Replacing the Clutch
Paradise Garage

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© 2003 Brian F. Schreurs
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Eighteen tons, and what do you get? A bigger truck!
When the clutch started slipping on a 1999 Pontiac Firebird Formula, we wheeled it in to Paradise Garage for a clutch swap. But the newer clutches are so much better than the crap they put on the earlier cars that we planned a mild upgrade: a somewhat more aggressive clutch and the improved GM slave cylinder for better holding power without sacrificing driveability. To achieve this combination, we went with a SPEC Stage I clutch (SPEC is a rather forced acronym for "Star Performance Engineered Clutches").

To do this job, we called Thunder Racing to get the slave cylinder (#20-1256514) and clutch (#100-SC731). Then to make sure we had everything we'd need, we called Dal Slabaugh and told him to send us everything we'd need. He sent us lots and lots of bolts and nuts: a bag of flywheel bolts (GM #12553332), six bolts for the pressure plate (GM #12561465), a U-bolt (GM #14076942) and two nuts that we didn't actually use for anything, and a bag of ten bolts (GM #1151473), out of which we needed exactly two for the slave cylinder. We also got some genuine hydraulic clutch fluid from GM.

Jack up both ends of the car. You're going to need to do it sooner or later anyway, so you might as well get it over with.

The drain plug.
You may not be aware of this, but manual transmissions have fluid in them. It needs to come out for this job; it's about four quarts of normal Dexron III automatic transmission fluid, nothing terribly exotic. The drain plug is at the back of the transmission, passenger side, cleverly labeled "DRAIN". It's got a sunken square head, conveniently the exact same size as a 3/8-drive ratchet.

With the trans merrily peeing on the floor, you can consider the big philosophical question: to remove the shifter or not. In the long run, you can probably do this job with the shifter attached to the transmission. The question is whether you'd want to: it causes all kinds of clearance headaches, and in the long run it's not really all that hard to remove. Check out installing a shifter to see what that job is like. In any case you'll need to remove the shifter knob and handle, detailed in the other tech article.

Come on. Don't be a fool. Remove the shifter. While you've got it off, replace it with a better one.

Once you've got the shifter issue sorted, it's time to start removing all the other stuff attached to the transmission. Start with the driveshaft (GM calls it a propeller shaft). Release the e-brake, if you have it engaged, so you can rotoate the axle; while you're under the car to observe the bolt alignment, have your assistant turn the wheels so that it is possible to reach the bolts. There are four bolts, all 11mm. Be sure to matchmark the driveshaft and the differential so that they can go back in the exact same alignment -- it's balanced. The bolts are holding the shaft and pinion together with a pair of little brackets that go over the joint. You'll probably need to pry the driveshaft off the pinion -- carefully! -- then the driveshaft slides backward out of the car. If the axle is sitting low, it may need to be raised for the driveshaft to clear it. The driveshaft will bring a small amount of transmission fluid with it. Try to keep the shaft clean of any dirt or debris, as you don't want to get any grit up in the trans.

Now it's time to start removing all the stuff holding the transmission in place. In the back, this includes the crossmember and torque arm. There's a flange that goes from the passenger side of the transmission to the passenger side exhaust pipe. It's held to the exhaust system with two 15mm bolts; remove them. Next, the crossmember will come off, so it's time to get a trans jack under the tranny. We use a scissors jack. Whatever you use, make sure the trans is secure. Depending on the type of trans jack you have, you may need to remove the two lower trans bolts before putting the jack in place because of clearance issues. The trans bolts are 15mm.

The crossmember is held by four perimeter bolts, all 15mm, and one large 18mm bolt in the middle. Remove all of these, but watch for the wire loom that has a clip attached to the crossmember -- you don't need to make chassis rewiring part of the project! Pry the clip off the crossmember with a screwdriver.

