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1948 Brake problem

Started by cadillac60, May 25, 2014, 09:10:28 AM

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cadillac60

The rear brakes were replaced as well as new wheel cylinders & a new master cylinder.  The car appeared to brake fine until I was on the highway for a period of time & I noticed the brake pedal was very high and hard.  After feeling a drag in the car I stopped & saw that the left rear wheel was extremely hot. Thinking that the adjustment was not correct the brake was backed off & the wheel could be turned with one hand. This didn't seem to change anything, I ended up getting a tow home. What would cause this to happen & what do I do to fix it?

Bruce W
Bruce Watson

Hilarius

Change the rear brake hose(s).
Hilmar Schneider #26898
1930-162, "353", 4D-SDN-7P
1940-7567, 2D-CCP-2/4P
1948-7519X, 4D-SDN-5P
1952-6019X, 4D-SDN-5P
1973 Mercedes 107R, 2D-CCP-2P
2015 Cadillac SRX, 4D-SDN-5P

35-709

#2
Same advice here.  As a matter of fact, change ALL of the rubber brake hoses if none have been changed in the last 10 years or so.  They deteriorate and swell on the inside allowing brake fluid to be pushed past under pressure but do not allow the brake fluid to flow back when the brake pedal is released.  Been there.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Steve Passmore

make sure you didn't over fill the master cylinder. If one brake is binding slightly it will overheat and expand the fluid locking the brakes on. Cylinder should be half full.
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

Alan Harris CLC#1513

I have had the experience of the pushrod on the MC being adjusted too long. The piston can't come back far enough to allow the MC to allow fluid to flow back into the reservoir.

If it seems to build up pressure with driving, I would suspect this, since you did change the MC.
It happened to me on a 1951, which is similar to your car. Getting the rod right is trial and error.

Bill Ingler #7799

Hi Bruce: I second to what Alan has said about the master cylinder pushrod being adjusted too long. I have a spare master cylinder so here is picture below of what Alan is talking about when the pushrod is not adjusted correctly. If the pushrod is not adjusted correctly and when you let up on the brake pedal, the pressure that was exerted by you pushing down on the brake pedal has to go someplace to release the pressure on the brake shoes so the pressure goes back and enters the master cylinder through the very small hole you see in the left of the picture. Now if the push rod is not adjusted correctly, then the release return hole is blocked and each time you push down on the brakes, the pressure builds up on the shoes and they ride harder, then you get a locked up hot brake. I have been on several CCCA CARavans  where on the first day out, someone gets the brakes locked up because of improper adjustment of the master. It is amazing how many people do not test their cars out with a test run before going on say a 1000 mile tour.   Bill

Jon S

I also concur with Alan and Bill. I had the same problem and the push rod was adjusted too long. A simple fix!
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

walt chomosh #23510

OK guys,
  I've had BOTH MC rod adjusted too long (insufficient play) PLUS rubber brake hoses (at different times) cause brakes to drag,expand,then lock up! .....walt...tulsa,ok

cadillac60

Thank everyone for their input--one more question  does any one know the recommended  rod adjustment measurement on the Master Cylinder for the 48 Caddy?

Bruce W
Bruce Watson

Steve Passmore

Its usually about 1/4" - 1/2" of pedal movement before you see any movement of the master cylinder rod.
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

cadillac60

Bill Ingler,

Thank you for the info and photo of the Master cylinder.  The picture shows a larger hole on the right & a small hole on the left, which hole is the one that would block the return & possibly cause the problem?

Bruce W
Bruce Watson