BRAKE PERFORMANCE INCREASED REAR BRAKING REVISED

MODELS: 1985-1987 M VANS

THIS BULLETIN CANCELS AND SUPERCEDES TRUCK SERVICE BULLETIN 86-T-136 DATED FEBRUARY,1987, ALL COPIES OF WHICH SHOULD BE DISCARDED. THIS BULLETIN IS BEING REVISED TO INCLUDE SOME 1987 MODEL VEHICLES.

Safari/Astro vans are designed to carry varying loads, and therefore, they are equipped with brakes that are capable of good stopping performance under a variety of conditions. Some customers who operate their Safar/Astro vans heavily loaded most of the time may prefer additional rear braking. If so, the following procedure is an acceptable method of increasing rear braking on 1985, 1986 and some 1987 Safari/Astro vans. It will result in a higher rate of deceleration at wheel slide and shorter stopping distances in a heavily loaded condition. The customer should be informed that there will be an in- crease in rear brake perforrnance and the potential for rear wheel skid in unladen applications. Safar/Astro vans, in both their original condition or as changed by this bulletin, meet all tbe stopping requirements of Federal Motor Vehicle Safety Standard 105 for Light Duty Trucks.

Service Procedure

Important: Care must be taken to prevent brake fluid from contacting any painted surface.

1985-1986 Models:

Always ensure that the brake system is operational after performing brake work and before returing the vehicle to the customer.

Steps A, B, and D involve all subject vehicles. Step C is engine dependent.

A. Replacement of the combination valve, (Figure No.1)

1. Disconnect negative battery cable.

2. Disconnect the four brake lines at the combination valve.

3. Disconnect electrical harness at the combination valve.

4. Disconnect combination valve at bracket on the brake booster and discard valve.

5. Install new combination valve (P/N 15571205).

6. Reverse above procedure for reinstallation and tighten bracket nuts to 50 Nm (37 lbs/ ft).

7. Reinstall brake lines and torque nuts to 25 Nm (18 lbs/ft).

B. Replacement of the brake shoes, wheel cylinders, and link pins (Figure No. 2).

1. Loosen lug nuts on rear wheels.

2. Hoist vehicle and remove lug nuts and rear wheels.

3. Remove brake drum retaining clips (2).

4. Remove brake drum. 5. Remove brake shoe hold down and retainer springs. 6. Remove brake sboes and discard. 7. Disconnect brake line at wheel cylinder 8. Remove wheel cylinder and discard. 9. Install new wheel cylinder (P/N 18004888) after inserting link pins (2) (P/N 5464748). 10. 'fighten wheel cylinder bolts to 18 Nm (13 lbs/ft). 11. Connect brake line to cylinder, torque nut to 20 Nm (14.5 lbs/ft). 12. Install new brake shoes (P/N 12321427). 13. Adjust running clearance to .030 +/- .005" adjustment clearance. 14. Reinstall brake drum, retainer clips, and wheel. 15. Bleedbrakes,(RefertoSafari/AstroService Manual, pages 5-5 and 5-6). 16. Repeatonoppositewheel.

1985 Model 4.3L Carbureted Engine C. Reduce cold idle speed to 1600 rpm. 1. Remove dash extension. 2. Remove engine cover 3. Install tacbometer. The tachometer (tach) terminal is next to the engine control switch (bat) connector on the distributor cap (See Figure No. 3). Notice: The tachometer terminal must never be allowed to touch ground, because damage to the module inside tbe dis- tributor and/or ignition coil can result. 4. Reduce cold idle speed to 1600 rpm by ad- justing the fast idle screw. Refer to tune up label for procedure. 5. Remove tachometer and reinstall engine cover and dash extension. 6. On a clean dry surface, next to tbe existing tune up label located on the fan shroud, place label P/N 10066488

1986 Model 4.3L TBI E@nes C. ReplacementgftbePROM(FigureNo.4). 1986 model vebicles built before VINS listed below require PROM replacement.