The torque arm mount on the transmission side.
Disconnecting the torque arm can look tricky. The torque arm mount on the trans side has two bolts: one passes through the trans housing, and the other is a blind bolt welded to the mount. The removable bolt has a 15mm head and a 15mm nut on the other side -- holding the exhaust bracket to the trans. Some people like to remove this exhaust bracket but in truth it may not be necessary (if you find it necessary, it's held on by that 15mm nut plus one other 15mm nut right next to it, which corresponds to the blind bolt on the torque arm bracket). Just remove the one 15mm bolt that provides clamping force to the torque arm bracket. On the other side of the torque arm, remove the two huge 13/16" nuts attached to two huge 13/16" bolts -- probably with a breaker bar. Then make sure the axle is raised (not dangling) to get the arm off. It'll just slide backward.

Confused? Heck, we're confused just trying to write about it. When you get under the car it'll make more sense. Just remember: big 15mm bolt front, two big 13/16" bolts rear.

Remove the transmission mount by undoing the two 13mm bolts, if you think it's necessary, but from looking at it we're not sure why you'd want to.

Next, unplug electrical connectors, starting with rear of driver side:

  • blue/grey connector goes to a big solenoid at the top back left side of the trans: that's the reverse lockout.
  • purple/black connector, below the blue/grey connector, which goes straight into the trans: the vehicle speed sensor.
  • a plug toward center top of the driver side: the notorious skip shift solenoid.
  • remove one push pin halfway down the trans and one near the top.

And on the passenger side:

  • brownish/greenish connector towards front of the passenger side: the backup lamp switch.
  • a "rosebud clip" for the wiring loom at front of trans needs to be watched as it's held down by one of the trans bolts, and is also clipped to the vent tube -- disconnect the loom at the oxygen sensor to provide more slack.

The hydraulic line. Good luck with that.
See that steel braided line on the driver side of the transmission? That's the hydraulic line. If you're not replacing the slave cylinder, leave it alone! The slave can just hang from the line with no worries while you replace the clutch. But if a slave upgrade is part of your plans, you'll want to disconnect it now while it can't wiggle around so much. To remove the hydraulic line, you'll find a white ring around the connector at the transmission. Use two flathead screwdrivers to push the ring into the housing. When the ring is all the way in, you'll be able to pull the hydraulic line out. This can take some time and can be frustrating; it's not so easy to do.

Now it's time to get at the transmission itself. It's held to the bellhousing with eight 15mm bolts. You may have removed some of them already before putting the jack on the trans. The ones along the top can be tricky to reach, and two are recessed compared to the others -- they're easy to miss. The top right bolt is holding the wiring harness on that side with the evil rosebud clip. Once you've got all the bolts off, the trans will slide backward without too much fuss. You'll get about two inches of clearance if you left the shifter in place, more if you removed it (remove it remove it remove it!).

Before going any further, reach in and disconnect the slave cylinder. It's held to the transmission with two 10mm bolts, one on each side. It'll slide right off the input shaft, and either hang freely from the hydraulic line (if you aren't exchanging it) or is now in your hand (if you are).

This is as much of the slave cylinder as you'll be able to see.
There are almost no visual differences between the old slave cylinder and the new. That might be expected, as the new one is OEM replacement for '01 and newer F-bodies. The only difference is a number stamped on the housing: "8" on stock and "16" on the new.

Now the bellhousing has to come off. It's held by eight 13mm bolts, and a couple along the top are a pain to get at. Swivel socket joints and a couple feet of extension bars are mandatory, and even so, it's still no day in the park.

The bellhousing also has a couple of dowel pins holding it to the engine, so after removing all eight 13mm bolts it'll still just sit there. It may prove very difficult to remove actually. There is a little groove at the bottom of the bellhousing that you can use as a starting point for your prying efforts. Count on it taking a fair bit of effort to pry this darn thing off.

Once you have the bellhousing off... oh, okay, we can wait.


Once you have the bellhousing off, you can remove the pressure plate. It's held to the flywheel with six 13mm bolts. As you remove it, the clutch will also come loose (it's held in with pressure -- hence "pressure plate" -- so as the pressure is released the clutch comes free) so it may be wise to start at the top and work your way down. Watch for the clutch falling out and bonking you. If you're really careful you may be able to get it all off as a unit.

