716 Checking crownwheel and pinion tooth contact

Prepare crownwheel for examining tooth contact marks (Fig. 7.8) After setting the correct backlash, the crownwheel and pinion tooth alignment should be checked for optimum contact. This may be achieved by applying a marking cream such as Prussian blue, red lead, chrome yellow, red or yellow ochre etc. to three evenly spaced groups of about six teeth round the crownwheel on both drive coast sides of the teeth profiles. Apply a load to the meshing gears by holding the crownwheel and allowing it to slip round while the pinion is turned a few revolutions in both directions to secure a good impression around the crownwheel. Examine the tooth contact pattern and compare it to the recommended impression.

Understanding tooth contact marks (Fig. 7.8(a-f)) If the crownwheel to pinion tooth contact pattern is incorrect, there are two adjustments that can be made to change the position of tooth contact. These adjustments are of backlash and pinion depth.

The adjustment of backlash moves the contact patch lengthwise back and forth between the toe heel of the tooth. Moving the crownwheel nearer the pinion decreases the backlash, causing the contact patch to shift towards the toe portion of the tooth. Increasing backlash requires the crownwheel to be moved sideways and away from the pinion. This moves the contact patch nearer the heel portion of the tooth.

When adjusting pinion depth, the contact patch moves up and down the face-flank profile of the tooth. With insufficient pinion depth (pinion too far out from crownwheel) the contact patch will be concentrated at the top (face zone) of the tooth. Conversely, too much pinion depth (pinion too near crownwheel) will move the contact patch to the lower root (flank zone) of the tooth.

Ideal tooth contact (Fig. 7.8(b)) The area of tooth contact should be evenly distributed over the working depth of the tooth profile and should be nearer to the toe than the heel of the crownwheel tooth. The setting of the tooth contact is initially slightly away from the heel and nearer the root to compensate for any deflection of the bearings,

Crown Wheel And Pinion Design

(b) Correct tooth contact

Fig. 7.8 (a-e) Crownwheel tooth contact markings

(b) Correct tooth contact

Fig. 7.8 (a-e) Crownwheel tooth contact markings crownwheel, pinion and final drive housing under operating load conditions, so that the pressure contact area will tend to spread towards the heel towards a more central position.

Heavy face (high) tooth contact (Fig. 7.8(c)) Tooth contact area is above the centre line and on the face of the tooth profile due to the pinion being too far away from the crownwheel (insufficient pinion depth). To rectify this condition, move the pinion deeper into mesh by using a thicker pinion head washer to lower the contact area and reset the backlash.

Heavy flank (low) tooth contact (Fig. 7.8(d)) Tooth contact area is below the centre line and on the flank of the tooth profile due to the pinion being too far in mesh with the crownwheel (too much pinion depth). To rectify this condition, move the pinion away from the crownwheel using a thinner washer between the pinion head and inner bearing cone to raise the contact area and then reset the backlash.

Heavy toe contact (Fig. 7.8(e)) Tooth contact area is concentrated at the small end of the tooth (near the toe). To rectify this misalignment, increase backlash by moving the crownwheel and differential assembly away from the pinion, by transferring shims from the crownwheel side of the differential assembly to the opposite side, or slacken the adjusting nut on the crownwheel side of the differential and screw in the nut on the opposite side an equal amount. If the backlash is increased above the maximum specified, use a thicker washer (shim) behind the pinion head in order to keep the backlash within the correct limits.

Heavy heel contact (Fig. 7.8(f)) Tooth contact area is concentrated at the large end of the tooth which is near the heel. To rectify this misalignment, decrease backlash by moving the crownwheel nearer the pinion (add shims to the crownwheel side of the differential and remove an equal thickness of shims from the opposite side) or slacken the differential side adjusting nut and tighten the crownwheel side nut an equal amount. If the backlash is reduced below the minimum specified, use a thinner washer (shim) behind the pinion head.

7.1.7 Final drive axle noise and defects

Noise is produced with all types of meshing gear teeth such as from spur, straight or helical gears and even more so with bevel gears where the output is redirected at right angles to the input drive.

