Roadmaster V8-305 5.0L (1992)
Band: Technical Service Bulletins
A/T - 3-4 Clutch & 2-4 Band Service Information
Bulletin:
92-74L60-4
Date:
Sept. '91
Ref. No.: 92-30-74L60
Corp. Ref. No.: 177119
SUBJECT:
3-4 CLUTCH - 2-4 BAND SERVICE INFORMATION
(4L60 TRANSMISSION)
MODELS AFFECTED: 1991-92 ROADMASTER
BULLETIN COVERS:
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 performing 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. If the seal does not 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 does not fit properly.
^
Pump Body Bushing --- Disassemble the pump and examine the pump body bushing for wear. A worn bushing can create an internal leak in the
pump and cause lower line pressure which can cause reduced lube oil flow. 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 --- 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.
^
1-2 Accumulator --- Inspect the 1-2 accumulator piston and bore for scoring.
^
3-4 Accumulator --- Inspect the 3-4 accumulator piston and bore for 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 few areas to pay special attention to when servicing a transmission for a 3-4 clutch or 2-4 band
condition:
