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What is a brake band in an automatic transmission?

An automatic transmission band is a steel strap with friction material bonded to the inside surface. One end of the band is anchored against the transmission case while the other end is connected to a servo. At the appropriate time hydraulic oil is sent to the servo under pressure to tighten the band around the drum to stop the drum from turning.

Simply put, a band wrapped around a drum becomes a brake, so to speak. When it is applied or squeezed, it stops the drums rotation. In fact, before hydraulic brakes were invented, brakes worked on the same premise, except they were operated manually. Essentially we can call this a ‘brake band’ since it stops drum rotation when it is squeezed tight around the drum.

When the valve body provides a signal to the band apply mechanism called a servo assembly, the band is slowly closed around the drum. This clamping of the band around the drum stops drum movement, spinning up the proper planetary gear, therefore providing the gear range being selected by the valve body.

Most transmissions use anywhere from one to three bands. The only automatic transmission that uses no bands is a TF-604. When a band wears out, it is most likely time to rebuild your transmission, get a pre-tested used transmission or even a new transmission.

Not to worry though, with proper maintenance and friendly driving habits, bands rarely wear out prematurely. However all transmissions from GotTransmissions.com are equipped with new factory original bands.

Read more of our GotTransmissions.com blog for diagnosis articles, repair articles and unusual transmission information. You may be surprised.

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The ‘valve body’ is the brain of your automatic transmission…

The valve body is the control center or brain of the automatic transmission. It contains a maze of channels and passages that direct hydraulic fluid to the various valves which then activate the appropriate clutch pack or band servo to smoothly shift to the appropriate gear for each driving situation. Each of the many valves in the valve body has a specific purpose and is named for that function. For example the 2-3 shift valve activates the 2nd gear to 3rd gear up-shift or the 3-2 shift timing valve which determines when a down shift should occur.

The most important valve is questionable, since every valve is vitally important. The one that gives you direct control over the transmission is the manual valve. The manual valve is directly connected to the gear shift handle and covers and uncovers various passages depending on what position the gear shift is placed in. When you place the gear shift in Drive, for instance, the manual valve directs fluid to the clutch pack(s) that activates 1st gear. it also sets up to monitor vehicle speed and throttle position so that it can determine the optimal time and the force for the 1 – 2 shift.

The other valve, should your valve body have it is the T.V. valve, and the governor. These components apply to non computerized transmissions such as the T-700R4 Chevrolet transmission and many other transmissions.

On computer controlled transmissions, you will also have electrical solenoids that are mounted in the valve body to direct fluid to the appropriate clutch packs or bands under computer control to more precisely control shift points. and, a manual lever position switch too.

Simply put, the valve body makes all of the shifting decisions for your transmission. Different inputs from various switches and sensors provide the valve body with the necessary information for the transmission to do it’s job properly. Got a question about a valve body, or a comment? Ask it right here in the comment area of GotTransmissions.com Blog..

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Part-3: Solving rebuilt transmission problems..

Part-2: Solving rebuilt transmission problems..

The bottom line is that someone or something is not right. I will go on record now, and say I ran the best transmission repair shop anywhere. That is the way I felt about our operation. I’ll be the first to say that, at leat on non computerized transmissions, the problem was human error. Either the installer did not flush the cooler good enough, or made a mistake during the installation, like damage a T.V. cable or linkage. You don’t get many parts problems.

That being said, the pressure test should be run first, just after a visual examination of the entire transmission and cable setup. The exact pressures, whether they are high or low or correct must be known first. Incorrect pressure readings may indicate contamination is present, or that the front pump is worn pretty bad and should have been replaced.

Another thing that even happens to professional installers sometimes, and home installers a lot is…not getting the torque converter all the way into the slots in the pump of the transmission and grinding up the pump…So,

My next move would be: the transmission pan needs to be lowered and checked for contamination. If you see any contamination, especially on a freshly rebuilt unit, than something was not cleaned or a bad hard part was missed upon inspection and is shedding more material and sticking valves in the valve body or governor.

The last thing that concerns me is that many re-builders don’t install the whole soft part rebuild kit, using ‘good’ soft parts over again. More serious is not reading the upgrade kit directions every time you use one, becuase the directions change sometimes without being told..And last, not comprehending the complicated directions well enough to install the upgrade kit fully and correctly.

I have run out of ideas. I hope this helps. Hopefully your problem is easy to solve. GotTransmission.com blog’s last two posts were Part-1 and Part-2 of Solving rebuilt transmission problems. Please read those first if you are new..

