POSSIBLE LACK OF LUBRICATION THM 700-R4 TORQ CONV TCC DIAG.

MODELS: LIGHT DUTY TRUCKS WITH THM 700-R4 TRANSMISSIONS

When overhauling a THM 700-R4 transmission which shows signs of high oil temperature (such as bumed transmission fluid, parts tumed a blue color, etc.) be certain to check the lubrication passages as follows:

1. Flush oil cooler and cooler lines as shown in section 7A of the 1983 service manual.

2. Air check the lubrication passages in the case and oil pump cover. See Figures No. 1 and No. 2.

3. Air check the lubrication passage in the input housing. See Figures No. 3 and No. 4. Check the input housing to, output shaft lip seal for wear or damage. Replace with part number 8642178 if necessary. See Figure No. 4.

4. Flush and air check the lubrication passages in the output shaft. See Figure No. 5.

When replacing the converter assembly or any intemal parts which shows signs of high temperature such as a blue color, be certain to find and correct the restriction in the lubrication circuit which feeds that part. However, do not confuse a wear pattern with lack of lubrication. (i.e. a wom thrust washer or any part which shows a localized heat pattern is not generally caused by lack of lubrication. Whereas if the part is completely turned blue this indicates lack of lubrication.) Any example of a localized heat pattern is a blue color around a pinion pin (or pins) in the input or reaction carrier. A blue color around these pins is generally caused by worn pinion washers or *key-stoned pinion needle bearing rollers, not lack of lubrication.

An important point to remember on the THM 700-R4 (or any THM automatic overdrive transmission) is that the converter clutch must be functioning when the vehicle is driven in 4th gear or above normal oil temperatures can result. The higher oil temperatures may cause wear of the transmission parts and should not be confused with lack of lubrication. Above normal transmission oil temperatures can result in deterioration of the oils lubricity.

*Keystoned needle bearing rollers means - The rollers are wedged together by twisting each end of the rollers in opposite directions. This procedure is used to retain the rollers inside the pinion gear during assembly. After assembly is complete a gentle tap will loosen the keystone and allow the pinion gears to turn freely.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.