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1940 LaSalle Dragging Rear Brakes

Started by Tom Roche 20925, July 07, 2005, 11:56:38 PM

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Tom Roche 20925

    I have a 1940 LaSalle 52.  Rebuilt the master cylinder & reinstalled it without changing the adjustment rod lenght.  Drove the car 3 to 4 miles and the rear brakes locked up (rear break lights ON with the brake pedal released).  
     Stuck a wire thru both the by-pass & vent holes in the master cylinder supply reservior.  Holes are open & still no pressure is relieving.  After it cooled down (about 45 mins.) I could move the car.
     How did this get out of adjustment when I changed nothing?
I have since removed the master cylinder and had it rebuilt. Any suggestions as to how to adjust the master cylinder prior to installing it (Im doing this on jack stands) and any suggestions on adjusing the pedal operating rod once installed, it is very difficult to get at.  
 
   Thanks for any help.  
   
   Tom Roche     (630) 983-7825
   rcafleet@AOL.com

JIM CLC # 15000

07-07-05
TOM, I do not belive there is any adjustments on the Master Cylinder, only on the push-rod.
I know this means a lot of work and choise words, but I dont see any out for you. If there is no adjustment on your MC, then remove the clives-pin and adjust the push rod to the point where the pin will move the brake pedal connection just slightly when the cotter pin-pin is inserted. Otherwise, what Im saying is to have a little slack in the push-rod. I would make it no more then .20 of an inch.
Good Luck, Jim
P.S. It could be that the flex-hose(s) are bad.

Bill Sullivan

Tom:

I have experienced the same sort of problem.  I found that the Master Cylinder kits have differences in the dimensions of the piston -- some pistons appear to fit, but actually are too long.  It is important that the tiny bleed port in the working part of the cylinder be exposed when the piston is retracted fully.  If not, the brakes tend to pump up slightly with each application until they are locked up.  Usually you can get the car home by opening a bleed screw somewhere to get the brakes off, but it will happen again unless that little port is clear and exposed every time the pedal is released.

As Jim mentioned, an improperly adjusted actuating rod can do the same thing by not letting the piston return to bottom when the brake is released.  But since you did not have this problem before, I think it is more likely your kit is not correct for your master cylinder.  These cylinders may be swapped around over time with old cars, so there is no guarantee you have what was originally supplied with the car.  Hopefully, you still have the old piston.  If adjusting the rod doesnt solve the problem, you need to take out the piston and compare it carefully with the old one.  You may need to get another kit or put that original piston back in there.

Good luck!

Bill.