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Part-2: Solving rebuilt transmission problems..

Part-1: Solving rebuilt transmission problems..

1. Check the automatic transmission fluid level first..This test is obvious. The transmission has to be full of fluid. Low fluid causes slippage and damage.

2. Checking the radiator, cooler lines, fan clutch and cooling system out and being in sold shape. It is imperative that the cooling system performs to maximum capacity. The radiator cools the transmission too.

3. The automatic transmission cooling lines and the cooling portion of the radiator are flushed out using a hi-dollar transmission cooling system flushing machine or a nice product being sold that is in an aerosol can and hooks to the cooler line. It has a built in adapter for the cooler line and uses the proper cleaning agent to get the metal, brass and clutch material crud out of the cooling coils of the radiator and auxiliary cooler if so equipped..If not do it now, well worth installing one, especially if this is a hot-rod or commercial application. O.K. this is simply the most important procedure that has to be done before a rebuilt, or any fresh transmission can be installed. It would shock you to see how much crud builds up inside the transmission cooler portion of the radiator. Unbelievable amounts of contaminants build up in the coils and tiny holes inside this portion. New automatic transmission fluid is full of detergents, because automatic transmission fluid is not changed very often.

The instant warm or hot transmission fluid goes through a dirty or partly dirty transmission cooler, it melts away the crud build up. The crud goes right into your rebuilt transmission and sticks and or restricts the delicate movement of the valves in the the valve body. And the governor too, on non computerized T700-T4’s or the 4L60E.

3. Examine all linkages such as the T. V. cable for proper movement during the entire range of use age. The T.V. cable has to work smoothly, allowing the cable to slide back and forth smoothly. Or buy a new one. It may be why your transmission failed!

4. Adjusting the T.V. cable to specs. Then fine tuning it during the road test.

5. Hook up hydraulic gauge/s to transmission main line port and check pressures as per manual in R, 1st, 2nd, 3rd, O. D., N, R  and Park. Since automatic transmissions operate off of hydraulic pressure, meaning the ATF creates pressure by a pump assembly built into the transmission, we need to know what the main pressures are in the above gear ranges. The pressures in all ranges must match factory pressures or the pressure recommended by the upgrade kit company. If the pressure is off in one or all of the ranges, something is wrong…

6. Hook up scan tool for extra measure. This is not a computerized transmission, but what the heck, lets see if we have any codes. There is almost no chance this can be a computer problem, since the T-700R4 is non computerized. But, what the hey, if you can scan it, do so..

The final verdict will be my next post. We at GotTransmissions.com Blog feel so strongly about this whole issue that we are presenting it in 3 pieces. We want you to understand. Thanks and enjoy.

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Part-1: Solving rebuilt transmission problems..

Comment:
I just had a700r4 rebuilt with supposely all performance parts and upgrades. It never shifted with a solid shift from the start and after about 10 miles it now has low gear only. upgrades were supposed to be from complete b@m rebuild kit. Is the trans burnt or just me?

You did not say if you had the transmission repair shop (unless a friend did it) do the whole job or if you removed the transmission and had it rebuilt and reinstalled it yourself.

With out having the vehicle in my presence I can only lay out some scenarios. The first thing I would do if the shop you used did the whole rebuild and upgrade job. In other words, you dropped the car off and they did the rebuild  to the trans with the B&M upgrade kit and reinstalled it, and you picked the car up completed. If this is the case, take it back for warranty work and discuss the matter with the shop owner in a gentlemanly way. Go for a ride together so there is no mistake about your concerns.

If this is the scenario, than it should be completely covered under warranty. No hassles.

If you did the installation of your rebuilt transmission, than there are a lot of gaps to fill. Installing a used, rebuilt or even new transmission is an art form. It is way more than just tightening a bunch of bolts..Good transmission installers are hard to find and hard to train..There may be more good re builders than installers.

If my shop did the job, it never would have left the shop. We road tested cars for about 15 to 30 minutes, depending largely on whether the car was using a computerized transmission or non computerized unit. I understood that transmissions have heat related issues. I also know that if you wanted certain upgrades such as a B&M kit installed, then it should shift firmly from the first time you hit the road for a test drive..

FYI, I don’t care for B&M products. I always used TransGo upgrade kits, unless they did not make it.

Here is what should be done in order to diagnose why your T-700R4 is not working right…..I’m going to assume that no matter who installed the rebuilt transmission, that these routine installation procedures where followed to a tee.

