Vibration on the highway.

[The Big Car, T.C.]

I just got home from a 500 mile weekend, and about 100 miles from home, my 95 Town Car picked up a vibration between 60 and 80 mph. It's comming from the rear or under the car. The steering wheel doesn't shake, but the seats do. I have had a noise under the car when backing, one of my co workers said it sounded like u-joints were bad. I lifted the car today, and tugged on the driive shaft and it seems tight. My wheel weights haven't moved and the vibration doesn't change if the car is out of gear. I notice it is worse when the tank is full of gas, so weight must play a roll in it. I have no idea what it is, unless it is u- joints...... anybody got a clue? There is no noise like a wheel bearing or rear axle. Could a tire have went bad?

Thanks,

E

1995 LTC Executive "Money Green"

[Towncar]

I seem to remember a TSB on driveshaft balance wieghts falling off near the rearend. Check the TSB's at Alldata.com. Other than that, I'd do whatever's necessary to rule out tires first.

[The Big Car, T.C.]

I couldn't find any TSB's maybe I'm looking in the wrong place, but aldata said I need to buy a membership. What do these weights look like and where do I take a driveshaft to be balanced? Would they install new u joints too? I see u joints are cheap. I'm taking it in on Tuesday to the Tires Plus to have the tires balanced and checked. This car used to ride so smooth, now it rides like crap. I hope the rear end isn't failing.

[Towncar]

Its here:
http://alldata.com/TSB/32/95320545.html

But your right, I don't see anything specific there either. I'm checking the actual text of:
99-11-1
98-8-7
962517

I'll be right back...

20 min later...I'm back... Couldn't find that driveshaft vibration problem anywhere in the TSB's.

I'll post the section on "Vibration" just below....

[Towncar]

Analysis of Vibration

Few vibration conditions are caused by the rear axle assembly. On a vibration concern, follow this diagnosis procedure unless there is a good reason to suspect the axle.

Most vibrations in the rear end are caused by tires or driveline angle.


Traction-Lok Differential

WARNING:
NEVER RUN ENGINE WITH ONE WHEEL OFF THE GROUND. A VEHICLE EQUIPPED WITH A TRACTION-LOK DIFFERENTIAL WILL ALWAYS HAVE BOTH WHEELS DRIVING. IF, WHILE THE VEHICLE IS BEING SERVICED, ONLY ONE WHEEL IS RAISED OFF THE FLOOR AND THE REAR AXLE IS DRIVEN BY THE ENGINE, THE WHEEL ON THE FLOOR COULD DRIVE THE VEHICLE OFF THE STAND OR JACK. BE SURE BOTH REAR WHEELS ARE OFF THE FLOOR.


Tires

WARNING:
DO NOT BALANCE THE REAR WHEELS AND TIRES WHILE THEY ARE MOUNTED ON THE VEHICLE. POSSIBLE TIRE DISINTEGRATION AND/OR DIFFERENTIAL FAILURE COULD RESULT, CAUSING PERSONAL INJURY AND/OR EXTENSIVE COMPONENT DAMAGE. USE OFF-VEHICLE WHEEL AND TIRE BALANCER ONLY.

CAUTION:
Some vehicles are equipped with directional tires (refer to the tire rotation arrows on tire sidewall). If a directional tire is removed for service, it must be remounted in its original location.

Vibration is a definite concern with modern, high-mileage tires if they are not "true" both radially and laterally. They are more susceptible to vibration around the limits of radial and lateral runout of the tire and wheel assembly. They also require more accurate balancing. Wheel and tire runout checks, truing and balancing are normally done before axle inspection.

Sometimes a vibration concern can be corrected by properly rotating or inflating the tires. The best tires should be on the rear to minimize vibration, especially on vehicles with rear springs.


Axle Shaft Runout

Runout of the axle shaft at either end is an infrequent, but possible, cause of rear end vibration. It is advisable to check the axle shaft for runout of the following surfaces as shown in the illustrations:


Drive Pinion Stem and Rear Universal Joint Flange

Rear axle universal joint flange runout should be checked as a potential cause of vibration.

Another cause of excessive rear axle universal joint runout is improper installation of the rear axle drive pinion seal. If the spring on the rear axle drive pinion seal is dislodged, it will jam up and cock the rear axle universal joint flange. The flange should also be indexed before replacing the gearset because of flange runout.


