FRONT BRAKE BACKING PLATES #  (with 12 "  brakes)

These parts are prone to fail, especially the return spring retainer (which is also a spring.., i call it "return spring retainer spring" or rsrs in this page). When it fails, the drum locks and you must go rearward to unlock.  I've a friend who had exactly the same problems and symptoms on his '59 Dodge Coronet. He spent many $$ in buying new parts to replace his already new parts w/o result... The only thing that cures the locking  was to put a pair of backing plates from a wrecked Dodge (but the backing plates were in good conditions).

See a message from G. Riehl to a member of the 300 list which had locking problem with one front drum of his 300C :

Mark;
Your problem is a simple one. The square "spring" ( = return spring retainer spring) inside the center plane is broken. That "spring" tends to apply pressure on the brake shoes from toe to heel. When the "spring" breaks, unequal pressure is applied to one of the shoes. One end of the shoe is then forced into the drum, generally the toe.
When that happens, the shoe is forced into the drum and acts like a wedge, locking the shoe into the drum. Then unlocking it requires to back the car up to release the shoe. Everything is fine until you apply the brakes again.
The solution to this is to get another centerplane from another car, like a New Yorker. N.Yers have the same centerplane as the 300. They must be from the designated front wheel only. The rears are different as they have only one cylinder. Most likely, $50 would make the fix. Why spend $500. for a disc brake conversion? Those brakes were the best in the industry at that time. It sounds like you had the correct and proper work done to the shoes and drums originally. But with just the broken "spring", why go overboard?
People that change to disc brakes are just not able to do a correct brake job on the old cars. All my cars (300s) have their original systems and they stop just fine at any speed.
Transistor ignition, radial tires, sterio radios, CD players, disc brakes, changing rear axle housings, modified engines, later model transmissions, wire wheels, fender skirts, all of this takes away from the originallity of the car. Just look at the Model A Fords. I have never seen one that came from the factory that is still original. Every accessery that could have been after market are on them. Even Pinto engines! I am a firm believer of originallity. These 300s deserve the best we can do to keep them as they were intended to be. They are a part of automotive history.
George Riehl

2 pics of the '57 Imperial "after" brake backing plate. Note position of the "return spring retainer spring" (rsrs) on pic # 2 at bottom which can bring you some troubles if weaken of broken !

click to enlarge click to enlarge

  

 

1957

1958-59

 

Serial  up to  and including

Backing plate # 
  up to 

Backing plate #  after 

Backing plate #

PLYMOUTH  (1)

 

1635506-7

1635506-7

1676050-1

DODGE

?

1633088-9 (2)

1676050-1 (2)

1676050-1

DESOTO

S25 : 55364191 frt rt
S25 : 55364354 frt lt

S26 : 50418226 frt rt
S26: 50418376 frt lt

1633088-9 (3)

1676050-1 (3)

1676050-1

CHRYSLER

C75-1 : W57 28028
C75-2 : L57 17049
C76 :  N57 18340

1633088-9

1676050-1

1676050-1

Chrysler wagon

? (same as above ?)

1633090-1

1676050-1

1676050-1

300

?

1633088-9

1676052-3

1676052-3

IMPERIAL

C57 17931

1633090-1

1676052-3

1676052-3

(1) : according to part lists, Plymouth models couldn't have 12" drums in 1957. Not sure for 58-59

(2) : to be verified (some sources indicate same # as Plymouth). Also for S27 Firesweep Desoto.

(3) : except S27 (Firesweep)

Sources:

57 Mopar Passenger Car Parts List (canadian issue)

Interchange 52-59 Chrysler & Imperial sheets

Backing plate of my '57 Imperial (early model so 1633090-1). Do you see differences with the "after" or late model (1676052-3) of the 2 pics above ? Seems that the spacer where the rsrs is hooked looks different ? I haven't the two plates on my desk, one is on the car and the drum isn't removed ! See reply from G. Riehl below the pic.
Other pics at this page.

Another reply from G. Riehl:

 I do have "spare" center planes for my '57 300C. I did notice that the "early" ones had a spring that was more "rectangular" in cross section than the more "square" spring in the later type. I looked at a '57 Saratoga plate and it has the "rectangular" cross section. I think that the "early" spring was prone to breakage and it was an engineering "fix" to go to the "square" spring cross section. Other than that, both plates look identical in construction. It is strange that the parts books do not list the "fixed" spring, only for the New Yorkers. Could be that Chrysler put the later spring on the 300s, but then we know how that is not a constant thing with the people on the line installing the brakes. And who knows, it could have been a "running" installation on the line. Chrysler did not always keep precise records.
In 1954 I bought a brand new '54 New Yorker Special DeLux "Golden Falcon" 2 dr. H.T. that had cronic brake problems. A factory rep. came to the dealership. Found that the brake shoes and drums were "wrong" for the car (?). Got all new shoes, drums, seals, bearing, backing plates,etc. Brakes worked fine. Car only had 450 miles on it. The dealership re-adjusted the brakes about 5 times before the "fix" was made. Never adjusted the brakes for another 54,000 miles. Never got a good explination what was wrong with the original brakes.
Your list looks correct according to my books.

 

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