disc brake conversion
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Suspension, Steering, Brakes & Wheels
Forum Description: What makes it stop, turn, and smooths the ride
URL: https://theamcforum.com/forum/forum_posts.asp?TID=42959
Printed Date: Apr/16/2024 at 11:39am
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: disc brake conversion
Posted By: cc gremlin
Subject: disc brake conversion
Date Posted: Sep/03/2012 at 6:01pm
| converting my 73 gremmy to discs which I already have installed however I am a little clueless on what master cylinder to use I do know 3 were offered on that car but Im sort of looking for a part # also would a wagoneer or jeep master bolt up (originaly the car had drum brakes with power booster) Thank you In advance Chris |
Replies:
Posted By: ramblinrev
Date Posted: Sep/03/2012 at 8:06pm
|
You could probably use the original Power drum brake master and booster, if you remove the residual check valve from the port going to the front brakes. '73 Gremlins also could be optioned with manual drum brakes. You can find a new version of that MC. Someone else can inform you on the whether a Jeep one will interchange. ------------- 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) |
Posted By: jcisworthy
Date Posted: Sep/04/2012 at 5:24am
| When I convert my cars I use a disc brake master cylinder master for the vehicle. I think the fluid capacity is larger than the drum brake master but not positive. It was always a bolt up change over. I actually have a GM master on my 68 Javelin right now which is a bolt up with the right rod from the brake pedal to the back of the master and it has an 1 1/8" piston which makes for less pedal effort to stop with the manual disc brakes I have compared to the manual disc AMC set up. Lines come out on the opposite of master so some plumbing is necessary but it works well. |
Posted By: FuzzFace2
Date Posted: Sep/04/2012 at 8:18am
|
Thing is the power option I dont know if there was a power disc option but if there was you should be able to get that master and bolt it up to the booster.
Most of the disc options were non-power and I dont know if that master would bolt up to the booster or not?
As said you could just pull the valve out of the drum master and use it as said above.
Dave ---- ------------- TSM = Technical Service Manual 75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
Posted By: amx39068
Date Posted: Sep/04/2012 at 8:57am
|
Do not use your drum master. By nature of their design, disc brakes require more fluid to operate, especially the large single piston discs. Any late model Jav or Hornet master should work. Likewise, the disc booster has a dual diaghram whereas the drum is a single diaghram due to the pedal effort being greater with discs over drums. A single diaphram booster can be used can be use discs but will result in a harder pedal. Any disc brake booster from an American/Rogue or Hornet will work on your car. It is the same booster used on the SC/Ramblers as well. ------------- Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development 
|
Posted By: billd
Date Posted: Sep/04/2012 at 9:39am
|
While I'd agree with Dan, capacity.... I've also seen factory disk with a master that is 50/50 rather than what's closer to 60/40 for disk. The large piston does indeed take more fluid - but one argument for using a 50/50 drum (of the correct PISTON size) is that once you start to push the pedal, the reservoir is closed off from the system, so all you get is what's in the cylinder bore being pushed by the piston. In other words, once the foot starts to push the pedal, the master reservoir size no longer matters. However, if for some reason the piston was retracted just a tad more, say a rotor that's not true, out of parallel, etc. or a loose wheel bearing, then you would want the extra reserve as the second application of the brakes is going to pull more fluid in, fluid you may not have if it's a bit low already. It's a safety factor as well as filling the need for extra fluid. I would also add it's partially dependent on the size of the master cylinder as well - some simply hold more fluid. I've seen some drum brake masters I'd never use on disk as the reservoir is simply too small. In ANY case, no matter what, make sure there is no residual pressure check valve in the outlet you use for the disk. A disk master won't have it - but if you go cheap and get a reman, DO check. Those fools slap parts together, and don't know or care about application during assembly, and in some cases, things are boxed or marked incorrectly, or are a "will-fit" application intended for 4 wheel drum or disk/drum applications. Because I'm a real stinker on safety, including YOUR safety, my preference is to use the correct master intended for disk brakes and be done with it. No guessing; no "gee, I wonder why the brakes didn't work when I REALLY needed them on that rough curve back there" as you slam into the side of a soccer mom's van full of kids.  -------------  http://theamcpages.com" rel="nofollow - http://theamcpages.com http://antique-engines.com" rel="nofollow - http://antique-engines.com |
Posted By: cc gremlin
Date Posted: Sep/05/2012 at 6:51pm
| Thanks to all for your opinions I have to dig more into this I should have also added the fact Im sizing up a mustang rear end with discs maybe adapting the whole ford assembly(master and boost ) might be an option or of course there is always the boat anchor and rope |
Posted By: farna
Date Posted: Sep/05/2012 at 8:40pm
|