Axle Noise

The following is a glossary of axle noise terms:

l Gear noise is the typical "howling" or "whining" of the ring gear and pinion due to an improper gear pattern, gear damage or improper bearing preload. It can occur at various speeds and driving conditions or it can be continuous.

l Chuckle is a particular "rattling" noise that sounds like a stick against the spokes of a spinning bicycle wheel. It occurs while decelerating from 64 km/h (40 mph) and can usually be heard all the way to a stop. The frequency varies with the speed of the vehicle.

l Knock is very similar to chuckle, though it may be louder and occurs on acceleration or deceleration. The teardown will disclose what has to be corrected.

l Clunk may be a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE, or it may occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components. It is "felt" or heard in the axle.


Non-Axle Noise

There are a few other conditions that may sound like axle noise and must be considered in pre-diagnosis.

The most common are exhaust, tires and trim mouldings.

l In certain conditions, the pitch of the exhaust may sound very much like gear whine. At other times, it can be mistaken for a wheel bearing rumble.

l Tires -- especially snow tires -- can have a high-pitched tread whine or roar similar to gear noise. Radial tires, to some degree, have this characteristic. Any non-standard tire with an unusual tread construction may also emit a roar or whine-type noise.

l Trim, grille and mouldings can also cause whistling or whining noises.

Make sure that none of these is the cause of the noise before proceeding with an axle teardown and diagnosis.


Analysis of Gear Noise

Gear Howl and Whine

Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks and axle shafts / rear wheel bearings as possible causes.

The noises described under Road Test usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are, of course, the type of noise heard on the road test and the driving conditions.

Bearing damage will normally be obvious at disassembly. As noted earlier, differential pinion bearings make a high-pitched whistling noise, usually at all speeds. However, if there is only one damaged differential pinion bearing, the noise may vary in different driving phases.

Differential pinion bearings are frequently replaced unnecessarily on axles with low mileage under 24,139 km (15,000 miles) when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific differential pinion bearing noise. Examine the large end of the rollers for wear. If the differential pinion bearing original blend radius has worn to a sharp edge, the differential pinion bearing should be replaced.

Remember that the low-pitched rumble of a damaged wheel bearing can also be caused by the exterior luggage rack or tires.

Rear wheel bearing noise might be mistaken for pinion bearing noise. Look at the rear wheel bearing carefully before tearing down the axle.

Rear wheel bearings are pressed into the axle housing tubes, making them more difficult to check. However, the axle shaft is the inner race for the bearing. If the bearing is damaged, the roller surface on the axle shaft may also be damaged. The rollers run approximately on the center of the polished surface.


Chuckle

Chuckle is a particular "rattling" noise that sounds like a stick against the spokes of a spinning bicycle wheel. It occurs while decelerating from 64 Km/h (40 mph) and can usually be heard all the way to a stop. The frequency varies with the speed of the vehicle.

Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the differential gear hub and the differential case bore. It can also be caused by a damaged tooth on the coast side of the pinion or ring gear.

Any damage to a gear tooth on the coast side can cause a noise identical to chuckle. Even a very small tooth nick or ridge on the edge of a tooth is enough to cause the noise.

WARNING:
ALWAYS WEAR SAFETY GOGGLES. IF SOLVENT OR COMPRESSED AIR GETS IN YOUR EYES, SEVERE IRRITATION OR PERMANENT INJURY SUCH AS BLINDNESS COULD RESULT. SEEK MEDICAL ATTENTION IMMEDIATELY.

You can often correct this condition and eliminate the noise simply by cleaning up the gear tooth nick or ridge with a small grinding wheel. If the cleaned up or damaged area is larger than 3.2 mm (1/8 inch), it is advisable to replace the gearset.

To check the differential ring gear and pinion, remove as much lubricant as possible from the gears with clean solvent. Wipe the gears dry or blow them dry with compressed air. Look for scored or damaged teeth. Also look for cracks or other damage.

If either gear is scored or damaged badly, the differential ring gear and pinion must be replaced. If there is metal broken loose, the rear axle housing must also be cleaned to remove particles that could cause damage later. Any other damaged parts in the rear axle housing must be replaced.


Knock

Knock, which can occur on all driving phases, has several causes. In most cases, the technician will discover one of the following conditions:

1. A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.


2. Note: Be sure to measure the end play with a dial indicator and not by feel.

Knock is also characteristic of excessive end play in the axle shafts. Up to 0.762 mm (0.030 inch) is allowed in most axles. The frequency of knock will be less because the axle shaft speed is slower than the driveshaft.

CLUNK

Clunk is due to backlash in the driveline or loose rear suspension components. To determine whether driveline clunk is caused by the axle, make a check of the total axle backlash as follows.

