Shifting gears to bring transmission work into your bays

Jan. 1, 2020
Removing a transmission on a late-model vehicle can often involve removing an entire subframe and steering rack, and using an array of special holding and lifting tools. It's a huge endeavor, so checking carefully to see if there are other possible c

You can get more trans work in your bays.

undercar transmissions tranny work remvoing transmissions transmission work rebuilding transmissions automotive repair automotive aftermarket In order to keep the bills paid, it may be time to think about adding a few tricks to your arsenal of skills. Maybe even — gasp — transmission work.

I know, I know, most techs shudder at the thought of having to diagnose, repair and recheck something that tranny shops are more than happy to do for them. But it's a new economic reality out there, and it may be worth keeping some of the transmission service work in-house in order to keep revenue coming in, and only sending out the vehicles you're sure need overhaul work.

Face it: Removing a transmission on a late-model vehicle can often involve removing an entire subframe and steering rack, and using an array of special holding and lifting tools. It's a huge endeavor, so checking carefully to see if there are other possible causes for the problem can be a great timesaver, too.

Before condemning a tranny or sending it to a transmission shop, perform a few basic inspections first. See if the problem can be fixed by checking for and repairing any DTCs, see if there are any published TSBs (Technical Service Bulletins), and certainly inspect the fluid condition. Many "transmission" complaints are actually not related to the transmission at all. They're caused by electrical problems such as wiring or component failure, or are related to module or fluid issues.

A systematic approach often can locate the cause of those problems without removing the transmission at all. That might be a bit scary if the last transmission you had apart was in trade school, but it can be financially rewarding if you're ready for the challenge. There are a few things to keep in mind, though, because the rules have changed, just as with every other vehicle system. But if you're careful, you'll be fine — and possibly a bit more profitable.

Check for TSBs, DTCs, Programming Updates and Easy Fixes

After verifying the customer's complaint, the next diagnostic step — as with any other system — is checking for DTCs, TSBs and programming updates. Here are a few examples I've run into.

One frustrated customer — after seeing two different shops for transmission work that didn't fix the concern — brought a car to our shop to fix a "shuddering" problem on the highway. Turned out, the car had a cracked spark plug insulator that was causing a misfire and not a transmission problem at all.

Another car was sent to the transmission shop because it wouldn't shift out of third gear. The problem turned out to be a corroded range switch harness on the side of the transmission, which could've been repaired easily without removing any major components.

Still another vehicle, a light truck, was setting transmission DTCs, which were traced to a faulty ignition switch (the wiring diagram showed the common components) and had nothing to do with the transmission at all.

Control units are critical to transmission operation.

Sometimes controllers contain ATF monitors that must be reset (sometimes with a scan tool) after service. Sometimes the only way to fix a problem is by updating the calibration in the controller (much easier than yanking the transmission). And often they store DTCs that can help pinpoint the cause of the problem.

But just because transmission DTCs are present, it doesn't necessarily mean that the transmission needs to come out.

Not every transmission problem is caused by the transmission itself. Having a look at the wiring diagram after the DTCs are read can often help solve the problem without even cracking loose a bell-housing bolt.

On that note, be careful

That thing that looks like a transmission filter may not be a filter at all. Some manufacturers are mounting their transmission control units inside the transmissions, as is the case for the GM 6T70. (The unit in the pictures had a broken spring plate on the reverse clutch pack, resulting in no reverse gear.) It'd be an expensive mistake to rip it out and discard it. Service information will explain this, too, but it's good to know what to watch for ahead of time.

Understanding the things controllers do besides shifting the gears around and storing DTCs can reduce misunderstandings and comebacks, so it's worth reading up on the system before charging ahead.

Find Your Fluid

Lubrication is as critical as ever, but there are new rules about what goes into a transmission. True, this isn't really the newest change, but it's worth repeating because the cost of forgetting can be really high.

The trend in fluids now seems to be moving away from a single, one-fluid-fits-all transmission lubricant. Instead, manufacturers seem to be using their own blends with their own unique formulas. The most recent fluids aren't currently compatible with each other, and are absolutely not interchangeable. And some formulas can be surprisingly expensive, so verifying the price before contacting the customer is a good idea. "Menu" pricing can backfire.

The only way to be safe is to look up the OEM specifications and follow them carefully. It's a simple thing to do, but it's so important.

Fluid level matters, too. As little as a half a quart either way can make a huge difference to shift quality, so this check really is critical.

This can sometimes be a bit tricky, because it's not always a matter of checking the dipstick. Some cars have a "special tool" to check the level (really just a dipstick on some Chrysler/MB models).

An increasingly common way to check transmission fluid level is by removing a specific bolt and waiting for fluid to drain out, indicating that the fluid is at the correct level. If it's too low, no fluid will drain out (after the initial drips that make their way into the channel). And if it's too high, it will drain out until it's at the correct level. Service information explains the process for each vehicle.

