A very important improvement in the hydraulic section of the 1955 power brake unit has recently gone into production. This improvement will prevent the possibility of air entering the hydraulic lines, will facilitate bleeding, and will result in an even more satisfactory brake pedal during brake application. We wish to incorporate this change on all 1955 power brake equipped cars previously built, and urge that this be accomplished as quickly as possible.

To make this change, it is necessary to install a special kit (Group 4.898, Part #5455066) which is available from all parts warehouses.

Figure 52 (A and B) illustrates the first and second jobs hydraulic cylinder parts arrangement, and indicates the parts which should be replaced.

1955 Buick Hydraulic Brake Cylinder Parts

1955 Buick Hydraulic Brake Cylinder Parts

Figure 53 illustrates the latest hydraulic cylinder parts arrangement, labeling the parts which are to be installed from the latest kit (Group 4.898, Part #5455066.)

1955 Buick Hydraulic Brake Cylinder Assembly

1955 Buick Hydraulic Brake Cylinder Assembly

It is important that the following marking procedure be carried out on every car campaigned:

After the latest kit has been installed and the job completed, paint a light green “X” on ventilator air duct (blister) on the left side of the cowl. This “blister” is the plate which holds the windshield washer jar. Painting an” X” on every job campaigned will indicate to anyone who raises the hood that the power brake unit has had the new kit installed.

NOTE: A white “X” may appear at this location. If so, paint the light green “X” over the white.

Following is the list of serial numbers for jobs requiring installation of Hydraulic Cylinde1 Kit Group #4.898 Part #5455066.

All 1955 power brake equipped cars produced up to and including these serial numbers will require installation of the hydraulic cylinder kit, if not previously installed as indicated by a green “X” on the cowl.

Serial Numbers – Assembly Plant

B1041182 – Flint
B2010618 – South Gate
B3012527 – Linden
84012829 – Kansas City
B5009423 – Wilmington
B6010043 – Atlanta
B7005824 – Framingham
B8007133 – Arlington

We suggest that each dealer immediately make up a list of all 1955 power brake jobs sold, showing the owner’s name, address, and car serial number. The list should also provide a column for inserting the date the kit was installed. After determining the number of jobs which require kit installations, submit an order to your parts warehouse for a supply of kits. – 1955 Power Brake Hydraulic Cylinder Repair Kit, Group 4.898, Part # 5455066.

Old parts, shown in Fig. 52, (A or B) must be tagged and returned to the Zone M.R. Room, before credit will be issued, and only (1) job may be listed per AFA.

Each AFA submitted should include car serial number, model, part number, R.O. number and date.



  1. Check fit of rubber vacuum hoses connecting vacuum pipes to vacuum “T” on power brake unit. After clamps have been loosened a slight drag should be felt when hose is disconnected from vacuum “T” indicating snug fit. If hose fits loose, is distorted, or otherwise damaged, it should be replaced with a new hose. Group 4.931, Part #1165712.
  2. New hoses should fit snug when installed on vacuum pipe and “T” connection without pressure of clamps. Clamps must be installed at each end of hose and clamp jaws must not bottom to prevent sufficient holding. If clamp bottoms, it should be replaced with a new clamp either No 7 1/2 or 11/16″ ID, Group 4.931, Part #111603. Hoses should overlap ends of all vacuum pipes at least 3/4″.
  3. Remove power brake unit from car.
  4. Plug all openings to exclude foreign material from entering unit. Brush and thoroughly clean dirt from area where hydraulic cylinder attaches to power cylinder housing. NOTE: Remove all undercoating from brake cylinder.
  5. Remove four (4) hex nuts, then remove hydraulic cylinder and gasket from housing. NOTE: Opening in head nut should be vented to atmosphere before separating hydraulic cylinder from power cylinder housing, otherwise vacuum will be created making separation difficult.
  6. Clamp hydraulic cylinder in a vise as shown in Figure 9-22, Page 53 of the 1955 Product School Manual, being careful not to damage the loose vent pin (wire) in flange of cylinder. Tighten vise only enough to hold cylinder firmly; excessive tightening may distort or crack casting.
  7. Unscrew and remove cylinder plug from hydraulic cylinder body, using Spanner wrench J -5794. Then remove secondary seal, cup support, vacuum cup retainer, vacuum cup seal and „O“ rings from cylinder plug.
  8. From cylinder body, remove the following:

1st Type Jobs – Fig. 52 -A- Remove secondary cup retainer, piston bearing, primary cup ring (blue steel washer), primary cup and primary cup retainer.

