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'84 Subaru GL10 front wheel drive brakes seized,

Sent to Car Experts July 8 2006 at 3:26 PM
   

'84 Subaru GL10 front wheel drive brakes seized, one front and opposite rear. Changed both front calipers and rear cylendars and it did it again. What causes this? Someone said proportioning valve, someone else said bad brake lines. How do determine if it is proportinging value or something else?

Customer (name blocked for privacy)
Status:  Closed   Value: $9
Answer
July 8 2006 at 7:20 PM (3 hours and 54 minutes and 38 seconds later)
         
ACCEPTEDCheck Mark
It's most likely a problem with fluid returning to the master cylinder. It could be debris blocking the return port to the reservoir. Or one of the pistons sticking or prevented from returning by the push rod.

To determine where the pressure is building up, get the brakes to start dragging. Then loosen the brake lines one at a time, starting at the master cylinder line closest to the booster(primary piston). You should get a bit of a spurt, when you get to the line in question, and the brakes will free up. If it's the line at the primary piston, make sure your brake pedal fully returns. Also the booster push rod can be out of adjustment. To determine if it is, create the brake drag, then loosen the master cylinder mounting nuts. Then see if the brakes free up. If pressure releases at the secondary piston, the problem is in the master.

If you don't find a problem at the master, then follow the lines to other components (hill holder etc.), and do the same tests.
RonRepair -- Auto Mechanic/Tech -- 95% Positive Feedback on 67 Car Accepts
40 years of experience on all makes, 15 yrs. ASE Master Tech, 5 yrs. Certified Toyota Tech
Reply
July 9 2006 at 6:45 PM (23 hours and 24 minutes and 29 seconds later)
         
Reply to RonRepair's Post: You didn't even mention the proportioning value at all. Are you saying it is in no way the proportioning value, or does that fit in after the hill-holing deal?
   It doesn't hold on the hills.
   This process of getting it to drag and then doing the tests will be challenging as it has happened three times, once at the end of a 400 mile drive, once after half a day of driving around Portland and once as my son was trying to go back to Boise from Portland. I loaned him my 4Runner and i'm stuck with trying to resolve this.

I don't know how successful i'll be at getting it to brake down at my house to do these tests. Each time, the brakes freed on their own after about an hour. Any further guidance?
Merv
Customer (name blocked for privacy)
Answer
July 10 2006 at 3:43 AM (8 hours and 58 minutes and 22 seconds later)
         
REPLIEDCheck Mark
The only information I have on a proportioning valve is a G-load sensing valve. If this were a problem, it would involve one or both rear wheels. It also says it was available on european models. If you could provide me a description of what you're referring to as proportioning valve, and where the lines go, I can tell you if it could be the problem.

A hill holder is available on manual transmission models. If you have one, you can find it by following one of the cables from the clutch fork. Then follow the lines and see if it involves the wheels in question.

You might be able lift the front wheels off the ground and pump the brakes, to duplicate the condition. The most likely problem is the master cylinder, but without verification, it's just an educated guess.

If you have additional question or information, let me know.
RonRepair -- Auto Mechanic/Tech -- 95% Positive Feedback on 67 Car Accepts
40 years of experience on all makes, 15 yrs. ASE Master Tech, 5 yrs. Certified Toyota Tech
Reply
July 10 2006 at 5:47 PM (14 hours and 3 minutes and 47 seconds later)
         
Reply to RonRepair's Post: I loosened one then the other of the two brake lines on the master; first the one further from the fire wall, then the other. In neither case did the brakes free up. Then i loosened the master mounting bolts and they released. (Since the brakes release after a while anyway, i wanted to duplicate the problem once again before buying a new master cylendar.
So I tried to duplicate the drag by riding my brakes as a drove about 5 miles each way. Although they smelled hot they unfortunately didn't seize up.

YOu say "If pressure releases at the secondary piston, the problem is in the master." I'm not sure exactly what that means. How do i know it's at the secondary; because they released when i loosened the mounting bolts?
Customer (name blocked for privacy)
Answer
July 10 2006 at 6:46 PM (58 minutes and 58 seconds later)
         
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RonRepair -- Auto Mechanic/Tech -- 95% Positive Feedback on 67 Car Accepts
40 years of experience on all makes, 15 yrs. ASE Master Tech, 5 yrs. Certified Toyota Tech
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