A/T - THM 125C Torque Converter Clutch Shudder
Number: 84-171
Section: 7A (VIIc)
Date: July, 1984
Subject: THM 125C TORQUE CONVERTER CLUTCH SHUDDER DIAGNOSIS SUPERSEDES CHEVROLET BULLETINS 82-T-125, 83-T-41, AND 83-T-53
Model and Year: ALL THM 125C
TO: ALL CHEVROLET DEALERS
Some THM 125C transmissions may exhibit torque converter clutch (TCC) shudder as the TCC applies and/or after it applies when the accelerator pedal is depressed slowly (Crowd Shudder). These types of shudders are best described as a jerking sensation. In some cases, the shudder may cause the instrument panel to vibrate.
Listed below are items which may cause a "TCC Apply Shudder" and/or a "TCC Crowd Shudder":
Condition Cause and Correction
TCC Apply TCC Crowd
Shudder Shudder
X X 1. An intermittent incorrect signal
from the vehicle speed sensor (V.S.S.). Dirt or grease on the reflective bar in the V.S.S. may be sending an incorrect or erratic signal so that the converter clutch engages early. Remove the V.S.S. and clean it.
X X 2. The auxiliary valve body cover
attaching bolts may be loose or the bolt threads/holes may be shallow. If the holes are shallow, the bolts will bottom out without torquing the cover down.
X 3. Some 1982 models were built with
either an exhaust hole or an orifice cup plug in the auxiliary valve body cover. The auxiliary
Condition Cause and Correction
TCC Apply TCC Crowd
Shudder Shudder
valve body cover was changed to a solid cover (no exhaust hole or orifice cup plug) in 1982. The service auxiliary valve body cover, P/N 8643645, should be used on all models to prevent shudder. The service part does not have an orifice cup plug (see Chevrolet Bulletin 83-T-41).
FIGURE 1 - AUXILIARY VALVE BODY (COVER SIDE):
x 4. There are two types of auxiliary valve
bodies in service. One has an orifice cup plug and the other does not (Figure 1). If the transmission being serviced has the auxiliary valve body with the orificed cup plug, particles of the auxiliary valve body cover gasket may have torn loose. This material may be sticking the torque converter clutch apply valve and/or plugging the converter release orifice in the control valve body spacer plate. If this is found, disassemble the auxiliary valve body and thoroughly clean. Also, be sure to remove any gasket particles in the valve body spacer plate converter release orifice hole and replace the auxiliary valve body cover gasket, P/N 8653947.
x 5. Check the valves in the auxiliary valve
body for freeness. (They must move in and out of their bore without sticking).
FIGURE 2 - THM 125/125-C TRANSMISSION I.D. NAMEPLATE:YPSILANTI, MICHIGAN:
FIGURE 3 - THM 125/125-C TRANSMISSION I.D. NAMEPLATE WINDSOR, CANADA:
x 6. For gas engine/transmissions, the
auxiliary valve body converter clutch control regulator spring may be weak and require replacement with the new spring, P/N 8637888. On February 20, 1984, for U.S. built and March 5, 1984 (Julian Date 065) for Canada built THM 125C transmissions (refer to chart 1 for serial number breakpoints). The new spring P/N 8637888, went into production and has a stronger load. For explanations of nameplates, refer to Figure 2 (U.S.) and Figure 3 (Canada).
x x 7. Inspect the pump shaft to valve body seal
for cuts, damage, distortion.
Condition Cause and Correction
TCC Apply TCC Crowd
Shudder Shudder
x x 8. A new governor pressure switch went into
production for diesel models only, in late April, 1982. This change corrects the "shudder" feel, by raising the converter clutch apply speed. In servicing diesel model transmissions for this condition, refer to the following chart for proper model usage for 1982 models:
Governor Switch
Model Part Number
0P, HU, HY, H6, HR 8643369
HW 8637296
HS 8643368
CD, HI, HC 8643367
FIGURE 4 - Converter Feed:
FIGURE 5 - TURBINE SHAFT SEAL REPLACEMENT:
x 9. Inspect the turbine shaft teflon seals
and 'O' ring seal for damage, cuts, distortion (see Figure 4 for these parts). If the teflon seals require replacement, make sure they are installed and sized as shown in Figure 5..
FIGURE 6 - Turbine Shaft Seal:
x 10. Inspect the turbine shaft seal grooves. A
step in the bottom corners of the seal groove will keep the seal from contacting the side wall of the groove and will prevent proper sealing (Figure 6). If this condition is found, replace the turbine shaft and seals.
FIGURE 7 - CASE COVER - VALVE BODY SIDE:
x 11. Check the case cover sleeve converter feed
oil hole for being out of alignment with the oil channel in the case cover (Figure 7).
x 12. Check the converter end play, using tool
J29830A. The end play specification is .5 mm (.020"). Converters with end play more than .05 mm (.020") must be replaced.
x 13. The turbine shaft sleeve may be leaking
excessively. If all of the above items are O.K., replace this shaft.
New converter clutch control regulator spring serial number breakpoints.
CHART 1 - U.S. MODELS
Serial Serial
Model Number Model Number
CA 2226 EQ 11686
CB 156657 EW 1007
CE 67281 HC 1748
CF 5938 HM 2235
CT 4574 HP 1154
EB 2639 HS 11705
EF 6579 HX 4897
EI 5544 HY 20840
EJ 1006 PD 2080
EK 8843 PE 50353
EL 3594 PF 22983
EM 3062 PG 47268
EN 4984 PJ 6007
EP 2085 PW 67271