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All 4 breaks seize up?!?

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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: Sep/11/2014 at 6:29am
Silicone fluid won't mess up seals. It will hold a bit of air and feel slightly spongy though, and it will expand more with heat. I ran it for a while, but the last time I accidentally put regular fluid in and had to flush the system I quit. No advantages unless you're storing a car for a long time as it doesn't draw/hold moisture like regular brake fluid. If you mix the two the brake fluid gells! The only way to fix it is to flush the system with alcohol. I've used rubbing alcohol both times, but purer denatured alcohol is probably better. If you have used silicone and drained it and replaced with regular, or the other way around, and put the other in without flushing, then there are probably plugs of gelled fluid in the lines. Flush with alcohol and re-fill. Synthetic fluid should be compatible with regular fluid, may gell if added to silicone.

I have had a problem with silicone and heat. Not in a car, but in a motorcycle. The exposed front calipers (black painted) would get hot enough in the summer to cause the silicone fluid to expand and lock the brakes. The rear MC had silicone also, but it and the rear caliper were shaded by the bike and didn't lock, just the front. Had to pop the bleeders to move the bike in the late afternoon! Those don't use much volume to apply brakes though. F1 cars used silicone when it first came out. They had brake dragging issues due to heat as well, but they are moving at 100-200 mph and braking hard constantly.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70javluvr Quote  Post ReplyReply Direct Link To This Post Posted: Sep/28/2014 at 1:04pm
Loosened off master cylinder and breaks loosened right off so what's the next step replacing booster or adjusting rod?
Adjusted the push rod and the booster did not look good.  Should the rod be able to easily be pulled out of the booster as mine just slides right out.  I adjusted the rod in a bit but thew breaks still seized up.


Edited by 70javluvr - Sep/28/2014 at 1:57pm
70 Javelin Donohue Tribute car Sonic Silver/Shadow Mask/360/Custom Interior
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Sep/28/2014 at 2:15pm
I would say theres a problem with the pushrod being too long. and flush the old brake fluid out. leaving the lid off for 3 days is a no no....
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69 ambassador 390 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Sep/28/2014 at 2:49pm
The booster brackets/bell crank assembly almost always are frozen and need a rebuild. Every one of the cars we have done that I have been involved with in the last 3 years had this issue. Including mine and even all the southwestern cars. I would say you need to address this issue. it's a pain to fix but not complicated. You would not believe the difference when the repair is completed. Someone is also selling the pushrod gauges here on the forum. A proper push rod setting and a rebuilding of the bracket/bell crank will fix you rite up. Contact Dan Curtis at AZ AMC Restorations about having me do your rebuild on the brackets if you want.
Steve Brown

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69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special



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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: Sep/29/2014 at 12:00pm
Make sure the linkage all works well first. As mentioned, if that's stiff or frozen it will cause the issue you're having. There is a bracket holding the booster away from the firewall. The bracket is there to lift the booster a few inches up so it clears the engine (used until 75 or so). There are three pivot points -- where the rod connects to the booster, then a pivot shaft, then where it connects to the brake pedal. The shaft can get stiff. Take the bracket off and make sure that's free, if not some penetrating oil and working it should free it up, but pulling the shaft and cleaning thoroughly would be a better, longer lasting fix.

If that's free then the pushrod needs adjusting. Should have a threaded end, so just turn it in a little. In this case a little makes a lot of difference! Try a couple turns, and if it works make a few good hard stops. If the pedal goes down a little further than you like make it half the distance longer and see what happens. The 70 TSM says the pushrod is 0.995-1.000" on the 7.75" and 9.50" single diaphragm boosters, 1.185"-1.200" on the 7.75" double diaphragm booster. Measure from the MC mounting surface up. AMC had a gauge card but you can make one. Cut a 1" wide by the proper height "notch" in a piece of cardboard about 3" wide x 2" tall, adjust rod to notch.
Frank Swygert
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