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DIAGNOSIS
INTRODUCTION
The Turbo Hydra-matic 350 transmission trouble shooting
guide is designed for field service personnel who have had a
minimum amount of training or experience in working on the
Turbo Hydra-matic 350 transmission. It will be valuable to a
service organization from service writers and road testers to
the mechanic who performs the repair operation.
This trouble shooting guide is not intended to take the
place of the Turbo Hydra-matic 350 Section in the Chevrolet
Chassis Service Manuals. It is intended to supplement it by
making available to you a practical method and systematic
approach to solving transmission malfunctions with the infor
mation that can be gained by oil pressure checks which can be
made without a road test.
Internal oil leaks within the transmission that are fed
through an orifice or orifices (porosity, sand holes, etc.) will
not show up on an oil pressure check as low pressure; however,
by following the Trouble Shooting Charts and with the infor
mation gained from the pressure checks, you will be led to the
possible cause or causes of the malfunction and the corrective
action.
ancies the malfunction still exists, the next step of the proce
dure is to make oil pressure checks.
Install the pressure gage and proceed to follow the steps on
the Preliminary Checking Procedure Chart and record the pres
sures and compare them with the normal pressures provided
for each condition on Page
If the malfunction is unknown and a road test can be
made, it can be combined with the Preliminary Checking Pro
cedure. If a road test cannot be made, and the complaint is
delayed or no upshifts, and high pressures are recorded on the
pressure checks, the detent linkage should be disconnected
from the transmission and oil pressures rechecked. Normal
pressures on recheck indicate that the cause of the malfunc
tion is in the detent linkage to the transmission, such as
misadjusted, broken or sticking cable.
With the information you have obtained through the Pre
liminary Checking Procedure, and Road Test, if it was re
quired, you can now apply it to the chart or charts in the
Trouble Shooting guide that fits the malfunction.
Road Test
Preliminary Check Procedure
"Preliminary Checking Procedure" has the normal oil pres
sure ranges under specific conditions listed. All of these can be
made without a road test. Deviations from the normal oil pres
sure ranges are indicators to specific areas and causes of trans
mission malfunctions. But like working a jig-saw puzzle, in
order to finish the picture, you need all the pieces. In this case
you need all the pressure readings the chart lists and they can
be made in the shop and do not require a road test.
In the majority of malfunctions, this information will be
required in order to efficiently diagnose the malfunction. If
the customer complaint is unknown other than it just doesn't
work right, the preliminary oil pressure check will be necessary
to aid you in determining if a malfunction exists and in what
area to look for the case. However, an important and often
overlooked aspect of diagnosis is precise determination of the
customer's complaint. For this purpose, a short ride with the
customer will often prove beneficial. It may be found that the
condition the customer wants corrected is standard and should
not be altered.
When the malfunction or complaint is known, you can
proceed to the Trouble Shooting Chart or Charts that cover
the specific condition. In some instances, you may correct the
condition in the first few steps of the chart; in others, it will
require that the pressure check be performed in order to lead
you in the right direction to remedy the malfunction.
The first step when searching for the cause of a malfunc
tion is to check the Transmission Oil Level the procedure is
outlined on Page
The second step when searching for the cause of a
malfunction is to check the Outside Manual Linkage refer to
Page
If discrepancies are found in these first two steps, they
should be corrected and the vehicle road tested to see if the
malfunction has been corrected.
If no discrepancies are found, or if after correcting discrep
Check all Shifts in the Following Manner:
NOTE: 1969 pressures are approximately 7 PSI lower
than 1970.
Drive Range:
Position selector lever in DRIVE RANGE and accelerate
the vehicle from 0 MPH. A l-2 and 2-3 shift should occur at all
throttle openings. (The shift points will vary with the throttle
opening). As the vehicle decreases in speed to 0 MPH, the 3-2
and 2-1 shifts should occur.
Low L2 Range:
Position the selector lever in L² RANGE and accelerate
the vehicle from 0 MPH. A 1-2 shift should occur at all throt
tle openings. (No. 2-3 shift can be obtained in this range). The
1-2 shift point will vary with throttle opening. As the vehicle
decreases in speed to 0 MPH, a 2-1 shift should occur.
NOTE: The 1-2 shift in INTERMEDIATE RANGE is
somewhat firmer than in DRIVE RANGE. This is normal.
Low L' Range:
Position the selector lever in L' RANGE and accelerate
the vehicle from 0 MPH. No upshift should occur in this range.
2ND Gear - Overrun Braking: (L² )
Position the selector lever in DRIVE RANGE, and with
the vehicle speed at approxomately 35 MPH, move the selector
lever to L² RANGE. The transmission should downshift to
2nd. An increase in engine RPM and an engine braking effect
should be noticed. Line pressure should change from approxi
mately 100 PSI to approximately 125 PSI in 2nd.
1ST Gear - Overrun Braking: (L' )
Position the selector lever in L² RANGE at approximately