Dan is partially correct. The small 2.6" piston Bendix and Delco calipers, as well as the 2.75" piston Kelsey-Hayes calipers, can be used with a drum master cylinder once the residual pressure valve has been removed from the front brake outlet. The 3.1" piston Bendix calipers (only used 75-78 -- 75-76 on all, 77-78 Matador only) need a larger bore MC... 1.125" IIRC. Drums and the smaller calipers all use a 1" bore MC with approximately the same stroke. I've used the drum MC with the small calipers for many years on several cars with stellar performance. I adapted a Ford Ranger booster an MC to my 63 Classic. The Ranger MC is a disc/drum MC but I have four wheel discs. My rear discs are 86 Jaguar dual piston (one on each side of the rotor). The Ranger 8" dual diaphragm booster doesn't have quite the power of a typical 60s/70s American disc brake booster, but a little more than the single diaphragm 63-66 Classic drum booster (which I ran until it failed). I like having a little more brake feel while not having to push real hard to stop. ------------- Frank Swygert |
Posted By: amx39068
Date Posted: Sep/05/2012 at 10:15pm
|
Exactly what part was incorrect Frank? AMC used a larger resevoir for discs on the master than for drum brakes regardless of the type of disc brakes, fact not opinion. AMC used the larger dual diaphram booster for disc brakes compared to drum brakes, fact not opinion. The piston in the single piston KH caliper is huge when compared to the dinky little pistons on the earlier Bendix system, fact not opinion. When you say "paritally correct' it would be helpful to all to see the facts that you are basing your comments on rather than your opinion. Furthermore, the comments you make about your setup have nothing to do with what the OP asked about and in particular your comments regarding Ranger MC and Jaguar rear discs are irrelevant to what he was asking about. For his applicagtion he needs to use the master and booster that was used on the Jeep or Wagoneer brake setup came from. Regardless, do you really think that all engineers at AMC were a bunch of know nothing idiots for designing the larger booster and big resevoir master all because you have had "stellar performance" while using the smaller calipers and rotors on your small Americans? The OP was asking about using AMC parts from AMC vehicles that the AMC engineers determined needed the larger MC and dual diaphram booster so your answer was both misleading and potentially putting the OP at risk of having substandard brake performance with the parts he was inquiring about. ------------- Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
|
Posted By: farna
Date Posted: Sep/06/2012 at 5:59pm
|
I thought I was clear, but will address a couple things you brought up. "Partially" correct was pointed out -- the drum MC will work fine (with the small calipers), you stated the drum MCs weren't usable. I pointed out what I was using to illustrate that there are options. If you don't understand hydraulics and brake systems you shouldn't do any modifying. That's usually understood, but maybe I should have stated such. The reservoir is bigger for the disc portion in an effort to idiot proof the system. It has no effect on brake performance at all. The larger reservoir holds enough fluid to last the life of the pads and still supply brakes even if you never check the fluid level. Cars made over the last 10+ years have abandoned this design and use same size and even partially shared reservoirs. It's the bore and stroke of the piston that determine braking power. Billd more or less pointed this out. The larger booster used with disc brakes is there to make the brakes easy to apply. AMC also made disc brake systems without boosters. Boosters aren't needed at all -- how much boost you want is pretty much a personal preference, or a physical necessity in some cases. I don't think non-power discs were available on the big V-8 cars, but they were on Javelin and small cars. The big cars may indeed need boosters for the disc brakes, haven't researched that. The big drum brake cars did come with manual brakes (no boost). Not having boost (or enough boost) could mean longer stopping distances. Part of that depends on how much effort you're physically capable of, part of it is in the pedal ratio. Boosters are made so that even a small person can have great brakes, and are necessary even for big strong legged people in heavy vehicles. I've talked extensively with the experts at Master Power Brakes. This was maybe 5-6 years ago when researching a major AMC brake article. I understand your concern for safety, but would appreciate a bit more of a professional attitude when replying to something I've posted that you think might be misleading or in error. ------------- Frank Swygert |
Posted By: amx39068
Date Posted: Sep/06/2012 at 11:00pm
|
How would you like me to phrase a response to a post that potentially exposes the OP to a dangerously inadequate brake fluid resevoir when converting to old school disc brakes with a large resevoir engineered into their design? The OP already clearly stated that he is a little clueless about what master/booster combo to use. Adding variables that only serve to further confuse the issue rather than simplify it serves no purpose, does not answer the original question and creates the potential that the OP will use parts that do not work well thus be exposed to unnecessary risk of brake failure. Not sure what part of Bill's post you read that supported your position but what I read clearly stated that if all is not working as intended and designed there is the potential that the smaller master disc resevoir could run dry. Just because a responder may be comfortable taking that risk on their own car, it is not appropriate to impose that added degree of risk on others who may or may not be as knowledgable about brakes and/or as diligent about checking the fluid levels as the person providing the response may be. ------------- Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
|
Posted By: toolmanxiii
Date Posted: Sep/07/2012 at 4:41am
|
Any small body disc brake booster /master will fit . I installed one from an 86 eagle into a 74 Gremlin X. just remember the large bowl is always the disc brakes .
