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Automotive Repairs


What is a transmission?

An automatic transmission, also called auto, self-shifting transmission, n-speed automatic (where n is its number of forward gear ratios), or AT, is a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually. Like other transmission systems on vehicles, it allows an internal combustion engine, best suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for vehicular travel. The number of forward gear ratios is often expressed for manual transmissions as well (e.g., 6-speed manual).

The most popular form found in automobiles is the hydraulic automatic transmission. Similar but larger devices are also used for heavy-duty commercial and industrial vehicles and equipment. This system uses a fluid coupling in place of a friction clutch, and accomplishes gear changes by hydraulically locking and unlocking a system of planetary gears. These systems have a defined set of gear ranges, often with a parking pawl that locks the output shaft of the transmission to keep the vehicle from rolling either forward or backward. Some machines with limited speed ranges or fixed engine speeds, such as some forklifts and lawn mowers, only use a torque converter to provide a variable gearing of the engine to the wheels.

Besides the traditional hydraulic automatic transmissions, there are also other types of automated transmissions, such as a continuously variable transmission (CVT) and semi-automatic transmissions, that free the driver from having to shift gears manually, by using the transmission’s computer to change gear, if for example the driver were redlining the engine. Despite superficial similarity to other transmissions, traditional automatic transmissions differ significantly in internal operation and driver’s feel from semi-automatics and CVTs. In contrast to conventional automatic transmissions, a CVT uses a belt or other torque transmission scheme to allow an “infinite” number of gear ratios instead of a fixed number of gear ratios. A semi-automatic retains a clutch like a manual transmission, but controls the clutch through electrohydraulic means. The ability to shift gears manually, often via paddle shifters, can also be found on certain automated transmissions (manumatics such as Tiptronic), semi-automatics (BMW SMG, VW Group DSG), and CVTs (such as Lineartronic).

The obvious advantage of an automatic transmission to the driver is the lack of a clutch pedal and manual shift pattern in normal driving. This allows the driver to operate the car with as few as two limbs (possibly using assist devices to position controls within reach of usable limbs), allowing amputees and other disabled individuals to drive. The lack of manual shifting also reduces the attention and workload required inside the cabin, such as monitoring the tachometer and taking a hand off the wheel to move the shifter, allowing the driver to ideally keep both hands on the wheel at all times and to focus more on the road. Control of the car at low speeds is often easier with an automatic than a manual, due to a side effect of the clutchless fluid-coupling design called “creep” that causes the car to want to move while in a driving gear, even at idle. The primary disadvantage of the most popular hydraulic designs is reduced mechanical efficiency of the power transfer between engine and drivetrain, due to the fluid coupling connecting the engine to the gearbox. This can result in lower power/torque ratings for automatics compared to manuals with the same engine specs, as well as reduced fuel efficiency in city driving as the engine must maintain idle against the resistance of the fluid coupling. Advances in transmission and coupler design have narrowed this gap considerably, but clutch-based transmissions (manual or semi-automatic) are still preferred in sport-tuned trim levels of various production cars, as well as in many auto racing leagues.

The automatic transmission was invented in 1921 by Alfred Horner Munro of Regina, Saskatchewan, Canada, and patented under Canadian patent CA 235757 in 1923. (Munro obtained UK patent GB215669 215,669 for his invention in 1924 and US patent 1,613,525 on 4 January 1927). Being a steam engineer, Munro designed his device to use compressed air rather than hydraulic fluid, and so it lacked power and never found commercial application.[1] The first automatic transmission using hydraulic fluid may have been developed in 1932 by two Brazilian engineers, José Braz Araripe and Fernando Lehly Lemos; subsequently the prototype and plans were sold to General Motors who introduced it in the 1940 Oldsmobile as the “Hydra-Matic” transmission.[2] They were incorporated into GM-built tanks during World War II and, after the war, GM marketed them as being “battle-tested.”[citation needed] However, a Wall Street Journal article credits ZF Friedrichshafen with the invention, occurring shortly after World War I. ZF’s origins were in manufacturing gears for airship engines beginning in 1915; the company was founded by Ferdinand von Zeppelin.[3]

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Transmission Service

Because of the many demands placed on your transmission fluid, it is often called the hardest working fluid in your car. First, it must lubricate the hundreds of moving parts in your transmission. Second, it works as a coolant to reduce the tremendous temperatures created in normal use. Third, it has detergents, which keep the transmission clean and free of contaminants. After doing all that, it still must maintain the hydraulic properties that allow your transmission to shift properly under constantly changing conditions.

