HYDRAULIC SYSTEM 999 SERVICE/MAINTENANCE MANUAL
2-8
Published 05-16-17, Control # 233-03
SAE Straight Thread Connection
This type connection leaks most often because the jam nut
and washer are not backed up before assembly.
When the jam nut and washer are not backed up, there is not
enough room for the O-ring when the squeeze takes place
and the washer cannot seat properly as shown in Figure 2-3
,
View A. The compressed rubber between the washer and
the spot face will cold flow out of compression, causing the
fitting to loosen and leak as shown in Figure 2-3
, View B.
Tighten SAE straight thread connections, as follows:
1. Back up jam nut and washer to end of smooth portion on
fitting as shown in Figure 2-4
, View A.
2. Lubricate O-ring with clean oil; this is very important.
3. Thread fitting into port until washer bottoms against spot
face as shown in Figure 2-4
, View B.
NOTE: If an elbow is being used, back it out as necessary
to align it with hose.
4. Tighten jam nut. When fitting is properly installed, O-ring
will completely fill seal cavity and washer will be tight
against spot face as shown in Figure 2-4
, View B.
Table 2-3. Straight Thread Leakage
View BView A
O-Ring
Washer
Jam Nut
FIGURE 2-3
Washer cannot seat properly on spot face.
Compressed rubber between washer and spot
face will cold flow out of compression, causing
fitting to loosen and leak.
When jam nut and washer are not
backed up, there is not enough room
for O-ring when squeeze takes place.
S107
View A
View B
O-Ring
Washer
Jam Nut
FIGURE 2-4
Nut and washer backed up to
end of smooth portion on fitting.
S106
Spot Face
Causes Cures
Jam nut and washer not
backed up, causing O-ring to
be pinched.
Replace O-ring and tighten
fitting properly.
O-ring cut. Replace.
O-ring wrong size. Replace with proper size.
Sealing surfaces gouged or
scratched.
Repair if possible or replace
damaged parts.
Sealing surfaces dirty. Clean and lubricate.
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