1. Raise the vehicle on a frame or twin post hoist so that the wheels are free.

2. To maintain driveline balance, mark rear driveshaft centering socket yoke and rear axle universal joint flange so they may be installed in their original positions.

3. Remove bolts and disconnect driveshaft from the rear axle universal joint flange. Support driveshaft.

4. Install Companion Flange Holding Tool T78P-4851-A between the rear axle universal joint flange and a part of the frame or body so that the rear axle universal joint flange cannot move.

5. Lock the LH rear wheel to keep it from turning.

6. Using a torque wrench and locating on one of the lug nuts, rotate RH wheel slowly to a torque of 6.8-8.1 N-m (5-6 lb-ft). Hold a chalk marker on side of tire 304.8 mm (12 inches) from center of wheel.



7. Rotate wheel slowly in opposite direction to a torque of 6.8-8.1 N-m (5-6 lb-ft).

8. Measure the length of the chalk mark which is the total axle backlash. Total axle backlash should be 25.4 mm (1 inch) or less.

If the backlash is within this limit, the clunk will not be eliminated by disassembling the axle.

Check for these conditions if the backlash is excessive.

l Elongation of the differential pinion shaft holes in the differential case.

l Missing differential case or differential side gear thrust washer.

l Galling of the differential pinion shaft and bore.

If none of these conditions is present, there may be a loose fit of the axle shafts to the side gear splines. Continue as follows until the correction is made.

9. Install new differential side gears and check the backlash.

10. Install two new axle shafts.

11. Replace the differential case.

12. Install the driveshaft so the index mark on the driveshaft slip yoke is in-line with the index mark on the driveshaft centering socket yoke. This ensures original driveline balance. If vibration exists after installation.

13. Tighten rear axle universal joint flange bolts to 95-130 N-m (70-95 lb-ft).


Bearing Whine

Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by damaged pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine which usually comes and goes as speed changes. However, if there is only one differential pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Differential pinion bearings are frequently replaced unnecessarily on axles with low mileage under 24,139 km (15,000 miles) when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific pinion bearing noise. Examine the large end of the rollers for wear. If the bearing's original blend radius has worn to a sharp edge, the differential pinion bearing should be replaced.


Chatter on Corners

Chatter on corners is a condition where the whole rear end vibrates when the vehicle is turning. The vibration is plainly felt and heard. In conventional axles, extra differential thrust washers cause a condition of partial lockup that creates this chatter. Chatter noise on Traction-Lok axles can usually be traced to erratic movement between adjacent clutch plates and can be corrected with a lubricant change that includes Ford Friction Modifier F3TZ-19B546-MA or equivalent meeting Ford Specification WSP-M2C196-A.


Click at Engagement

Click at engagement is a condition on axles of a slight noise, distinct from a "clunk," that happens in REVERSE or DRIVE engagement. Correct this condition by installing a rear axle drive pinion shaft oil slinger between the rear axle universal joint flange and differential pinion bearing.


Axle Shaft Noise

Axle shaft noise is similar to gear noise and differential pinion bearing whine. However, axle shaft bearing noise will normally distinguish itself from gear noise by occurring in all driving modes (drive, coast and float), and will persist with transmission in NEUTRAL while vehicle is moving at problem speed. If the vehicle makes this noise, remove suspect axle shafts, replace rear wheel bearings and install a new set of axle shafts. Re-evaluate vehicle for noise before removing any internal components.


Bearing Rumble

Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning pilot bearing. The lower pitch is because the pilot bearing turns at only about one-third of driveshaft speed.

Bearing malfunctions will normally be obvious at disassembly. As noted earlier, damaged pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if there is only one pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Pinion bearings are frequently replaced unnecessarily on axles with low mileage under 24,139 km (15,000 miles) when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific pinion bearing noise. Examine the large end of the rollers for wear. If the bearings original blend radius has worn to a sharp edge, the bearing roller and cup should be replaced.


Analysis of Inoperative Conditions

If the axle fails to operate, there may be a low or no lubrication condition, or worn or damaged parts.


Broken Welds

Rear axle housing welds, if completely broken, call for replacement of the rear axle housing.


Wheel Bearing Malfunctions

Because of the severe loads, rear wheel bearings may require replacement at high mileage. If a rear wheel bearing fails at low mileage, it is often caused by overloading.


Axle Lock-Up

Lock-up or seizure of the rear axle usually indicates inadequate lubrication. The lubricant prevents friction and helps cool the parts as they heat up. Without enough lubricant, the heated parts get soft and may eventually weld together. Check for lubricant leaks after servicing.

[The Big Car, T.C.]

I was the U joints. Smooth as glass now.