Piston Slap: The Cavalier's Not-So-Silent Ricochet

TTAC Commentator Silent Ricochet writes:

Hey Sajeev, it’s been a long time since I sent my first email about my 2002 Cavalier Z24 making rattling noises at low RPM. The noise has since then gotten slightly more noticeable and I finally decided to take some action and really look into it. As a quick refresher, in First and Second gear, between 1500 and 2000RPM under moderate throttle, the car will make an awful rattling noise, like that of pennies in a coffee can kind of noise.

After looking at several cavalier and J-Body forums I stumbled upon a ridiculously popular thread that contained all the information I would ever need…

The 2000+ Cavalier Z24s either shipped with a 4spd GM Automatic Transmission, or a Getrag F23 5spd Manual Transmission (which I have). This problem only exists with the 5spd cars as you may have guessed. The problem, has since been wiped out after the year 2003, so between years 2000 and 2002, there were pages and pages of complaints and GM did little about it years ago. The problem IS the transmission, not a heat shield, not my exhaust, not my clutch. People described my problem to the T, I knew they were all experiencing what I was. Turns out, there’s two problems with the transmission, both producing similar but different noises. I kid you not here is the post that revealed it all which contains mostly copy and pasted General Motors Technical Service Bulletins for this exact problem:

Document ID# 854232 Subject: Grinding/Rattle Type Noise Coming From Transmission

Condition:

Some customers may comment on a grinding or rattle type noise coming from the transmission. The noise usually occurs with the transmission in first or second gear at low RPMs and can be intermittent.

Cause

This condition may be originated by the natural harmonics of the engine that leads to a vibration in the transmission.

Correction

There are two separate noises. Follow the diagnostic procedures listed below to determine which noise the vehicle has and perform the outlined repair. If you are comparing like vehicles, you must compare vehicles with the same motor and similar mileage.

Diagnosis for Noise #1

This is a very distinct noise that is usually much louder than the second noise that can be associated with this transmission. If the vehicle is not making any noise when trying to verify the condition, it can be induced by making several tight left hand circles with the vehicle at normal operating temperature. Making a sharp right hand turn will usually stop the noise. While the noise is occurring, in order to distinguish between the two noises, you can press lightly on the clutch pedal without releasing the clutch and the noise will NOT go away or change. As a second diagnostic aid, while the vehicle is making the noise, shift to third gear and the noise will stop. If the noise is determined to be this type, perform the repair for noise #1.

Repair for Noise #1

Replace the transmission fluid with Saturn Manual Transmission Lubricant, P/N 21018899. Overfill to a capacity of 2.4L (2.6 qts). A possible side effect of this repair may be a higher shift effort.

Diagnosis for Noise #2

This noise, commonly referred to as gear rattle, can be induced by lugging the engine in any gear, but is usually most noticeable in first or second gear. While the noise is occurring, if you press lightly on the clutch pedal without releasing the clutch, the noise will be reduced or eliminated.

Repair for Noise #2

Do not attempt to repair this noise. This is a characteristic of the vehicle and any vehicle equipped with a manual transmission can be made to make a similar noise. Driving at slightly higher engine RPM levels will reduce this noise.

I would classify my noise as noise and after reading other topics, many have recommended OVERFILLING my transmission from the recommended 1.8L to 2.4L as stated in the bulletin. This concerns me as I can only see this as extra stress on my transmission… Why would GM suggest such a thing? Not to mention that Saturn Manual Transmission fluid is no longer available.. Since then, General Motors has released another fix for this problem, but after years of driving, Cavalier owners have discovered that the fix actually makes things worse. The Rattling noise itself isn’t damaging to the transmission, but GM’s secondary fix to the problem (which was to install a Wave Spring between 3rd and 4th gear) was. Eventually, a 3rd and 4th gear grind would develop, which is obviously harmful to the transmission.

This leaves me with a tough choice. Many people swear by the overfilling method, and that it has completely fixed their rattling issue. The recommended fluid for my transmission is GM’s Very own DEXRON III ATF, which is quite thin from what I’ve read. Many people recommend using other fluids but that also worries me. I can’t really afford to pay for a new transmission.. So All in All, I have found the fix for this irritating problem, while at the same time, the risks could potentially outweigh the advantages. Feel free to give me some insight on this, I’m bringing the Cavy to the local mechanic’s shop soon to look further into this problem. Hopefully we settle on what needs to be done once and for all.

Sajeev answers:

If my Internet sleuthing is correct, the Getrag F23 is originally spec’d to use 1.8 quarts of oil. So a jump to 2.6 quarts is a bit scary. I honestly think you have nothing to lose if you do anything: even if you trash it, a junkyard replacement from a later model should be simple, somewhat cheap and better than buying another set of problems in another used vehicle.

With that in mind, what I recommend is a two part deal:

1. Do a fluid service, and replace the stock Dextron stuff with an aftermarket alternative. Either Mobil 1/Amsoil synthetic alternative Dextron or B&M Trickshift (some people swear by this stuff) or Synchromesh. I personally have noticed a big difference when switching to GM Synchromesh in two vehicles.

I can’t find a big warning on the Internet saying Getrag gearboxes and Synchromesh are a bad pairing. So do it, and fill up to the factory level.

2. If not satisfied, add the extra 0.8 quarts of fluid as per GM’s service bulletin.

Like I said before, if this fails, putting in a replacement gearbox isn’t the end of the world. But the odds of that being necessary isn’t likely. I suspect you will perform step 2 and be fairly happy with the results.

Good luck.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.