Dieter on Driveability

“The transmission slips”. When a customer brings in a vehicle with a transmission complaint, that’s normally the extent of the feedback between technician and motorist. That’s too bad for both owner and repairer, because there are many driveability issues that aren’t about clutches and bands. Dieter Schmitz is an Oakville, Ontario-based 15-year veteran with Mr. Transmision, and has seen most driveability problems on the road and inside the case and has lots of useful information for technicians looking at a tough diagnosis.

One area that Schmitz notes as a major problem area is fluids.

“Let’s talk about late model Fords”, says Schmitz: “People that install a transmission in an attempt to save a buck are putting in the wrong fluid, like Dexron II or Mercon instead of Mercon V. They won’t buy the specific fluid, leading to shudder. It’s the same with Chrysler; they’re very fluid-specific. In the course I teach, I tell the guys to put the right fluid in. That can cause driveability issues with shudder and the torque converter clutch and also with the clutch application which affects changing gears.”

Schmitz is particular about fluids and carries several types in stock. “It’s really complicated stuff,” he states. “Mercon V, for example, is semi-synthetic. It’s designed to work with the friction characteristics of the linings inside the transmission. The characteristics between the clutches and fluid are engineered to work together. If you change one, it just won’t work right and you can develop shudders. For Chryslers, for example, I buy 7176 ATF +3, Mercon V and for 2000 and up Chryslers, ATF +4 which is a better version of the “+3”. I don’t believe in buying “regular” fluid and putting in additives that change it into the required fluid. A lot of people do it, but I don’t want to guess. It costs a little more, but it’s worth it. I carry four types, with Dexron and Mercon III in bulk, ATF +3 in 205-L drums and Mercon V and +4 I buy by the case. It’s not coming through as often.”

Schmitz notes that fluids are one area where the rebuilder has no control when selling units over the counter. “That’s a problem with carry in units. I worry about them putting the right fluid in. It’s important.”

On the preventative maintenance side, Schmitz agrees with the industry consensus that flushing just isn’t on the motorists’ radar unless asked. How often do consumers think about flush and fill service? “Generally it’s never,” he declares, adding, “they have to keep in mind that with the development of the new fluids, especially synthetic, companies like GM are basically building “fill for life”. My 2000 Cirrus is the same, using the ATF +4 synthetic. The fluid is able to take more punishment, especially heat. Heat is what kills fluid the quickest. We recommend a service at 50,000-kilometer intervals. People are still reluctant to have their transmissions checked and serviced. We usually see them when there’s a problem. When a customer comes in after 70 or 80 thousand kilometers and says they’ve never had the transmission serviced and now they do, it’s usually a red flag indicator that there’s an underlying problem that they’re not telling us about. We have to do a little detective work. They let problems slide and hope that a service will correct it. Usually, it’s too late. Service is definitely neglected.”

Schmitz regards a service as a full pan drop fluid and filter change.

“There’s been the evolution of those flushing machines that attach to the cooling lines that change all the fluid. It’s a great idea, but the pan isn’t removed and the filter changed. With the old fashioned way, however, not all the fluid is changed so there are pros and cons to both. Ultimately the best service would be to change the filter where you can, and then change all the fluid.”

In the old days, a transmission rebuilder would sniff the fluid to detect a problem, and Schmitz thinks that it’s still a useful strategy. “I do it all the time. That will never change. I pull the stick and smell it. Some things die hard.”

The other essential to good diagnosis, according to Schmitz, is the road test. “The road test is going to make it or break it for you. A lot of cars come in and it’s often not even a transmission problem. The word “slipping” is generic, and customers will use it for any kind of transmission problem, and often with today’s vehicles, is if you have a bad plug or wire, when the torque converter clutch engages under a specific load, you’ll really feel it. It can be misdiagnosed as a transmission problem, specifically a converter clutch problem. General Motor’s 3.8L front wheel drives are notorious for that problem. Get it up to 60 to 80 km/h on a slight incline, then tip in the throttle, it breaks down and the car bucks and surges.”

For that and similar diagnostics, the technician needs to be able to distinguish between the lockup feel and a misfire. States Schmitz, “I equate a lock up shudder as what it would feel like when you drive over those wake-up strips on the side of the highway. It’s a steady, rhythmic feeling. If it’s erratic, like someone bumping you from behind, it’s generally an engine miss.”

