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'73 Javelin Brakes

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CoffinMaster View Drop Down
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    Posted: Nov/08/2018 at 11:47pm
So, after a lot of work, I've put everything I needed to on the car, and now the brakes hardly work. I bought the front disc brake conversion from American Parts Depot, and I put it all on and it can hold them well, but after a drive around the brakes barely slow down the car. Also, the bleeder screws on both calipers leak from the threads when I go to bleed the brakes, and I was unsure if there was a fix for that or just tough luck. I bought a power brake booster from autozone for a Javelin but it is single diaphragm and meant for all drum, and I have a new Master Cylinder that is power front disc rear drum, and this combination does not work from what I've seen. I've bench bled the master, probably around 100 pumps to make sure there's no leaks and no bubbles, and once I reinstalled it into the car and bled the system, after starting the car I noticed that the master was leaking between it and the booster. My most recent test was with no vacuum to the booster, and the brakes were very poor and still leaked a bit I believe. In addition to this, my rear brakes are very poor. It's a v8 Javelin so it should have the v8 brakes, but when I got it, it had the v6 brakes on the back, but with 10x2 1/2 drums and shoes. I replaced the wheel studs and they were off of a 68 roadrunner, which made me think the rear brakes were some combination of roadrunner and javelin parts. I ended up putting on 68 roadrunner wheel cylinders which fit, with all the other hardware being Javelin parts, but then the brake shoes stopped the old brake drums from fitting so I had to go up to 11 inch drums just to make it fit. Now the rear brakes do nothing, so I'll have to use different drums, but currently if the brakes are depressed or the parking brake is on, only the primary shoe moves, and it seems like it moves to far and gets stuck so I can hear it rubbing on the inside of the drum. My brake lines for the rear are lined up to fit the v6 wheel cylinders but the car has a 401, so I'll need to bend the lines in the back to fit I assume. Is there anyone who can point me to a fix for any of these problems? Bleeder screws with leaking threads, leaking master cylinder in the car but not out of the car, incorrect parts and lines while the correct parts don't fit, sticking primary shoes on both sides, and yet still horrible braking, all of these are just ruining me and I don't have the time or money to buy all new parts a 2nd time and spend a day overhauling it, as I get maybe 2 hours a day at most. 

P.S. 68 Roadrunner Wheel studs due to 68 roadrunner 8 3/4" differential.
1973 AMC Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Nov/09/2018 at 9:10pm
Well to start you cannot have leaks. A small leak will produce very poor braking. Trying new bleed valves would be my first thoughts.
For a booster you need vacuum - have to find out why you have no vacuum to the booster. If the engine runs then it must produce some vacuum, so start at the engine manifold with the booster connection plugged, fix any leaks and then move up to the booster itself.
The rear drums - unless you really know your parts, mix and match does not work well. I'd start over with one system right through, Chrysler on the 8-3/4 differential would be the likely way to go. I doubt anybody can troubleshoot a mix match like this on a forum unless they have had experience with the exact combination you have.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Nov/09/2018 at 9:23pm
Back when I installed a 69 Coronet rear in my 73 Javelin, I swapped my original rear drum line over to the Dodge rear, installed the E-brake cable, and bled the rears. It had bigger brakes than the stock v8 drums of the AMC20.

A bit touchy if hard braking.

Sounds like you have more than one issue going on with the back. I'd get a manual on the dodge brakes and redo the installation of the hardware to make sure things are proper.

As for the fronts not grabbing, it's possible you need new front hoses, and a master cylinder. Just I would not trust anything over 20 years. Had failures with brake hoses after 30, might as well do it right from the start than to deal with it later.

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote amxess Quote  Post ReplyReply Direct Link To This Post Posted: Nov/09/2018 at 9:35pm
Sounds like a few problems. Master cylinder may be faulty if leaking between it and booster (I only buy them from NAPA). Also, did you change the check valve on the booster, cause they do go bad and brakes will not work with a faulty one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CoffinMaster Quote  Post ReplyReply Direct Link To This Post Posted: Nov/10/2018 at 3:31am
I do have vacuum going to the booster, I should have specified, I had brake fluid leaking, no vacuum leak. I'll see if I can find new bleeder screws for the calipers, as far as I know they don't leak when they are tightened but they leak when I try to bleed from them so it makes bleeding a bit iffy. As for the mix and match, I'd like to keep the rear brakes from the Javelin, as most of the parts I have are for the Javelin, but I may need to get a new backing plate since the v8 javelin wheel cylinders wouldn't fit. I have a new master cylinder, maybe a month old, and new front brake lines, metal lines and rubber, and none of them leak so far. The check valve on the booster is fine as it is new, I had no problems with the booster other than not being the right one and that for some reason it would cause my master cylinder to leak when the car was running. I've never heard of a master cylinder that leaks only when the car is running, as when I bench bled it it had no leaks from the piston and when I bleed the system in the car it doesn't leak, but as soon as the car is on and I test drive it, whether the booster is connected and working or disconnected, it would leak. If anyone knows where to get Javelin backing plates, or has a picture of their design so I could see if mine are comparable.

Edited by CoffinMaster - Nov/10/2018 at 3:57am
1973 AMC Javelin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Nov/10/2018 at 5:49am
Originally posted by CoffinMaster CoffinMaster wrote:




I do have vacuum going to the booster, I should have specified, I had brake fluid leaking, no vacuum leak. I'll see if I can find new bleeder screws for the calipers, as far as I know they don't leak when they are tightened but they leak when I try to bleed from them so it makes bleeding a bit iffy. As for the mix and match, I'd like to keep the rear brakes from the Javelin, as most of the parts I have are for the Javelin, but I may need to get a new backing plate since the v8 javelin wheel cylinders wouldn't fit. I have a new master cylinder, maybe a month old, and new front brake lines, metal lines and rubber, and none of them leak so far. The check valve on the booster is fine as it is new, I had no problems with the booster other than not being the right one and that for some reason it would cause my master cylinder to leak when the car was running. I've never heard of a master cylinder that leaks only when the car is running, as when I bench bled it it had no leaks from the piston and when I bleed the system in the car it doesn't leak, but as soon as the car is on and I test drive it, whether the booster is connected and working or disconnected, it would leak. If anyone knows where to get Javelin backing plates, or has a picture of their design so I could see if mine are comparable.


Put a wanted for Wagner big body rear drum backing plates. There is Bendix backing plates, but they are for early 71 and prior cars.

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote CoffinMaster Quote  Post ReplyReply Direct Link To This Post Posted: Nov/10/2018 at 5:03pm
So I just spent some time trying to identify my backing plates since I thought those are a good place to start to make sure I'm fitting the right parts together, and I now see that they are Mopar backing plates. I still have yet to find what size they are and what parts but any progress is good for me. The weirdest part is that from what I've seen, the Mopar rear brake springs and self adjusting parts look completely different than AMC or Ford parts, but all the parts on the car when I got it were AMC, so the previous owner did have some weird mix of AMC and Mopar parts on the rear. I'm hoping if I get the correct shoes and drums that might remedy the situation at least for the rear.

Edited by CoffinMaster - Nov/10/2018 at 5:07pm
1973 AMC Javelin
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