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Surprise · 06-12-2012, 11:10 AM

After examining the parking brake on my mo, I realized it has a tranny brake and not a conventional "cable to the rear wheels" type. Does anyone know how to service or adjust this? It looks like a wheel drum, the kind with brake shoes inside???

DaveFL · 06-12-2012, 11:35 AM

If it is like later model AS, parking brake is mostly working if it is not locked up as the biggest problem reading this forum is when the pressure switch or valve gives out, the pressure it exerts on keeping brake from being applied is lost and the spring takes over. So be careful on adjusting, make sure you are on level surface and chock the wheels. I tested mine by running vehicle up ramp applying and when it didn't roll back I knew they were working.

dznf0g · 06-12-2012, 12:20 PM

I'll see what else I can dig up.

#76-50-11: SMU-SEC. 5F1- HYDRAULIC AUTO APPLY PARK BRAKE - NEW INFO - (Jul 25, 1997)

SUBJECT: SERVICE MANUAL UPDATE- SECTION 5F1- HYDRAULIC AUTO APPLY PARK BRAKE- NEW INFORMATION FOR THE 1990 P32/42 MODELS

MODELS: 1990 CHEVROLET AND GMC P32/42 MODELS

THIS SERVICE MANUAL UPDATE IS PROVIDING NEW INFORMATION THAT WAS NOT COVERED IN THE 1990 P32/42 SERVICE MANUAL.
FIGURES: 00 ATTACHMENTS: 04

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.
COPYRIGHT 1997 GENERAL MOTORS CORPORATION ALL RIGHTS RESERVED.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.

dznf0g · 06-12-2012, 12:25 PM

#46-50-08: SMU - SECTION 5F1 - ELECTRIC/ AUTO PARKING BRAKE - (Nov 3, 1994)

SUBJECT: SERVICE MANUAL UPDATE - SECTION 5F1 - ELECTRIC/AUTO PARKING BRAKE

MODELS: 1994-95 CHEVROLET AND GMC TRUCK P CHASSIS MODELS

THE ATTACHED PAGES REFLECT INFORMATION NOT AVAILABLE AT TIME OF PRINTING OF SECTION 5F1 OF THE P3 + P/G SERVICE MANUAL. PLEASE INSERT THE ATTACHED PAGES 5F1-1 THROUGH 5F1-12 IN YOUR SERVICE MANUAL.
FIGURES: 0 ATTACHMENTS: 12

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.
COPYRIGHT 1994 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

dznf0g · 06-12-2012, 12:26 PM

#46-81-10: SMU - SECTION 8A - 46 ELECTRONIC PARK BRAKE - (Oct 25, 1994)

SUBJECT: SERVICE MANUAL UPDATE - SECTION 8A-46 - ELECTRONIC PARK BRAKE

MODELS: 1994-95 CHEVROLET AND GMC TRUCK P CHASSIS MODELS

THE ATTACHED PAGES REFLECT INFORMATION NOT AVAILABLE AT TIME OF PRINTING OF SECTION 8A OF THE P3 + P/G DRIVEABILITY, EMISSIONS AND ELECTRICAL DIAGNOSIS MANUAL. PLEASE INSERT THE ATTACHED PAGES 8A-46-0 THROUGH 8A-46-4 IN YOUR SERVICE MANUAL.
FIGURES: 0 ATTACHMENTS: 5

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.
COPYRIGHT 1994 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these 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 your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

dznf0g · 06-12-2012, 12:29 PM

Those should get you going. Although they are not specific to youe exact year, this system changed little, if at all over the years. I didn't start handling the P chassis until 1994, but I think you'll find it much the same. We did not go all the way back prior to 1997 and make all the service manuals web based. So I only have bulletins on the old stuff.

dznf0g · 06-12-2012, 12:33 PM

The following posts will be from the 1997 Service Manual

Hydraulic Auto Apply System Components
Warning Lamp

The AUTO PARK warning lamp turns on when the system pressure is less than 3 100 kPa (450 psi) or when the electric/hydraulic pump motor is running due to the pressure maintenance switch being closed. The pressure maintenance switch and the light switch supply B+ to the circuit for lamp operation. Releasing the parking brake causes the warning light switch to open the circuit and turn the lamp off. This lamp will flash at partial release pressures.
Pump Assembly

The parking brake pump assembly is located in a component box on the passenger side of the vehicle. The component box is on the inside of the right frame rail in front of the rear axle. It consists of an electric pump and a fluid reservoir. The pump provides fluid pressure to operate the system. A pressure relief valve in the pump limits system pressure to 12 400 kPa (1800 psi).
Pressure Maintenance Switch

The pressure maintenance switch mounts to the parking brake pump assembly housing. It is a hydraulic pressure switch that operates within a certain pressure range, turning the pump motor on and off. The pressure maintenance switch closes when the system pressure is below 8 300 kPa (1200 psi) and opens when the system pressure reaches approximately 1100 kPa (1600 psi). The pressure maintenance switch applies B+ to the coil side (control side) of the relay switch.
Solenoid Valve