1. Check the automatic transmission fluid level first..

2. Checking the radiator, cooler lines, fan clutch and cooling system out and being in sold shape.

3. The automatic transmission cooling lines and the cooling portion of the radiator are flushed out using a hi-dollar transmission cooling system flushing machine or a nice product being sold that is in an aerosol can and hooks to the cooler line. It has a built in adapter for the cooler line and uses the proper cleaning agent to get the metal, brass and clutch material crud out of the cooling coils of the radiator and auxiliary cooler if so equipped..If not do it now, well worth installing one, especially if this is a hot-rod or commercial application.

3. Examine all linkages such as the T.V. cable for proper movement during the entire range of usage.

4. Adjusting the T.V. cable to specs. Then fine tuning it during the road test.

5. Hook up hydraulic gauge/s to transmission main line port and check pressures as per manual in R, 1st, 2nd, 3rd, O. D., N, R  and Park.

6. Hook up scan tool for extra measure. This is not a computerized transmission, but what the heck, lets see if we have any codes.

These are the most basic tests to do before a decision can be rendered.

This is such a critical issue, that I will continue it tomorrow on our GotTransmissions.com Blog..See you then.

What do we get from the tests and cleaning procedure results.

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My automatic transmission only has reverse…What’s up?

We received this question, since it is a popular question in the transmission world, here is the answer.

Question: I have a 99 dodge 1500 4×4 with a gas v-8, at first you had to put it into 1st and shift up, now it thinks that every gear is reverse. have checked fuses and relays, I think that it is a 46 transmission not for shure seems a lot of people are having trouble with these. What do you recomend? Thanks Rick

BTW, it is a 46RE transmission or more commonly called a TF-518…

Without getting too detailed, you have a transmission failure. It is an educated guess though. It is mandatory to have your transmission diagnosed to prove it. Taking someones word over the phone or Internet is risky and you can get ripped real easily or get into parts changing battle until you find the problem.

I’ll cut to the point. What has happened is through a lack of maintenance, overheating the engine and transmission or the using wrong transmission fluid, a situation has occurred where the reverse clutch pack has literally welded itself together. Generally from being overheated or overworked. With the reverse clutches locked up, it can’t go forward and most likely has no neutral and pulls or tugs in park.

It is possible the reverse band, which works with the reverse clutches, has become dislodged and wedged on, so it can not get any gear but reverse.

I say this from much experience. It can happen to any vehicle that uses clutch plates in an automatic transmission. Which is at leat 99 percent of the automatic transmissions in use.

Once you get it checked by a specialist, if you have to replace your Dodge transmission, you will need a strategy. I would recommend a heavy duty 46RE Dodge rebuilt transnission and add an auxiliary external transmission cooler and use genuine Mopar/Chrysler/Dodge transmission fluid. No substitutes or additives.

I hope this is helpful, sorry for a less than pleasant answer. We have more articles on the GotTransmiisions.com blog that may be of help. Please enjoy.

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Part-1: CVT- continuously variable transmission

Some say you can’t teach an old dog new tricks. But the continuously variable transmission (CVT), which has been around, since DaVinci conceptualized it some 500 years ago. He had no means to make one and prove it..it is currently replacing planetary rebuilt automatic transmissions in some automobiles

Since the first toroidal CVT patent was noted, in 1886, the technology has been refined and improved. Today, several car manufacturers, including General Motors, Audi, Honda and Nissan, are designing their drivetrains around CVTs.

­In this article, we’ll explore how a CVT works in a typical rear-wheel driven car, answering several questions on the way:

How does a CVT compare to a conventional, planetary automatic transmission?
What parts does it have and how do those parts work?
What advantages do CVTs offer over conventional automatic transmissions? What about disadvantages?
What’s the driving experience like in a car with a CVT?
What kind of makes and models incorporate CVTs?
Are there any other applications for CVTs other than automobiles?
First, we’ll look at how a CVT compares to a traditional automatic transmission.

These are the questions we will answer in a series on CVT transmissions in the GotTransmissions.com blog. Don’t be shy, feel free to ask questions or comment on anything you feel like. This blog is for YOU, check it out and put it to good use.

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MLPS manual lever position sensor is a vital automatic transmission input device…

The MLPS or manual lever position sensor is one of the vitally important inputs to the transmission control unit (TCU) of a vehicle with modern computerized automatic transmission. Every car made in the last 50 years has a switch similar to an MLPS. The names range from MLPS, to inhibitor switch to neutral safety switch.

