Chevrolet 10 1971 Series Chassis Service Manual page 311

from engine and lower it away from vehicle.
Use converter holding Tool J-5384
CAUTION:
when lowering transmission or keep rear of
transmission lower than front so as not to lose
converter.
The installation of the transmission is the reverse of
the removal with the following additional steps.
Before installing the flex plate to converter bolts,
TURBO HYDRA-M ATIC 400 D IA G N O SIS PROCEDURE
In the event of a major transmission
CAUTION:
failure, replace filter assembly, and flush oil
cooler and cooler lines.
Accurate diagnosis of transmission problems begins
with a thorough understanding of normal transmission
operation. In particular, knowing which units are involved
in the various speeds or shifts so that the specific units
or circuits involved in the problem can be isolated and
investigated further. Analytical diagnosis will protect the
technician from come backs and certainly will improve
owner satisfactiion.
An important and often overlooked aspect of diagnosis
is finding out specifically what the customer is complain­
ing of. For this purpose a short ride with the customer
will often prove beneficial. It may be found that the con­
dition the customer wants corrected is standard and
should not be altered.
The following sequence, based on field experience, pro­
vides the desired information quickly and in most cases
actually corrects the malfunction without requiring the
removal of the transmission. Details of the items listed
in this sequence are covered further in the text.
SEQUENCE FOR TURBO HYDRA-MATIC 4 0 0
D IA G N O SIS PROCEDURE
1. Check oil level and condition.
2. Check and correct detent switch.
3. Check and correct vacuum line and fittings.
4. Check and correct manual linkage.
OIL LEVEL AN D CO ND ITION CHECK
Always check the oil level before road testing. Oil
must be visible on dip stick prior to operating the vehicle.
Erratic shifting, pump noise, or other malfunctions can
in some cases be traced to improper oil level.
Oil level should be checked with the selector lever in
the Park (P) or (N) Neutral for 30 Series Trucks posi­
tion, engine running, and the vehicle on level pavement.
Fluid level should be to the FULL mark with the trans­
mission at normal operating temperature (180°F.). With
warm fluid (room temperature 80°F.), the level should
be at or 1/4 inch below the ADD mark. (See checking
procedure)
If oil level was low, refer to Oil Leaks.
The condition of the oil is often an indication of whether
the transmission should be removed from the vehicle, or
to make further tests. When checking oil level, a burned
smell and discoloration indicate burned clutches or bands
and the transmission will have to be removed.
*A " black light" testing unit may be obtained from several different tool supplies.
CLUTCHES AND TRANSMISSIONS 7-35
make certain that the weld nuts on the converter are
flush with the flex plate and the converter rotates freely
by hand in this position. Then, hand start all bolts and
tighten finger tight before torquing to specification. This
will insure proper converter alignment.
After installation of transmission check
NOTE:
linkage for proper adjustment.
13. Remove truck from hoist.
M ANUAL LINKAGE
Manual linkage adjustment and the associated neutral
safety switch are important from a safety standpoint.
The neutral safety switch should be adjusted so that the
engine will start in the Park and Neutral positions only.
With the selector lever in the Park position, the park­
ing pawl should freely engage and prevent the vehicle
from rolling. The pointer on the indicator quadrant
should line up properly with the range indicators in all
ranges.
OIL LEAKS
Before attempting to correct an oil leak, the actual
source of the leak must be determined. In many cases
the source of the leak can be deceiving due to " wind
flow" around the engine and transmission.
The suspected area should be wiped clean of all oil
before inspecting for the source of the leak. Red dye is
used in the transmission oil at the assembly plant and
will indicate if the oil leak is from the transmission.
The use of a " black light" * to identify the oil at the
source of leak is also helpful. Comparing the oil from
the leak to that on the engine or transmission dip stick
(when viewed by " black light" ) will determine the source
of the leak.
Oil leaks around the engine and transmission are gen­
erally carried toward the rear of the truck by the air
stream. For example, a transmission " oil filter tube to
case leak" will sometimes appear as a leak at the rear
of the transmission. In determining the source of an oil
leak it is most help'ful to keep the engine running.
POSSIBLE POINTS OF OIL LEAKS
1. TRANSMISSION OIL PAN LEAK
a. Attaching bolts not correctly torqued.
b„ Improperly installed or damaged pan gasket,
c. Oil pan gasket mounting face not flat.
2. REAR EXTENSION LEAK
a. Attaching bolts not correctly torqued.
b. Rear seal assembly - damaged or improperly
installed.
c. Gasket seal - (extension to case) damaged or im­
properly installed.
d. Porous casting.
3. CASE LEAK
a. Filler pipe " O" ring seal damaged or missing;
misposition of filler pipe bracket to engine -
" loading" one side of " O" ring.
10-30 CHEVROLET TRUCK SERVICE MANUAL