Looking in the Rimmer's parts catalogue I can see that there were five different brake servo's fitted across the dolomite range and having both a single line and a dual line 1500HL I am aware that the dual line servo for the 1500 is a lot larger in diameter. What I can't find any info on is the boost ratio for the dual system. From various documents I have found that the single line has a boost ratio of 2.2:1. I am assuming that the dual line system with the larger diameter servo has a higher boost ratio to make up the loss in rear braking efficiency caused by having to fit the smaller diameter slave cylinders. The single line cylinders are 3/4 inch diameter and the dual are only 5/8 inch so I think this works out to be a 25% drop in force being applied to operate the rear brake shoes.
Can someone please tell me the dual boost ratio and how do you identify the various servo types as a have not found any marking on the ones that I have.
I have also noted that the single line 1850 has the same boost ratio as the 1500 but the rimmer's catalogue shows its servo to be a different type to the 1500.
Some questions about dolomite brake servo's
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Richard the old one
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Edin Dundee