Besides the road test, he also uses a scan tool with every diagnostic.

“We use the scan tool regardless. What the technician can do is talk to the customer, because we get the vehicle, not the customer. Ask the customer if they’ve had the vehicle since new, how long have they had the problem, and if they’ve had any service done on the vehicle recently. I’ve had many vehicles where work done on the intake manifold changes the way the transmission works. An example is the GM 3.1L V-6’s where the geometry of the accelerator linkage on the throttle body is different from the original. The transmission cable hooks onto it, changing the internal pressure in the transmission.”

Shops installing rebuilt units can occasionally generate problems by accident that are not directly transmission-related, but can appear that way, notes Schmitz.

“There are a couple of areas where an installer can make a mistake. There are three that come up often: On the Mazda 929 there’s an O2 sensor connector and a transmission connector that are similar. If you mix them up it can create a short circuit that can cause fires. On GM 4T65E transmissions, one of the bellhousing bolts is shorter than the rest. If you put the long bolt in there you punch through the block. An installer can put problems into the vehicle, but only if he makes a mistake.”

Even simple speedometer drives can be an issue, declares Schmitz. “Early model Chryslers, for example, had a speedometer cable that was separate from the output speed sensor. It wasn’t critical. The later model Chryslers drive the speedometers from the output speed sensor. Gear ratios become an issue, since differentials and sprockets have different ratios. Fords are the same. There’s a sensor that reads to the driven sprocket with an exciter wheel. If you mismatch the tooth counts the computer will set a code because the computer expects to work in a specific RPM parameter, so if you change it, it gets confused, just because you put in different sprockets.”

Schmitz notes that the problem is more likely to occur with an exchange unit unless the installer is careful to match numbers. Just because the unit fits, doesn’t make it the right part. As a result, rebuilders like Schmitz don’t carry large inventories.

“We don’t often do exchanges anymore. Now you need to know internal gear ratios. We rebuild what comes out of it and hope that nobody’s touched it before and that it’s the original unit. We don’t keep many units on the shelf. I know some shops may keep the Chrysler units in stock because they move a lot, but even when we do that, we tag the ratios to avoid putting the wrong one in. That information is readily available.”

Are modern transmissions better than the legendary Turbo Hydramatics, Torqueflites and C-series Fords? Schmitz feels that modern vehicles are hard on their transmissions.

“They’re putting undue stress on them. The Turbo Hydramatic 350’s and 400’s, the Torqueflight 904’s
, they were heavy-duty. Everything was steel except the case. Now they’re going the other way, with aluminum to lighten the vehicle. I don’t think they can take the punishment of the older units, but the fluids are better, so overall, they last about the same. When I see them come in, I always recommend a cooler. And I wonder how many people know how to hook up a cooler correctly. You have to hook it up in series. You need to find the return line, where the fluid goes back to the transmission from the radiator. If you reverse it, you can cool the transmission fluid, then heat it up to the radiator fluid temperature. It won’t work as well. A lot of guys pick the easiest line they can find. Dodge Ram Pickups are an example of an easy installation, but a ’97 Taurus is a nightmare. It’s three to five hours to install a cooler, because you have to pull the whole front end. It’s the same with ’96 and up Caravans.”

Schmitz notes that with the advent of the minivan, towing isn’t the only form of hard service that a transmission can endure.

“Even if you don’t tow, think about what vehicles like minivans can haul. With seven adults, you’ve put a significant load in the vehicle. There’s always a plus to keeping transmission fluid cool. When the fluid breaks down, the O-rings and seals in the transmission harden, and you get internal leaks. Transmission fluid is to a transmission what blood is to our bodies. It’s that important. If your engine is down a litre, you probably won’t notice, but if your transmission is down a litre or a litre and a half, depending on the model, it can neutralize going around corners. It’s doing damage.”

For Dieter Schmitz, however, getting the problem repaired and the customer satisfied often takes a little interrogation. “It’s like being a detective. Sometimes, they’re not too forthcoming. I think that they believe that the more they tell you the more it will cost, but in fact it’s the exact opposite. The more we know the better we can diagnose the problem.”