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Brake light on, 74 AMX |
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MartyB 
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Joined: Apr/24/2018 Location: Plano, TX Status: Offline Points: 37 |
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 Topic: Brake light on, 74 AMXPosted: Oct/31/2018 at 6:21pm |
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First time I have ever had this happen...actually have had it happen when the parking brake on sensor locked up...but I have checked that and it is not the problem. I have front non-power disk and rear drum. Reading the TSM it says there is a pressure differential. I did not detect any difference in braking. Front hoses are fairly new and did not see any bulges or worn areas. Did see a bit of possible wetness around one of the rear wheel cylinders on the backing plate. Also removed the connector from the pressure valve and it was clean and shiny. Could the bit of wetness at the one rear cylinder cause the problem? Have not had time to remove the wheel and drum yet.
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george w
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Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Posted: Oct/31/2018 at 6:28pm |
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Have you checked the brake fluid level to see if there has been a fluid loss ? How about checking the switch/wire contact on the parking brake to make sure this isn't grounded causing the brake light to be on. This assumes that the parking brake and the brake pressure differential warning circuits use the same light.
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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MartyB
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Joined: Apr/24/2018 Location: Plano, TX Status: Offline Points: 37 |
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Posted: Oct/31/2018 at 6:33pm |
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Have not had a chance to check the bf level yet. Did check the park brake contact (even disconnected it) and the light stayed on.
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Oct/31/2018 at 6:39pm |
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Did you release the differential switch when b leading the brakes. There is a tool for keeping the differential switch in reset position.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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mstrcrftr
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Posted: Oct/31/2018 at 8:09pm |
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are you sure the parking brake is fully released?
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scott
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Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3500 |
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Posted: Nov/01/2018 at 2:53pm |
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Unplug the wire on the pressure differential valve & see if the brake light goes out. If it does go out, that tells you where to start looking for the problem.
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304-dude
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Posted: Nov/01/2018 at 4:54pm |
That is the best option, until verified light is still on. If it is, there is a short from pinched wire to the brake warning switch, sometimes it is in the instrument panel, when reinstalling a bulb and not checking the wiring before the assembly is put in place.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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MartyB
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Joined: Apr/24/2018 Location: Plano, TX Status: Offline Points: 37 |
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Posted: Nov/11/2018 at 9:48am |
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Thanks for all of the info/ideas...did not think the bit of wetness on the backing plate was substantial...checked the bf level and rear supply was completely empty...hence the pressure differential and the light, working as it should! Right rear cylinder was leaking, replaced both, did the proper bleed (w diff plunger pulled out) and all is back to normal!
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scott wrote: