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Rebuilding the Brake System!!! |
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Red20
AMC Addicted Joined: Jan/29/2013 Location: Oceanside CA Status: Offline Points: 1556 |
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Posted: Nov/02/2014 at 2:23am |
I'm working on a '69 Javelin that sat for over 20 years. It's a 4 wheel drum car, and I'm planning to use Scarebird's front disc kit. I'm planning to rebuild all of the hard and flex lines and need to get a good grasp on what other parts I need. I'm no brake expert, but I'd like to think I get the basic concepts.
First, I'll be getting a new booster and disc/drum MC. I'm assuming that the MC will handle the residual pressure for the drums and I won't need a residual pressure valve. Can I use the pressure differential valve in the engine bay on the passenger side or do I need just a metering valve up front and an adjustable proportioning valve (or stock replacement) in the rear line? I'm considering buying a huge brake system builder's kit with a bazillion fittings that should cover everything and a ton of hard line. The flex lines I'll get stock replacements for. And the rear drums will have to get completely rebuild. What am I not thinking about here? |
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1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018
1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
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TX390AMX
AMC Addicted Joined: Dec/27/2012 Location: Indiana Status: Offline Points: 803 |
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Red,
Something to consider when switching to a power brake booster is the power booster mount bracket that mounts to the firewall. They are common to all early Javelins/AMX's and maybe Rebels, but are getting hard to find. They are also a bit of a pain to install as there are 2 studs on the firewall and 2 studs on the bracket which go thru the firewall. The nuts on the bracket studs are up above the brake pedal pivot. Easiest way I've found is to remove the instrument cluster and use a looong extension and a flex socket. American Parts Depot has pre-bent brake lines, easier than the generic ones, but your choice. Probably something else I'm forgetting, but look around for a power booster bracket before you get too deep into this brake project. Good luck,, Terry EDIT: The valve on the firewall, under the heater motor is not a proportioning valve on the early cars (pre 71), it is a brake pressure differential valve, used only to activate the dash light in the event of a brake pressure failure in the front or rear system. Go-Pac cars (with 4 piston front discs) used a delay valve located on the right rear frame rail, this was to delay the drum brake pressure til the discs were activated I think. Some folks have used aftermarket proportioning valves to allow for adjustment between the front/rear systems when installing aftermarket disc systems. Still probably something I'm forgetting, but you'll hopefully get other responses on here. Good luck, Terry Edited by TX390AMX - Nov/02/2014 at 3:18pm |
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Terry
68 AMX 390 4 Sp Rally Green 68 AMX 390 4 Sp Matador Red 68 AMX 390 4 Sp Calcutta Russet 56 Chevy Sedan Delivery 2016 Can AM Spyder 55 Chev pickup |
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Red20
AMC Addicted Joined: Jan/29/2013 Location: Oceanside CA Status: Offline Points: 1556 |
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Good advice, thanks. I wasn't aware of the differences in boosters. I was just gonna get a stock replacement and throw a disc/drum MC on it.
I'm tracking on the brake pressure differential valve. I think I can actually get a combination valve that will take the lines right out of the MC and function as an adjustable proportioning valve, front disc metering valve, brake warning switch and residual pressure valve for the rear drums. That would simplify things assuming it works as advertised. |
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1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018
1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Online Points: 19610 |
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Get the common GM combination valve and run it, would simplify things. You may need to change the wiring connector that goes to the pressure switch, but that's all. All the hot rod shops sell the GM combo valve, but you can order on from MPbrakes.com. Order for a street rod, if you tell them it's for an AMC they will tell you they don't carry parts for an AMC. It's a legal issue... street rod implies you are assuming liability as it's a custom build. They used to have a lot of brake tech info on their site, but it has bee redesigned and all that is gone. Best primer on brakes I could find on short notice is http://www.how-to-build-hotrods.com/brake-system.html. Explains everything simply!
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Frank Swygert
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Red20
AMC Addicted Joined: Jan/29/2013 Location: Oceanside CA Status: Offline Points: 1556 |
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I do like the combination valve idea. As I'm no brake man, I have a few questions hopefully someone will be able to answer.
Does the AMC disc/drum MC have a residual pressure valve built in for the rear drums or should I put one in the rear line? Will a GM combination valve for a similar weight car proportion the line pressure for the front and rear well or should I be thinking about an adjustable prop valve as well? Wouldn't matter if the rears are too soft, I guess. Finally, does anyone have any experience with this Wilwood adjustable combination valve. http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-11179 I can't tell if it functions as just a fluid path to the front and rear with proportioning for the rear or if it does metering for the front as well to prevent nosedive. You can run a single out for the front or both left and right straight out of the valve. |
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1969 Javelin SST "Screamin' Banana" - Totaled Feb 2018
1973 Hornet Sportabout X "yellajack" - 360/727/TracLoc DAILY DRIVER |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Online Points: 19610 |
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Most combo valves that have left and right front outlets have a metering valve -- at least the factory AMC models did. They were only used 4-5 years in the 70s. By the late 70s the metering portion was eliminated as it really didn't do much good. Pressure ramps up in the brake lines pretty fast -- the rears starting to drag a few 10ths of a second before the fronts really has little to no effect.
The distribution block doesn't have the residual pressure valve in it. The residual pressure valve is in the rear brake outlet of the master cylinder. It won't hurt if you have two though. So if the Wilwood combo valve has one it's fine. The combo will hold pressure between it and the rear wheel cylinder, the MC between it and the combo. I don't know of any combo valves that have the residual pressure valves in them, but newer cars might. The only time you don't want the residual pressure valve is with disc brakes -- they don't need it. Only drum brakes need the RPV to hold enough pressure to keep the wheel cylinder seals from leaking -- it's the way the seals are designed. |
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Frank Swygert
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Online Points: 5787 |
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Does the GM combo valve have the same bolt spacing as the AMC one, thinking of using one as I am doing a front drum to front disc conversion on a 71 Javelin and don't have the AMC one, would be nice if it used the same mounting holes.
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pit crew
Supporter of TheAMCForum Joined: Jul/08/2007 Location: delete Status: Offline Points: 5341 |
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Don't know if this will help but Summit Racing sells a combo that will bolt in the same place as the cast iron KH combo valve that AMC used.
http://www.summitracing.com/parts/clp-pv-2/overview/ |
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73 Hornet - 401EFI - THM400 - Twin Grip 20 |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Online Points: 5787 |
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That's the one I was looking at, just wanted to know if it would use the factory AMC mounting holes.
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