Chevrolet 10 Series 1970, Service Manual

Page: 398 / 671

ENGINE-ELECTRICAL 6Y-6
p ro p erly fille d (activation ) o r im p ro p erly s e rviced .
P o o r s e rv ic e and short B attery life w ill result.
SPECIFIC GRAVITY READINGS
A h ydrom eter can be used to measure the sp ecific
g ra v ity o f the e le c tro ly te in each c e ll (fig . 6b).
The hydrom eter m easu res the percentage o f sulphuric
acid in the battery e le c tro ly te in term s o f sp ecific
g ra v ity . A s a battery drops fro m a charged to a d is ­
charged condition, the acid le a v e s the solution and enters
the p lates, causing a d ecrea se in sp e c ific g ra v ity o f
e le c tro ly te .
An indication o f the concentration o f the
e le c tro ly te is obtained with a h ydrom eter.
When using a h ydrom eter, ob serve the follow in g points:
1. H yd rom eter must be clean, inside and out, to insure
an accurate reading.
2. H yd rom eter readings must n ever be taken im m ed i­
ately a fte r w ater has been added. The w ater must be
thoroughly m ixed with the e le c tro ly te by charging
fo r at least 15 minutes at a rate high enough to cause
vigorou s gassing.
3. If hydrom eter has b u ilt-in th erm om eter, draw liquid
into it s e v e ra l tim es to insure c o rre c t tem perature
b e fo re taking reading.
4. Hold h ydrom eter v e r tic a lly and draw in just enough
liquid from battery c e ll so that float is fr e e floating.
Hold hydrom eter at eye le v e l so that float is v e rtic a l
and fre e o f outer tube, then take reading at surface
o f liquid. D is re g a rd the curvature where the liquid
r is e s against float stem due to surface tension.
5. A void dropping b attery fluid on car o r clothing as
it is ex trem ely c o r r o s iv e . Any fluid that drops
should be washed o ff im m ediately with baking soda
solution.
The sp e c ific gra vity o f the e le c tro ly te v a r ie s not only
with the percentage o f acid in the liquid but also with
tem peratu re. A s tem peratu re in creases, the e le c tro ly te
expands so that the s p e c ific g ra vity is reduced. A s
tem peratu re drops, the e le c tro ly te contracts so that the
s p e c ific g ra v ity in c rea ses. Unless these va ria tion s in
sp e c ific g ra vity a re taken into account, the sp ecific
g ra v ity obtained by the hydrom eter may not g iv e a true
indication o f the concentration o f acid in the e le c tro ly te .
A fu lly charged B attery w ill have a sp ecific g ra vity
reading o f approxim ately 1.270 at an e le c tro ly te tem ­
p eratu re o f 80 °F. If the e le c tro ly te tem peratu re is
above o r below 80 °F., additions o r subtractions must
be made in o rd e r to obtain a h ydrom eter reading c o r ­
rected to the 80°F. standard. F or e v e ry 10° above 80°F.,
add four sp ecific g ra vity points (.004) to the hydrom eter
reading.
Example: A h ydrom eter reading o f 1,260 at
110°F. would be 1.272 co rre c te d to 80°F„, indicating a
fu lly charged B attery. F or e v e ry 10° below 80°F., sub­
tra ct four points (.002) fro m the reading. Example:
A h ydrom eter reading o f 1.272 ot 0°F. would be 1.240
co rre c te d to 80°F., indicating a p a rtia lly charged B attery.
SPECIFIC G RAVITY CELL C O M P A R IS O N TEST
T h is test may be used when an instrument tester is
not availab le. T o p e rfo rm this test m easure the sp ecific
g ra v ity o f each c e ll, re g a rd le s s o f state o f charge, and
in terp ret the resu lts as follow s:
• If s p e c ific g ra vity readings show a d ifferen ce b e­
tween the highest and low est c e ll o f .050 (50 points)
o r m ore, the B attery is d efective and should be
replaced.
INSTALLING BATTERIES
B attery installation v a rie s depending on the truck
m odel and s e rie s . T o install p ro p erly , it is important
to ob serve the follow in g precautions:
• Connect grounded term in al o f B attery last to avoid
short circu its which may damage the e le c tric a l
system .
• Be sure there a re not foreign objects in the c a r r ie r ,
so that the new B attery w ill re s t p ro p e rly in the
bottom o f the c a r r ie r .
• Tighten the hold-down evenly until snug (60-80) in.
lb s.). Do not draw down tight enough to d istort o r
crack the case o r co ver.
v • Be sure the cables a re in good condition and the
term in als a re clean and tight. Make sure the
ground cable is clean and tight at engine block or
fram e.
• Check p o la rity to be sure the B attery is not r e ­
v e rs e d with resp ect to the generating system .
• When assem bling b olt-typ e clam p term in a l, loosen
the bolt so the term in al w ill fit o v e r the post, push
the term in al on to battery post as fa r as possible,
at lea st flush with o r below top of post. Tighten
bolt until the term in al is snug with the post.
CHEVROLET TRUCK SERVICE MANUAl