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Manual drums to power disc |
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turdferguson
Supporter of TheAMCForum Joined: Sep/28/2021 Location: Lombard, IL Status: Offline Points: 90 |
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Posted: Oct/23/2021 at 9:47am |
So before I begin, I know there's multiple posts that cover bits of this topic but I have a couple different questions so bear with me and links to THE thread that covers either of my questions are much appreciated!
Upgrading my manual drum '68 AMX to power disc ('77 gremlin caliper set-up). 1. In 68-69, were all disc brake cars equipped with a brake booster? I'm looking at the APD site and there's only one option for brake lines with disc brakes while the drum lines have both power and manual. So I just need the disc brake set? 2. I have donor parts from a disc brake '68 Javelin (automatic trans): Complete pedal assembly, booster, master cylinder. Do I need to use the interior pedal assembly? My AMX has a manual trans so the giant POWER BRAKE pedal isn't going to work but do I need to use parts of the interior assembly? All of it but the pedal? Just the bellcrank? I've read somewhere on here that AMC was "all over the place" on this topic so all help and first hand experience is greatly appreciated! Thanks Guys, Turd
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ramblinrev
Moderator Group Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11545 |
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All '68-70 AMXs equipped with disc brakes were Power Disc Brakes. IF you are using a system from a '77 Gremlin, the lines for a '68-70 AMX will likely not match up, at least without some adapters. I believe you can use the actual pedal in your car, but I don't know what you'll need in terms of lever/rod to match up properly with a '77 booster/master.
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74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
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turdferguson
Supporter of TheAMCForum Joined: Sep/28/2021 Location: Lombard, IL Status: Offline Points: 90 |
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Ok, I can order the disc brake lines from APD then.
The calipers are already sorted. I've read somewhere that the lever mechanism ratio in the pedal assembly is different going from manual to disc but there didn't seem to be a definitive answer. |
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BU1
AMC Addicted Joined: Aug/11/2016 Location: MN Status: Offline Points: 2019 |
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Don't forget to add a proportioning valve to the rear brake line.
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AMO #2726
#1 1968 AMX Rally Green 343 Z code 4spd since 1975 #02642 #2 1968 AMX Rally Green 290 N code 4spd since 2019 #02959 |
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TX390AMX
AMC Addicted Joined: Dec/27/2012 Location: Indiana Status: Offline Points: 803 |
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As BU1 said, don't forget the delay valve (or hold-off valve) for the rear brakes. On the AMX/Javelins, it is located on the right rear frame rail, just ahead of where the frame rail kicks up over the rear axle. I did the same disc conversion on a non Go-Pak drum brake 68 AMX, used a Matador single piston setup on front. I found a replacement delay or hold-off valve for a late 60's Camaro to be the same as the ones on my other GoPak AMX's. I think it came from The Right Stuff, but a Google search should find it. Ask for a disc brake hold-off valve, it actually holds off the application of pressure to the rear brakes until the fronts have applied. Keeps the rear end from getting squirrely until the disc brakes bite. The Camaro valve is identical to the one AMC used, down to the tab on the mounting bracket that fits in the hole next to the tapped hole for the mount bolt. You will also need a disc brake rear line set. With the addition of the hold-off valve, the plumbing is different than for a drum brake car. The disc brake line set is 2 pieces, the 2nd short piece goes from the hold-off valve to the hard point where the flex line attaches to the rear axle. While you're at it, now is a good time to clean/rebuild the brake distribution valve located on the firewall under the heater motor. It is not a proportioning valve, it just senses any imbalance between the front/rear brake systems and if working properly, will illuminate a red dash light if you have a serious loss of pressure on either system. Of course, if you have a serious loss of front or rear brake pressure, you'll probably know it before the red light alerts you to the problem, but hey, it was a Federal Safety Standard requirement. Good luck with the disc conversion, it's worth the effort. Edit: Just re-read your post. If you have a 68 Javelin donor, the hold-off valve should be on the right rear frame rail. The only difference between the Jav and the AMX plumbing is the length of the main rear brake line, all else is the same. Terry
Edited by TX390AMX - Oct/24/2021 at 8:35pm |
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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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turdferguson
Supporter of TheAMCForum Joined: Sep/28/2021 Location: Lombard, IL Status: Offline Points: 90 |
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I wasn’t aware of the hold off valve. Found one for 67-69 Camaro I’m guessing that’s the one you found as well. Thanks guys!
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turdferguson
Supporter of TheAMCForum Joined: Sep/28/2021 Location: Lombard, IL Status: Offline Points: 90 |
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I had the Javelin but it’s long gone now. Got everything I thought I needed off of it and just before I had it towed away someone pulls into my driveway and offered me what I paid for it.
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turdferguson
Supporter of TheAMCForum Joined: Sep/28/2021 Location: Lombard, IL Status: Offline Points: 90 |
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Ok Now I have another question. I have a rear disc brake conversion kit that I’ll be installing once I get the front/power discs sorted. Will I still need the hold off valve or just the proportioning valve once I convert the rears?
The rear kit came with the proportioning valve.
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4473 |
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No hold off valve is needed if disc brakes are used all around.
Yes, you will need a proportioning valve, as the brake lines from the MC have to be plumbed in together, front and rear. Some install it in the "traditional spot," p/s of the firewall ('68-'70). Others put it near the MC. Whichever company you're using for the disc brakes should be able to advise you on which pv to purchase.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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1977 Gremlins came standard with front disk brakes and they were manual, not power assisted. Power assist was an option. So, if you are using 1977 Gremlin brakes a power booster is not mandatory. I drove a 1976 Hornet with manual disks compared to my 1977 Hornet with power disks and they both drove fine.
There was also no combination valve or proportioning valve. Just a differential pressure switch for the warning light. It is possible to build a good functioning disk/drum braking system without a proportioning valve. You just size the wheel cylinders accordingly to produce a good front to rear braking balance during hard braking. Your balance will be off during light braking though....it's all be towards the front with the back brakes doing little to nothing. But it works fine. It's what AMC did for several years and I've driven a lot of miles in those cars. |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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