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Remote brake booster selection


BlownCorona

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On 27/03/2021 at 08:46, Kiwibirdman said:

I know enough to be dangerous here. I believe that not all VH40 boosters are the same. Some are application specific. Check with the supplier that it is the correct replacement.

Yes you're correct. There are 3 different VH40 slave cylinder sizes, they all run the same 7 1/2 inch vacuum diaphragm.

Smallest is the VH40EL at 9/16";  at 20' of vacuum it can produce 1825 PSI.

Largest is the VH40D at 7/8";  at 20' of vacuum it can produce 840 PSI.

Middle ground is the most common - VH40, VH40AJ, VH40AL, & VH40L; at 5/8" , at 20' of vacuum they can produce 1470 PSI.

They are also fitted with simple and compound type control valves which vary the cracking pressure from 20 to 35 psi.

The good new is that 9 times out of 10 it will be 5/8" bore, there is not a huge difference between simple & complex valves and the model difference is left or right hand mount - easy job to convert from one to the other.

As an added note a PBR Hydrovac failing to release is usually caused by a sized control valve piston in the booster or a blocked  compensation port in the master cylinder - the latter being more difficult to diagnose because with the booster disconnected there can often not be enough residual pressure to detect with a road test. 

 

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