Chevrolet 70 Series 1970, Service Manual

Page: 35 / 841

CAB AND BODY MOUNTINGS 1-4
PAINTING NEW ALUMINUM PARTS
AND REPAINTING OLD PARTS
1. Thorough cleaning is essen tial; a ll c o r ­
ro sio n , g r e a se , and other foreign m atter m ust be
rem oved. Solvent cleaning, p r e ssu r e stea m clean ­
ing, w ire brushing, and hand sanding methods are
recom m ended.
2. C om pletely rem ove old paint by u se of o r ­
ganic so lv en ts. Do not u se alkaline paint rem over
on alum inum . If old p rim er is very difficult to r e ­
m ove and there i s no evidence of m etal c orrosion ,
old p rim er may be left on, but a ll lo o se paint must
be rem oved.
3. Wipe the entire area to be refinished with
cloth s saturated with DuPont No. T -3812 reducer
(or equivalent). Wipe dry.
4. T reat any scra tch ed or abraded a rea s with
DuPont No. VM -5717 m etal conditioner (or equiv­
alent) reduced one (1) part by volum e with four (4)
p a rts of w ater.
a. Apply the above m ixture with a sponge or
brush and allow to stand approxim ately th ree (3)
m inutes.
b. Wipe area with a damp cloth. D ry thor­
oughly.
5. Apply a coat of p r e -p rim er (so m etim es
c a lle d w a sh -p rim er), preferably by spraying to a
uniform and com plete coverage coat on a ll su r ­
fa c e s . T his type p rim er u se s a sp ecia l a c c e le r a t­
ing agent containing phosphoric acid which p r o ­
duces an ex cellen t bond to m etal. A P -10 or A - 158
made by M & T C hem ical Co., X E -5220 made by
B ak elite Corporation, and 818-012 (2 p a rts), plus
T8539 (1 part) made by DuPont, or any equivalent
m aterial made by a reputable paint m anufacturer
should be acceptable. T hese m a teria ls m ust be
u sed within a few hours after addition of a c c e le r ­
ator, th erefore, d irection s of m anufacturer should
be ob served carefully. Apply by spraying. Allow
p a rts to dry.
6
. U se a zinc chrom ate p rim er such a s Du­
Pont No. 63-150 or Pontiac V arnish Company's
G M T-434, or any equivalent m aterial made by a
reputable m anufacturer. Apply p rim er, preferably
by spraying, to a minimum thickness of
0 . 5
m ils.
A llow parts to dry.
7. Apply fin ish coats:
a. For understructure and other p arts not
requiring color, apply a second coat of DuPont No.
63-150 or Pontiac V arnish Company's GM T-434,
or equivalent.
b. To exposed body p a rts, apply d esired color
coats in accordance with standard p ra ctice.
c. Apply DuPont No. 181-65751 aluminum
enam el top coat for final refinishing p r o c e ss in
th ose a re a s w here anodized aluminum panels are
to be m atched.
ALUMINUM CAB FRAME
AND PANEL REPAIRS
CAB FRAMING
G eneral Information
P rin cip le cab fram ing is com posed of box-
type m em bers of w elded alum inum construction.
T his a s s u r e s a s t r e s s r e sista n t foundation d esign ­
ed to fortify cab against tw isting and flex in g . F u r­
ther rigid ity is achieved by str a te g ic a lly located
rein forcem en t b r a c e s and b rack ets.
Cab F ram e R epairs
R iveted and w elded m ajor cab se c tio n s and
fram ing should be regularly in sp ected for damage
and repaired im u e d ia te ly . L o o se o r m issin g r iv ets
and fractured w elds can resu lt in considerable
dam age to cab structure u n le ss r e p a irs are made
prom ptly.
Since rep a irs to aluminum com ponents require
sp e c ia l s k ills , cab understructure rep a irs should
only be perform ed by com petent craftsm en with
proper to o ls and equipment.
W henever repairing or rep lacin g aluminum
p a r ts, carefu lly follow accepted and recom m ended
p r a c tic e s . The Aluminum Company of A m erica w ill
furnish, upon req u est, booklets title d "Riveting
Aluminum" and "Welding and B razing A lum inum ."
The booklets explain detailed p roced u res n e c e s ­
sa ry in repair and replacem ent of alum inum p a rts.
P rop er precautions must be ob served , p a rtic­
u larly with r eferen ce to w elding, rein forcin g, co r ­
rosion prevention, and rep lacem en t, a s follow s:
1. W elding of m ajor alum inum structural
m em b ers or any aluminum p a rts subject to strain
o r com p ressio n without proper rein forcem en t is
not recom m ended. To maintain proper body strength
rep la ce dam aged stru ctu ral m em b ers with new
p a rts obtained from the factory.
2. To prevent galvanic co rro sio n of aluminum,
a ll su r fa ce s of d issim ila r m etals in contact with
alum inum m ust be properly coated w ith paint an d /
or plating. T his a lso applies to attaching p arts
such a s b olts, w a sh ers, nuts, and r iv e ts .
3. When cutting a stru ctu ral m em ber, cut at
an angle of 30 d e g r e e s. Thus, actual length of cut
i s tw ice width of p ie c e being cut, and s t r e s s or
load is distributed over a lon ger joint when w elded.
Cutting can be done bv torch, although u se of saw
i s p r eferred sin ce l e s s m aterial is rem oved.
4. Avoid m ixing s te e l and alum inum stru ctu res
o r parts when making r e p a ir s. Do not substitute
s t e e l fo r aluminum in stru ctu ral p a r ts. G reater
d eflection of alum inum c a u se s s te e l m em bers to
tend to take en tire load when u sed in com bination
with aluminum p a r t s .
5. B efo re rein forcin g any part of v eh icle,
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL