1956 Buick Brakes Service

The vise grip, installed in Step 2, will hold spring in position once it 1s expanded around drum.

Center-punch the drum at five (5) equally spaced locations so that each of the five (5) clips will rest in the depression provided by the center-punch mark, insuring positive retenstion. See Figure 72.

NOTE: It is desirable to point center-punch toward outside of drum away from backing plate when making depression. Obviously, this spring and clip will not correct squeaks due to scored drums or metal imbedded in lining. It is, therefore, recommended that on a squeak complaint, drums and shoes be inspected and drum turned if necessary, then sand linings by use of a spindle mounted type of brake shoe grinder or other suitable method.

Flat Rate time for installing spring is:

One Wheel .4 hr.
Each Additional.3 hr.
All Four Wheels1.2 hr.

 

POWER BRAKE REPAIRS

According to information received on product reports, indications are that some dealer service men are installing a small compression spring between the foot pedal and floor pan of power brake equipped cars to relieve a bind in the pedal, and in some cases are performing grinding operations on other related parts to obtain full pedal travel.

Complete information on checking alignment of the power brake eccentric pivot pin and pedal has been covered inBPS2.387datedNovember23, 1955. Any deviation from factory recommended service procedure may be detrimental to the performance of the power brakes and the factory cannot assume any responsibility for unauthorized procedures; therefore, this practice must be stopped.

 

BRAKE CYLINDER LUBRICATION

1956

We have been advised by our Engineering Department that Dynaflow oil is no longer recommended for lubricating the power brake piston or cylinder housing. When servicing a power brake unit, only power brake cylinder oil Gr. 4.898 Part #1165078 should be used to lubricate the piston and cylinder. Therefore, will you please make this correction in the 1956 Shop Manual on page 9-30, paragraph c, step 16.

 

PARKING BRAKE PEDAL SLIPS

1956 Models

Reports have been received that some parking brake pedal and lever assemblies would not hold in the applied position because of being improperly adjusted. Whenever this condition is encountered it may be corrected by adjusting the parking brake release rod trunnion so that when the parking brake is in the fully released position, the release rod spring will be compressed approximately 1/4″ to give it a desired preload of approximately 4 to 6 lbs. It is important to have this spring pressure exerted against the lever trigger because it is this pressure that insures proper holding of the pedal.

This important adjustment can be accomplished by performing the following:

1. Disconnect battery.
2. Lower fuse block to gain access to release rod trunnion.
3. With parking brake pedal in fully released position, disconnect trunnion from release lever trigger. See Figure 73.

With trunnion disconnected from lever trigger, push trigger toward cowl as far as possible; then, while holding trigger in this position, lengthen release rod by turning trunnion until it extends approximately 1/4” beyond hole in trigger while holding release rod lightly against spring pressure.

Connect trunnion to release lever trigger.

NOTE: Rattles have been reported to exist at this location because some early 1956 models had the release rod trunnion secured in position by a cotter pin. However, this can be corrected by installing the 1956 after job Clip Gr. 4.602 Part #1173439 which retains the rod and trunnion assembly to trigger lever See Figure 73.

4. After the above adjustment has been performed, approximately 1/8” clearance should exist between release knob and escutcheon. Proper clearance at this location may be obtained by loosening screw in knob and positioning knob as required to obtain specified clearance; then tighten knob screw.

NOTE: If knob is pushed on shaft as far as possible and clearance exceeds 1/8” and is objectionable to the owner, it will be necessary to install a washer of proper thickness in front of release rod spring as shown in Fig. 73. Doing this will reduce the clearance by the thickness of the washer installed. After washer installation it will be necessary to repeat steps 3 through 6.

5. Reconnect fuse block and battery cable.

 

IMPROVED MASTER BRAKE CYLINDER

The following is a reprint from Special Service Letter (Red Band) – Dealer #174, pated March 7, 1956.

We have been advised by Engineering that several changes are being incorporated in our 1956 direct acting brake master cylinder. Figure 8 shows comparison between first type and second type cylinder. The master cylinder bearing has been redesigned in that the primary cup insert is now an integral part of the bearing, with the primary cup washer made captive on bearing. See insert Figure 74.

In order to make the primary cup an integral part of this bearing in manufacturing, it was necessary to provide a recess in end of bearing opposite primary cup support which, in turn, made it necessary to lengthen the secondary cup retainer. The secondary cup retainer is, therefore, approximately 1 /16″ longer than the retainer used in early production cylinders.

Another change made in the bearing was the addition of a groove which extends outward from each of the five (5) holes at front end (primary cup support end) to O.D. of bearing. These holes in the bearing conduct fluid from the reservoir to the hydraulic cylinder and by providing the additional grooves, fluid flows around the primary cup lips more quickly during pedal release action to fill the hydraulic cylinder.

In addition to the above changes, both ends of the primary cup spacer now contain slots to facilitate passage of fluid at each end; previously, only end opposite primary cup was slotted.

The afore-mentioned changes improve the seating action of primary cup on primary cup support and piston; they also improve passage of fluid within the hydraulic cylinder, and passage of fluid from reservoir to hydraulic cylinder.

The Parts Department has revised the hydraulic brake master cylinder repair kit Gr. 4.649 Part No. 5455438, to incorporate these new changes; therefore, the new kit will be made available under Gr. 4.649 Part No. 5455765. Also, arrangements have been made so that all orders on hand for the 5455438 kit will be automatically filled with the new kit 5455765.

When installing the new kit, thoroughly clean hydraulic cylinder, including inside of reservoir to make certain that all traces of foreign material are removed. Lubricate new seals with clean brake fluid prior to installation. Figure 74 shows the position in which new parts should be installed.

NOTE: It is imperative that all parts contained in Kit #5455765 be installed. Under no circumstances should first type kit parts be used with those contained in second type repair kit #5455765.

The new repair kit does such an effective job that zones will not accept AFAs for brake master cylinder assemblies in the future.

In addition to the above changes the present master cylinder Gr. 4.650 Part # 5455250 will be replaced by a new master cylinder Gr. 4.650 Part #5456000 which will incorporate the new parts shown in the inserts of Fig. 74.Also, a bearing package Gr. 4.653 Part #5455788 will be made available and will include the new bearing assembly, primary cup spacer and secondary cup retainer (parts identified in inserts Fig. 74) and will replace the following parts contained in first type cylinder.

 

BRAKE PEDAL CORRECTION

1956

NOT A CAMPAIGN

A few reports have been received that the suspended brake pedal on early 1956 Dynaflow jobs tends to twist and bend the pedal plate, during brake application. This condition can be corrected by first removing the pedal pivot lock nut, bolt and pedal, as well as the dash insulator retainer shown in Figure 75.

Center punch hole location in cowl panel through unused hole in bracket. Then drill a 9/32″ hole through cowl and install a 1/4 x 20 x 3/4″ bolt, flat washer, lock washer, and nut and tighten securely to the cowl panel. See Figure 76.

This additional bolt has been installed in production and may be observed when the hood is raised as shown in Figure 77 and 78.

On some power brake jobs only, another problem may be encountered in that the angle of the pedal plate on which the brake cylinder and pedal are mounted, does not conform with the angle of the cowl panel. When this condition exists the pedal plate may become distorted when bolted to the cowl, causing an out-of-alignment condition between pedal and power cylinder; it may also cause interference between push rod and air valve sleeve. Correction for this misalignment should first be attempted by performing the following:

1. Loosen pivot bolt lock nut on right side of bracket, shown in Figure 75.
2. With pedal in fully released position, turn eccentric pivot bolt at left side of pedal bracket until just enough clearance exists between push rod and air valve sleeve to prevent contact at any point in pedal travel. See Figure 79.

Securely tighten lock nut, making certain that adjustment does not change.

If this out-of-alignment condition cannot be corrected by the eccentric bolt adjustment, it may be necessary to shim between the pedal plate and power cylinder using flat washers as shown in Figure 80.

