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Car and Truck Repairs at Bob's Garage

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How Tires Work

Posted by Brian Brown on March 19, 2010 at 3:46 PM Comments comments (0)

How Tires Work

by Karim Nice

 What All the Numbers Mean

Each section of small print on a tire's sidewall means something:

Tire Type

The P designates that the tire is a passenger vehicle tire. Some other designations are LT for light truck, and T for temporary, or spare tires.

Tire Width

The 235 is the width of the tire in millimeters (mm), measured from sidewall to sidewall. Since this measure is affected by the width of the rim, the measurement is for the tire when it is on its intended rim size.

Aspect Ratio

This number tells you the height of the tire, from the bead to the top of the tread. This is described as a percentage of the tire width. In our example, the aspect ratio is 75, so the tire's height is 75 percent of its width, or 176.25 mm ( .75 x 235 = 176.25 mm, or 6.94 in). The smaller the aspect ratio, the wider the tire in relation to its height.

Two tires with different aspect ratios but the same overall diameter

High performance tires usually have a lower aspect ratio than other tires. This is because tires with a lower aspect ratio provide better lateral stability. When a car goes around a turn lateral forces are generated and the tire must resist these forces. Tires with a lower profile have shorter, stiffer sidewalls so they resist cornering forces better.

Tire Construction

The R designates that the tire was made using radial construction. This is the most common type of tire construction. Older tires were made using diagonal bias (D) or bias belted (B) construction. A separate note indicates how many plies make up the sidewall of the tire and the tread.

Rim Diameter

This number specifies, in inches, the wheel rim diameter the tire is designed for.

Uniform Tire Quality Grading

Passenger car tires also have a grade on them as part of the uniform tire quality grading (UTQG) system. You can check the UTQG rating for your tires on this page maintained by the U.S. National Highway Traffic Safety Administration (NHTSA). Your tire's UTQG rating tells you three things:

• Tread Wear: This number comes from testing the tire in controlled conditions on a government test track. The higher the number, the longer you can expect the tread to last. Since no one will drive his or her car on exactly the same surfaces and at the same speeds as the government test track, the number is not an accurate indicator of how long your tread will actually last. It's a good relative measure, however: You can expect a tire with a larger number to last longer than one with a smaller number.

• Traction: Tire traction is rated AA, A, B or C, with AA at the top of the scale. This rating is based on the tire's ability to stop a car on wet concrete and asphalt. It does not indicate the tire's cornering ability. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires that have been in the news have a traction rating of B.

• Temperature: The tire temperature ratings are A, B or C. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded. Underinflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires have a temperature rating of C.

Service Description

The service description consists of two things:

• Load Ratings: The load rating is a number that correlates to the maximum rated load for that tire. A higher number indicates that the tire has a higher load capacity. The rating "105," for example, corresponds to a load capacity of 2039 pounds (924.87 kg). A separate note on the tire indicates the load rating at a given inflation pressure.

• Speed Rating: The letter that follows the load rating indicates the maximum speed allowable for this tire (as long as the weight is at or below the rated load). For instance, S indicates that the tire can handle speeds up to 112 mph (180.246 kph). See the chart on this page for all the ratings.

 

Tire Traction

Did you know?

Safety grooving, the technique of cutting grooves into a paved road to increase tire traction, originated at a NASA research center. Learn about other NASA innovations in this interactive animation from Discovery Channel.

There are a lot of different terms used today in the tire industry. Some of them actually mean something and some do not. In this section, we'll try to explain what some of the terms mean.

All-Season Tires with Mud and Snow Designation

If a tire has MS, M+S, M/S or M&S on it, then it meets the Rubber Manufacturers Association (RMA) guidelines for a mud and snow tire. For a tire to receive the Mud and Snow designation, it must meet these geometric requirements (taken from the bulletin "RMA Snow Tire Definitions for Passenger and Light Truck (LT) Tires"):

1. New tire treads shall have multiple pockets or slots in at least one tread edge that meet the following dimensional requirements based on mold dimensions:

a. Extend toward the tread center at least 1/2 inch from the footprint edge, measured perpendicularly to the tread centerline.

b. A minimum cross-sectional width of 1/16 inch.

c. Edges of pockets or slots at angles between 35 and 90 degrees from the direction of travel.