2nd Type Jobs -Fig. 521-8 -Remove secondary cup expander, secondary cup expander spring, piston bearing, primary cup ring (blue steel washer), primary cup and primary cup retainer.

  1. Remove head nut with gasket, check valve, and spring from cylinder body.
  2. Set aside parts indicated in either “A” or “B” of Fig. 52 depending upon which cylinder is being serviced.
  3. Clean remaining parts in clean brake fluid. For reassembly, use parts furnished in new kit, Group 4.898, Part #5455066. NOTE: Inspect all parts contained in the kit to be certain they are not damaged in any respect, and be certain to use only kits showing the above part number. (Illustrated in Figure 53)
  4. Install new check valve seat washer on head nut. Place spring and new check valve with concave side outward in cylinder body, then install head nut with new gasket and tighten securely.
  5. Place primary cup retainer in cylinder body with notched end inward. Dip new primary cup in clean brake fluid and install with flat side outward, using care that lip is not turned back at any point.
  6. Center the primary cup ring (blue steel washer) on cup and install new piston bearing with notched face outward, pressing bearing down against shoulder in body.
  7. Dip new vacuum seal and secondary cup in clean brake fluid. Install vacuum seal in cylinder plug with flat side inward, center the vacuum cup seal retainer (ring) on seal, then install secondary cup with flat side inward against support. Place new „O“ rings in the two (2) outer grooves of plug, making certain that center groove with vent holes is left open. Lightly coat „O“ rings with silicone grease or clean brake fluid.
  8. Center new secondary cup (dark color) retainer on piston bearing, then place spring steel expander over retainer (ring) with outside fingers pointing downward toward casting bore. Screw cylinder plug into cylinder body using care not to damage „O“ rings or secondary cup. Tighten plug firmly, using Spanner wrench J-5794.
  9. Place gasket on hydraulic cylinder with one notch at vent hole, install power cylinder housing (with air cleaner on same side as head nut), then install four nuts and tighten securely. Check operation of power piston to make certain that a bind does not exist.
  10. Reinstall power brake unit. (Be certain undercoating is not present in vent hole at loose wire.)

NOTE: When the power brake unit containing new kit has been installed, and the bleeding procedure outlined in paragraph 9-7 of the 1954 Shop Manual has been followed, perform the following vacuum check to insure that there are no leaks in the vacuum lines. (The use of a pressure type bleeder with the car approximately level during bleeding will result in a better job.)

  1. Make certain brake pedal is in fully released position, properly adjusted, and no bind exists.
  2. Start engine and run until reasonable smooth idle is attained, to build up vacuum in reservoir.
  3. Shut off engine.
  4. Wait two (2) minutes and apply brake pedal. If vacuum is holding properly, pedal should have normal vacuum assist.

If proper vacuum assist is not found when above check is made it will be necessary to check all other vacuum connections for proper fitting of hoses and clamps and replace hoses that do not have a snug fit on pipes. Also replace clamps as necessary.

  1. Paint a 2” light green “X” on left ventilator air duct (blister) on left side of cowl.

When job is completed, use the empty repair kit container to package all parts which were set aside in step No. 10. These parts should be returned with an AFA for credit.

Complete flat rate operation covering work described in this letter is as follows:

POWER BRAKE KIT (Gr. 4.898, Part #5455066)

Install Oper. 5-163 2.2 hrs.

Includes: R&R starter splash pan, checking fit of hoses and clamps at vacuum “T”, R&R power brake unit, bleeding hydraulic system, and performing two (2) minute vacuum check.


  1. Cylinder to check valve line hose and/or clamps (2) at ”T” fitting R&R

Oper. 5-163-1 1 hr.

  1. Cylinder to vacuum reserve tank line hose and/ or clamps (2) at “T” fitting R&R

Oper. 5-163-2 .1 hr.

  1. Vacuum reserve tank line hose and/or clamps (2) R&R

Oper. 5-163-3 .1 hr.

  1. Check valve line hose and/or clamps (2) R&R

Oper. 5-163-4  .1 hr.