However, if neither the eccentric bolt and shimming adjustment does not correct the out-of-alignment condition, it will be necessary to remove the pedal plate and bracket assembly and replace it with a new one.

Flate rate time to install the bolt on all jobs is .6 hrs. This includes R & R Brake Pedal, rubber dash insulator retainer, and drilling hole in cowl.

On power brake jobs, if shimming operation is required, an additional .5 hrs. may be added. If necessary to replace the pedal plate assembly, another .5 hrs. may be added. However, in 90% of the cases, the bolt installation will correct this condition.

 

POWER BRAKE VACUUM LEAKS

1955 and 1956

Reports have been received that on some cars the power brake pedal was slow in returning or would not return completely to its normal position. It has also been reported that the following sources of vacuum leaks have been found to exist in the power brake cylinder. These leaks can be classified into three categories:

1. Broken air valve. A broken air valve may be detected by pushing in on the push rod. This will separate the valve and piston assembly from the power piston. With these two parts separated, gently move the end of the air valve (covered by rubber boot) back and forth in a sideways motion. If an abnormal amount of play exists, it is an indication that the air valve is broken. CAUTION: Excessive side thrust may break a good valve when performing this check.
2. Punctured vacuum hose
3. The valve and piston assembly (small piston) not returning to the unapplied position completely, causing a vacuum leak between the valve reaction plate to piston seal and power piston (large piston).

In most cases these vacuum leaks will cause a rough engine idle. However, in order to eliminate the possibility of a vacuum leak elsewhere as the cause of the rough idle, it is suggested that all other possible sources of vacuum leaks be checked thoroughly before attempting any service work on the power brake cylinder. The corrections for the above described condition are as follows:

1. Replace air valve with new air valve, using procedures outlined in Shop Manual.
2. Replace vacuum hose with new hose using procedure outlined in Shop Manual.
3. In order to correct the above described condition, Engineering has developed a new inner piston return spring Gr. 4915 Part #5455800. The new spring has a slightly higher compression load, causing more positive seating of the valve reaction plate to piston seal. The new spring is readily identified by its greater length and larger coil diameter than the first type.

To install this spring, the following procedure must be followed:

1. Remove the power brake cylinder as outlined in section 9-3 sub. par. e of the 1956 Product School Manual.
2. Mount power cylinder in vise with hydraulic cylinder down, being careful not to damage any parts. Tighten vise only enough to hold cylinder firmly; excessive tightening will distort or crack cylinder.
3. Remove push rod boot and retainer from housing cover. Do not attempt to remove push rod which is anchored in air valve by a spring type lock.
4. Remove the air cleaner assembly.
5. Remove two housing cover screws, cover and gasket. While holding power piston down, disconnect vacuum hose from vacuum tee and remove tee and gasket from housing. Slowly release power piston to control the pressure of piston return springs, as pistons emerge from the housing. Make sure that lip of leather piston cup does not catch in holes in housing.
6. Remove the center return spring (valve and piston return spring) and replace it with the new spring Gr. 4915 Part #5455800.
7. Center the new piston return spring in the cylinder housing, then place the large return spring around it with its smaller end down, locating the bent end of the spring wire between one of the bolt heads and the adjacent dimple pressed in cylinder housing.
8. Place power piston with attached parts on the large return spring so that the bent end of the spring wire rests between two of the round bosses on piston guide. Locate the piston so that when it is pressed into housing the side of boss opposite the vacuum hose clears the vacuum tee hole in housing by approximately 3/4″ . See Figure 81.

Push power piston down into cylinder housing, entering the hydraulic piston into hydraulic cylinder and hold piston down while installing vacuum tee with gasket and two screws. Push end of vacuum hose up on tee about 5/8″.

Push power piston down and allow springs to return it several times to check for free operation and proper position on springs. (Step 8), then install gasket and cover on cylinder housing with two screws.

Install air filter assembly and rubber boot.

Install assembly back into car following the procedure outlined in Section 9-3 sub. par. e of the 1956 Product School Manual.