Swapping Late-Model Vented Disk Brakes
Into Your AMC
By Jeff Barfield <firstname.lastname@example.org>
Using these instructions you should be able to convert any AMC with front
drum brakes to front disk brakes. Anyone who has done some brake work and
has a reasonable amount of mechanical knowledge should be able to perform
this swap. When you read in the instructions "bleed the brakes" if you
don't know how to perform that function stop now and get help from someone
with more mechanical experience. These instruction assume that you know
enough about brakes to properly bleed them, check for leaks and test their
stopping power in the driveway before going out on the highway. If the
previous statement in not true for you stop now and get assistance. David
Crooks said it best in a response about this message:
"If you're not well versed in brake systems get help from someone who is.
If you modify your brake system you could be liable if it fails and you
hurt someone or destroy property. Brakes aren't difficult to work on, once
you've been taught how, but they're one of the most important parts of a
car, and deserve a lot more respect than they usually get."
Parts you will need from a donor car:
Rotors Including Bearings
Spindles Including All Bolts Nuts Etc.
Caliper Mounting Brackets and Mounting Bolts
All Front Metal Brake Lines
Power Booster Including Check Valve (For power brake systems)
Parts you should buy new or rebuilt (You can take these from the donor car
but unless you know it to be a good system I would not):
Calipers (These are cheap for rebuilt ones approx $20.00 each)
Front Flexible Brake Lines (Kennedy American had these on special
for under $20.00) Replace these, do not reuse old ones.
REMOVING PARTS FROM DONOR CAR
Find a donor car, almost any 71 and up AMC with front disk brakes will make
a good donor car. I highly recommend that you not use the four piston
caliper setup from 70 and down disk brake cars, (instruction are included
to swap this older type to the newer type) they are far more expensive and
harder to maintain and from what I am told they just plain don't work as
well. There were 2 types of single piston caliper systems used in
different years, not sure which was used when, but there were Kelsey Hayes
Bendix systems, some people prefer one system some the other, both work well
and the instructions provided here will work for either brand. Be sure that
you know what kind of car that you used for a donor so that you can order
brake parts later.
Remove all parts listed above from the donor car (take the calipers for
cores if you are buying rebuilt) this should be fairly simple and self
Be sure to make a quick drawing of the proportioning valve and where each
line runs from each connection in the valve, when you go to install it you
will be glad that you did.
I have been told that there were 2 different proportioning valves used that
had different pressure ratios front to rear, to assure that you have a
correct one for your car be sure that the donor car is of similar weight,
(Ambassadors and Rebels will use one while Javelins, Concords, Gremlins,
etc. will use the one for lighter cars) If your donor car is of the wrong
variety to use the proportioning valve of the donor car you may look for
the correct valve from another car (don't know if they are available new or
not) or you may purchase an adjustable valve. If you choose the adjustable
valve you should have a brake expert adjust it for you I would not attempt
this myself, misadjustment is asking for trouble.
Also there is a short metal line going to a double female sleeve and then
to the rear brakes, be sure to get this line and the sleeve, if you do your
old rear brake lines will connect right up.
Have the rotors turned and checked to see if they are in specs.
DISASSEMBLING YOUR CURRENT BRAKES
Remove the drums and all brake hardware from the car.
Disconnect the metal line from the flexible line that runs to the wheel
cylinder, this can be difficult flare wrenches may help or in my case I had
to resort to vise grips.
Remove the nuts holding on the backing plate and spindle.
Remove all the bolts, there is a gotcha here one of the lower bolts may
hit a 90 degree turned spacer between the lower control arm and the strut
save yourself the hour I spent removing the strut rod and stripping a bolt
and take a hacksaw and cut off the bolt, you can use one from the donor
car. Since the bolts come in from the front on the disc system this will not
be a problem in reassembly.
Remove the master cylinder, power booster and all front metal brake lines
as well as the brake pressure warning unit.
Install the spindles, backing plates and mounting brackets, if you watched
how everything came off this should be easy. The calipers should mount
toward the top front of the rotor.
Mount the rotors onto the spindles and secure the bearings with the washer,
nut and cotter pin and put on dust cap.
Connect the new flexible brake lines to the calipers, another gotcha here,
if your car is equipped with the loveable trunnions, like mine, then the
metal part of this brake line may want to run right through the middle of
your trunnion. I overcame this problem with a tubing bender, if you have
to do this connect the line to the caliper first then bend the brake line
down and toward the middle of the car to run behind the trunnion. Bend it a
little at a time and keep setting the caliper in place until the line is no
longer touching the trunnion. Others have told me this was not a problem
when they did the install, I have to assume that the brakes lines come out
of the calipers at different angles depending on who manufactured the
calipers you are using, if you don't have this problem it will save you
about an hour on the install.
Install caliper with brake pads.
Connect the free end of the flexible line to the mounting plate inside the
Install the power booster from donor car being sure to connect the vacuum
line, this is an excellent time to clean it up and paint it.
Install the master cylinder and be sure to bench bleed it first.
Run all the metal brake lines that you removed to their appropriate places
and connect securely, do not mount the proportioning valve yet, let it hang
by the brake lines until you have finished. The brake lines may require
some custom bending to mount to the firewall but this isn't too difficult,
just be careful not to crimp or break them.