As time and miles go by, transmission fluid loses its ability to do all these things. If the fluid is left in beyond its useful life, wear and deterioration of the bearings, clutches, and other internal components will result. Eventually the transmission will fail and require overhaul or replacement. The cost of a transmission rebuild can run from $1500 to $5500, and even higher on some cars.

A Transmission Service should be done every 50,000 miles as part of routine maintenance. It is not recommended for all cars, so please ask if your car would benefit from it.

Now That You’re Here, Let’s Talk About Your Problem!

That transmission or drive train that isn’t quite doing what you want it to. The first thing we’ll tell you, although it probably won’t help much, is that you’re not alone. We estimate that about ten percent of the automobiles and trucks in Amarillo experience some sort of a transmission and/or drive train problem each year. With over 447,000 registered vehicles in 33 county of the Texas panhandle, vehicle owners, will experience that sinking feeling that you are coping with right now. So let’s talk about how to fix the problem.

Here’s a few things you don’t do:

Don’t Call Around Out Of The Yellow Pages To Find Someone To Give You A Quote For Repairs Over The Phone.

This is a guaranteed way to create confusion and chaos. No one, “AND WE MEAN NO ONE” can tell you what it will cost to repair your transmission without looking at it. The image below shows what a typical transmission looks like. The picture will give you a quick idea of the hundreds of parts involved in making your transmission function properly. The idea that someone could tell you which one of them is broken or malfunctioning is as ridiculous as calling your physician and asking what is causing your stomach to ache.

transmission diagram

Do Look At The Bright Side! It’s very possible that nothing is wrong with your transmission. It could be as simple as a electronic switch or sensor that isn’t allowing the transmission to shift at proper intervals or engage as it was intended. Again, something that we won’t know until we look at it for you. If it’s a clutch or other repair, it could be a slave cylinder, or other peripheral part that is malfunctioning.

How Is The Cost Determined? No matter who you use to repair a transmission, the parts all cost the same. (Unless you are using a new car dealer. In that case the parts are usually more expensive, our cost and yours.) When that transmission is apart on the bench, there are basically going to be three piles of parts. Those that are good parts to be serviceable for your transmission, those that are questionable, and then those that are obviously going to have to be replaced. At G&M TRANSMISSION, those questionable parts are going to be replaced. Ask yourself what the company who gives you that low ball bid over the phone is going to do with those parts.

Don’t Use The Dealer Other Than For Warranty Repairs.

Unless of course you are a close relative to Bill Gates or Warren Buffet. Your dealer is in the business of SELLING CARS. Warranty service is what he wants to do most and he will charge the same full price shop rates and standard replacement rates quoted in his little book of how to charge the customer no matter what. What that means is, while you will be using a means of getting your problem solved, the method will most likely be costly and they will want to completely rebuild or replace your transmission before they will issue you any kind of warranty. It’s the business they are in. Your older car or truck, out of warranty, isn’t really of interest unless they can charge you their full rates to cure your problem.

What To Do If You Don’t Listen To Us And Try Calling Everybody in Amarillo Who Ever Looked At The Inside of a Tranny.

Ask about warranties, guaranties and replacement parts. Are they buying new parts or scavenging parts from an old transmission to just get you going again. Remember, their costs are the same as ours. The average transmission requires a total of 12 hours with some requiring as much as 18 hours, to remove, repair, and replace. Somewhere in that low ball price, that shop owner is making up his costs at your expense.

Don’t Make Comparisons Using the Cost of a Remanufactured Transmission.