  1. Intake manifold vacuum line hose and/or clamps (2) R&R

Oper. 5-163-5 .4 hr.

Since all cars will not require new vacuum hoses and/or clamps, the listed combination operations will not be handled on a campaign basis. Dealers will receive credit for hose and clamp replacements at regular AFA rates.

The following information applies to AFA handling:

  • Submit one (1) AFA per car for kit installation (one quart of brake fluid allowed per kit installation).
  • Submit one (1) AFA per car for hose and/or hose clamp replacement. Use time allowances set forth in this letter.
  • Do not include more than one car per AFA nor combine hose and clamp installation with kit installation, on the same AFA.
  • All parts replaced should accompany AFA.



On January 15, production started setting 1955 Buick brakes with a very accurate fixture. This fixture will set the anchor pin within .0015 of correct location, also the brake shoes are expanded into the drum with a torque control. The anchor pin is then tightened and the adjustment backed off for clearance. All 1955 Buick brakes are set alike and can be adjusted far better and closer than by a hand operation in a service department. This adjustment is practically fool proof.

Due to manufacturing tolerances, it is not possible to get 100% Lining contact with the brake drum as this can only be accomplished on the car with braking operation, and without any further brake adjustments. We purposely control the finish on the brake drums to make this wear in of lining to fit the drum as quickly as possible. Our experience indicates that the drum finish should be from 80-115 Micro Inches which produces a turning fuzz (no deep turning grooves) and will wear the lining fast enough to produce a good contact as quickly as the Motor is broken in.

It is not recommended that a brake adjustment be made at time of new car make ready. It is suggested, however, that in cases where a brake pull is noticed by the customer that a burnishing operation be made as follows:

Drive car with transmission in low range and enough pressure on brake pedal, with approximately half throttle not to exceed 15 MPH for 1/4 mile, let brakes cool. If brake pull is not completely gone, make another application and a third. This will hasten the wear in period.

NOTE: Do not abuse car or allow 1955 Buick brakes to become hot enough to smell smoke.

If the above procedure does not eliminate the pull, then look for scored drums, oil or grease on lining, out of round brake drums, or paint on lining. In case of an out of round brake drum, it can be felt on brake pedal, and the drums should be recut. In case of oil, grease, and paint, the shoes should be replaced and scored drums should also be re-cut, making sure that the lining does not have steel particles embedded into it before replacing drums.

If the inside of brake looks as if it were free of the above troubles, look for spotty brake lining contact and if found use the Brake Dokter to true up the lining. Note (Do not remove any more lining than is necessary in this operation).

There are a good many causes for brake pull which are as follows:

  1. Road surface not uniform.
  2. Variation of tire tread.
  3. Brake drum finish not uniform.
  4. Brake Drum Material not uniform.
  5. Brake Lining Variation in friction.
  6. Brake Lining Area in contact with drum.
  7. Radius of lining and drum will vary from one wheel to other.
  8. Oil or Grease on Lining.
  9. Paint on Lining.
  10. If parked in dusty lot, wind will blow road sand, etc. into drum and effect friction.
  11. Water or Dampness will effect friction.
  12. Variation of caster and camber on front wheels.

Our Engineering Department advises they have found by using the 1955 Buick brakes, most cars will come into good brakes sooner than if re-adjustments were made. The anchor pin setting is the last thing which should be changed as changing anchor pin location means a new wear pattern is immediately started and will extend the length of time required for lining to wear in.



1955 Power Brake

Engineering advises that vacuum check valve group 4.955, part 1162534 on 1955 first jobs could be noisy because of the following reasons:

  1. A leak in the vacuum system between the check valve and vacuum tank or a leak in the check valve itself.
  2. The driver may be riding the brake pedal and partially applying the brake causing a drain on the vacuum supply. If this is the case, it may be pointed out to the driver that this practice could cause absence of reserve vacuum and if the engine should stall, the power assist would not be available to aid in stopping the car.

Note: When the noise is present, it may be caused by one or a combination of the above mentioned conditions. In order to eliminate the first condition as a possible source of trouble a two minute vacuum check may be performed as follows:

  1. Make certain brake pedal is in fully released position, properly adjusted, no binds in it, and the check valve is free of foreign material and operates freely.
  2. Start engine and run until a reasonably smooth idle is attained to build sufficient reserve vacuum in vacuum tank.
  3. Shut off engine.
  4. Wait two (2) minutes and apply brake pedal. If vacuum is holding properly, pedal should have normal vacuum assist, if not, a leak exists and should be corrected.