Once you have the brake lines securely fastened then secure the
proportioning valve inside the engine compartment.
Lastly bleed the brakes on all four wheels, check for leaks, and test for
Please also note that for true balance on the brakes the braking system
with disk brakes were designed to be used with 10" rear brakes which I
believe came on all disk brake equipped cars and all V8 equipped cars, the
I6s with front drums, came with 9" rears. There are some people running
front with the 9" rear brakes and working fine, but to accomplish optimum
balance between front and rear if the rear brakes are not already 10" drums
these should be swapped as well (this swap is not covered here).
Many people also mentioned the swap of early disk (70 and back four piston
caliper non vented rotors) to late disk (71 and up single piston calipers
with vented rotors). This is accomplished the same as above except the
master cylinder and power booster are identical to the later model cars and
the proportioning valve and metal brakes lines should work just fine. All
parts at the wheel including spindles, backing plates, mounting brackets,
calipers, rotors, and flexible brakes lines should all be replaced as
69 Javelin SST 343 (Now with disc brakes)
Jerry Casper (GremlinGT@aol.com) adds: I went thru my Carlisle-acquired
book called Motor Crash Estimating Guide to find out how much the front hubs
interchanged. Apparently all 70-78 AMC drum hub bearings and all disc brake
hub bearings are the same size, so even if the other parts don't line up, I
"should" be able to use any AMC hub from those years to get this Pacer
rollin', supposing I actually am able to acquire it. I don't see any
reference to Bendix brakes, though, and they don't list the spindle itself,
either. But the bearing size should be the best indicator anyway, so I"m
going with that assumption. And since I went to all that trouble, here's
the list I created for the front drum and disc brake interchange, complete
with part #'s:
Front Hub and Drum
3219569 - 74-78 Matador, Ambo, 70-74 V8 Hornet, 70-73, V8 Gremlin,
3153621 - 70-72 Hornet, 70-72 Gremlin
3219568 - 73-76 Hornet, 73-76 Gremlin
3219570 - 74-78 Matador, Ambo SW 6-cyl, SW
304/360/401, 75-76 Hornet, 74-76 Gremlin
Front Disc and hub
3210408 - 74 Matador, Ambo, 71-74 Hornet, 70-74 Gremlin
3229565 - 75-78 Matador, Ambo, 75-76 Hornet, 75-76 Gremlin, 75-76 Pacer
4488470 - 70 Hornet
3229048 - 77 Hornet, 77-78 Gremlin, 77-78 Pacer
3250578 - 79-80 Pacer
Drum: Inner - 3141139
Outer - 3141140
Disc: Inner - 3223343
Outer - 3223345
That's all for now. I'm gonna have to acquire some more of these Crash
Estimating guides, they're great reference material. Even list the decals
like Levi's and Cassini for the fenders and their part #'s.
NOTES from Andrew Hay (email@example.com):
Bendix 2, 3, and 'delco' mix-n-match parts like rotors and pads.
2a seems to be the same caliper as 2 but thick pads and thin rotors.
Bearings are listed as 'timken set 6 inner, set 2 outer' for -all- drum and
disk '58-'83 -except- '74-'78 Bendix, which take 'set 17 inner, 16 outer'.
Oil seals are listed as 47523 for '74-'78 Bendix, 46130 for all other disk
Pre-70 4-piston Bendix
74-78 big Bendix
77-79 4-cyl Bendix [thin rotors]
and probably a host of others...
NOTES on PROPORTIONING VALVES from David Crooks (firstname.lastname@example.org)
> THE POINT: It is best to leave the original "proportioning valve" in the
> older, pre-70 cars (I don't know exactly when a real proportioning valve
> was used), but make sure you change the master cylinder.
Real proportioning valve's were used earlier than 1970, as my 69 TSM shows.
The difference was that they weren't combined with the pressure switch to
make the combo design until later. According the the book, the
proportioning valve was only used on cars with front disks, and was located
on the body side sill just ahead of the rear axle. The valve limits the
pressure going to the rear brakes to 200psi on the lighter cars (AMX,
Rambler etc.) and 400psi on the heavier ones (Rebel, Ambo etc.).
There's more to it though. A brake system should be balanced. If the
back's lock up to fast, you're going to be in trouble. If the back's don't
come on strong enough you're not stopping as quickly as you could. Cars
equipped with front disks also got Bigger rear drums, to help maintain this
balance. If you're going to swap front disks onto an all drum car my two
You must swap the whole front assembly, spindles, rotors, caliper mounts,
You must swap the master cylinder assembly (no check valve and a bleed
hole for the fronts to prevent residual brake line pressure)
You should also swap the rear brakes (i.e. drums, cylinders etc.) to the
larger size used with the front disks.
This last may be a problem, as the rears don't swap as easily as the
If your donor car is the same size/weight as your receiving car then swap
the proportioning valve. If your donor is different than your receiving
get an adjustable proportioning valve. These are available on the after-
market from many sources, and will allow you to adjust your brake balance.
I'll be learning more about this, as I'm currently hunting up a donor
vehicle to convert my 70 Javelin to front disks, and will post any other
suggestions I come up with.
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