M/T - Neutral/Drive Gear Rattle
88chevy27Number: 88-351-7B
Section: 7B
Date: OCT., 1988
Subject: NEUTRAL/DRIVE MANUAL TRANSMISSION GEAR RATTLE
Model and Year: 1980-88 CHEVROLET VEHICLES WITH MANUAL TRANSMISSIONS
TO: ALL CHEVROLET DEALERS
Various levels of minor gear "rattle" are inherent in all manual transmission gear boxes. Customers may perceive gear "rattle" as clutch, engine and/or transmission noise. The noise "rattle" is normal and will not affect the function or durability of the vehicle.
The amount of "rattle" is dependent on several factors including the size and design of both the transmission and engine, as well as the temperature of the transmission fluid. Generally, the larger transmissions have more "rattle", however, smaller engines generate a higher level of torsional vibrations which induce gear "rattle". As the temperature of the fluid increases, so will the level of rattle.
Neutral "Rattle"
Verify that the customer noise comment is neutral gear "rattle" by using the following steps. Also use the statements as guidelines for addressing the condition.
1. Place vehicle on a level surface with engine at idle, transmission in neutral, and parking brake set.
2. Depress the clutch pedal and check to see if the noise disappears.
a. If the noise does disappear, then neutral gear "rattle" most likely exists:
- Check the transmission fluid level and fill if necessary. Low fluid level can result in increased "rattle". Also, verify that the correct fluid is being used.
- Check the shifter boot for tears and proper attachment and replace or service as required.
- Check for any other service bulletins which may release specific service parts for a vehicle line with a known gear rattle concern.
- "Only" (after checking the above items and no corrections can be made) install a replacement clutch driven disc. A replacement disc may decrease "rattle" due to production variations in damper spring rates and/or hub to spline clearances, however, for the same reasons "rattle" may increase.
IMPORTANT: DO NOT CHANGE THE FOLLOWING COMPONENTS AS THEY WILL NOT AFFECT GEAR RATTLE.
- Release Bearing
- Hydraulic Clutch Linkage Assembly
- Clutch Cover Assembly (Pressure Plate)
b. If the noise doesn't disappear, then the source of the noise is likely to be engine related.
- Look for any holes in the front-of-dash which may not be properly sealed. This could result in additional engine compartment noise passing into the passenger compartment.
Drive "Rattle"
A customer noise comment of drive rattle must be verified by duplicating the driving condition (acceleration, deceleration, road load, grade) and gear at which the noise is heard. Drive "rattle" will generally disappear as the vehicle engine speed approaches 1800 to 2200 RPM in each gear.
Once the noise has been determined to be drive "rattle" then use the above statements in section (a) of step (2) as guidelines for addressing the condition (also see IMPORTANT).
If the noise is not transmission related, use section (b) of step (2).