Top, the original GM clutch. Bottom, the new SPEC clutch.
Some differences between the old and new clutches:

  • the "pad size" is bigger on the new clutch -- 10 pads instead of 24
  • the width of the contact material is greater on the new clutch -- all the way into the center disc instead of having an air gap
  • five springs instead of four
  • ten anchor points for the friction disc instead of eight

Then, the flywheel is attached to the engine with six 15mm bolts. Pay attention to the location of the alignment hole so that the replacement flywheel can go on the same way. These guys are on pretty tight so it may take some work to get them off. One suggestion is to use another socket as a handle on a different bolt. The flywheel may come off on its own, but ours was stuck to the engine and had to be gently pulled off. This is preferable because it is seriously heavy, not something you'd want to catch with your ribcage.

To put the new flywheel in, set it on the end of the crankshaft, making sure that the alignment hole is in the same position as the original. Use a couple of old bolts to hold it down. Then use the new GM flywheel bolts, which come delivered with threadlock on them. Be sure to replace the two you used to hold it up too.

The flywheel bolts need to be walked up to the proper torque, and they need to be torqued in the proper order. The official steps are:

  1. 20 Nm (15 lb-ft)
  2. 50 Nm (37 lb-ft)
  3. 100 Nm (74 lb-ft)

Our torque wrench can't do 15 lb-ft, so we did "barely tight at all" then 30 lb-ft then 40 lb-ft and finally 74 lb-ft. The flywheel is gonna want to spin as you reach 74 lb-ft. We took a small prybar and used the flywheel teeth to jam it up against the starter.

The proper tightening pattern for the flywheel and pressure plate.
Once the flywheel is on, clean the contact area with brake cleaner so that it is perfectly clean. Then never touch it again. Mount the clutch onto the clutch alignment tool and put it on top of the flywheel. Wiggle the tool a bit to make sure it is fully seated; the tool should slide in and out freely.

Clean the mounting surface of the pressure plate then put it over the flywheel, lining it up with the dowel pins. Attach using the six 13mm bolts, nice new ones from GM. It may be a bit difficult to get it mounted; there are a couple of notches that have to match up in addition to the dowel pins. Tighten to 52 lb-ft (70 Nm) using the same pattern as before.

Retrieve the clutch alignment tool. Give the bellhousing a good scrubbing, coz you know after all those miles it's absolutely filthy. Then try to push the bellhousing back over its dowel pins -- a task not much more fun than getting it off the pins in the first place. You may need to gently prod it into place with a rubber mallet.

Install the new slave cylinder. Don't overtighten; its spec is only 6 lb-ft. Leave the little dust cap in place for now.

Now lift the transmission back into place. We had some trouble getting the trans around the exhaust system when we took it out, and it wasn't much of a picnic getting it back either. In essence, we lifted the back of the trans up and over the exhaust, then with one person holding it there the other jacked the front of the trans to catch up with it. This seemed to work pretty well.

Getting the trans input shaft to line up perfectly with the clutch is a bit of a trick, but luckily we have a scissors-type trans jack that allowed for very small adjustments. It needs to be aligned in all three dimensions: lined up front to back so that the input shaft is parallel with the clutch, lined up left to right for the same reason, and rotated at a perfect 12 o'clock for all the dowels and bolts to match up. Fiddly? Yes. Best to have an inspector watching the aligning area and a grunt man pushing and twisting the trans. If the splines of the input shaft don't match up, you can turn the input shaft with your fingertips with no problem. Sooner or later, you'll get it lined up close enough that you can get a bolt through the trans and into the bellhousing. Make certain that it is going in straight, as it's super easy to cross-thread aluminum! Once you have the first bolt a couple of threads in, try to get a second bolt on the opposite side of the trans started.

The new SPEC clutch, flywheel, and pressure plate installed.
With two bolts started, you can very carefully walk the trans back into its natural position by tightening one bolt a couple of turns and then tightening the other a couple of turns, until it is finished seating. Note that the bolts must be sufficiently spaced apart and must not be cross-threaded for this to work.

Before trying to put the rest of the trans bolts in, wouldn't it be nice to have that trans jack out of the way? All you'd need to do is put the crossmember back. Of course, you need to put back a few other things before you can get to the crossmember:

  • the trans mount. No problem.
  • the exhaust bracket. Piece of cake.
  • the torque arm hanger. Easy.
  • the torque arm itself. AARRRGGGGHHH!!