What's really important is knowing which bolt to remove to check the level, and getting the temperature in the correct range. It's usually pretty obvious which bolt it is (as on a Malibu), but looking it up anyway can be a real timesaver, because what looks like a drain plug on the bottom of the pan may actually be the level inspection bolt (as with certain Toyota models). But the temperature requirement varies — it's important to look that specification up for each vehicle. Most often, the fluid needs to be checked at a specific temperature or within a specific temperature range, not just at operating temperature with the engine running.

And of course, don't over-torque the bolt when you reinstall it, since the threaded metal can be surprisingly soft. Thoroughly cleaning the fluid off the case afterwards prevents the residue from leaking on to the customer's parking spot.

"Fill for life" units are another recent transmission development. Under normal conditions, "fill for life" transmissions are just that.

However, few owners operate their vehicles "normally," so check the recommendations from the OEM in the "severe" use maintenance recommendations.

The owner's manual supplement spells out what severe service means, and it's usually a much more aggressive maintenance plan than normal. And it may include recommendations for fluid service that the normal maintenance schedule does not.

Either way, much like cooling systems with "long-life" engine coolant, the system still needs to be serviced, even if that service is just checking the levels, hoses, connections and cooler condition. The system can't just be ignored; that's asking for trouble.

Even with all the changes in transmission technology, fluid type, level and condition can have a big influence on how a transmission performs. Procedures and specifications vary drastically among vehicles, and looking up the proper procedures in your service information is the only way to go to prevent what could prove to be a costly mistake.

Check the Electrical Systems

Too many "transmission" problems are traced to electrical concerns — easy ones.

Corrosion is often one of those problems. The connections and harnesses that go to the transmission get exposed to the harshest elements, so checking for tell-tale black or green rot is a good idea. Problems are often easy to spot, and can extend throughout the length of the wire harness. Any place that salt and goo build up — like wheel wells — is a good place to examine extra carefully.

Additionally, voltage drop testing can identify faulty transmission components and switches quickly — but only if it's done correctly.

Putting one lead to positive and one lead to ground, like you would a test light, is testing for voltage, not voltage drop, as there is a difference.

To check for voltage drop, put one meter lead on a positive point in the circuit (usually one side of the connector or component), and one lead at a negative point in the circuit (usually the other side of the component or connector being tested). Operate the circuit and check how much voltage got eaten up between the two leads of the meter. That's the "voltage drop" across that part of the circuit, and it can quickly identify problems.

Connectors and wires shouldn't be eating up too much voltage, maybe 0.1 or 0.2 of a volt depending on the wire and circuit. Any more than that will likely interfere with the circuit. It's a simple check, and it really works.

Along with checking for voltage drop, check the terminals inside the connector to see if they've gone bad – and not just by looking at them. I've been told by folks far smarter than I am that after a GM connector has been disconnected and reconnected three times, it's considered a weak spot in the circuit and the terminals may need to be replaced.

So, if a critical transmission sensor has been unplugged a few times, the weak electrical connection is quite capable of producing intermittent faults as the terminals inside the connector shift and vibrate as the vehicle travels down the road.

The best way to test these terminals is by performing a "grip" test. That means taking the correct male terminal (not one that's already too big or too small) and checking if the female connector "feels" like it has a positive grip or a light drag between the two terminals. If not, it must be replaced. It's a subjective test, but it works, and it can make you look brilliant.

Testing the electrical system before yanking the transmission can help solve many problems and keep the repairs in-house as much as possible. And these days, that's so important to keep your bottom line healthy.

Go For It

Keeping simple transmission problems in-house can be financially rewarding — as long as you're careful and understand what you're doing. As one wise transmission specialist said, it's just like working on an engine, only with a few more parts to deal with.

Servicing a transmission by ordering a filter kit and filling it with bulk fluid is just not OK anymore, because filters are in difficult places and fluid is often a proprietary chemical cocktail. And connectors and controllers can do a good job of hiding the faults in a vehicle, which may be incorrectly blamed on the transmission and needlessly removed or sent out for repair.

There are amazing opportunities waiting for technicians who do the prep work and accept the challenge of learning something new. It's well worth the effort to update your bag of tricks in the crazy days ahead. Following a systematic approach to diagnosis and always using the service information and manufacturer's instructions can keep the headaches to a minimum, and profits high.

Vanessa Attwell is a Master Technician for two major manufacturers and has also worked on the bench of an independent shop. She has developed and delivered training for both vehicle manufacturers and independents, and helped develop government training and regulations standards.

About the Author

Vanessa Attwell

Vanessa Attwell is a Master Technician for two major manufacturers and has also worked on the bench of an independent shop. She has developed and delivered training for both vehicle manufacturers and independents, and helped develop government training and regulations standards. She drinks too much coffee and spends her spare time sitting in traffic.

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