K 2500 Truck 4WD V8-379 6.2L DSL VIN C FI (1989)
Accumulator: Customer Interest
A/T - 4L60 Slipping or No 3rd/4th Gear
GMC NUMBER:
91-7A-139
GROUP:
7A Automatic Transmission
DATE:
August, 1991
CORPORATE
NUMBER:
177119
SUBJECT:
HYDRA-MATIC 4L60 (THM 700-R4) TRANSMISSION 3-4 CLUTCH/2-4 BAND
MODELS:
1982-1991 S/T, C/K, R/V 1-2 SERIES TRUCKS, M/L AND G 1-2 SERIES VANS
The following information will be helpful when servicing a HYDRA-MATIC 4L60 transmission for a "no third or fourth gear" or "slipping in third or
fourth gear" condition. Many root causes for these problems have been identified, and more than one cause may exist at the same time. This bulletin
covers some causes that may not be obvious when doing a normal repair procedure.
Service Information:
Before servicing the transmission, check the following:
^
TV Cable Setting -
Make sure the TV cable is set to the correct position. Never adjust the cable to hide a shift complaint or to change performance. This can mask the
root cause and damage the transmission.
^
Fluid Level -
GM Powertrain cannot emphasize enough how important fluid level is to transmission performance. Both high and low fluid levels can cause
problems.
A low fluid level causes low line pressure. This can burn clutches by not allowing the clutch to apply quickly enough or by not keeping the clutch fully
applied.
A high fluid level allows fluid to become foamy when the fluid is churned through the gearsets. Since air is compressible, the foamy fluid does not
apply the clutches with as much force as they need.
^
Cooler Flow -
Perform a cooler flow check as outlined in the cooler flush procedure. Cooler lines can be partially blocked so it is important to know that cooler flow
is adequate.
During overhaul, look at the following items:
^
Filter Neck Seal -
Examine the filter neck seal for evidence of heat set. It the seal doesn't properly seal around the filter, air can get into the pump and cause low line
pressure or aerated fluid. Replace the seal if you suspect it doesn't fit properly.
^
Pump Body Bushing -
Disassemble the pump and examine the pump body bushing for wear. A worn bushing can create a large leak in the pump and lower line pressure
which can cause lube flow to be cut off. Replace a worn bushing. If the bore seems to be out of round (excess wear in one area), replace the pump
body.
^
3-4 Clutch Boost Springs -
Examine the boost springs (if present) for evidence of polishing on the spring tabs. This can occur when the outer diameter of the 3-4 clutch friction
plates rub on the boost springs. Replace the boost springs as necessary.
^
Input Housing -