It's not horrible, but it's harder than it needs to be. Put the front end through its bracket but leave it loose. At the back, you'll have to get your grunt buddy to lift the axle just right -- not only does it need to be the right height, but it also needs to be the correct angle. On our first attempt we found our jack point was too far forward, causing it to twist too much. There is a perfect sweet spot where the torque arm practically snaps onto the differential, and it's fiddly trying to find it with a hydraulic floor jack. Patience is the watchword here.

Once you've got those lined up right, go back to the front and tighten down the bolt that clamps the torque arm hanger. If the trans isn't sitting just right, it may not allow the bolt to start. Try lifting on the trans a little to improve the alignment if necessary. Then go back and tighten down the back bolts. Now you can lower the axle again.

With the torque arm in place, you can put the crossmember on. Then remove the trans jack!

Now go put the rest of those trans bolts in. We'll wait.

Done? Cool! It only took us an hour to do it. If you think you might try to take a shortcut and not reconnect the clip on the passenger side, we'd advise against it: if you don't anchor the wires, they get in the way.

Driver-side transmission electrical connections.
Reconnect all the electrical plugs. Make sure to get that oxygen sensor too.

Put the driveshaft back in. You'll need to lift the rear axle again to get it in there. Make sure to align the marks you were supposed to make when you took it off. Put some threadlock on the bolts.

Now put trans fluid back into the trans. How much? Well, until it pours out. Remove the fill plug using a 3/8 drive ratchet, but rather than trying to actually fill from that hole, fill from the top where the shifter goes. Have your grunt buddy under the car watching the hole; when he says stuff is coming out the bottom, stop pouring it in from the top! Not real scientific, but effective. It'll take just short of four quarts.

That's about it for the underside. If you removed the shifter, reinstall it.

Now, the LS1 has a hydraulic clutch, so replacing the slave cylinder means we need to bleed it (if you left the slave cylinder alone, then you won't need to bleed it). Look for the clutch master cylinder near the brake master cylinder. It's smaller and located closer to the fender. Open the clutch fluid reservoir and suck as much of the old fluid out as possible -- a turkey baster works well for this. Then fill the reservoir with new fluid.

A Mity Vac works great for bleeding the clutch; if you don't have one, it's well worth the money, as it has tons of uses. Add some new clutch fluid to the Mity Vac's reservoir and to the tube running from the reservoir to the end going into the clutch fluid reservoir. Pick a rubber end for the Mity Vac that will fit into the base of the reservoir where it has a hole going to the line down to the transmission. The end we used was fairly long and pointy, because the line to the transmission is narrow.

Push this end into the hole at the base of the reservoir and pump up the Mity Vac. It's important that you push the rubber end firmly and completely into the hole, so that you have a good seal! Otherwise, the pumping and bleeding won't work.

Pump it up to about 20 psi, then remove the hose while releasing the vacuum on the Mity Vac. If you do everything right, little bubbles and old fluid will get pulled into the reservoir of the Mity Vac.

Repeat the pumping and releasing two or three times -- until there are hardly any bubbles. Then top off the car's reservoir and try pushing the pedal. It should have gone from very mushy to quite firm after the bleeding.

After a drive, the pedal may feel mushy again. Repeat the bleeding two more times over the next couple of days, until it seems that bleeding isn't improving the situation anymore, and the pedal is back to normal firmness. Basically, it's not an exact science.

It's hard to tell the difference with the clutch since we haven't had a chance to race it yet. It requires a 400 to 500 mile break-in period with lots of city (stop and go) driving before we're allowed to shift under high load/rpm. We're a couple hundred miles into the break-in period, so we're getting there. We can't wait to see how it goes above 5000 rpm! Near the end of its life, the old clutch was slipping like crazy above 4500 rpm from first to second.

The clutch feels a lot like stock, and the only things worth noting is that it was hard to be smooth and it was a little shuddery for a while going into first. That's fairly normal for aftermarket clutches during the first few hundred miles. It's already going away and the clutch feels normal now.