Originally called a neutral safety switch when introduced to the automotive field because it’s only duties were to make sure the car only start in neutral and park, and to activate the reverse lights when you shift into reverse.

As automatic transmissions became more technically advanced the MLPS duties increased. Now the MLPS or inhibitor switch is a key input to the TCM and ECM on every modern car I can think of. In fact, the switch, whatever name you call it has a great deal to do with controlling what gear your automatic transmission is in and how it shifts, and when the torque converter locks up, as well as it’s original duties.

In most cases the switch is located on the side of the transmission, essentially hooked to the shift lever in the car. That way when you move the lever, it  moves the switch to the appropriate gear range. some cars have a remote mounted switch, however the responsibility remains the same.

On transmissions with a side mounted switch, GotTransmissions.com often provides a new switch with their transmissions where failure’s are more prevalent. If it is not included with the transmission, it is a good idea to scan the car before any transmission work is done to make sure that did not cause the problem. At my shop, we almost always changed every one when we did a rebuild on a transmission. Either way, I would advise putting a new factory MLPS on your car if you do have to exchange a worn out transmission for a rebuilt transmission, unless it is cost prohibitive.

Most of the time when an MLPS goes bad, you will know you have something wrong with it. This is the time to  have it checked by a qualified transmission mechanic at a competent transmission shop.

Many folks who own affordable hand held code readers can find out what the problem is before hand. In many cases if you are mechanically handy you can change it yourself. If you choose to take that route. don’t forget to clear the code and re-drive the vehicle and recheck to make sure you cured the problem.

These particular switches are on the outside of the car as we mentioned earlier and are exposed to the road elements. Therefore causing a hi rate of failure. Geographically speaking, problems can occur from salt being used to melt snow in the north to water damage from a heavy rain.

Don’t forget to  properly maintain your transmission on a regular basis. Feel free to sign up for our GotTransmissions.com blog for free. You may find more money saving and drive-ability tips in your mailbox regularly.

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Transmission control unit (TCM) or Engine control unit (ECM)..

A transmission control unit or TCU is a device that controls modern electronic automatic transmissions. A TCU generally uses sensors from the vehicle as well as data provided by the Engine Control Unit (ECU) to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.

Most TCU are not part of the transmission, GotTransmissions.com advises potential customers to have the transmission scanned before transmission removal, (if you have a transmission failure or functional problems), in order to determine if that was the problem.

Electronic automatic transmissions have been shifting from  hydro-mechanical controls to pure electronic controls since the late 1980’s. Since then, development has been interactive and todays designs exist from several stages of electronic automatic transmission control development. Transmission solenoids are a key component to these control units.

The evolution of the modern automatic transmission from the hydroelectric controls and the integration of pure electronic controls have allowed great progress in recent years. The new era automatic transmission is now able to achieve better fuel economy, reduced engine emissions, greater shift reliability, improved shift quality, advanced shift speeds and improved vehicle driveability. The  range of programability depends on the vehicle and it’s purpose. Made possible by a TCU (transmission control unit) that allows the modern automatic transmission to be used with appropriate transmission behavior for each application.

Simply put, the TCM receives input from a variety of devices such as the VSS, TPS, MLPS, Brake switch and more depending on the vehicle. Obviously if you do experience a transmission problem or failure it is wise to use a scan tool on the inputs as well.

GotTransmissions.com blog will provide realistic information on the inputs and how they work in order to make better use of this post.

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Hydra-Matic 6T70 (MH2) six-speed automatic transmission…

2008 Hydra-Matic 6T70 (MH2) FWD Six Speed FWD

2008 Hydra-Matic 6T70 (MH2) FWD Six Speed FWD

General Motors new Hydra-Matic 6T70 six-speed automatic transmission, an advanced automatic  transmission with clutch-to-clutch shift operation for front and all-wheel drive vehicles, debuted in the all-new 2007 Saturn Aura midsize sedan. Co-developed with Ford Motor Co., the new six-speed joins the already announced Hydra-Matic six-speed rear-wheel drive family of automatics and Allison 1000 six-speed automatic as part of GM’s mission to produce 3 million six-speed automatics annually by 2010.

FYI—GotTransmissions.com can provide you with G.M. transmission immediately if the situation were to occur.

The 6T70’s clutch-to-clutch operation allows for reduced complexity and compact packaging. A wide, 6.04:1 overall ratio spread helps the transmission deliver both performance and fuel economy, enabling up to 8 percent improved performance and up to 4 percent improved fuel economy when compared with current front-wheel drive four-speed automatics.