Always remember that your transmission is your transmission. It came out of your car, it may not need a complete overhaul, it could be a minor interior or exterior problem. All things we won’t know until we look at it. If the cost of parts required to properly repair your transmission exceed that of a remanufactured transmission, we will tell you, and let you make your own decision at that point. Remember that the remanufactured transmission, like your own that we rebuild in our shop, still has parts in it which were a part of the original. We don’t know how many miles are on the rebuilt, we do know how many are on yours, and we’ll warranty your parts. Like all other “rebuilt” parts, there is a right way and the ‘the cheap” way. Prices on rebuilts will range all over the spectrum.

Don’t Buy A Used Transmission.

Used transmissions come from “JUNK YARDS”. There is a reason they are called that. Remember how well your transmission was operating just three or four months ago. It’s even worse if you are intending to do this little chore by yourself in the comfort of your carport. Even if the “JUNK YARD” gives you some kind of warranty, (usually ninety days or ninety feet, whichever comes first) you are going to go through this little exercise more than once. If someone else does it for you they will charge you each time they have to remove and replace this transmission. If the “JUNK YARD MECHANIC” is going to do it for you, remember that what he does all day is remove “JUNK PARTS FROM JUNK CARS”. Your transmission’s reliability requires the expertise of a knowledgeable professional to install and to adjust the many peripheral functions that are critical to the life of the transmission and you and your families safety. Most do it yourselfer types, (carport mechanics and “JUNK YARD MECHANICS”) are ill equipped, in proper equipment, technical education, and physically to handle this highly complicated process.

You’re rolling the dice with this approach and unless your intending just to get the vehicle operating to sell it or give it to your brother in law in exchange for the money you borrowed from him, this is not the way to insure you and your families security while traveling in 100 degree temperatures across the TEXAS panhandle.

torque converters

Torque Converters Explained

Torque converter — a torque converter is a fluid-coupling device that also acts as a torque multiplier during initial acceleration.

The torque converter consists of four primary components:

  • Cover — the cover (also referred to as a front) is the outside half of the housing toward the engine side from the weld line. The cover serves to attach the converter to the flywheel (engine) and contain the fluid. While the cover is not actively involved in the characteristics of the performance, it is important that the cover remain rigid under stress (torsional and thrust stress and the tremendous hydraulic pressure generated by the torque converter internally.)
  • Turbine — the turbine rides within the cover and is attached to the drive train via a spline fit to the input shaft of the transmission. When the turbine moves, the car moves.
  • Stator — the stator can be described as the “brain” of the torque converter, although the stator is by no means the sole determiner of converter function and characteristics. The stator, which changes fluid flow between the turbine and pump, is what makes a torque converter a torque converter (multiplier) and not strictly a fluid coupler. With the stator removed, however, it will retain none of its torque multiplying effect. In order for the stator to function properly the sprag must work as designed: (1) It must hold the stator perfectly still (locked in place) while the converter is still in stall mode (slow relative turbine speed to the impeller pump speed) and (2) allow the stator to spin with the rest of the converter after the turbine speed approaches the pump speed. This allows for more efficient and less restrictive fluid flow. The sprag is a one-way mechanical clutch mounted on races and fits inside the stator while the inner race splines onto the stator support of the transmission. The torque multiplier effect means that a vehicle equipped with an automatic transmission and torque converter will output more torque to the drive wheels than the engine is actually producing. This occurs while the converter is in its “stall mode” (when the turbine is spinning considerably slower than the pump) and during vehicle acceleration. Torque multiplication rapidly decreases until it reaches a ratio of 1:1 (no torque increase over crankshaft torque.) A typical torque converter will have a torque multiplication ratio in the area of 2.5:1. The main point to remember is that all properly functioning torque converters do indeed multiply torque during initial acceleration. The more drastic the change in fluid path caused by the stator from its “natural” return path, the higher the torque multiplication ratio a given converter will have. Torque multiplication does not occur with a manual transmission clutch and pressure plate; hence the need for heavy flywheels, very high numerical gear ratios, and high launch rpm. A more detailed discussion of torque multiplication can get very confusing to the layman as high multiplication ratios can be easily considered the best choice when in fact more variables must be included in the decision. Remember, the ratio is still a factor of the engine torque in the relevant range of the torque converter stall speed, i.e.: a converter with a multiplication ratio of 2.5:1 that stalls 3000 rpm will produce 500 ft.-lbs. of torque at the instance of full throttle acceleration if its coupled to an engine producing 200 ft.-lbs. of torque at 3000 rpm. However, if this same engine produces 300 ft.-lbs. of torque at 4000 rpm, we would be better off with a converter that stalled 4000 rpm with only a 2.0:1 torque multiplication ratio, i.e.: 300 x 2.0 = 600 ft.-lbs. at initial acceleration. Of course it would be better yet to have a 2.5:1 ratio with the 4000 rpm in this example (provided his combination still allows the suspension to work and the tires don’t spin.) This is just a brief overview as the actual scenarios are endless.
  • Impeller pump — the impeller pump is the outside half of the converter on the transmission side of the weld line. Inside the impeller pump is a series of longitudinal fins, which, drive the fluid around its outside diameter into the turbine, since this component is welded to the cover, which is bolted to the flywheel. The size of the torque converter (and pump) and the number and shape of the fins all affect the characteristics of the converter. If long torque converter life is an objective, it is extremely important that the fins of the impeller pump are adequately reinforced against fatigue and the outside housing does not distort under stress.
  • Stall speed — the rpm that a given torque converter (impeller) has to spin in order for it to overcome a given amount of load and begin moving the turbine. When referring to “how much stall will I get from this torque converter”, it means how fast (rpm) must the torque converter spin to generate enough fluid force on the turbine to overcome the resting inertia of the vehicle at wide open throttle. Load originates from two places (1) From the torque imparted on the torque converter by the engine via the crankshaft. (This load varies over rpm, i.e. torque curve, and is directly affected by atmosphere, fuel and engine conditions.) (2) From inertia, the resistance of the vehicle to acceleration, which places a load on the torque converter through the drive train. This can be thought of as how difficult the drive train is to rotate with the vehicle at rest, and is affected by car weight, amount of gear reduction and tire size, ability of tire to stay adhered to ground and stiffness of chassis. (Does the car move as one entity or does it flex so much that not all the weight is transferred during initial motion?)

