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[VintageLambo] Re: Front/Rear brake proportioning

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Wow, fun to catch up with the list. I"ve been so busy lately haven"t been on much. Anyway, there was no proportioning valve on any of the early V12 cars. They all have a single master cylinder with a split feed to two vacuum assisted servo cylinders. The output of these servos feed the front and rear respectively, and the differentiation in braking was accomplished by the puck size of the F/R slave cylinders or the pad size or both. If your brakes just developed this malignancy, I would suspect the following in order of listing; 1 Vacuum servo. A very high failure item. Allows fluid to bleed from the cylinder to either the outside or into the vac canister, then to the accumulator tank, and then to the vac source(engine) which will soon wash the left front holes of the engine, and ruin the pistons and rings. DON"T DRIVE IT THIS WAY! 2 Slave (wheel) cylinder. also a fairly high failure item. Does one of the rears lock up sooner than the other? Steering pull? If not, see above. 3 Glazed pad, or cracked disk in front. Been driving hard lately? If you cracked a disk, it should modulate the pedal, but maybe not. The pads should appear dull dark gray. If you see silver, or shiny pads, just take them to a big brake shop and have the pads renewed on the existing backing plate. I"ve done this with a bunch of cars, and saved tons of money over buying pad sets from dealers. 4 Clogged line from servo to wheel. Brake fluid being hydroscopic, accumulates water in the system. Usually winds up clumped near the wheel cylinder, I don"t know why. Causes poor brake action at the point of accumulation. All of these can be repaired without too much trouble. Look for brake fluid near the rubber hose that comes off the left front vacuum at the intake. If there is ANY FLUID there, plug the vac line and drive carefully without servo assist until you rebuild or replace the servos (both). Take the front wheel cylinders apart and clean them with brake cleaner. Inspect the pads. Reassemble and test it. Do the same with the rear. Flush the lines with cheap brake fluid new from a can. Then use Super Blue racing fluid (NOT Synthetic) in the system from now on. Use lots of fluid to flush, you"ll see the super blue when it comes through the line. Inspect under the dash, near the steering column for any leakage, could be master or clutch cyl. White Post will restore any cylinder or servo you have for a price($$$). Please don"t smash your car up with brake problems. I want to buy a Jarama S some day. Right now I"m on a car diet.... Doc --- In VintageLambo@yahoogroups.com, "Noah Mackenroth" wrote: > Hi Brake Exerts (I know you"re out there): > > I"ve recently noticed that I"m getting far more brake dust on my rear wheels than on my front wheels. Curious, I made a few panic-stop tests to investigate; sure enough, the rears lock up well before the front ones. My unconfirmed impression is that the fronts are working, though. > > How should I approach this situation? My brakes had major work done on them recently, but as it was farmed out, I don"t know exactly what was and what was not done. > > Can I just tweak the proportioning valve? Is it adjustable? Where is the thing (something that looks like such a mechanism is located below my brake fluid reservoirs on top of the left front wheel well)? > > Any help available would be greatly appreciated - Thanks in advance, > > Noah Mackenroth > 1973 Jarama S #10488 Your use of Yahoo! Groups is subject to