Vehicle noises coming from tyres, transmission, propellor shafts, universal joints and front or rear wheel bearings are often mistaken for axle noise, especially tyre to road surface rumbles which can sound very similar to abnormal axle noise. Listening for the noise at varying speeds and road surfaces, on drive and overrun conditions will assist in locating the source of any abnormal sound.

Once all other causes of noise have been eliminated, axle noise may be suspected. The source of axle noise can be divided into gear teeth noises and bearing noise.

Gear noise Gear noise may be divided into two kinds:

1 Broken, bent or forcibly damaged gear teeth which produce an abnormal audible sound which is easily recognised over the whole speed range.

a) Broken or damaged teeth may be due to abnormally high shock loading causing sudden tooth failure.

b) Extended overloading of both crownwheel and pinion teeth can be responsible for eventual fatigue failure.

c) Gear teeth scoring may eventually lead to tooth profile damage. The causes of surface scoring can be due to the following:

i) Insufficient lubrication or incorrect grade of oil ii) Insufficient care whilst running in a new final drive iii) Insufficient crownwheel and pinion backlash iv) Distorted differential housing v) Crownwheel and pinion misalignment vi) Loose pinion nut removing the pinion bearing preload.

2 Incorrect meshing of crownwheel and pinion teeth. Abnormal noises produced by poorly meshed teeth generate a very pronounced cyclic pitch whine in the speed range at which it occurs whilst the vehicle is operating on either drive or overrun conditions.

Noise on drive If a harsh cyclic pitch noise is heard when the engine is driving the transmission it indicates that the pinion needs to be moved slightly out of mesh.

Noise on overrun If a pronounced humming noise is heard when the vehicle's transmission overruns the engine, this indicates that the pinion needs to be moved further into mesh.

Slackness in the drive A pronounced time lag in taking the drive up accompanied by a knock when either accelerating or decelerating may be traced to end play in the pinion assembly due possibly to defective bearings or incorrectly set up bearing spacer and shim pack.

Bearing noise Bearings which are defective produce a rough growling sound that is approximately constant in volume over a narrow speed range. Driving the vehicle on a smooth road and listening for rough transmission sounds is the best method of identifying bearing failure.

A distinction between defective pinion bearings or differential cage bearings can be made by listening for any constant rough sound. A fast frequency growl indicates a failed pinion bearing, while a much slower repetition growl points to a defective differential bearing. The difference in sound is because the pinion revolves at about four times the speed of the differential assembly.

To distinguish between differential bearing and half shaft bearing defects, drive the vehicle on a smooth road and turn the steering sharply right and left. If the half shaft bearings are at fault, the increased axle load imposed on the bearing will cause a rise in the noise level, conversely if there is no change in the abnormal rough sound the differential bearings should be suspect.

Defective differential planet and sun gears The sun and planet gears of the differential unit very rarely develop faults. When differential failure does occur, it is usually caused by shock loading, extended overloading and seizure of the differential planet gears to the cross-shaft resulting from excessive wheel spin and consequently lubrication breakdown.

A roughness in the final drive transmission when the vehicle is cornering may indicate defective planet/sun gears.

7.2 Differential locks

A differential lock is desirable, and in some cases essential, if the vehicle is going to operate on low traction surfaces such as sand, mud, wet or waterlogged ground, worn slippery roads, ice bound roads etc. at relatively low speeds.

Drive axle differential locks are incorporated on heavy duty on/off highway and cross-country vehicles to provide a positive drive between axle half shafts when poor tyre to ground traction on one wheel would produce wheel spin through differential bevel gear action.

The differential lock has to be engaged manually by cable or compressed air, whereas the limited slip or viscous coupling differential automatically operates as conditions demand.

All differential locks are designed to lock together two or more parts of the differential gear cluster by engaging adjacent sets of dog clutch teeth. By this method, all available power transmitted to the final drive will be supplied to the wheels. Even if one wheel loses grip, the opposite wheel will still receive power enabling it to produce torque and therefore tractive effect up to the limit of the tyres' ability to grip the road. Axle wind-up will be dissipated by wheel bounce, slippage or scuffing.

