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Project BMW 325is Part 6: Light Flywheel, clutch and shifer

Dan Barnes
Feb 26, 2004 SHARE
0401_01z+1993_bmw_325is_coupe+front.jpg_ Photo 1/9   |   Project BMW 325is Part 6: Light Flywheel, clutch and shifer

The first time I took Project 325 to the drag strip for testing, launching was impossible. With a stock engine, 90-degree weather and 235/40-17 ContiSportContact 2 tires, I could leave the line at 3500 rpm and bog to 2400, or I could leave at 3800 and watch the revs rise to 4300 as the rear wheels gradually caught up to the engine. That moved a lightweight flywheel and heavy-duty clutch up the priority list.

0401ec_bmw_03_z Photo 2/9   |   Project BMW 325is Part 6: Light Flywheel, clutch and shifer

Project 325's stock flywheel weighs 27.2 lb. As always, I sought to trim fat. Reduced vehicle weight improves performance, regardless of rotational factors, but testing with other cars on european car's Dynojet has shown more torque at the wheels in first and second gears with a light flywheel. Every time I have replaced a dual-mass flywheel with a solid, lighter flywheel, driveability has improved. Potential downsides are a tendency to stall off the line and the rattle of gears cushioned only by automatic transmission fluid. I have never had a problem with the former, and the latter is largely addressed by clutch selection.

Nearly every BMW performance supplier has an aluminum flywheel for the E36. Many are private-labeled from one manufacturer. Most use an E36 M3 clutch disc and pressure plate, an upgrade for any lesser E36. However, the solid M3 clutch disc was designed for a dual-mass flywheel and transmits all the crankshaft's torsional vibrations and any driveline shocks straight through to the gears. The most obvious symptom is gear chatter at idle.

I found two alternatives. Rogue Engineering uses a custom-made, sprung-hub disc with M3 dimensions, featuring carbon/aramid friction material on one side, designed to work with Rogue's own 11.5-lb, aluminum flywheel and M3 sport pressure plate. Rogue Engineering's Ben Liaw states that this package will hold up to 600 hp at the wheels, a figure I have yet to see coming from any E36 engine.

UUC Motorwerks' Stage II flywheel is a little less extreme. It uses the O.E. Sachs clutch package from the 3,800-lb, 310-hp, 1991-93 M5, which used a sprung-hub disc. Larger and beefier than any O.E. E36 clutch, it will handle substantial power increases. The E36 tuning world has settled on 11- to 12-lb flywheels as a good balance for the street. UUC's Stage II flywheel weighs just 8.5 lb, but with the heavier M5 clutch attached, comes out the same as UUC's 11-lb flywheel and an M3 clutch. The made-in-USA, 6061-T6 aluminum, Stage II flywheel's 1050 steel friction surface is replaceable, so an abused or worn system can be serviced without replacing the entire flywheel. BMW factory mounting hardware is included. The UUC Stage II flywheel fits all 1992-99, six-cylinder, 3 Series BMWs. I chose it for Project 325. Since the transmission would be out of the car, it was the perfect opportunity to also try UUC's Ultimate Short Shifter.

I again turned to Web-based Import Parts Specialists for stock parts. Its prices to the public are on par with distributor pricing available in Southern California, and the numbers it shows as "list" are well below the local BMW dealer's. Combine that with friendly, knowledgeable and consistently prompt service, and IPS is an all-star among Project 325's supporters. It provided the M5 clutch disc, pressure plate and throwout bearing (they were in stock) as well as the driveshaft guibo and bushing.

I try to do as much of the work as possible on Project 325, but installing the flywheel was one thing I knew I'd be better off letting a pro handle. Watching evosport's Ken Brightwell work on my car is like watching myself, except he's already done everything many times and has more and better equipment. He is careful, thinks about what he's doing and cuts no corners.

A few snags popped up, because a car was being worked on. BMW's starter bolts have a reduced-size head that tends to round off if the bolt has gone a long time without being removed. Have new ones ready. Project 325's guibo was ruined by ATF leaking from the transmission's selector shaft seal. It's good to plan on replacing the guibo and driveshaft bushing anyway "while you're in there"--it's cheap insurance. evosport replaced the leaking selector shaft and engine rear main seals, taking the time to do the job right.

I was immediately pleased with the action of the M5 clutch. It is O.E., and has all the civility one would expect. Engagement is smoother, because there is a clear indication of its beginning. The stock flywheel tended to wind up at the beginning of engagement, masking the signal, and then recoil just as the clutch began to transfer torque. Shifting also tended to be accompanied by a lurch, as I stay on the throttle late and get on it early. The Stage II flywheel makes those habits smoother. Driveline lash is also noticeably reduced in gear; throttle inputs in a corner are more precise, acceleration when the throttle is opened sharper. Power delivery is more precise in every way with the Stage II flywheel, the car more responsive and enjoyable to drive.

I have lived with the UUC Stage II flywheel and Ultimate Short Shifter for a few months. The clutch has already survived abuse that would have destroyed the old one. Both clutch and shifter have improved with break-in. Where I used to be able to hear a small amount of gear chatter at idle, pressing the clutch in now makes no difference in sound. I'm running Red Line D4 ATF, not a noise-silencing heavier lube.

The shifter began as almost undriveable in this car. Merely notchy around town, it simply would not move into the next gear quickly if shifted at redline. I adjusted the height to maximum, and effort was significantly reduced. With more miles, it has become smoother, but it still sometimes hangs up going into third or fourth, even puttering around town. I don't know whether to complain about the UUC shifter, BMW's choice of transmission, or unknown internal wear that has occurred over 100,000 miles. Rifle-bolt precision is not as important to me as being able to get to the next gear quickly. My jury is still out on the Ultimate Short Shifter until I play with it some more, and maybe try a competing product.

I had been dissatisfied with UUC's red transmission bushings and tranny mount enforcers. Vibration was transmitted into the cabin at 1200 and 2000 rpm, with a general harshness in the 3000 to 4000 range. T.C. Kline noticed it when checking out his suspension installation, saying he'd never observed it and it wasn't right for a BMW. Discussion with UUC's Rob Levinson, as well as dealers and users, raised improper mount installation and a failing dual-mass flywheel as possible causes. With the Stage II flywheel installed, both were eliminated as culprits, but the vibration remained, if slightly reduced. Switching to UUC's black transmission bushings and no enforcers eradicated the noise, turning Project 325 back into a BMW.

If you were paying attention last month, you noticed UUC Motorwerks' Stage II flywheel was chosen as one of european car's Select Gear items. I am that happy with it. Project 325 still isn't perfect, but it's much closer to being the car I've hoped it would be.

At a Glance
Installers:evosport
Estimated time:8 hours shop labor @ $85/hour = $680
Upgrade costs:UUC Stage II flywheel: $499.00, UUC Shifter and upgrades: $245, Sachs E34 M5 clutch parts: $353.18 ,Guibo, driveshaft bushing, driveshaft support, selector shaft seal, rear main seal: $116.31
Total:$1,893.49
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evosport
Huntington Beach, CA 92649
888-520-9971
http://www.evosport.com
By Dan Barnes
78 Articles

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