My 71 hornet now has the complete system from a 77 hornet wagon
And a drum master cannot hole enough fluid to support disc calipers . That is an accident waiting to happen. as pad wear the calipers need more fluid to take up the space . ------------- 71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed) |
Posted By: farna
Date Posted: Sep/07/2012 at 4:53am
|
Point taken Dan. Bill just made the comment that once the fluid is in the piston that's it as far as the reservoir is concerned (more or less). As I previously stated, the reservoir size has nothing to do with the braking capacity or performance. Modern cars no longer use the larger reservoir. If you don't check the brake fluid for 30-40,000 miles (roughly the life of pads) there will be enough fluid in the large reservoir so that the front discs remain fully functional, that's the only purpose of the large reservoir on an old style disc brake MC. You know this, but for others... As the pads wear the piston doesn't retract as much and a little more fluid remains in the caliper, unlike drum brakes that have return springs that pull the wheel cylinders back to the same position all the time (the adjustment screw is at the bottom, doesn't affect wheel cylinder position). ------------- Frank Swygert |
Posted By: 73hornut
Date Posted: Sep/07/2012 at 7:30am
|
I have front disk on the gremlin with the drum master, and have no problems with fluid level. Just check more often, say when you get oil changed.
------------- 71 Javelin 74 Gremlin 79 Spirit AMX Rogue Valley Rumblers Like Us on FB https://www.facebook.com/groups/1602825606650796" rel="nofollow - https://www.facebook.com/groups/1602825606650796 |
Posted By: toolmanxiii
Date Posted: Sep/07/2012 at 10:34am
|
I worked at a Garage a few years ago with an older mechanic . He was almost killed when a car fell off the jack and broke his arm. when asked by investigators what happened he said "I don't understand , I've been doing it this way for 20 years" ..... Just because you can does not make it right . If drum masters were made for disc's why make one for disc's . Just my 2 cent's ------------- 71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed) |
Posted By: farna
Date Posted: Sep/07/2012 at 4:01pm
|
If you don't understand the differences and why they are there, and why they MAY not matter, then you don't need to make changes. In some cases, such as for the 3.1" piston "Big Bendix" calipers, the MC needs to be different. Some disc system have a longer stroke as well as a larger piston, and some have a stepped piston with a larger section for the front brakes and a smaller one for the rear (I know that's how Wagner made some of their early drum dual MCs, not sure if anyone makes a disc/drum setup like that or not). I can tell you from taking the MCs apart that the small piston calipers use the same internal dimensions as the drum brake MC. The only difference is the size of the reservoir, and I've already explained why the reservoirs were originally designed that way -- as well as why they aren't any more. At least the older 60s cars also used a different pedal for power vs. manual brakes. The reason is that the power brake cars used a bell crank to transfer motion up 3-4" for clearance. That's why the bracket holds the booster out from the fire wall, so there is room for the bell crank and the booster can be moved up to clear the intake on sixes, left cylinder bank on V-8s. The bell crank needs a bit more pedal stroke, not much, an inch at most. If you use a booster setup with a manual brake pedal the pedal will go to about 1/2" from the floor. You have to change or modify the pedal to sit about an inch higher to have the needed stroke without feeling like you're running out of brake pedal. ------------- Frank Swygert |
Posted By: toolmanxiii
Date Posted: Sep/07/2012 at 6:28pm
|
I understand the difference in masters . I have rebuilt enough of them . but read what you just said . we do not know what he is running for calipers or master . so its better to go with the proper parts . yes some internals are the same . but what happens if you take the car in and tell the mechanic to top up the brake fluid while getting the oil changed and he forgets ? I check mine often as I do all fluids . but most people don't . sorry if you think I'm saying you are wrong that was not the intent . I think you should build a car for the next guy that might own it . ------------- 71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed) |
Posted By: ramblinrev
Date Posted: Sep/07/2012 at 6:41pm
|
Gentlemen, I think we have a difference of opinion here. Farna has made his points clearly, and they haven't satisfied all of you. I never encourage cutting corners on brake work and I don't sense that Farna does either. Maybe give it a rest...
------------- 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) |
Posted By: toolmanxiii
Date Posted: Sep/08/2012 at 3:52am
|
http://rust-free-parts.com/BP.html" rel="nofollow - http://rust-free-parts.com/BP.html
------------- 71 360 Hornet sst 83 2wd 360/727 Eagle wagon (crashed) |
Posted By: amx39068
Date Posted: Sep/08/2012 at 9:29am
That's Greg Beyer's website. He is no longer in Phoenix and rumor has it that he moved up to NoCal in Lodi to work with someone who was formerly an AMC vendor. It is my understanding that Greg was able to move most of his small parts but not sure if he ended up scrapping all the cars or not. ------------- Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
|
toolmanxiii wrote:Posted By: farna
Date Posted: Sep/08/2012 at 10:14am
|
Don't worry -- I'm giving it a rest.
------------- Frank Swygert |