Auto Service World
Feature   May 1, 2008   by Jim Anderton, Technical Editor

Tips from an expert on how to have no trauma transmissions

A top transmission rebuilder on how to "re and re" for trouble-free service.

Dieter Schmitz, Dieter to everyone who knows him, knows something about transmissions. In fact, Dieter, the well-known southern Ontario transmission “guru” working out of the Stoney Creek, Ont. location of Mister Transmission, has rebuilt and serviced everything from the venerable Turbo-Hydramatic to the sort of European exotica that propels BMW and Mercedes. Dieter, in short, is the guy you send a bad transmission to even when you can handle the “re and re.” While subcontracting automatic transmission rebuilds is almost universal these days, that division of labour adds a catch: when things go wrong, is the rebuilder or installer at fault? Here are some of Dieter’s key installation tips that can save any shop lots of time, aggravation and money.

Do the diagnostics

So the vehicle comes in sounding like an oil drum full of ball bearings. However, that doesn’t mean that you should dive straight into the toolbox. According to Deiter, technicians “need to road test the vehicle before the ‘re and re,’ including a scan for codes. Some codes point straight to the problem, like Chrysler’s “Clutch Volume Index,” which points to wear on clutch packs. GM has codes like “Shift Adapt” and there are others.”

Dieter recommends that codes for speed and throttle position sensors be looked at carefully since many shift programs need reliable sensor data to command the appropriate shift. Naturally, if there’s an issue, it should be corrected and then the vehicle road tested again. If you’re down to no codes or only transmission codes for internal trouble, then it’s time to break out the sockets.

Use the correct fluid

While this tip sounds too obvious to mention, there are more fluid options today than the Dexron/Type F/ATF-3 world on which many techs trained.

According to Dieter, “Fluids are formulated to work with the friction qualities of the linings, they’re not all the same. ‘Universal’ fluids are O. K. for common units, but they don’t work well with European transmissions. They’re strict about fluid types, which for the European units can sometimes cost $25-$30 a litre.”

Dieter notes improper fluid fill is more common than most techs believe and the source of the misinformation is often the technician’s parts supplier. If there’s any doubt, Dieter suggests asking your rebuilder, not the jobber.

Flush the system thoroughly

Whether its heat and wear or the kind of catastrophic failure that turns the transmission’s innards into cornflakes, the result is the same, says Dieter: “The contaminated fluid with metals circulates through the entire transmission and into the cooler lines and radiator.”

This contamination coats the inside surface of the cooling system loop, which can hold more metal than most techs suppose, given the small diameter of cooler lines and the size of the fluid radiator. The reason is simple, says Dieter: “If you were to cut open a cooler and look inside, you’ll see lots of surface area; it’s easy to contaminate it with metal.”

The only option is a thorough flush to prevent the trapped metal from flowing back from the cooler and into that freshly rebuilt unit. “We use a compressed-air powered flusher, (but some) shops may not have one. Canned flushing compounds are available that can do the job if they’re used properly.”

Dieter notes that some units use a thermostat to prevent flow through the cooler in a cold transmission which needs to be bypassed or flushed hot to make sure the flushing solution really goes through the entire cooling loop. If the general shop is using canned aerosol cleaners, it’s worth it to disconnect lines, especially at the radiator and flush in both directions. Keep going until the flushing agent comes out completely clean.

Seat the converter properly

Automatic transmissions have a universal property that makes them difficult to work with: they’re heavy. They also have some brittle, fragile and delicate internal parts that don’t respond well to a sledgehammer “re and re” technique. The torque converter or more accurately, where the converter keys into the pump, is such an example.

“When you bolt the bell housing up tight to the block, there should still be play in the converter,” says Dieter.

So what is the telltale sign that something is not right? “If the converter is up against the flexplate and the bell housing isn’t against the block, stop and check the converter,” Dieter says, and the consequences of ignoring this advice can be expensive. “They can smash the pump. If a tech torques up the housing bolts and hears a “ping,” take it out and inspect. You should always be able to push the transmission up to the block by hand, if you need to draw it up with the bolts, something’s wrong.”

Use the correct converter bolts

This tip is little known, but Dieter reports that it’s more common than most techs think. The scenario goes like this: The installing tech loses one or all of the converter bolts from the original installation and then goes and substitutes similar-looking bolts from another vehicle or from the parts bin. The installation goes smoothly and the road test is fine, but the converter fails in days. What happened?

“If they use converter bolts that are too long, they’ll dimple the converter body, damaging the turbine blades inside,” says Dieter, who notes that this mistake is easy to make because of the design of most converters. The threaded mounting “nut” welded to the converter body is a strong piece but behind it is relatively thin sheet metal, so there isn’t a positive stop to give the installing tech good “feel” when bolting up the unit.

Small things matter

A good bolt-up installation is only part of the path to a reliable transmission. Older units require careful set-up of the shift linkage.

But times have changed, according to Dieter: “The linkage isn’t as critical anymore. Today the shifting is usually controlled by solenoid. Grounding can be an issue.”

Dieter notes that it’s easy to forget to replace a ground strap, creating some difficult to diagnose electrical problems as current grounds randomly

through the driveline and along alternate paths like the speedometer drive and shift linkages. With multiple electrical connectors in play, small and almost invisible damage can cause frustrating problems. Dieter warns that a lot of the newer connectors use rubber boots to seal out dirt and if the locking tabs are broken, the boot eventually ejects the connector.

Engine mounts, shaft seals and O-rings are all still in play in transmission “re and re,” as is the control module and its software. With the complexity of electronic controls of modern automatic transmissions, it’s easy to forget that the whole process starts with a good installation.

You may not have Dieter Schmitz to answer your questions, but maintaining good communications with a knowledgeable rebuilder can save time, money and frustration, which in transmission service as everywhere else, is what a good shop is all about.


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