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Grabbing Brakes

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Grem70 View Drop Down
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    Posted: Jun/07/2015 at 11:17pm
Hope someone can help/advice on my '70 Gremlin brake problem.(power brakes-shoes)
Brakes grab "violently". I bought this Grem about 8 years ago with this problem. Seller said previous owner had same problem.

Long story/short.....I think finally I found problem. Too much vacuum.
I put clamp on vacuum line leading to booster and when I tighten clamp, just right, to restrict vacuum, brakes work normally-no grab-99% improvement. I'm thinking booster is faulty.
My question is....can I get booster repaired? or where can I buy a new master cylinder/booster? Or any other solution?
I suspect other cars must have used same booster/cylinder combo. (For example I installed a '77 Plymouth Volare booster combo on my '59 Plymouth and it fits and works perfectly)
Any help appreciated.      
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Grem70 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/07/2015 at 11:48pm
Just did some checking and found O'Reillys and Autozone have Boosters for '70 Gremlins.

So anyway, if anybody has grabbing brakes, check out your vacuum.
I've been screwing around with this off and on for a loooong time, and a local stock car driver suggested clamping the vacuum line as a test and he was right.
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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jun/08/2015 at 7:30am
You can get a new check valve for the booster. That might be the whole problem. The check valve keeps the booster from leaking vacuum, but it also has a restriction in it to keep it from pulling too much. I'm surprised you don't have some idling problems if it has that little restriction on it though.

If it was converted to power brakes they may have a big car booster on it, or a dual diaphragm designed for power disc brakes. That's assuming you have drums on front. Could also be the wrong master cylinder, or the push-rod between booster and master is too long. The originals have an adjustment.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Jun/08/2015 at 8:29am
Drum brakes (power or manual) can also grab if someone accidentally switched the primary and secondary shoes (ask me how I know!)

That would be an easy-and easily overlooked-fix.
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62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384
70 AMX 360 4-speed (since 1981)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cornelius Rambler Quote  Post ReplyReply Direct Link To This Post Posted: Jun/15/2015 at 12:57am
I'm not sure if this helps or not, but does anyone know if the pedal is different between power brake and non-power brake AMC's in certain years?

The pedals in 1967-1973 Mustangs and Cougars, for example, were different lengths because the pivot point on the brake support was different to reduce the leverage on power brake cars in order to counteract the problem that I believe that you are describing.  

If the same thing was true with various AMC models and a PO added a booster without changing the pedal, that may account for the "grabbing."
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george w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote george w Quote  Post ReplyReply Direct Link To This Post Posted: Jun/15/2015 at 5:44am
X2 on the primary and secondary shoe reversal. Primary shoe is toward the front of the car and has the shorter lining. This applies to all 4 wheels.
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gwryder Quote  Post ReplyReply Direct Link To This Post Posted: Jun/15/2015 at 6:14am
Originally posted by ramblinrev ramblinrev wrote:

Drum brakes (power or manual) can also grab if someone accidentally switched the primary and secondary shoes (ask me how I know!)

That would be an easy-and easily overlooked-fix.



Sounds interesting. How?

John
John
70 AMX



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