The parking brake solenoid valve is a solenoid and valve assembly located in the component box on the underside of the vehicle. The solenoid controls when the fluid can return to the pump reservoir. When the parking brake is released, the valve closes to hold pressure in the system. When the parking brake is applied, the valve opens in order to allow the fluid to return to the pump reservoir.
Actuator

The actuator is located in the component box on the underside of the vehicle. It is a spring-loaded device that operates the parking brake cable. A large spring inside the actuator applies the parking brake. When the fluid pressure against the piston is great enough, it overcomes the spring tension and pushes the piston to release the parking brake.
Cam-Actuated Switch

The cam-actuated switch is located to the left of the steering column intermediate shaft. It is a normally open switch that closes when the column shifter is moved out of the P (Park) position. B+ is applied to the solenoid valve and to the pressure maintenance switch when the cam-actuated switch is closed.
Relay

The parking brake relay is located in the component box underneath the vehicle. The relay receives B+ from the pressure maintenance switch and acts as the automatic control circuit for the high current required to run the pump motor. When the pressure maintenance switch supplied B+ to the relay switch, the contacts close to complete the feed circuit to the pump motor.
Light Switch

The parking brake light switch is a hydraulic on/off switch located in the component box underneath the vehicle. The light switch is mounted with a fitting on the back of the actuator assembly. The light switch controls the ground side of the AUTO PARK lamp. The lamp switch closes when the system pressure is below 3 100 kPa (450 psi), turning on the light when the ignition is ON.
Brake Switch

The parking brake switch is a manual on/off switch on the instrument panel. The location is determined by the body builder. Pushing in the switch releases the parking brake. Pulling out the switch applies the parking brake.

dznf0g · 06-12-2012, 12:35 PM

Hydraulic Auto Apply Actuator Cable Adjustment
Adjustment Procedure

CAUTION:: If the actuator will not hold pressure, do not unthread the parking brake cable from the actuator piston. The cable is under tension and unthreading the cable will cause the cable to spring and can result in personal injury.

1. Block the vehicle's wheels.
2. Turn the ignition ON.
3. Place the shift lever in N (Neutral).
4. Loosen the parking brake jam nut on the actuator assembly.
5. Adjust the cable fitting until tension is obtained.

Tighten
Tighten the jam nut to 45 N·m (33 lb ft).

Refer to Fastener Notice in General Information.
6. Place the shift lever in P (Park).
7. Measure the actuator cable/piston rod stroke.
The distance must be between 30 mm (1.20 in) and 37 mm (1.44 in) while moving the shift lever from P (Park) to N (Neutral).
8. Remove the wheels blocks.
9. Check the operating and holding ability of the parking brake.
10. Repeat the procedure if necessary.

dznf0g · 06-12-2012, 12:36 PM

Hydraulic Auto Apply Control Rod Adjustment

1. Move the column shift lever to P (Park).
2. Loosen the jam nuts on the adjusting rod.
3. Adjust the rod ends on the adjusting rod until ⅜ inch drill bit slides through holes A and B.
4. Secure the jam nuts to the rod ends.
5. Adjust the cam-actuated switch. Refer to Hydraulic Auto Apply Cam-actuated Switch
6. Check the operating and holding ability of the parking brake.
7. Repeat the procedure if necessary.

dznf0g · 06-12-2012, 12:37 PM

Lining Adjustment
Adjustment Procedure

Important: This parking brake assembly does not have a brake shoe adjusting screw. Adjustment is done at the cam lever clevis.

1. Block the vehicle's wheels.
2. Turn the ignition ON and move the column shift lever to N (Neutral).
3. Remove the cotter pin and the clevis pin.
4. Slide the clevis from the cam lever.
5. Move the cam lever slightly upward in order to take up the slack between the cam and the brake shoe web.
6. Adjust the clevis in or out in order to align it with the hole in the cam lever.
7. Install the clevis, the clevis pin and the cotter pin.
8. Remove the wheel blocks.
9. Check the operation by applying the parking brake. Note the brake's holding ability.
10. Release the parking brake and check that the linings are completely free of the drum.
11. Repeat the procedure if necessary

dznf0g · 06-12-2012, 12:37 PM

I think that's it on adjustments. It's been over 10 years since I've played with these, so bear with me. I have more info, just ask specifics.

Keyair · 06-12-2012, 01:03 PM

Hold up...
This is an 84...
I think its a simple mechanical cable control...
Mine is an '84 345 and has a parking brake lever on the left of drivers seat...
Couple of pic from the underside of mine...

Rear view..

View from drivers side showing a cable bracket and cable entering the drum..

Mine does not work so well either so I will be glad to get some good info on adjustment!