If vacuum assist is obtained, the check valve should not chatter unless the driver has the habit of riding the brake pedal as described above. In this case, a road test with the owner should be made explaining why the chattering exists and the consequences of this undesirable practice. If the owner still is not satisfied, then install a new power brake check valve, Group 4.955, Part 5455046 observing the following procedure:

Note: Under no circumstances should an attempt be made to rework a check valve by installing rubber washers behind valve spring to cushion valve operation.

  1. Remove the vacuum line from the vacuum check valve to the vacuum ”T” connection.
  2. Remove the cap from the old valve body and remove the spring and valve. NOTE: Leave valve body attached to the frame. Discard the valve and spring. See Figure 54.
1955 Buick Power Brake Vacuum Check Valve

1955 Buick Power Brake Vacuum Check Valve

  • Cut the vacuum pipe just ahead of the first bend. (From “T” connection end.) Install 3/8 Pipe flare nut then flare the pipe. See Figure 54.
  • Install the new valve on the end of the pipe that was just cut off and flared. See Figure 54.
  • Replace the old valve cap (without spring and valve.)
  • Install the new valve and vacuum line as an assembly and make sure the hose at the ”T” connection makes sufficient contact with the new valve.
  • Make the above described 2 minute vacuum check to insure that no leaks exist.



    Following is a reprint of Special Service Letter

    Dealer No. 148, dated September 8, 1954.

    The following method of adjustment is intended to be used when brake action is unequal, erratic, squeaking or otherwise unsatisfactory. If done exactly as outlined, this procedure will correct a very high percentage of pulling, diving and squeaking brake complaints.

    1. Air tires to 24 pounds – jack up car in a safe manner.
    2. Expand brake to a two hand drag in a forward direction. (Do not tighten excessively so as to distort drum.) Do not attempt to expand brake by having another mechanic apply pressure to brake pedal.
    3. Loosen brake anchor pin nut 3/4 turn.
    4. Rap brake backing plate around outer circumference with heavy hammer to allow anchor pin to position itself.
      IMPORTANT: Do not rap directly against anchor pin while performing Step D.
    5. Tighten anchor pin nut securely.
    6. Check pull necessary to rotate wheel in forward direction.
    7. If drag is less than before, it is an indication that the anchor pin has moved from its original position. In this event, expand brake one notch at a time until original drag is obtained. Repeat steps C, D, E, and F until amount of drag remains constant.
    8. Loosen brake adjustment 15 notches. (If anchor pin is properly set and brake parts are free, brake should begin to free up at 6 notches.)
    9. Repeat above procedure on all remaining wheels. (If any brake has noticeably more drag than the others after releasing adjustment 6 notches, repeat the anchor pin adjustment procedure on that brake. If still not comparable to the others, remove wheel and check brake assembly and backing plate for cause of binding and correct condition.)
    10. If, during the foregoing procedure, anchor pins moved on one or more brakes, car should be driven on the road and a number of brake applications made. Usually, during the first few applications, the original condition, either squeak or pull, will exist. However, after several fairly hard applications, the conditions will begin to improve until after 15 to 20 applications, when brakes will begin to operate normally.

    Anchor Pin Adjustment – Flat Rate Operation 5-5 is .8 hrs.

    If 1955 Buick brakes do not operate normally after foregoing work has been done or if during steps A through I, none of the anchor pins moved from their original position by even a small amount, it is evident that no correction of the difficulty was made and that further internal brake work is necessary.

    In this event, remove all wheels, blow dust from 1955 Buick brakes and drums, being careful to protect wheel bearings from dirt. Check color markings on the side of each brake shoe at approximately the center of the shoe to determine if proper type lining is installed, by referring to the following information.

    Color Marking on Side of Brake Lining

    Power Brakes – 1953 and 1954 – All Series

    Primary – front and rear brakes – Blue Secondary – front brakes only – Black Secondary – rear brakes only – Orange

    Standard Brakes- 1953 and 1954- Series 40, 60, 50

    Primary – front and rear brakes – Blue

    Secondary – front and rear brakes – Orange


    Primary and secondary – front and rear brakes – no marking


    Combination of above specified for 40-60-50, except that both sides must be alike.