2. The new tire tread contact surface void area will be a minimum of 25 percent based on mold dimensions.

The rough translation of this specification is that the tire must have a row of fairly big grooves that start at the edge of the tread and extend toward the center of the tire. Also, at least 25 percent of the surface area must be grooves.

The idea is to give the tread pattern enough void space so that it can bite through the snow and get traction. However, as you can see from the specification, there is no testing involved.

To address this shortcoming, the Rubber Manufacturers Association and the tire industry have agreed on a standard that does involve testing. The designation is called Severe Snow Use and has a specific icon (see image at right), which goes next to the M/S designation.

In order to meet this standard, tires must be tested using an American Society for Testing and Materials (ASTM) testing procedure described in "RMA Definition for Passenger and Light Truck Tires for use in Severe Snow Conditions":

Tires designed for use in severe snow conditions are recognized by manufacturers to attain a traction index equal to or greater than 110 compared to the ASTM E-1136 Standard Reference Test Tire when using the ASTM F-1805 snow traction test with equivalent percentage loads.

These tires, in addition to meeting the geometrical requirements for an M/S designation, are tested on snow using a standardized test procedure.They have to do better than the standard reference tire in order to meet the requirements for Severe Snow Use.

Automotive Brakes

Posted by Brian Brown on March 13, 2010 at 2:38 PM Comments comments (0)

Automotive Brakes

Summary: Nothing stinks worse than having brake trouble and getting taken for a ride by your mechanic. Get the best information on brake repair so you do not get scammed at the garage. The braking system is a complex system which needs proper maintenance and care over the lifetime of your car.

 

Before you start work, make sure you have a good repair manual. We recommend an online manual from ALLDATA for step-by-step instructions on changing your brakes. You can even find out things only the dealer knows about your vehicle with TSBs, which are included with your ALLDATA manual.

Your car's brake system is a complex grouping of parts which serve a critical role in keeping you safe. No other system in the car is as important for your safety. Keeping your brake system in tip-top shape should be your top priority.

 

Let's start with the pedal and work our way down the braking system to better understand how it works. The Pedal is a strong steel lever which transmits the force from your foot to the master cylinder. The pedal typically has a switch attached to it, to turn on your brake lights when you press the pedal down.

When you push down on the pedal, the master cylinder is pushed via a push rod. The master cylinder consists of a piston and a fluid resevoir. When the piston is moved, it pushes the brake fluid through the brake lines and into the caliper or wheel cylinder.

 

Most all cars have disc brakes on the front wheels, and many have disc brakes on the rear also. When disc brakes are not used on the rear, drum brakes are used. The fluid being pushed from the master cylinder through the brake lines pushes a piston in the brake caliper. This in turn applies force to the brake pads.

The brake pads are typically made from a hard organic or metallic compound. The pads are made to survive under high heat and pressure. When the brake pads contact the rotor, there is friction and heat is created. This is how your car stops, by turning the rotating energy of your wheels into heat through friction.

 

The last part of your braking system is the rotors. Typically made from cast iron and made heavy enough to dissipate heat and not warp over time. Unfortunetly, in todays cars, many of the rotors are not large enough, and can warp within a few 1,000 miles. The rotor is bolted between the wheel and the spindle, and rotates at the same speed as the wheels.

 

 

Common problems:

- Wear: The braking system does a lot of work and the brake pads take the brunt of the punishment. It is a good idea to have you brake pads checked every 6 months or when you suspect a problem. Symptoms include squeaking, grinding, or increased stopping distance. Most pads have a thin metal tab which vibrates against the rotor when the pads wears down to a dangerous level. Some pads do not have this and if not checked periodically can wear down far enough to ruin the rotors. A modern trend is to make the brake pads very hard thus extending life. This harder material can squeak and sound like the wear indicators. Brake dust can also cause squealing but can be fixed by spraying brake cleaner on the brake system to remove the dust.

 

- Warped Rotors: More common in newer cars, but possible on all disc brake systems. Rotors warp due to being overheated or incorrect tightening of the wheel. A warped rotor will give a pulsing feeling when applying the brakes. This pulsing can be annoying and dangerous. Most newer cars have rotors which are very thin and warp very easy. Furthering the problem, the manufacturer does not leave enough material to resurface the rotor. Check with you mechanic to make sure you can safely have the rotors machined or replace with new rotors. To resurface, the rotor is placed in a lathe and a cutting tool removes a few thousandth's of material from the braking surface. This restores the flatness of the rotor and eliminates the pulsing sensation in the pedal. Make sure when your mechanic puts everything back together that he torques the lug nuts to proper specifications and never uses an impact wrench. If the lug nuts are not tightened evenly the rotor can warp and you are back to square one. Note: Some shops use a torque stick, which attaches to an impact wrench and does not allow the torque wrench to tighten more than it should. This is acceptable. If your mechanic does not use a torque wrench or torque sticks, find another mechanic.

