The main reason for the failure of automatic transmissions is overheating of the transmission and transmission fluid.
Other causes for automatic transmission failure may include the following:
1. Abuse. Using the transmission for application above what it was designed for.
2. Not using transmission fluid as specified by manufacturer.
3. Dirt in the oil/gearbox.
4. Transmission fluid change intervals.
5. Transmission Fluid level to high.
6. Transmission Fluid level to low.
If the transmission fluid’s colour is not cherry red but a darker red to brown colour the chances are good that the oil overheated and the fluid should be replaced.
If the transmission fluid smells like burnt toast it became too hot, it burnt and serious oxidation took place and the fluid must be replaced.
Foamy fluid is caused by a too high fluid level or an internal fluid leak.
Solid (bits of band material or metal abrasives) clinging to the dip stick indicates excessive wear of internal parts.
2. Results of Automatic Transmission Fluids Overheating.
Automatic fluids are designed to last thousands of kilometres under normal operating conditions.
Overheated fluid forms sludge and carbon particles that will block valves and fluid lines. This overheated fluid will also oxidise faster breaking down the chemical properties of the fluid.
The following table indicates the results of high automatic transmission fluid temperatures and what influence it has on the expected life (measured in kilometres) the fluid will last.
The automatic transmission fluid specified for the Pajero Automatic Transmission (like most automatic transmissions) is a Dexron III spec.
About Dexron Specified Automatic Transmission Fluid.
1. DEXRON is the name for a group of technical specifications of automatic transmission fluid created by General Motors (GM).
2. GM licenses the name and specifications oil companies which manufacture and sell the fluid under their own brands.
3. Dexron III was the specification used by GM for automatic transmission fluid used in automatic transmission built into GM vehicles up to 2005
4. Dexron VI was introduced in 2006.
5. All Dexron III licences expired at the end of 2006 and were not renewed.
6. Any fluids claiming Dexron III type performance that is sold under abbreviated names are not regulated by GM any more.
7. Dexron VI is backward compatible and can be used in applications covered by earlier GM ATF specifications.
The links below is very informative and it is suggested that you read at least the document in the first link.
http://www.sandyblogs.com/techlink/2009 ... on-vi.html
http://en.wikipedia.org/wiki/DEXRON
http://www.imakenews.com/lng/e_article000384801.cfm
4. COOLING OF AUTOMATIC TRANSMISSION FLUID.
By installing an oil temperature gauge to monitor the temperature of the automatic transmission fluid, the decision can easily be made weather it is necessary to install an additional oil cooler to help cooling the fluid.
Keep the following in mind:
a. The operating temperature of the automatic transmission fluid is between 70° and 80° C.
b. It is recommended that the temperature of cooled fluid does not go below 60° C.
c. The aim will be to have the temperature of the fluid exiting the transmission to be kept below 110° C.
d. The most heat is generated by the torque convertor (keep the slip on the convertor to the minimum and check the stall speed -- unnecessary slip is building up heat and is eating fuel).
5. CHANGING AUTOMATIC TRANSMISSION FLUID.
a. Change the fluid as per your vehicle manufacturer’s recommendations.
b. It is recommended that fluid changes must be done at a maximum of 100 000km intervals.
6. CONCLUTION.
Do a bit of surfing on the web. Communicate with transmission manufacturers and you will understand why the transmission manufacturers are of the opinion that an automatic transmission should outlast the engine of your vehicle if it is looked after.
I will start a new thread where I will explain the route I took to install an extra cooler and an oil temperature gauge to monitor the transmission fluid at three stages: 1 – Coming out of the gear box; 2 – After it went through the coolers and 3 -- In the transmission sump. (Using one oil temperature gauge).