5. INSPECTION OF TRANSMISSION COMPONENTS
A gearbox has many parts assembled together with great precision. Any abnormal wear in a part will not only make the gearbox noisy but will also cause gear slipping and break in power transmission. Therefore, it is very important that all the parts are inspected carefully taking due note of the specified dimensions and clearances between mating parts.
5.0
Objectives After going through this lesson you will be able to: Inspect the idle gears and input shaft. Inspect gears and synchronizer rings. Inspect counter shaft. Inspect shifter fork and shafts.
i. ii. iii. iv. v.
5.1
Introduction
In previous lesson, the transmission was dismantled and its components removed. Let us now inspect the various components of the transmission. Before starting with inspection of components ensure that all the parts are clean.
5.2
Inspection of Input Shaft
Let us first inspect the two reverse gears, one each on the input shaft and the countershaft, and the idle gear. To do this, inspect the chamfered edges of the gear teeth of the three gears. If the edges are worn badly, replace the gears. Abnormal noise caused by gear slipping in reverse drive is often due to the worn tooth edges of these gears. Next, the input shaft and its bearings are inspected. • •
•
If any of the input shaft gears is found with chipped or broken teeth, the input shaft needs replacement. Check each bearing of the input shaft by spinning its outer race by hand to feel the smoothness of rotation. Replace the bearing if it is found to exhibit sticking, resistance or abnormal noise when spun by hand. Check the splines of the input shaft for wear and damage. Replace the input shaft if the splines are found to be defective.
1
Fig. 5.1: (a) Reverse gears. (b) Idle gear.
5.3
Inspection of Gears and Rings
It is noteworthy that three types of synchronizer rings are used and one must make sure to use them correctly with each gear. These are shown below.
Fig. 5.2: Identification of synchronizer rings
Let us now inspect the combination of the gear and the synchronizer ring for wear.
Fig. 5.3: (a) Synchronizing ring and gear. (b) Checking gear to ring clearance with feeler gauge.
2
First, to inspect the top gear with its mating ring: • Fit the ring onto the cone of the top gear. • Check the clearance between the ring and the cone, as shown in the figure, with a feeler gauge. • If the clearance is less than or equals the service limit of 0.5 mm, replace the worn part. Similarly, the rest of the gears are inspected one by one. The standard clearance between the gear and the ring is specified as 0.8 to 1.2 mm. The service limit is 0.5 mm. To inspect the external cone of the gear and the internal cone of the ring for abnormal wear, it must be ensured that the contact patterns on these surfaces indicate uniform and full-face contact. It should also be seen that the surfaces are free form any wavy wear. A badly worn member must be replaced. Proper synchronizing action while shifting gears can be expected only if the ring to gear clearance and the condition of the cone surfaces among other things are satisfactory. The teeth, dog teeth, external cone surface and the bore of the low speed gear are then inspected to make sure that these are not worn out. Next, each synchronizer ring is inspected for key slot wear by measuring the width of each slot. If the width exceeds the limit shown in the table below, the ring should be replaced. Table 5.1: Key slot widths Key slot width Standard Service Limit Low gear 8.0 mm 8.3 mm Second gear 10.0 mm 10.3 mm Third and top gear 9.6 mm 9.9 mm
• • • • •
5.4 • • •
To complete the inspection of the gears and rings, one must also: Inspect the keys, which fit in the hub and the sleeve. They should not be worn. Check the play between the teeth of the ring and the sleeve. It should not be excessive. Check the chamfered edges of internal teeth of the sleeve. They should not be worn. Slide the bearing over the splined bush, which fit in the third and second gears and check that there is no play between the bush and the bearing. Inspect the ball bearing, which fits on the other end of the countershaft.
Inspection of Countershaft Inspect the teeth of the differential pinion for chipping and wear. Inspect the bearing journals. These should be smooth and shiny and there should be no evidence of any wear or scratch marks. Inspect the splines of the countershaft. These splines have the hubs mounted on them and rotate the countershaft.
3
• •
Inspect the splines on which the driver gear of the speedometer is mounted. At the end of the shaft, check the threads for damage.
Fig. 5.4: Countershaft.
5.5 Inspection of Shifter Fork Shafts • • • •
Inspect the three-shifter fork shafts. They should not have any scratch marks and should not be abnormally worn. Inspect the locking groove of the shaft for wear. Inspect the two shifter forks for wear. Inspect the surface of the forks, which fits in the sleeve for wear.
If any fork is excessively worn, it should be replaced. It should not be repaired.
Self-check Questions 1. How many different types of synchronizer rings are used? 2. Clearance between the ring and the cone should not be less than ______ 3. Key slot width in each ring is same. State whether True/False
5.6
Class Assignment
1. Discuss causes of gear noise and slipping.
5.7
Summing Up
In this lesson, we studied the inspection of the countershaft and saw that chipped or broken teeth, worn or chamfered edges of the gear or damaged splines of the shaft call for replacement of the part. Also, proper synchronizing action during gear shifting can be expected only if the ring to gear clearance and the condition of the contact surfaces is satisfactory. We also studied about the inspection of input shaft, gears, rings, and shifter fork shafts.
4
5.8
Possible Answers to Self-check Questions
1. 3, one each for low gear, second gear, and third and top gear 2. 0.5 mm 3. False
5.9
Terminal Questions
1. Explain the inspection procedure of input shaft and counter shaft. 2. Describe the inspection of synchronizer rings.
5.10
References
1. Maruti 800 Service Manual
5