These unwanted reactions will occur when travelling over slippery soft or rough ground where true rolling will be difficult. Since the tyre tread cannot exactly follow the contour of the surface it is rolling over, for very brief periodic intervals there will be very little tyre to ground adhesion. As a result, any build up of torsional strain between the half shafts will be continuously released.

7.2.1 Differential lock mechanism

One example of a differential lock is shown in Fig. 7.9. In this layout a hardened and toughened flanged side toothed dog clutch member is clamped and secured by dowls between the crownwheel and differential cage flanges. The other dog clutch member is comprised of a sleeve internally splined to slot over the extended splines on one half shaft. This sleeve has dog teeth cut at one end and the double flange formed at the end to provide a guide groove for the actuating fork arm.

Engagement of the differential lock is obtained when the sleeve sliding on the extended external splines of the half shaft is pushed in to mesh with corresponding dog teeth formed on the flanged member mounted on the crownwheel and cage. Locking one half shaft to the differential cage prevents the bevel gears from revolving independently within the cage. Therefore, the half shafts and cage

Crownwheel And Pinion Tooth Contact

member dog clutch mernber

Fig. 7.10 Differential lock mechanism with air control member dog clutch mernber

Fig. 7.10 Differential lock mechanism with air control will be compelled to revolve with the final drive crownwheel as one. The lock should be applied when the vehicle is just in motion to enable the tooth to align, but not so fast as to cause the crashing of misaligned teeth. The engagement of the lock can be by cable, vacuum or compressed air, depending on the type of vehicle using the facility. An alternative differential lock arrangement is shown in Fig. 7.10 where the lock is actuated by compressed air operating on an annulus shaped piston positioned over one half shaft. When air pressure is supplied to the cylinder, the piston is pushed outwards so that the sliding dog clutch member teeth engage the fixed dog clutch member teeth, thereby locking out the differential gear action.

When the differential lock is engaged, the vehicle should not be driven fast on good road surfaces to prevent excessive tyre scrub and wear. With no differential action, relative speed differences between inner and outer drive wheels can only partially be compensated by the tyre tread having sufficient time to distort and give way in the form of minute hops or by permitting the tread to skid or bounce while rolling in slippery or rough ground conditions.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