 

Preventive Maintenance:

• Avoid "riding" your brakes. It's better to slow down with moderate pressure and then releasing the brake to cool, than riding the brakes and overheating them

• On steep grades consider downshifting to save your brakes. Only do this when traction conditions are good. In ice, snow, or even rain, downshifting into too low of a gear may cause a skid. Downshifting lets you engine do some of the braking instead of your brakes.

• Keep your wheels and braking system clean. Clean brakes work better and keep temperatures down. Use a good wheel cleaner which you know if safe for your wheel finish.

 

What to discuss with your mechanic:

• Be weary of low priced brake jobs advertised in the paper or TV. Some shops will try a bait and switch or find other parts which "need" to be replaced. Salesmen will try to make you feel guilty for putting your families safety on the line. They claim you need the premium pads and rotors, of course at a higher price.

• You mechanic should clean all the components of the brake system to ensure a dust and squeak free job.

• All bolts including lug nuts should have anti-seize compound on the threads to prevent them from rusting fast and causing headaches down the road.

• Have your mechanic use an anti-squeak compound on the back of the brake pads. This keeps the pads from vibrating and annoying you to no end. There are spray, and paste forms, with the paste working better for me.

• Insist on seeing the pads they removed from your car. There is no use paying to replace something that doesn't need to be replaced.

• National brake shops are not all bad. Some stores only do brakes so they should be pretty good at it. Ask around and get recommendations before you get work done. Quality depends on the owner of the national chain store, not the parent company so shop carefully.

• Do you need the lifetime brake pads? Well that depends on how long you will keep the car and how many rotors you plan on buying in the next few years. This initial cost is a little higher due to the fact the manufacturer knows he will most likely have to give you another set when yours wear out. Also these pads are made from a harder material and tend to wear down the rotors instead of themselves. You would be better off buying the basic pads and replacing them periodically instead of costly rotors every year or two.

• Make sure your mechanic uses a torque wrench or torque sticks on their impact guns. See above for the explanation.

Safety is important to you and your family. Stay safe by educating yourself and not by falling prey to the salesman. When you think you have a brake problem, take it to be checked by a mechanic you trust, for your families sake.

Why Rotate My Tires?

Posted by Brian Brown on March 12, 2010 at 12:15 PM Comments comments (3)

Why Rotate My Tires?

No matter how well your car or truck is in alignment, it will never be perfect. Front tires will tend to wear unevenly from side to side due to the minor changes in alignment as well as from the forces involved when turning. Also if your vehicle is rear wheel drive, the rear tires will wear quicker than the front.

 

What is the proper Tire Rotation Pattern for My Car?

The best pattern is found in your car's owners manual. The manufacturer has taken all variables into consideration and has determined the best pattern to prolong your tires life. Be aware that some vehicles have different size tires from front to back, so all you can do is swap wheels from side to side. Also be aware when buying tires, if they are directional (designed to run on the road in one direction only) you will have additional challenges in that you will have to dismount the tires and remount and balance if you want to cross sides. You can simply rotate front-back, back-front but that will more than likely not be the best for tire wear.

 

When should I rotate my tires?

Again, your owners manual will have the recommended intervals, but if you are ever in doubt, do it at every oil change to be safe. It's more important to rotate during the first 10,000 miles, so pay particular attention to new tires and their rotation schedule.

 

How Do I Actually Rotate my tires?

•Tools Needed: A floor jack or the jack from your car. A lug wrench or impact wrench and socket. Jack stands, sometimes called axle stands and a torque wrench. You will also need wheel chocks to keep the car from rolling away unexpectedly and some anti-sieze compound.

•Procedure: With the car on a hard level surface, make sure the car is in park or in 1st gear if you have a manual transmission and that the parking brake is on. Place the wheel chocks at the downhill side of the front or rear tires, depending on how your car is situated. We want to keep the car from rolling away if something bad happens.

