Pressure regulating valve — checking and adjustment (VW Lt 28)

1. This valve is located on the left side and is operated from the rear axle by means of a lever and spring.

2. To make sure the valve is working, have an assistant press the brake pad and quickly release it. The control valve lever should move.

3. Without a pressure gauge, it is impossible to check and adjust the valve, and the only rough method for assessing its installation is the amount of dust from the friction material of the linings in the rear drums. A small amount of dust indicates that hydraulic pressure is decreasing during braking.

4. If you have a pressure gauge, attach it to the rear wheel cylinder in place of the bleed nipple.

5. Place the vehicle on its wheels on a level surface without load.

Models LT 28 and 31

6. Measure the distance between the bottom of the rear axle shaft and the base of the side body panel. Find this value in the table below and determine the pressure. Now compare the pressure given in the table with the instrument readings, which must be taken with the brake pedal pressed.

Models LT 35, 40 and 45

7. Measure the distance between the centers of the upper and lower shock absorber mounting bolts. Find this measurement in the table below and determine the pressure value that corresponds to your model, now compare this value with the instrument readings that should be taken with the brake pedal pressed.

All models

8. If the measured pressure is too high, reduce the spring tension (i.e. shorten the effective length of the friendship), sliding the bolt within the oblong hole toward the mounting plate (see Figure 9.27).





9. If the pressure value is too low, increase the spring tension. by extending its effective length.

10. Never attempt to adjust the valve while the brake pedal is depressed. After completing the adjustment, check the pressure in the circuit.

Distance (a), mm	Pressure (bar)
	Pickup and Van	High-roof van
300 to 295	7 to 10	4 to 7
295 to 290	10 to 12	7 to 9
290 to 285	12 to 14	9 to 11
285 to 280	14 to 16	11 to 13
280 to 275	16 to 18	13 to 15
275 to 270	18 to 20	15 to 17
270 to 265	20 to 22	17 to 19
265 to 260	22 to 24	19 to 21
260 to 255	24 to 26	21 to 23
255 to 250	26 to 29	23 to 26
250 to 245	29 to 32	26 to 29
245 to 240	32 to 35	29 to 32
240 to 235	35 de 38	32 to 35
235 to 230	38 to 41	35 to 38
230 to 225	41 to 44	38 to 41

Distance (a), mm	Pressure (bar)
	LT 28 and 31	LT 35	LT 40 LT 45
425 to 420	24 to 30	27 to 33	—
420 to 415	30 to 35	33 to 38	—
415 to 410	35 to 41	38 to 44	—
410 to 405	41 to 48	44 to 51	—
405 to 400	48 to 55	51 to 58	—
400 to 395	55 to 62	58 to 66	58 to 65
395 to 390	62 to 69	66 to 74	65 to 72
390 to 385	69 to 77	74 to 82	72 to 60
385 to 380	77 to 84	82 to 91	80 to 88
380 to 375	84 to 93	91 to 101	88 to 97
375 to 370	93 to 101	101 to 111	97 to 107
370 to 365	101 to 110	111 to 120	107 to 116
365 to 360	110 to 119	120 to 131	116 to 128