Note: While referring to the resistance of the vehicle to move while at rest, the torque converter’s stall speed and much of its characteristics for a given application are also affected by the vehicle’s resistance to accelerate relative to its rate of acceleration. This resistance has much to do with the rpm observed immediately after the vehicle starts moving, the amount of rpm drop observed during a gear change and the amount of slippage in the torque converter (turbine rpm relative to impeller pump rpm.) A discussion involving how resistance to acceleration affects a torque converter involves more theory than fact and must involve all the dozens of other variables that affect rpm and slippage. The primary thing we want to remember about torque converter stall speed is that a particular torque converter does not have a “preset from the factory” stall speed but rather its unique design will produce a certain range of stall speeds depending on the amount of load the torque converter is exposed to. This load comes from both the torque produced by the engine and the resistance of the vehicle to move from rest. The higher this combined load the higher stall we will observe from a particular torque converter, and conversely, the lower the load, the lower the stall speed. Naturally, if the engine is not at wide open throttle we will not expect to observe as high a stall speed as we would under a wide open throttle.

Another point concerning engine torque is that we are only concerned with what we’ll call the “relevant range” of the engine torque curve when discussing initial stall speed. This means if our particular torque converter chosen has a design that should produce a stall speed in a range of say 2000 to 2600 rpm given the application then we would refer to this as the relevant range of our interest in the engine’s torque curve for this particular torque converter. In other words, only the torque characteristics of the engine torque in this rpm range will affect the amount of stall speed we actually observe. If we are using a high horsepower/high rpm engine that does not make much torque before 3000 rpm, it does not matter that the engine makes excellent torque over 3000 rpm if we are trying to use the torque converter in this example because its relevant range is 2000-2600 rpm and we would expect to see poor stall (2000 rpm or less) due to the poor torque produced by the engine in this range.

