Brake pressure not right - Rolls-Royce and Bentley Forums
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post #1 of 7 (permalink) Old 06-10-2019, 09:39 PM Thread Starter
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Brake pressure not right

I have new accumulators, hoses, fluid and rebuilt valves and pumps. Also new seals in height rams and height valves. Brakes and height control work well. But rear pump ticks and rear system (2) pressure light comes on with only 5 presses on brake pedal (engine off). Light goes out right away when engine on. I’ve tried bleeding and don’t see air bubbles.
Thanks for suggestions

1976 Shadow
VIN 22833
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post #2 of 7 (permalink) Old 06-10-2019, 09:59 PM
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Either your accumulator is bad or your ACV is bad.

Ticking in pumps very often occurs when there is not the expected back pressure in the system from a properly charged accumulator, so I'd check that first. If the rebuild did not go correctly or even if it did, but the valve leaked, you could easily have an accumulator that's almost gone flat. If the accumulator charge checks out, then you need to make yourself a system testing gauge and test the system to determine what's going on as far as the ACV. See: Building a Hydraulic Pressure Test Gauge (B.Vogel).


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post #3 of 7 (permalink) Old 06-10-2019, 10:32 PM Thread Starter
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Thanks. I can’t remember what the accumulators are like - do they have a valve on the nitrogen side that I can test for pressure/add nitrogen to if needed? I bought mine from flying spares

1976 Shadow
VIN 22833
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post #4 of 7 (permalink) Old 06-10-2019, 10:42 PM
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New (recent) accumulators? Did FS supply rebuilt pressure valves? The only definitive way to diagnose such issues is with a 0-3000psi gauge and read off the pressure valve bleeder. This is the easy have to understand and interpret what you see.

The pressure valves may not have been tested and shimmed to release at the right pressure. The best overhaul and test is when both can be tested together.

Testing at he pressure valve may also indicate a weak hydraulic pump. If any of the system components are not working properly the whole system suffers.

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post #5 of 7 (permalink) Old 06-10-2019, 11:17 PM
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Did you buy the disposable accumulator spheres or rebuilt exchange spheres from Flying Spares? You have either low pressure in the sphere, faulty accumulator valve, or faulty low pressure warning light switch. The only way to be sure of what is wrong is to fit a pressure gauge and test the system with it connected to the #2 system. On a 76 Shadow you can fit the pressure gauge to the pressure warning switches on the left front inner fender near the radiator, no need to climb under the car to fit one.

SRH8505 SRC18015 SRE22493 NAC-05370
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post #6 of 7 (permalink) Old 06-11-2019, 11:18 AM Thread Starter
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I bought the reconditioned ones: RH2390SXR
I will make a pressure gauge as described in the attachment above and see what that says.

1976 Shadow
VIN 22833
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post #7 of 7 (permalink) Old 06-11-2019, 02:51 PM
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Location: Orem, Utah
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Some knucklehead that lurks these forums has test gages ready to go:
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File Type: jpg IMG_7290.jpg (188.9 KB, 4 views)
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