If you have an impact wrench, procede to the next step, if not, then break loose all of your lugnuts while the car in on the ground. This will save you from fighting with wheels that will want to turn when jacked off of the ground.

Begin by jacking up the car at whatever end the wheel chocks are NOT located. This will assure that the car does not roll away while jacking it up. Once the car is high enough, place the jack stands at the approved locations (check your owners manual) or on a solid flat portion of the frame. Do not raise the vehicle any higher than is necessary to remove the wheels.

Remove all the lug nuts, remove the wheels and do the tire rotation shuffle ! You can use a crayon or chalk to mark the tires so you do not get confused. Mark the original or destination position, whichever is easier for you to remember. Once all the wheels are in their final resting place, place some anti-sieze compound on the wheel studs and tighten the lugnuts but not to the final torque.

Lower the car to the ground by reversing the sequence used to get the car on the jack stands. Once on the the ground, torque the lugnuts in a cross pattern with a quality torque wrench, not an impact wrench. Using an impact wrench may cause uneven torques and warp your rotors, so a torque wrench is critical here.

 

What Should I Look For When Having A Tire Shop Do My Tire Rotation?

Make sure they know the proper tire rotation pattern from your owners manual. Look it up before you take your car or truck in for service and leave the owners manual on the front seat with the proper page open to help your mechanic. Also make sure that the tire shop uses a torque wrench or "torque sticks" which are long sockets for an impact gun which prevent over torquing. Also it is a good idea to ask them to put some anti-sieze on the wheel studs before tightening the lug nuts, you will thank me if you ever get a flat on the side of the road.

Tips to Save on Transmission Repairs

Posted by Brian Brown on March 9, 2010 at 10:46 AM Comments comments (0)

1- How do I check the transmission fluid level?

Always check the fluid level with the engine running (except Honda), the transmission in "park" (except Dodge products which should be in neutral with the emergency brake applied), and with the engine at operating temperature. Remove the dipstick and wipe with a rag. Insert the stick fully and remove. Look at both sides of the stick to verify the same indication. Repeat the process.

The reason to check both sides of the dipstick is that after the fluid circulates through the transmission, it dumps back into the pan area and will cause an agitation of the fluid. This creates an uneven level and some fluid will "slosh" onto the stick and give a false reading. Some transmissions are worse than others.

Note: If you check the fluid level after the engine has been off for a long time, fluid from the torque converter will drain back into the pan area where the level is measured and give you a false high reading. When the engine is started, the fluid in the pan area is used to fully charge the transmission and torque converter. Also, the difference of fluid temperature will affect the measurement. The fluid volume expands when heated to operating temperature.

Another method of checking the fluid is to turn off the engine and immediately check the level. This will stop the agitation and give an accurate level (no agitation) before the fluid in the torque converter has had a chance to drain back into the pan area which would give a false-high reading.

Tip: If you have added fluid, go through the same procedure, but repeat the process several times before you look for a reading. Some of the added fluid will adhere to the side of the filler tube and can give a false reading.

Tip: If the fluid level is low, you have a leak! Transmissions do not consume fluid. Have the leak diagnosed and repaired to prevent more serious problems.

After you have added fluid, drive the vehicle for a mile or two, then recheck the level. This is especially important in front wheel drive vehicles.

 

 

2- I have a leak. Can you tell me how much it will cost to repair it?

There are numerous places that a transmission can leak. They include: the pump, shift lever seal/s, kickdown seal, electrical connection/s, governor cover, speedometer, rear output seal or axle seals, servo cover/s, filler tube, throttle cable, pan, side cover, cooler lines, and differential cover.

The real question is: What is/are the source/s of the leak/s. Most people can only see the bottom of the unit, and therefore conclude that the bottom pan gasket is leaking when, in reality, the leak is from above and running down and around the pan. Therefore, it is imperative that the unit be visually inspected to evaluate the leak situation!

So, the answer to the question is: No, I can't without seeing the vehicle.

 

 

3- Can I drive with a transmission leak?

It depends on the rate of fluid loss. A minor or slow leak will allow you to drive as long as you maintain the level in the normal range. You will have to establish the rate of loss and replenish as necessary. It should be obvious that if fluid is running out as a stream, that you won't go very far. A transmission will usually operate "normal" until the fluid loss is a quart or more. Then the unit will exhibit abnormal operating symptoms and internal damage is occurring. What started as only a leak can result in a major repair bill if ignored!