Choosing the correct application torque converter – The buyer of a performance torque converter normally has very specific “wants” to be filled, namely: They want to improve the performance of their vehicle. This can mean they may want the new torque converter to help the car run quicker, run faster, idle in gear better, leave from a stop harder, “chirp” the tires on the gear changes, or pull a steeper hill. The buyer may be looking for any or all of these performance improvements.

They want to improve the dependability of their vehicle meaning they want to get rid of existing drive train failures they are currently having with either OEM or competitors products such as short life (to what they perceive is a proper life), “trash” related transmission failures, overheating, hard part breakage, engine problems that they may believe is caused by torque converter and general unreliable performance.

They may have been told by friends, salespeople, advertising, technical articles, etc. that their particular application needs to have a “stall” converter. This is particularly true of first time performance camshaft purchasers where the salesperson or the camshaft catalog will recommend a higher than stock stall speed torque converter.

A torque converter does not function in a void by itself. The torque converter is an integral part of the total vehicle combination. While many vehicle combinations and applications are very similar and it may seem obvious what the best torque converter selection is, it is normally a wise step to take a look at the intended application and choose the best torque converter for the particular application. There is no “black magic” formula that the variables can be plugged into resulting in a definitive torque converter choice. Torque converter choices are made based on accumulated historical knowledge of performance in various applications and the use of all or several basic charts and ratios derived through this historical information. As with many other automotive performance parts, torque converter design and construction is a dynamic art and can not be patterned on the results of a “plug-in” formula or solely allowed to follow the historical applications.

Dependability concerns in choosing a torque converter – Regardless of the reason or “want” for buying an aftermarket torque converter, an educated buyer should look for several features in the product he is considering purchasing in order to assure that he can reasonably expect to receive dependable results and long life from the purchase.

Furnace brazed fins – greatly improves the strength characteristics of the fins. The furnace brazing causes the housing and fins to move and act integrally as one unit. This greatly reduces the amount of flex, which causes fins to bend and break. Also, the more rigid the fins stay while under pressure, the more consistent the behavior of the torque converter.

Needle bearings – properly selected and installed bearings withstand more pressure and provide less internal drag (drag robs horsepower and increases heat) than can be achieved with OEM style thrust washers. Thrust washers also tend to flake off material adding to contamination in the system (the transmission/torque converter hydraulic system.)

Service and time proven manufacturer – Ask for recommendations from leading car enthusiasts in your local area or check out what the racers are using.

Drivability concerns in choosing a torque converter – A performance torque converter should not compromise one aspect of car performance to achieve another. When investigating a converter purchase ask whether the particular torque converter being looked at may improve initial takeoff at the sacrifice of top end mph or other similar results, questions, etc. With the technology and product available today a buyer very seldom needs to sacrifice one area of performance to gain in another. However, without proper selection assistance or guidance (and with many under engineered products on the market today) it is unfortunate that many buyers end up with a product that does not best suit his needs or expectations. Too low a stall torque converter will not benefit the customer. If the user has an application which requires at least 3000 rpm stall and they purchase a 2000 to 2500 rpm stall range converter, it will normally not even give them the 2000 rpm stall. It will act very similar to the stock torque converter they just removed why? Because the engine needs to operate in its optimum rpm range and since the chosen torque converter is below that range, it is not getting enough load from the crankshaft side to operate as designed. Symptoms include engine stalling when in gear at a stop, low stall speed, hesitation when going to full throttle, a “bog” when leaving from stop at wide open throttle. Too high a stall range torque converter will not benefit the customer. You will see this situation most often when the customer does not have sufficient gear ratio for the converter stall range or the engine is not capable of the appropriate rpm range (too small a duration camshaft, inadequate valve springs, too low compression, etc.) Symptoms include high “revs” to pull away from stop, “marshmallow” accelerator feel when driving at part throttle, transmission and possibly engine overheating, and a pronounced engine rev when nailing the throttle from a cruising speed.

G&M TRANSMISSION hopes that this article has broadened your knowledge of this most commonly misunderstood component allowing you to be a more educated consumer.

Contact us

G & M Farnsworth Transmissions
4410 Canyon Dr. (I-27)

Call: (806) 358-8119

Fax: (806) 358-4112