Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Look at the splines on the inside of the input housing. If the sets of three splines show drag marks in the middle spline, the steel plates of the 3-4 clutch
are binding in the housing. New steel plates are available for service that have a smaller outer diameter to stop the binding condition. Reference
Corporate bulletin 077138 (GMC 91-7A-33) tor more information.
2-4 Band -
Check the 2-4 band for a lube window. A design change was made in September of 1989 which added a round lube window to direct fluid to the band
when it is not applied.
Install this new band if the transmission does not have one with the window. Reference Corporate bulletin 977161 (GMC 90-7A-121) for more
Output Shaft and Seal -
Changes have been made to the lube passages in 1991 production transmissions. Refer to Corporate bulletin 177118 (GMC 91-7A-134) for more
1-2 Accumulator -
Inspect the 1-2 accumulator piston and bore for scoring.
Inspect the 3-4 accumulator piston and bore tor scoring.
Debris inside the transmission can cause problems for the 3-4 clutch and 2-4 band. During any overhaul procedure, keep the area clean and clean all
parts well before reinstalling them. Here are a few areas to pay special attention to when servicing a transmission for a 3-4 clutch or 2-4 band
Third Accumulator Exhaust Check-ball and Retainer
Located in the case servo bore, this check-ball can get sediment stuck in it which doesn't allow the ball to seat. This can cause the band to drag or
the 3-4 clutch to not fully apply on a 2-3 upshift.
Third Accumulator Orifice Cup Plug
Also located in the case servo bore, this orifice must be kept unblocked. If sediment blocks the orifice, the third accumulator will not fill properly
due to trapped air in the cavity. This can cause apply and release conditions with the 3-4 clutch. The orifice cup plug also lubes the 2-4 band
through the band's lube window.
- 3-4 Clutch Exhaust Check-ball and Retainer
Located in the input housing, this check-ball helps exhaust the 3-4 clutch. It the check-ball cannot seat, the 3-4 clutch cannot fully apply. If the
check-ball is stuck in the seated position, the 3-4 clutch cannot fully exhaust.
New 3-4 Clutch Friction Material:
New friction plates have been released for limited applications in the 3-4 clutch of the HYDRA-MATIC 4L60. The new plates have increased heat
capacity, but cannot be used interchangeably with the previous friction material.
Transmission models are being recalibrated as time permits, and the new material has been phased into production during the 1991 model year. Model
codes changed as transmissions received the new 3-4 clutch material.
Since the new friction material has very different friction characteristics, each transmission modal has been re-calibrated for shift feel. The new friction
material cannot be used to back service any transmissions except tor those 1991 models listed below.
DO NOT USE THE NEW FRICTION MATERIAL IN ANY TRANSMISSION THAT IS NOT SPECIFICALLY CALIBRATED FOR IT.
IF THE NEW MATERIAL IS USED IN AN INCORRECT APPLICATION, SHIFT QUALITY WILL BE VERY POOR AND
TRANSMISSION DAMAGE CAN OCCUR QUICKLY. The first transmissions to contain the new friction materials were built in January
1991. Transmission models used with 5.7 liter engines were the first to receive the new material.
The following 1991 NEW transmission models contain the new friction material. The PREVIOUS models are the corresponding early 1991 models that
do not contain the new friction material.