Get My Free Ebook


Responses

  • Valentin
    What is the heel of the crownwheel?
    8 years ago
  • olli-pekka
    What cause crownwheel tooth crest marking?
    3 years ago
  • Archie
    How can i correct low flank teeth contact patens?
    3 years ago
  • marisa
    What causes the toe and heel in differential in a car?
    3 years ago
  • robert
    Which parts prevent deflection of crown wheel under laid conditions?
    3 years ago
  • j
    How to increase power for diesel engine from crown pinion?
    3 years ago
  • Alan
    Why diff.crown and pinion damage according contact pattern?
    3 years ago
  • IAGO GRUBB
    Who is driver in pinion crown assembly?
    3 years ago
  • Betty
    How do you chek baclash between crown wheel and pinion?
    3 years ago
  • melilot
    What noise will too much pinion backlash sound like?
    3 years ago
  • robur
    What happens to the tooth mark if the crown wheel backlash is reduced?
    3 years ago
  • IMPI
    How many teeth does an Isuzu kb280 crown wheel and pinion have?
    3 years ago
  • dina
    How to remove vech crown wheel?
    3 years ago
  • antti
    Which parts on final drive of heavy duty vehicle prevents deflection on crown wheel?
    3 years ago
  • TEUVO KETTERER
    What type of meshing required in crown wheel and pinion shaft?
    3 years ago
  • Temesgen Simon
    Which direction of intacked should crown wheel and pinion lay?
    3 years ago
  • bertha chubb-baggins
    How would you check the crownwheel and pinion backlush?
    3 years ago
  • LYNN
    Which two parts on the final drive of a heavy duty vehicle prevent deflection of the crown wheel?
    3 years ago
  • bibiana
    Where do you put engineers glue on the pinion or crown when checking tooth contact on a differential?
    3 years ago
  • Efrem
    How to check.for tooth contAct for a differential assembly?
    3 years ago
  • Robert
    How to align a crown wheel and pinion?
    3 years ago
  • josephine
    How to measure backlash between pinion and crown wheel?
    3 years ago
  • susanne
    Why putting load on the crown wheel when doing a tooth contact pattern?
    3 years ago
  • Temesgen
    How to adjust tooth contact pattern?
    3 years ago
  • Awate
    Why crown pinion backlash is to be check at 4 points?
    3 years ago
  • Yvonne
    What occur to the tooth mark if crown wheel backlash is reduced ?
    3 years ago
  • Ralph Freeman
    How to test the final drive and differetial unit?
    3 years ago
  • John
    What are the measurable checks carried out on the crown wheel and pinion?
    3 years ago
  • Tuomo Hiukka
    How to carry out tooth contact pattern on a final drive?
    3 years ago
  • ALCEO
    What is the method of setting and adjusting backlash on the final drive?
    3 years ago
  • TANTA
    How to test tooth contact in differential unit?
    3 years ago
  • abele
    How to test the tooth tip contact in a differential unit and the tools to use?
    3 years ago
  • carter
    How to adjusted the tooth contact pattern?
    3 years ago
  • rodney murray
    Where to adjacent if the tooth contact is more on toe in deferential?
    3 years ago
  • luam
    What is the crown wheel and pinion gear clearance on a Isuzu KB 280 LX diff?
    3 years ago
  • charis
    How 2 rectify pinion bearing preload on differential?
    3 years ago
  • Medhanie Abel
    How to adjust pinion gear to crown wheel?
    3 years ago
  • mattiesko
    How to adjust crown wheel inside a diffrential?
    2 years ago
  • Kati
    How to test for backlash in a defferential unit and what can u use?
    2 years ago
  • Carly
    How to reduce backlash on final drive assembly?
    2 years ago
  • trahand
    How to measures backlash of crown pinion?
    2 years ago
  • Einojuhani
    How do you check diff pinion teeth mesh with bearing blue?
    2 years ago
  • finn
    Why should you replace both pinion and crown wheel?
    2 years ago
  • VELI-MATTI
    What driving causes crown wheel damage on a differential?
    2 years ago
  • raffaella
    How do you know when a crown wheel and pinion is damaged?
    2 years ago
  • Rachele
    How to check the tooth contact between crown wheel and pinion?
    2 years ago
  • FESAHAYE
    How to tighten crown & pinion of isuzu?
    2 years ago
  • mantissa mugwort
    What effect does crown wheel have on planetary and Sun gear?
    2 years ago
  • Paul Gilbert
    How to carry out a end play fault in final drive?
    2 years ago
  • mary
    How to check end play in final drive?
    2 years ago
  • robert
    What can happen if pinion to crown wheel contact is out?
    2 years ago
  • HAMILCAR BROWNLOCK
    What is ment by gesr tooth contact and how is this checked?
    2 years ago
  • Justine
    What is the crown check for in differential?
    2 years ago
  • basso brandybuck
    How to rectify tooth contact on differential?
    2 years ago
  • lioba
    How to rectify tooth contact on diff?
    2 years ago
  • lisa hunt
    How to dismantle a differential unit carry out the following test correct tooth contact?
    2 years ago
  • kristian
    What are causes for crown wheel damage in front axle in tractor?
    2 years ago
  • olga loiri
    Does the crown pinion affect the removal of the diff axle?
    2 years ago
  • Orlando
    How to remove the crown wheel and pinion gear from a nissan 1400?
    2 years ago
  • eija-riitt peltonen
    What are the measurements carried out when dismantling the differential unit?
    2 years ago
  • PAULINA
    How to adjust differential crown wheel?
    2 years ago
  • Brhane
    How to calculate root,backlash,contact of gear alignment?
    2 years ago
  • SARADOC
    How many adjustmant are between pinion and wheel?
    2 years ago
  • Mikko
    What noise hear from differential incorrect tooth contact?
    2 years ago
  • Aatifa
    How to detect a faulty crown wheel on front wheel cars?
    2 years ago
  • rowan puddifoot
    How many teeth does a crown wheel of a quantum has?
    2 years ago
  • dana
    How take crown wheel surface check technices?
    2 years ago
  • mariam semere
    What is the procedure for checking crown wheel and the pinion gears?
    2 years ago

Post a comment