 

 

4- Can you tell me how much it will cost to overhaul my transmission?

My first question back to you is: Which model transmission do you have and how do you know it needs to be overhauled? Occasionally, a poorly running engine, restricted exhaust, computer or sensor, poor electrical ground, or other problem not internal to the transmission will be the cause of abnormal operation. Tragically, I have had numerous vehicles brought into the shop having had major work done on the transmission itself or the unit replaced, but the operation problem is still present. This usually turns out that the problem was never in the transmission, therefore never resolved. What a waste!

 

 

5- How long does a transmission normally last?

The is no accurate answer to that question. The mileage or time of use before major problems occur will vary greatly, and therefore, I don't see a correlation between mileage and expected transmission failure. It is not unusual that the first few years after a newly designed transmission hits the road, that early failures occur. But, in later years with updates to the original design, the units become more reliable.

The three major factors in the life expectancy are periodic maintenance, maintaining proper fluid level, and driving habits.

 

 

6- How can I make my transmission last longer?

Just like the dentist tells you, "Don't ignore them." Check the fluid level and condition periodically, repair any leaks/problems promptly, service the unit on a regular basis, and add an auxiliary cooler if the vehicle is used for towing, commercial, or high ambient temperature climates. Some units should have a shift kit installed.

Synthetic fluid may benefit some applications by lowering operating temperature resulting in a longer life, but not all transmissions can use the synthetic fluid.. Check with your local ATRA shop for their advice to your specific application and needs.

 

7- What is a "shift kit?"

The kit is an aftermarket service pack that has been researched and developed to compensate for design deficiencies discovered in a particular transmission. In most cases, the kit improves the quality of shifts, increases the internal pressure that operates the unit, and provides better lubrication.

Note: Not all transmissions need the kit.

 

8- Will it hurt to overfill the transmission?

In a word, no! Although, it is possible that gross overfilling can cause the fluid to be subjected to moving parts and become aerated which could cause abnormal operation. You may also notice leaks that ordinarily would not occur.

 

9- Will overfilling "blow" seals?

In a word, no! The transmission case is vented preventing pressure buildup in normally un-pressurized areas. Severe overfilling can raise the fluid level such that the transmission may lose fluid through the vent or leak from seals that are above the normal fluid level, but the fact remains that the seals that are under pressure and those that are not will not change because of the fluid level.

My "Check Engine" light is on. What does it mean?

Posted by Brian Brown on March 8, 2010 at 11:28 AM Comments comments (0)

It means your vehicle's onboard computer system has self-diagnosed some kind of problem. The "Check Engine" light, which is also called a "Malfunction Indicator Lamp" (MIL) or "Service Engine Soon" (SES) lamp, is there to signal you when a problem occurs that may require attention. This can include anything from a momentary hiccup that has has little or no noticeable affect on engine performance or driving safety to a failure of a major electronic component. There's no way to know what the light means without running a diagnostic scan on the system to determine the nature of the fault.

As a rule, a continuous Check Engine light usually signals a "hard fault" or failure that has occurred. If the light comes on and off, or only blinks momentarily, the problem may be minor or intermittent in nature.

To help identify the problem, it helps to make a mental note of the conditions that occurred when the light came on. Where you driving at a certain speed? Accelerating or slowing down? Shifting gears?

Onboard diagnostic systems are very complex and require a fair amount of expertise as well as special tools to troubleshoot. To find out what's wrong, a technician has to "get into" your system through a diagnostic connector which may be located under the dash, under the driver's seat or in the engine compartment. The diagnostic connector serves as a port of entry for accessing information and/or for putting your vehicle's computer system into a special diagnostic mode for further testing or displaying "fault codes".

Fault codes are numeric codes that are generated when a problem is detected. If a sensor circuit reads out of range or some electronic component fails to respond to a command from the computer, the computer recognizes it as a fault and records a number that corresponds to the nature of the problem. The technician must then retrieve the code and refer to specific diagnostic chart or "fault tree" that gives him the step-by-step checks he has to perform to isolate the failed component. It can be a very time-consuming process depending on the nature of the problem. Usually the process works but sometimes it doesn't. An intermittent fault can be very difficult to track down, and may require repeated attempts to repair it.


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