GMC GB524481 Federal Emissions GB524599 California Emissions Cbevrolet GB203188 Federal Emissions GB203623 California Emissions Vehicles built after these VIN breakpoints have PROM factory installed. Notice: Any time the PROM is installed back- wards and tbe ignition switch tumed on, the PROM is destroyed and must be replaced. 1. Disconnectnegativebatterycable. 2. Remove kick panel from right side of the vebicle (1 screw) interion 3. Remove ECM (2 screws). 4. Disconnect electrical harnesses from ECM module. 5. Remove ECM cover (2 screws). 6. RemovePROMfromECMandreplacewith new PROM, P/N 16068877 (Federal), P/N 16068926 (California). 7. Replace ECM cover 8. Reconnect electrical hamess. 9. Secure ECM module to its mounting loca- tion. 10. Replace kick panel.

1985 - 1986 2.5L TBI Erigile C. Vehicles equipped with this engine do not re- quire PROM replacements. D. Brake Bumish Procedure On a dry clean level roadway, make twelve stops using the following procedure: First Stop: Stop vehicle from 40 mph by apply- ing the brakes to achieve a deceleration rate of 10 fVsee/sec. (A 10 fVsedsec deceleration is equivalent to stopping the vebicle from 40 mph in 6 seconds.) Second tbrough Eleventh Stops: Stop vehicle from 50 mph by applying the brakes to achieve a deceleration rate of 15 ft/sec/sec. (A 15 fVsec/sec deceleration is equivalent to stopping tbe vebicle from 50 mph in 5 seconds.) Twelfth Stop: Stop vehide from 40 mph by ap- plying the brakes to achieve a deceleration rate of 10 ft/se&sec. In order to allow brake temperatures to stabi- lize, it will be necessary to drive V2 mile be- tween stops without applying brake s. Following

completion of burnish procedure (twelfth stop), drive vehicle 3 miles keeping brake usage to a minimum in order to achieve sufricient brake cool down.

1987 MODELS Effective 1987 start of production, all SafarVAstro models were manufactured witb new wheel cylinders described earlier in this builetin, however the new combination valve was not in- stalled in the first several months of production. The new combination valve was installed effective with the following Vehicle Identification Numbers: GMC: HB509335 Chevrolet: HB137507

1987 vehicles produced prior to these VIN break- points can be modified by following the service pro- cedure listed below:

SERVICE PROCEDURE:

. 1987 Model 2.5L TBI and 4.3L TBI engines Important: Care must be taken to prevent brake fluid from contacting any painted sur- face. Always ensure that the brake system is opera- tional after performing brake work and before retuming the vehicle to the customen Replacement of the combination valve (Figure No.1). 1. Disconnectnegativebatterycable.

2. Disconnect the four brake lines at the com- bination valve.

3. Disconnect electrical bamess at the combina- tion valve.

4. Disconnect combination valve at bracket on the brake booster and discard valve. 5. Install new combination valve (P/N 15571205). 6. Reverse above procedure for reinstallation and tighten bracket nuts to 50 Nm (37 lbs/ft). 7. Reinstall brake lines and torque nuts to 25 Nm (18 lbs/ft). 8. Bleed brakes (Refer to Safari/Astro Service Manual, Pages 5-5 and 5-6).

Parts are cuff ently available from GMSPO.

PARTS LIST

1 . Combination Valve (1) P/N 15571205 2. Wheel Cylinders (2) P/N 18004888 3. Brake Shoe Kit (1) P/N 12321427 4. Link Pin Ytit (2) P/N 5464748 5. Brake Fluid DOT 3 P/N 1052535 (as required) or equivalent 6. Label (1985 4.3L Engine) (1) P/N 10066488 7. PROM for 1986 4.3L P/N 16068877 Federal engine 8. PROM for 1986 4.3L P/N 16068926 Califomia engine

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.