Re: [AMC-list] Fw: large disc brake master cyclinder conversion help

[Frank Swygert <farna@xxxxxxx>]

Date: Tue, 6 Sep 2011 21:08:15 -0500
From: "Eddie Stakes"<eddiestakes@xxxxxxxxxxxxxxxxxxxx>
To:<baadassGremlins@xxxxxxxxxxxxxxx>,<amc-list@xxxxxxxxxxxx>
Cc:mdalton@xxxxxxxxxxxx
Subject: [AMC-list] Fw: large disc brake master cyclinder conversion
	help
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Eddie said you have a 76 Hornet disc setup to go on the American. That would be the master cylinder you need to use. The non-power disc master cylinder has a 1-1/16" bore. You would be fine using a 1" bore MC that the non-power and drum brake cars used though. The smaller bore will actually increase pressure to the brakes, but might be a little harder to push with the leg. I used a 1" bore MC on a couple non-power disc brake applications (61 and a 63 American, but with the smaller 2.6" piston Bendix calipers) with no problems. A 1" bore MC was stock on the 68 Americans, and most other AMCs and Ramblers. I don't think any came with a 15/16" MC (I checked the 68 TSM).

Armand had the best suggestion for plumbing the brakes. You can use new lines and run them like the Hornet. On dry pavement the brakes will work just fine without a proportioning device -- AMC didn't have one on late 70s/early 80s Concords and Spirits. If you find you need one or are more comfortable running one you have two choices:

1) plumb the brakes up to the stock 68 junction/brake light switch block. Add a late 60s Camaro/Javelin fixed proportioning valve (available from Inline Tube -- they call it a pressure limiter, and have it listed for the Javelin under Chrysler, IIRC) in the rear brake line. Easiest to add between the rubber line and axle end of the rear brake line. Just mount the valve on the "frame" rail and bend the original line over to the inlet, run a new length of line from the outlet to the bracket where the original line was mounted. I wouldn't try to cut the original line and put on a flare nut, just loop it over and make sure it's held against the body. The loop won't hurt a thing.

2) plumb the Hornet valve up just the way it came out of the Hornet and drop the original block. If you want to keep the original block for some reason, maybe to keep the original pressure switch, move it higher up on the firewall or fender well and run it between the MC and new combination valve. Get new lines from the auto parts store to go between the block and combo valve and block and MC. There were two different combo valves used depending on year and model. One has a metering valve one does not. The one with metering has two outlets for the front brakes, the one without has a T in the line between the MC and combo valve for the left front brake and the right front brake is connected to the combo valve front brake outlet. Either is fine. The generic GM replacement (also found on 90s Jeep XJ Cherokees) doesn't have the metering function.

No balancing device is needed as long as the brakes are sized properly. The problem here is you are increasing front braking, which takes some of the load off the rear brakes. That means the rears could lock up in a hard stop (especially a panic stop) even on dry pavement, and probably will on wet/icy pavement or other slippery conditions. I always check on a dirt road as I have plenty of those around. A wet asphalt parking lot (not just damp, but not in standing water either) is next best. Get up to 40-45 and brake normally. Should be no signs of locking. Do the same and brake real hard. The rears should just start to lock when you brake as hard as you can. That's okay -- it's to be expected. But you should be able to brake hard (but not quite a panic stop) without the rears locking, or with them just starting to lock. The Camaro/Javelin valve will usually work just fine, but you might want to get an adjustable valve and tweak it to your car and driving style. That's the bes
t way.


 ----- Original Message -----
From: "michael dalton"mdalton@xxxxxxxxxxxx


Eddie as per are conversation earlier. what i an looking for is a   larger master
cylinder bore for my non power  disc brake conversion. the bore size on my master cylinder
is 15/16 , i an going to need  something larger like 11/4 to make this non power bendix
disc brakes  to work well. can anyone out there recommend a master cylinder unit that will
work  on my 1968 american    mike



--
Frank Swygert
Publisher, "American Motors Cars"
Magazine (AMC)
For all AMC enthusiasts
http://www.amc-mag.com
(free download available!)


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