    Standard Brakes – 1953 and 1954 – Series 70

    Primary – front and rear – Blue

    Secondary – front and rear Orange



    40-60 Series

    Early production rear brake cables on 1955 40-60

    Series cars were found to be of excessive length in some cases, due to stack up of dimensions, and are not capable of sufficient adjustment to take care of initial cable stretch.

    This condition may be corrected as follows where trouble is encountered:

    1. Disconnect rear brake cable by removing nut and cable sheave.
    2. Cut a piece of 1/4 inch steel pipe or tubing will slip closely over the front cable rear shank to the length necessary to get ample adjustment. One inch length should be adequate. Install this spacer on the shank between the rear cable sheave and the adjusting nut. Adjust cable to proper tension and lock adjusting nut by installing a plain 5/16 inch nut as a jam nut and tightening securely against the adjusting nut.
    3. Check with parking brake in the fully applied position to be sure cable sheave does not come up to the rubber grommet. There should be at least 1/2 inch clearance.
    4. If cable sheave is within 1/2 inch of grommet in the fully applied position, remove hand brake cable support (rubber covered bracket) and weld a new one, Gr. 4.785, Part# 1311223, one to two inches farther ahead on the torque tube. The steel shank of the front cable must ride in the grommet and not the cable.



    To prevent interference between the right front brake pipe and the upper control arm, a clip (Group 9.793 Part No. 1334584) should be positioned over the brake pipe and secured to the right frame side rail. See Figure 55.

    1955 Buick Brakes Pipe Clip

    1955 Buick Brakes Pipe Clip

    This clip was omitted on some earlier jobs, therefore it is imperative that all cars be checked at time of New Car Servicing or 2,000 Mile Inspection to make sure clip is installed and brake pipe does not contact upper control arm.

    The clip can be installed as follows:

    Hold brake pipe away from the upper control arm, (See Figure 55). Center punch location in frame in approximate area indicated in Fig. 55. Then drill a .170″ diameter hole in top of frame rail. (A 1/4″ capacity electric drill is recommended for drilling) Carefully push brake pipe away from upper control arm, then install clip over brake pipe and tighten clip with a 10-16 x 1/2 self tapping screw to hold brake pipe in correct position.

    Flat rate time to install this clip is .3 hrs.



    1955-56 Models

    A change in brake drums has recently gone into production which will affect 1955 after jobs and

    1956 models. This change involves machining the drums .020″ over our past production drum sizes and may be identified by the way the drum is machined. The new drum has approximately 1/8” shoulder as shown in Figure 56.

    1955 Buick Brakes Drum Change

    1955 Buick Brakes Drum Change

    The new machined drum diameter will always insure having center point contact on initial break-in of the shoes with any variation in manufacturing tolerances, thus insuring greater uniformity in brake performance with less danger of brake pulling on new cars. This is because the shoe radius is always less than the drum radius.

    To get this same desired condition on replacement of shoes or drums, the fit up of shoe to drum must be such that the shoe radius is .020 less than that of the drum (or .040 less on diameter). This fit up may be accomplished by grinding the shoes or turning the drums if necessary to obtain the desired fit, whichever is the more practical. This procedure also applies in the case of drums which have been turned oversize because of scoring with which oversize linings are used to make the repair. 1955 Buick Brakes on both sides of the car must be fitted up the same to get equal action.


    If new linings are installed and are not ground by a spindle-mounted type equipment, it will be necessary to adjust anchor pin and brakes. It is imperative that this be done according to the procedure described in ”Brake Correction”, article in BPS 2.379 dated December 1, 1954.




    It has been brought to our attention that dealer mechanics have installed the reaction plate backwards on the hydraulic piston of the 1955 units. This not only results in faulty brake operation but makes it difficult to select the proper amount of shims as explained in the 1955 Shop Manual Paragraph 9-17 subparagraph c, Step 9.

    The reaction plate should have the concave side of the rim toward shoulder of piston and the rounded side of the rim against the reaction levers as shown in Figure 57.

    1955 Buick Power Brake Reaction Plate

    1955 Buick Power Brake Reaction Plate