diesel66 Posted July 13, 2011 Share Posted July 13, 2011 Hi all, I want to update the brakes on my 109 - presently single circuit servo assisted. I'm going to convert it to dual circuit but I can't clarify which pipe goes where! Rather which port on the master cylinder corresponds to which circuit? Can anyone help? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 14, 2011 Share Posted July 14, 2011 Pipe nearest the servo is for the rear brakes, outermost to the front. There's a brake failure valve in there as well, but most people do away with it. Les. Quote Link to comment Share on other sites More sharing options...
diesel66 Posted July 14, 2011 Author Share Posted July 14, 2011 Thanks Les, just the clarity I needed. Kind regards, Christian. Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 14, 2011 Share Posted July 14, 2011 Pipe nearest the servo is for the rear brakes, outermost to the front. There's a brake failure valve in there as well, but most people do away with it. Les. Mine was built by LR with the pipes crossing over, so the back end of the MC (nearest the servo) does the front brakes and the front end of the MC operates the rear brakes. The cross-over happened on exiting the PWDA valve on the chassis. I copied the system when I rebuilt the vehicle and it works perfectly with very effective braking. I don't know which configuration is normal, though. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 14, 2011 Share Posted July 14, 2011 I have the line drawing here - showing the route I have posted. Haynes manual mind, so there's no guarantee it's right. Les. Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 16, 2011 Share Posted July 16, 2011 I copied the original set up on the assumption that it was mainly hydraulic pressure in the front circuit that pressed the rear circuit's piston forward, with the intermediate spring there as a back-up to transfer pedal pressure if the front circuit sprung a leak. From the sectional diagrams of the MC, it appeared as if the front end of the MC had a smaller volume capacity than the servo end, but these diagrams aren't always well scaled. Quote Link to comment Share on other sites More sharing options...
secondjeremy Posted July 18, 2011 Share Posted July 18, 2011 The front piston is moved by the fluid between the 2 pistons - which operates the back (in cylinder terms) circuit. The springs are weak and really serve just to keep everything in the right place - after all with a servo on the back and say 70lb on the pedal, a mechanical advantage of say 4:1 on the pedal mechanism and a 1.9:1 servo you're looking at about 530 lb push on the piston. (These are not accurate figures - just approximations) Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 18, 2011 Share Posted July 18, 2011 The front piston is moved by the fluid between the 2 pistons - which operates the back (in cylinder terms) circuit. The springs are weak and really serve just to keep everything in the right place - after all with a servo on the back and say 70lb on the pedal, a mechanical advantage of say 4:1 on the pedal mechanism and a 1.9:1 servo you're looking at about 530 lb push on the piston. (These are not accurate figures - just approximations) That makes sense - I should have thought of the forces and tininess of the spring a bit more deeply... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.