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Old 10-12-2008, 02:40 PM
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Front disc brake conversion

I'm doing a front disc brake conversion on a 1958 Rambler American. The stock brakes are manual 4 wheel drum. The donor discs are from a 1977 AMC Hornet. I want to keep my OEM under floor single bowl master cylinder. It does have the primary and secondary piston cups. This way I won't need to fabricate a master cylinder and brackets or screw with the brake pedal mount or rod. Will this setup work if I add a proportioning valve? Your feedback is appreciated.

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Old 10-13-2008, 01:20 AM
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Does the master cylinder you have have 2 outlets?

Later, mikey
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Old 10-13-2008, 08:55 AM
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It just has a large single port out the back.
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Old 10-13-2008, 09:13 AM
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disc coonversion

You should check some of the brake conversion companies ...they have excellint information. for a disc system to work best (or mabe at all ) you need a master cylinder with enough capacity, disc need more fluid to operate, also you need a proportionation valve I woukd check out using the master cyl and valve from the donor car, firewall mounted pedal system, and self adjusting rear drums. and see if you can do a total system swap.
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Old 10-13-2008, 09:30 AM
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Quote:
Originally Posted by Sly's 53 Suburban
It just has a large single port out the back.
I've seen the single piston master cylinders work with small single piston disc brake calipers, (VW type II), on the front, and drums on the back, but I don't think the bigger AMC calipers will work...You won't have enough fluid delivery.

Is the pedal pivot assembly part of the master cylinder casting on that Rambler?

Can an adapter be made to put a modern dual master cylinder on ? There are companies that sell them as well. What is the mounting pattern on your current master?

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Old 10-13-2008, 11:57 AM
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I did a google search for the master cylinder that is installed in the 58.
It looks like it would be an easy swap to a dual master cylinder, the pedal would not need to be changed, the pushrod is easily modified,(if you even needed to), and if you used a 1" , 15/16" or possibly a 7/8" bore master cylinder, you wouldn't need to adapt a power brake booster. The bore size you will need depends on your pedal ratio, and the piston sizes in the calipers and rear wheel cylinders.

You would need to do some plumbing, and a disc brake combination valve or a adjustable proportioning valve for the rear, and a metering valve for the front would be a good way to make that system work really well. Some inline residual pressure valves are also advisable.

I'd be inclined to put an adjustable prop valve in the system even if you used a combination valve, as the front/rear bias adjustment in a universal type combination valve may be off slightly from what your car's weight distribution might need.

Some more info would help pin down your requirements.

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Old 10-13-2008, 08:56 PM
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I could use a master cylinder similar to the donor cylinder and fabricate a bracket to mount it under the floor. It's a little more difficult, but not too much more difficult. It seems the consensus for safety is go with the dual chamber master cylinder. I think I'll look for a master similar to the donor except go with a remote reservoir to eliminate the hole in the driver side floor. I'll post back with results and pictures. Thanks for all the input.
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Old 10-19-2008, 03:48 PM
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The 77 Hornet used 2.6" piston calipers, so capacity isn't a big problem. What you will need is a 2 psi residual pressure valve for the front brakes since the master cylinder is under the floor (lower than the calipers). See the tech pages at www.mpbrakes.com.

I agree -- adapt the dual outlet master cylinder. The old one is more likely to fail due to age also.

The onl;y problem with 77-78 Hornet/Gremlin brakes is the rotor. They use a big bearing spindle and rotor that can be hard to find and relatively expensive ($100 or more last time I checked). The caliper is a standard Bendix unit. 79-83 rotors are much cheaper and easier to find. They use a smaller bearing spindle. When swapping any AMC disc brakes you need the spindle to go with the rotors. 79-81 used a Bendix caliper, 82-83 used a GM.

www.scarebird.com has a new kit to convert AMCs to disc brakes using readily available components, they just make a bracket and a machined seal adapter, and send a parts list. They have it labeled as for 68-69 Javelin/AMX/Rebel, but it will work with others. The small six cylinder cars need additional spacers behind the spindle to properly center the caliper, but Scarebird is working on using a different rotor (less offset) to eliminate using spacers. Spacers aren't a problem, you just have to figure out how thick they need to be.
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Old 10-20-2008, 06:24 PM
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Mikey, The cars are of equal weight and wheel base. I like what you have said about not needing a brake booster. I'll try to find a non power brake master that will fit easily in the stock location with only fabrication of the mounting bracket and rod modifications. Thanks
farna thanks for posting with the information. I received my parts from a 1979 AMC Hornet with the Bendix calipers. I have the backing plates, rotors including bearings with dust caps, calipers, proportioning valve and lines. I'll use the calipers for cores and buy new. Purchase new bearings, hoses and lines. I researched the master cylinder and will drill a hole between the two chambers as well as through the side case for a remote reservoir connection. If my remote reservoir is mounted above the calipers I understand the 2 lb. residual valve is not necessary. Does this all sound appropriate to my application?

I really appreciate the feedback from you guys. As I bounce ideas around on Hotrodders things seem to come together much smoother.
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