Hi all, My son has a 90 Jetta. Recently he has had a problem where the rear drum brakes have to be bled weekly due to air. Any ideas on how this air is getting in the system? Both cylinders appear to be fine, with no fluid leaks. Is there any way the proportioning valve could be causing this? Any suggestions would be appreciated. Thanks Brian
Check for leaks at proportioning valves. A really small wet spot isn't important (I live for years with it with no problems), but anything more will let air in the system. If that's so, change them. Check the connections between the line and the cylinder. If they were ever disconnected and small grains of sand scratched or got imbedded in the contact surface, the air can get sucked in. Fine polish them if so.
TR
Brian McCloskey wrote:
Thanks Tom. Do you know if the proportioning valve can be repaired if there are any leaks? Or does it need to be replaced? Brian
On a second thought, on a 90 car you can get away with used. These things usually last for the life of the car unless something damages them. I had to replace mine because some of the holding clips broke and they rattled for about 6 mo. until I bothered to take a look underneath. I think I paid about $4 each at the junk yard, but this was 8 yrs ago. Be very careful to install them in the same direction, if reversed you call it BIG bubu. I can't remember if they are designated left and right and I can't find my spares to see if I marked them L&R. Bentley doesn't say anything about this. Most likely Fox and Golf of similar years have identical valves.
Brian McCloskey wrote:
Thanks My son and I are heading out to see what what's up with it. We will do a full brake line inspection from front to back to rule out any other connection points as you suggest. I couldn't see any leak on the proportioning valve, but it seems to be the common point between both the rear brakes and both sides end up with air, so it's either the valve, or maybe some common connection closer to the front. Brian
I had a problem with air in the rear brake cylinders of my '81 Toyota pickup. This truck has drum brakes in the rear. I expect that the slave cylinder set-up will be similar if you have drum brakes that are self adjusting. What fixed it was cleaning and lubricating the self-adjusting screws. It I believe that the inability of the screws to adjust freely caused the travel of the pistons to increase, this could be noticed by how much further the parking brake had to be pulled out to take effect. In cold weather (enough of that in Calgary) moisture would condense in the outer part of the cylinders and some pitting of the cylinder walls occured. The loss of brake fluid, which could be seen by checking the brake fluid reservoir, was negligible in the summer and severe in the winter. When bleeding the brakes are and ice/water/slush would come out.
It took me a while to figure out the cause and effect of the problem, but cleaning and lubing the screw assembly, after rebuilding the slave cylinders made the problem go away. After treating the adjusting screws one could see that self adjustment was taking place where before it was not.
I have noticed on my other truck that the parking brake is coming to the end of it's pull and that the brake fluid level is down. I know that I had better clean and lube the screws.
good luck, Rob
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