Oldsmobile/Buick: brakes, rear drum brakes, brake proportioning valve


Question
while moving and applying brakes .i hear a pop in left front wheel.brake light sometimes comes on while applying.i pump the brakes 1 time ,i hear another pop and the light goes out,any thoughts?1979 olds cutlass

Answer
Hi Craig,
Well there are a few factors that may be the culprit. It's a process of elimination when it comes to any brake system, so check all the following. Either way, your going to have to take the car in to be fixed. What bothers me is that your brake light is comming on. Driving the car under this condition is extreamly dangerous, because the next time you hit the brakes you may have none and the pedal will hit the floor. Yikes! You did not mention any leaking brake fluid, but you'll need to check this. Look for any spots of fluid on the pavement on the drivers side just behind the front wheel. Also, follow the brake lines behind the master cylinder and underneath the car for fluid trickling down. Just underneath you'll see the proportioning valve with the two brake lines feeding in to. If you've constanly had to add brake fluid, maybe once a week or so, then the diagnosis is quite simple. A leaking brake proportioning valve. Basically what this piece does is regulate fluid to the front disc and rear drum brakes. The leakage will make your front or rear brakes (depending on which side of the valve is leaking) take the majority to stop the car instead of evenly. This can cause the poping noise you hear, as the two little calipers are trying to stop 3,400lbs.! Oldsmobile had a lot of problems with these valves back in the 70's. The design was changed over several times starting in 1973. My  '73 Hurst/Olds suffered the same problem as the brake light kept comming on, glowed brighter and brighter. I'd hit the pedal and it go out. The proportioning valve was leaking just enough. Now here is the challenge. These valves are not made anymore, by anyone. You are going to have to search the junkyards or Oldsmobile sites like 442.com. I have a good number of connections and may be able to locate one for you. It'll save you some bucks. These little parts can cost up to $150.00 through other sources, so we may save you a few bucks. If you decided to look on your own, you'll need to find one specifically off a 1979 Cutalss only. Other year Oldsmobiles are not interchangeable. If the proportioning valve checks out ok and you have no leaks, you'll need to have a leak down test done on your power brake booster. The accordion type bellows can get brittle from heat and age and may need replacing. This part isn't cheap either, around $100 for the part, and is sold at many parts stores. Finally, if the power booster checks out ok, The last area is your brake calipers on the front. They may be binding due to broken pieces or due to a warped rotor. The rotor will have to be resurfaced or replaced if the metal is to thin. A brake shop can check the thickness with a micrometer and let you know, with out a major disassembly. Remember, if your brake problem is left unrepaired for a long lenghth of time it will eventually wear out your tie-rod ends and bushings and cause you to have to fork out cash for a front-end rebuild which is quite expensive. One other thing, check the condition of your shocks. Worn ones can cause the car to ride on the coil springs, and effect the braking sysyem as well. Last on the list of checks is plain ole' air in the lines. So you can see, there are many factors or a combination thereof that can cause brake problems. Hope I have not confused you, but given you every possible idea on where the problem may be comming from. Go ahead and take the car in as soon as possible and have a brake specialist give the car the once over. Tell them what's happening. They will find the cause quickly, and will let you know what needs to be done. Thanks for the question! Ray