Rear Suspension (Height Sensing) - Modulations
Number: 83-T-61Section: V
Date: July, 1983
Subject: REVISED REAR SUSPENSION ON VEHICLES WITH HEIGHT SENSING PROPORTIONING BRAKE SYSTEMS - 1982-83 "C/K" 30
TO: ALL CHEVROLET DEALERS
1982-83 "C/K" 30 series trucks are equipped with a rear suspension height sensing device that optimizes the brake proportioning valve setting for the load the vehicle is carrying. The height sensing system "fine tunes" the brake balance in vehicles subjected to a range of loading conditions.
Occasionally, vehicle modifications by body builders or owners influence the height sensing device. If a vehicle has had rear suspension modifications that affect its trim height or the spring rate, and the driver complains about the brake modulation characteristics of the vehicle, it is recommended that the height sensing system be removed and the brake system be revised as described below:
FIGURE #1 - REAR SUSPENSION:
1. Detach rear brake hose from lever and bracket assembly. Reference Figure #1.
2. Remove lever assembly and bracket from axle.
FIGURE #2 - DIFFERENTIAL:
3. Install rear brake hose bracket (P/N 348978) and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (P/N 358000 - shorter bolt removed in Step #2) in the upper cover hole. Reference Figure #2. Use Loctite 75 or equivalent on the bolt threads.
4. Attach brake hose to bracket with bolt from original installation.
5. Install a 3/8-16 x 1-3/4 bolt (PIN 14055557 -- longer bolt removed in Step #2) through spacer P/N 14055556 (removed in Step #2) in remaining axle cover attaching hole. Use Loctite 75 or equivalent on bolt threads.
FIGURE #1 - REAR SUSPENSION:
6. Disconnect brake pipes from height sensing valve and brake hose, and discard short brake pipe. Reference Figure #1.
7. Remove and discard height sensing valve, bracket and bolts.
8. Carefully reposition the rear brake pipe, and connect it to the rear brake hose.
9. Remove the brake combination valve per section 5 of the Light Duty Shop Manual.
10. Select and install a replacement combination valve, based on the vehicle wheelbase and type of rear wheels, from the chart below:
Valve Part
Wheelbase Rear Wheel Type Valve Code Number
131/135 Single DD 1257200
131/135 Dual EE 1257203
159/164 Single 1257203
159/164 Dual P 1257087
11. Bleed and test brake system per Section 5 of the Light Duty Shop Manual.