Re: 97 Dodge Caravan

Posted by Vic on January 23, 2002 at 08:04:19 from (4.54.141.158):

In Reply to: 97 Dodge Caravan posted by cdprimm on January 22, 2002 at 21:27:44:

All automatic transmissions manufactured today are being developed even as they are being sold to the customer because of requirements such as fuel economy, per unit cost targets, and reductions in product development time. The competition is ferocious!

Fuel economy targets dictated the use of a locking torque converter and along with that product a whole new set of problems of durability and drivability (shudder) were introduced into the product. Modulating of the converter clutch produced friction heat at the friction material converter cover interface. This degraded the oil and changed the friction material characteristics.

There are continuing problems associated with the development of the electronic pressure control valves. Three different types of valves are used, Pulse Width Modulated for the torque converter, Variable Force Solenoid for pressure control, and On-Off for shift scheduling. They first must be cheap, they must use a cheap but reliable driver in the ECM, they operate open loop, and the must operate accurately over the life of the vehicle regardless of the changes (leakage) in the components for which they are providing pressure.

Lube distribution has always been a problem due to variable pumping action of radial drilled passageways and speed range of the rotating components. The viscosity changes that the ATF exhibits throughout the operating temperature range (-40 to 300 degrees F. = 4 to 45,000 Centistokes) cause even more problems with flow at both ends of the temperature range. Synthetic oil solves some of these problems with a more uniform viscosity over the entire range of operating temperature. I it also has the ability to withstand the higher temperatures without degradation and therefore provides a more stable lubrication medium. (Be careful here since the manufacturer specifies several different oils for different transmission models, synthetics degrade Viton seals)

The cost of the product is constantly under scrutiny by the Transmission Chief Engineer because his or her bonus and performance payments are dependent on per unit cost. (Warranty costs are not figured into the initial per unit costs) Vendors are constantly being pressured to produce the same component at a reduced cost so they take chances on unproven processes and/or materials. The mechanical diode is a good example of cost over good engineering judgment.

The need for fuel economy is pushing the limits of the Simpson gear sets and friction elements in the modern transmissions.

The cost of making a design change after Job#1 includes changing manufacturing machinery, stocking new parts for both the old design and the post change design models, increased costs of vendor supplied components, etc. (can be very expensive and prohibit the improvement)

Testing the new design to ensure that it is superior and less costly than the part it is replacing adds costs and delays product release.

Transmissions are constantly being used on platforms other than the one for which they were initially designed. Sometimes this works and sometimes not. Unfortunately the customer is the scapegoat.

Do your homework before buying by using resources such as Consumers Report and other users reports to determine the reliability of the product. Many of these are available in your local library.

Yup, I work in transmission engineering at one of the big three and I am amazed every time I shift the transmission into gear and the vehicle moves!

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