an older aftermarket performance clutch, which was getting tired. It started chattering and wasn't holding sufficient pressure on the flywheel. And most aggravating, it was a bear to operate. Time to upgrade.

We're installing a Centerforce Dual Friction clutch (PN DF271739), which distributes pressure evenly over a 360-degree friction facing on one side of the clutch disc, and uses a segmented design on the other side to concentrate clamping pressure, hence the "dual friction" moniker. We chose this clutch because it combines excellent driveability with light pedal pressure.

Whenever you're replacing a clutch, always have the flywheel resurfaced or install a new flywheel. Just because it looks good doesn't mean it is good. Any clutch disc needs a flat surface to properly engage the flywheel, and about 500 miles of use to break-in properly. If your flywheel is glazed or uneven, the clutch disc will wear out in short order.

The engineering of this Centerforce pressure plate includes a centrifugal weight system. As engine rpm increases, the centrifugal force also increases due to these weights. This force increases the diaphragm pressure, resulting in more clamp load down through the pressure plate and disc to the flywheel. Simply put, this creates a clutch that functions more efficiently and with far less pedal pressure than a conventional finger-style clutch.

Here's the patient waiting for the clutch transplant. It's a 400hp, four-bolt main, 400-cid Ram Air III engine backed by a Muncie M-20 wide-ratio and a 3.55 factory GM 10-bolt

If you're installing a new clutch install a new throwout bearing. They're inexpensive, and are a critical part of the system. A worn bearing will usually be noisy and will not provide the proper release capabilities for the clutch. We're installing a Centerforce self-aligning bearing (PN N1716), but will first compare it with the one we remove from the car. They must be the same height, diameter, and have the right inside diameter to work properly. Always check before installing the new bearing. This bearing is the replacement for all GM applications that use a stamped-steel throwout bearing fork.

We are installing a new bellcrank and pedal-to-crank actuation rod. The attaching holes in the original crank are slightly out of round from four decades of wear, and this slop affects the precise action of the clutch.

Our installation took between four and five hours, working slowly. Allow a day if you are working on the floor. After we adjusted the clutch, the testdrive was amazing. The pedal pressure was half of what it was, and the clutch engagement was positive, smooth, and effortless, making the car a pleasure to drive. Let's proceed with the R&R of the clutch, and look at some other critical parts and procedures along the way.

Preinstallation Checklist
It's a good idea to have a factory service manual for your car
Have a can of brake cleaner handy to wash the machined flywheel
You'll need a torque wrench for the flywheel/clutch plate bolts
Do you have an alignment tool for the clutch assembly?
Do you have a replacement pilot bearing and removal tool if applicable?
You'll need a floor jack and four jackstands for on-the-ground work
Have a jack to support the transmission if working on the ground
Take pictures of all the components and linkages before removal
Refer to your vehicle manual service for clutch adjustment procedure

Here's the setup before we started the teardown. Unless you've done this before, always take photos of how the linkage and other parts are attached before taking everything apart. Also write down the order of your disassembly, and use the reverse order for installation.

Begin by disconnecting the e-brake cable, recording how long the threaded rod sticks out from the nut securing the cable. You can duplicate the exact original setting at reinstallation.

Now disconnect and remove the rest of the reverse lockout linkage rods. If you're working on a restored car, these parts can be cleaned and replated, or freshened up with Eastwood Detail Gray or Silver Cad paint.

The original bellcrank is now lowered free of the mounting. The speedo cable can also be disconnected and moved out of the work area.

The bellhousing lower cover can be loosened and left hanging until the bellhousing is removed, and both exhaust pipes disconnected. Why haven't they been replaced you ask? They are original to the car and are still solid. Replacement pipes are not shaped the same as the originals, which are crimped to clear the crossmember

Underhood, we disconnected the clutch actuation rod from the bellcrank and the reverse lockout rod at the steering column. The car can now be put up on a lift, which we luckily had, or up on four heavy-duty jackstands.

The engine is now supported on a floor jack or transmission stand prior to disconnecting and removing the crossmember

After removing the two transmission mount bolts and two bolts at each side of the crossmember, the part can be angled and removed from the chassis. The floor jack or trans jack is now supporting the engine and transmission.

We loosened the nuts on the U-bolts, which secure the driveshaft to the rearend yoke. It is a good idea to wrap a piece of masking tape around the needle bearing caps on the joint. Sometimes the caps can fall off, scattering the little needle bearings

The shifter handle was jammed on the shifter, so rather than damaging it, we simply disconnected the linkage rods and swung the assembly over the exhaust pipe. Take pictures of this step so you have a reference as to how it all goes back together. You don't want First where Second should be.

Unless you're a body builder, having a friend available makes trans removal and replacement a lot easier. It might need to be rocked around slightly while pulling back to get it free, and once it is free, it's heavy

Before removing the driveshaft, mark the original placement of the parts for correct reinstallation. A black marker works great.

Now remove the four bolts securing the transmission to the bellhousing. All four can be taken free, as the input shaft will hold the trans in place.

With the trans out, remove the bellhousing with the clutch fork in place. We discovered an older finger-style aftermarket pressure plate attached to the original flywheel. The lower trans cover can now be removed, as it was captive around the back of the starter. Remember, keep a record of how you took things apart.

Our flywheel was showing its age. There were several areas that were glazed. We inspected the pilot bearing, and it was in excellent shape, so it wasn't removed. Had it been original, or showing wear, we would have changed it

The Centerforce pressure plate was hung loosely with one top bolt in place. The disc, which is marked as to what side faces the engine, is then slipped up under the plate and located with the alignment tool. The tool fits all the way into the pilot bearing, exactly lining everything up for the 10-spline input shaft.

We had a spare flywheel resurfaced prior to starting the work, so we didn't have to stop to have the machining done. Either install a new flywheel or have a spare as we did for convenience. The contact surface was thoroughly washed with Justice Brothers Brake Cleaner. We torqued the flywheel bolts, moving side to side to 100 lb-ft, per the factory manual

With everything properly aligned, the plate bolts were crisscross tightened so the tightening pressure was evenly distributed, and then each bolt was finally torqued to 35-38 lb-ft

The throwout bearing is now inserted into the clutch fork. The large side faces the clutch and must be inserted correctly into the fork. The fork spring clips must be installed between the throwout bearing collar flanges. If the clips are installed above the top flange, you will not be able to properly adjust the clutch and you'll be doing the job twice

After reinstalling the transmission and bolting it all up, use your "before" photos to reattach the linkage. A slipup here can affect the gear positioning, so get it right the first time

Now reinstall the bellcrank, spring and mount, lockout rod, speedo cable, and other miscellaneous items. The crossmember and driveshaft follow in sequence. Consult your manual for how to do the final adjustment on your clutch.

Here everything is back in place and tightened. Notice the throwout bearing appearing to be off center. This is intentional as the bearing is self-aligning, and will be perfect once the trans input shaft passes through it

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