Out-Of-Round Or Tapered Drum; Shoes And Linings-Front Disc Brakes - Chevrolet CHEVY VAN G10 SERIES Service Manual

S m ooth up any slight scores by polishing w ith fine em ery
cloth. Heavy or extensive scoring will cause excessive brake
lining w ear, and it will probably be necessary to refinish in
order to true up the braking surface.
If the brake linings are slightly worn and the drum is
grooved, the drum should be tu rn ed ju st enough to remove
grooves. The ridges in the lining should be lightly removed
w ith a lining grinder.
I f brake linings are m ore than h alf w orn b u t do not need
replacem ent, the drum should be polished w ith fine em ery
cloth b u t should n o t be turned. A t this stage, elim inating all
grooves in drum and sm oothing th e ridges on lining w ould
necessitate removal o f to o m uch m etal and lining, while if left
alone, the grooves and ridges m atch and satisfactory service
can be obtained.
I f drum is to be refinished for use w ith standard size brake
facings which are worn very little, only enough m etal should
be rem oved to obtain a true sm ooth braking surface.
A brake drum m ust n o t be refinished m ore than .060" over
the m axim um standard diam eter, removal o f m ore m etal will
effect dissipation o f heat.

Out-Of-Round or Tapered Drum

A drum th a t is m ore than .006 out-of-round on the
diam eter will result in rough brake application and should be
refinished. O ut-of-round and the diam eter can only be accu­
rately m easured w ith an inside m icrom eter fitted w ith proper
extension rods.
An out-of-round drum m akes accurate brake shoe adjust­
m ent im possible and is likely to cause excessive wear o f other
parts o f brake m echanism due to its eccentric action. An
out-of-round drum can also cause severe and irregular tire
tread w ear as well as a pulsating brake pedal. When the braking
surface o f a brake drum exceeds the facto ry specification
limits in taper (an d /o r) being out-of-round, the drum should
be tu rn ed to true up th e braking surface. O ut-of-round as well
as taper and wear can be accurately m easured with an inside
m icrom eter fitte d w ith p roper extension rods.
When measuring a drum fo r out-of-round, taper and wear,
take m easurem ents at the open and closed edges o f m achined
surface and at right angles to each other.
Micrometer Method (Fig. 29)
1. Place the brake drum on a sm ooth surface.
2. Using m icrom eters, place the tips at the center o f the
drum face.
3. While sweeping horizontally and vertically, slowly adjust
the m icrom eter until m axim um contact is m ade. Record
this reading.
4. R otate the drum 45 degrees and repeat Step 3. C ontinue
until 4 readings have been m ade. The difference betw een
these 4 readings m ust not exceed .006.
Cleaning
New brake drum s in parts stock are given a light coating o f
rust proofing oil to prevent th e form ation o f rust on the
critical braking surfaces during the tim e that the drum s are in
storage.
Fig. 2 9 —M easuring D ru m fo r O u t-o f-R o u n d
This rust proofing oil m ust be carefully removed before the
drum is placed in service to prevent any o f this oil from getting
on the brake shoe facings.
It is recom m ended that a suitable volatile, non-toxic,
greaseless type solvent be used to clean the oil from the
braking surface o f the new brake drums before they are placed
in service to insure the cleanest possible surface.
Gasoline or kerosene should n o t be used as there is danger
th a t a p o rtio n o f the diluted oil substance m ay be left on the
braking surface.
N O T E : A ll brake drums have a maximum diameter
cast into them . This diameter is the m axim um wear
diameter and not a refinish diameter. Do not re­
finish a brake drum th at w ill not meet the specifica­
tions as shown below after refinishing.
O RIG IN A L MAXIMUM R EFIN ISH
DIAM ETER DIAM ETER
11.000 11.060
12.000 12.060
13.000 13.060
SHOES AND LIN IN G S —FRONT DISC BRAKES
The brake linings should be inspected any tim e that the
wheels are removed. Check b o th ends o f the ou tb o ard shoe by
looking in at each end o f the caliper. This is the point at which
the highest rate o f wear norm ally occurs. At the same tim e,
check the lining thickness on the inboard shoe by looking
down through the inspection hole in the top o f the calip er-see
" Brake In sp ection ."
The o utb o ard shoes have ears near the ou ter edge w hich are
b en t over at right angles to the shoe. The top ends o f the shoe
have looped ears w ith holes in them w hich the caliper retaining
bolts fit through. The large tab at the b o tto m o f the shoe is
b en t over at a right angle and fits in the cut-out in the
outb o ard section o f th e caliper (Fig. 30).
BRAKES 5-15
(REPLACEM ENT)
(DISCARD)
DIAMETER
11.090
12.090
13.090
C H E V Y V A N S H O P M A N U A L