Surprise · 06-12-2012, 01:16 PM

Yes, mine appears mechanical.

dznf0g · 06-12-2012, 01:22 PM

Ok, that was before my time with the P chassis and I don't have any manuals for that. In later years, only the non-motorhome commercial chassis' (except Frito lay trucks) were manual and the transmission had a parking pawl. The later, high GVWR motorhomes and Frito trucks were all auto apply and the trans had no parking pawl. IIRC they were Allison meduim duty transmissions.

I think yours is a straight forward cable adjustment and not at all complicated like the later electro-hydraulic systems.

Waipio Rim · 06-12-2012, 09:23 PM

parking brake adjustment.pdf

Not sure if my attachment will work, but it is the section out of the Chevrolet Motorhome Chassis Service Guide on parking brake adjustment.

dznf0g · 06-13-2012, 07:24 AM

Quote:

Originally Posted by Waipio Rim

Attachment 160889

Not sure if my attachment will work, but it is the section out of the Chevrolet Motorhome Chassis Service Guide on parking brake adjustment.

Yup, that's it for the non electrohydraulic older and commercial stuff. The hand and foot applies are spelled out in that document. BOY, is that a blast from the past for me!

raveson · 06-13-2012, 07:37 AM

I believe mine is mechanical too. If so, adjustment is accomplished by turning the top of the brake handle to either more or less pressure to apply. Basically very simple. Had to reduce the pressure on mine.

dznf0g · 06-13-2012, 07:52 AM

I don't have manuals prior to '97, but IIRC (and it has been a LONG time) it was sometime in the early to mid 90s when the electro-hydraulic system came to play. As I recall, the issue was retail motorhome owners were not in the habit of applying the park brake at EVERY stop, prior to placing in park. With the heavy GVWs of motorhomes, if one were to park on a hill, they may not get the unit out of park due to the high loads on the parking pawl in the trans.

So, the auto apply system was born. It was, I believe only on motorhome chassis...until Frito Lay came along. I cannot remember if the park pawl was still in the motorhomes after the auto-apply or if motorhomes ever got the Allison trans, but Frito wanted an Allison (which have no parking pawl) for a 21 year, (3 rebuild lives) duty cycle. That put the auto apply in their commercial chassis. That's where I came into the game. Motorhomes were serviced out of the fleet department, because they were so unique as opposed to retail smaller trucks, though they were handled by a coworker of mine. I just had tribal knowledge passed on by him.

Trivia, for what it's worth.

Lesson here, for you mechanical p-brake owners....always apply the p-brake prior to placing in park. It's a good habit anyway, but it may save you some trouble on a hill sometime, especially if you have a toad behind.

jking · 06-27-2012, 09:44 AM

That brake drum on the drive shaft is the parking brake. It is manual in the 1984 models. The lever on the driver's left side low down pulls the cable through a complicated mechanism, but it is adjustable. Check the brake shoes inside the drum first, and if they're OK then let me know and I'll email you a copy of the adjusting procedure. KJ4JK@ARRL.NET
Jamie

LM782 · 10-09-2020, 04:48 PM

Came across this old post because I recently purchased a 1985 345 that needs the parking brake adjusted. It has a mechanical propshaft drum parking brake with an orschelin lever (no electronics or hydraulics involved) that has the cable going into the drum like what is shown in Keyair’s pictures above.

For reference, here’s a link to the Chevy P30 Chassis Service Guide I’m using (https://www.gmcmi.com/wp-content/upl...sis-Manual.pdf). Figure 6-5 on page 6-4 captures the parking brake installed on my 345.

I can’t quite tell if a few details were inadvertently left off the cable adjusting procedure in the service manual.

Specifically, page 6-9 step 2 (at the very bottom of the page) states, “2. Apply parking” – that’s it, nothing else. The word “brake” is missing, no other details, and no period. Found it odd.

Step 3 states, “3. Loosen nut at intermediate cable equalizer and then adjust nut to give light drag at rear wheels. (See NOTE at end of this procedure.)"

Step 3 is confusing. “Loosen nut… and then adjust nut.” Huh? I think they meant loosen lock nut and turn adjustment barrel.
Far as I can tell, this cable equalizer is akin to a bicycle brake cable adjusting barrel – the longer you make it, the more slack it takes up from the cable.

See the attached marked up picture. In my attempt to adjust the parking brake cable, I loosened the 9/16” locknut, hold the cable flats with a small wrench or pliers, and turn the adjustment barrel (half-inch wrench). The barrel spins, but only half or a full turn before the cable toward the front vehicle begins to twist (within the housing).

It feels like the adjustment barrel is bound to the cable. Not enough penetrating oil? It does not turn freely and if I wrench it too far, I’m concerned the cable may fail. Does anyone know where the rotational play is supposed to be?

Am I turning and/or adjusting the right parts and attempting the adjustment correctly, or is there something I’m missing?