Co-development of the transmission allowed it to reach production in less time and enabled each company to reduce development costs by as much as 50 percent. A common design and many common components are shared between GM and Ford six-speed variants, but each company developed its own controls and calibrations to tailor the shift feel of the transmission to fit their brand characteristics.

Rated for engines up to 315 horsepower and 280 lb.-ft. of torque, the 6T70 helps maximize powertrain performance and economy through its wide 6.04:1 ratio – the spread in gear ratios between first gear and sixth gear. This configuration allows for a “steep” 4.48:1 first gear, which helps deliver exceptional launch feel, and a 0.74:1 overdrive sixth gear – the “tall” overdrive gear lowers rpm at high speeds, reducing noise, vibration and harshness. Fifth gear is 1:1 or direct drive.

“The additional gear states are almost like having two transmissions in one…The low first gear provides tremendous off-the-line acceleration, but the transmission is able to use the middle gears to evenly distribute the torque and offers an overdrive sixth gear that helps delivers great fuel economy.

Shorter steps between the gears, compared with a four-speed automatic, enhance performance and feel, as the transmission quickly finds the best gear for the vehicle speed and road conditions – there’s less “hunting” (shift busyness) on grades, for example. Also, the 6T70 offers the capability of driver shift control (DSC), which allows the driver to use tap-up, tap-down shifting to select the desired gear for specific road conditions, such as driving up a steep hill.

The Hydra-Matic 6T70’s highlights also include:

  • Compact dimensions of 357 mm in length and 197 mm in width for packaging convenience in a variety of front- and all-wheel drive vehicles with transverse-mounted powertrains – one the most compact transmissions in its competitive set
  • Clutch-to-clutch shift operation for all shifts except 1-2 reduces mechanical complexity and mass while enhancing shift feel
  • Integrated transmission electro-hydraulic control module (TEHCM) with driver shift control and performance algorithm shifting for shift feel and timing tailored to the driver
  • Internal control module reduces powertrain complexity
  • Auto grade braking and shift mode capability
  • Heat-treated gears are honed for a more precise fit, reducing noise, vibration and harshness
  • Narrow torque converter enhances packaging and maintains efficiency
  • Simple, less complex design has reduced number of seals
  • Adjustable capacity vane-type pump enhances fuel economy compared with non-adjustable gear-type pump

Although used in some low-volume high-performance sports cars and luxury sedans, six-speed transmissions are rare in most high-volume midsize cars and SUVs. GM and Ford Motor Co. recognized a need for a transmission that could accommodate increased powertrain performance while delivering excellent fuel economy. The compact size and reduced complexity afforded by the clutch-to-clutch design allowed engineers to answer the call for performance and economy with six forward speeds.

The 6T70’s advanced clutch-to-clutch operation is designed for smooth shift feel and packaging efficiency. All shifts except 1-2 (the transmission “free wheels” in first) feature clutch-to-clutch operation. This is achieved through three planetary gears, with three stationary clutches and two rotating clutches. It’s a simple, less complex design that enables the packaging of six gears in the space of a four-speed automatic.

A sophisticated transmission electro-hydraulic control module (TEHCM) is mounted inside the 6T70, reducing vehicle complexity. Similar to the control system used in the Hydra-Matic 6-speed rear-wheel drive transmissions, the TEHCM offers improved quality through its hard-wired connections and pre-calibration.

The unit is located entirely within the transmission and operates while bathed in transmission fluid. Locating the controller internally facilitates the modular design and assembly strategy while also shielding the unit from the outside environment.

Although it is not uncommon to have a transmission-control module that adapts to the specific transmission with which it is mated, and to also have programming that optimizes transmission performance characteristics according to a variety of vehicle inputs, the new Hydra-Matic six-speed automatic adds another level of adaptability. Certain components within the major subsystems that make up the transmission also “learn” from one another – via the controller software – in a unique form of self-adaptation that maximizes the interface of all the “networked” components. This procedure takes place as the transmission “tests” itself and the interaction of its internal components before it is shipped from GotTranmsissions.com.

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The TEHCM enables a host of performance-oriented and driver-controllable shift features, including performance algorithm shifting (PAS), driver shift control (DSC) “tap shift” and auto-grade braking.

The Hydra-Matic 6T70 is manufactured at GM’s Warren Transmission plant. It debuted in summer 2006, when production began on the 2007 Saturn Aura.

As always, be true to the maintenance needs of your transmission and expect longer life out of it.

Stay tuned to the GotTransmissions.com blog for more information on some of the new breed of transmissions.

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