M/T - (6-Speed M/T) Difficult Gear Selection
SI B 23 01 09Manual Transmission
May 2009
Technical Service
SUBJECT
Gears Difficult to Select in 6-Speed Manual Transmission - Diagnostic Hints
MODEL
E82, E88, E83, E9x with 6-speed manual transmission (GS6-17BG; GS6-37BZ; GS6-37BG)
SITUATION
The customer may complain that intermittently one or several gears are difficult to select (engage).
CAUSE
The possible causes may include:
^ Obstructed clutch pedal movement
^ Defective gearshift mechanism
^ Clutch hydraulic fluid contaminated with air
^ Clutch disc movement obstructed on the input shaft tampered splines
^ Internal defect of the transmission
INFORMATION
The following procedure should be performed when diagnosing a hard gear engagement complaint:
1. Make sure that the clutch pedal can be fully depressed to the floor without any obstruction. Additional floor mats or carpets may limit the clutch pedal travel and thus prevent a full disengagement of the clutch.
2. Make sure that the gear lever can be moved freely into all shift gates and/or gears, i.e., the shift path is not impeded by the gaiter on the gear lever, by the bellows beneath (black rubber boot), or by the shift level bearing.
3. If the aforementioned steps were performed without correcting the complaint, then the clutch hydraulic system must be checked for the presence of air in the system. If the hydraulic system is contaminated by air, the clutch pedal feels very spongy when depressed (particularly in the first half of the pedal travel). In addition, the clutch engagement point would be very low down when the clutch pedal is released ("clutch engages immediately after release").If you suspect air in the clutch hydraulic system, the clutch hydraulics must be bled in accordance with the Repair Instructions and then transmission gear engagement must tested.
4. If the problem still persists, then continue with the following procedure:
^ Engine running at idle speed
^ Depress the clutch pedal
^ Attempt to engage the gear which is difficult to select from the Neutral position. If the gear is difficult to engage, hold the gear selector lever at the point of resistance (approx. half way along the shift path) with a steady, light force.
^ When pressing the gear selector, switch off the engine. If the gear can now be fully engaged (i.e., the gear lever slides into the end position without any further/additional pressure), then the clutch mechanism is probably not disengaging properly.
^ If the gear lever remains at the point of resistance, the root cause may be in the gearbox, the external gearshift mechanism, or in the mechanical components of the clutch system.
5. Remove the gearbox.
6. During the removal of the transmission, the proper operation of the external gearshift mechanism (external selector rod, selector rod joint, selector arm, selector arm bearing, etc.) must be checked and replaced if found defective.
7. Check whether the two Dowel pins (sleeves # 1, 2) are fitted between the engine and the gearbox. The lack of adapter sleeves may cause a harsh gear engagement.
8. Check the tapered splines on the gearbox input shaft for corrosion or dirt.
9. Remove the clutch pressure plate assembly and place the clutch disc onto the tapered splines to check whether it can slide easily on the shaft without resistance (binding/catching). If the tapered splines are found to be contaminated and/or corroded, or the clutch disc jams when moved on the splines, proceed with the cleaning and lubrication procedure from step # 16.
10. Check the pilot bearing and replace if necessary.
11. Check ball pin # 6 (counter support for the release lever) and wire clip # 5 for wear and firm seating, and replace if needed.
12. Check guide sleeve # 7 for abrasion or damage. If there is major abrasion or entrenchment, the sleeve must be replaced.
Note:
bare points on the sliding surface of the guide sleeve are normal during usage of the gearbox. The guide sleeve is Teflon-coated and the coating can be polished off over time.
13. The surface rust deposits on the flexible tongues of the clutch pressure plate, on the release bearing, and on the guide sleeve do not have any negative effect on the disengaging behavior of the clutch, and should be a deciding factor when condemning the clutch assembly for replacement.
14. Check the dual-mass flywheel for leaks. A small amount of grease leaking from the flywheel does not have an adverse effect on the ease of gear shifting. The dual-mass flywheel needs to be replaced only if an excessive amount of leakage is found, which may also lead to contamination of the clutch disc surface.
15. Check the engine and the gearbox for traces of oil and/or transmission fluid leaks, and repair if needed.
16. Thoroughly clean the tapered splines on the gearbox input shaft and in the hub of the clutch disc.
17. Check the clutch for wear and replace if needed.
18. Grease the tapered splines on the gearbox input shaft with "Esso UNIREX S2 grease (P/N 83 23 9 416 138), using the following steps:
^ Insert the grease scraper ring (P/N 21 220/240) on input shaft # 1 until it reaches the edge of the guide sleeve.
^ Apply the grease evenly with a brush to the sides and the base of the splines, as far as the scraper ring.
^ Remove the grease scraper ring.
^ Also coat the shaft journal with a thin layer of UNIREX grease.
Note:
The guide sleeve in a 6-speed gearbox are Teflon-coated and must not be greased on the sliding surfaces.
19. Lubricate the release lever:
On the 6-speed transmissions equipped with the release module (release lever and bearing integrated into one component, introduced since 06/07),
grease should not be applied at the sliding surfaces (# 1 and # 2). Small
amounts of grease should be placed at the contact points with the slave cylinder actuating shaft and the ball pin (opposite ends of the lever).
20. The release lever lubrication points for vehicles produced prior to 06/07 (separate from the release bearing) are indicated in the illustration (F-friction surfaces)
21. The gearbox should be replaced in the following cases:
^ No defects were found in the external gearshift mechanism.
^ The gearbox input shaft was clean (not contaminated).
^ The lubrication on the tapered splines was still present.
^ The clutch disc could be moved freely on the tapered splines.
^ The adapter sleeves and clutch mechanical and hydraulic systems did not show any signs of damage or malfunction.
22. If the gearbox is replaced, the lubrication specifications as described in point 16 must also be followed. The new Dowel sleeves must be fitted between the engine and transmission.
WARRANTY INFORMATION
For information only
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