Much to our dismay, the lid on Aaron's M/C has been slowly leaking fluid
down onto the firewall and has eaten some of the paint off. I got
a new flashy chrome one and it leaks some too.

So, is there one of those newer master cylinders with the screw-on lid, rather than the lift-off lid held with the wire bail, that is a direct bolt-on for his Dart Sport (manual front disk - rear drum)? Any modifications necessary?

One other thing... the brake light stays on constantly. I'm guessing it's a problem with the proportioning valve. I know the emergency brake switch is OK.

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

The master cylinders that will bolt on either have the wire bail or a bolt down cap. The bolt down cap was common on earlier drum brake cars, but probably came on some disc brake stuff. It's likely they bolt down cap master cylinders are not available new. If you have a master cylinder that is smooth where the cap gasket seals and the wire bail is strong enough they usually don't leak. If you can easily open the master cylinder by hand the bail isn't tight enough. The master cylinders with the plastic reservoir and screw on caps came on 2 bolt aluminum master cylinders and require an adapter. Some folks also report a softer pedal with the aluminum master cylinder.

P.S. Ignorance is not knowig any better. Apathy is not caring. Stupidity is being told how to do it right and doing wrong anyway.

_________________
Joshua

the ones with the bolt on cap havent been used since 66 or 67 when they went to the dual chamber master. You wouldn't want to back step to a single master! Dunno about the softer pedal thing with the alum master. My 80 Volare has manual brakes, that would probably be pretty compatible with the weight of your Dart, but youd still need that adapter.

I've got a disc brake dual MC with the bolt-on cover. I think it's a 69 or so vintage. According to Advance, Auto Zone, Napa, etc, the only MC available are the ones with with wire.

The disc brake master cylinders all have the spring-bail retainer, clear back to 1967, the first year of dual-pot masters. Most of the '67-'70 drum brake master cylinders had a screw-down lid. The spring bail itself is not causing your leaks—you've got a problem with the cap gasket, or the cover is warped, or the master cylinder top surface is eroded and/or has been too-aggressively blast cleaned by a "remanufacturer".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

[quote="SlantSixDan"]The disc brake master cylinders all have the spring-bail retainer, clear back to 1967, the first year of dual-pot masters. Most of the '67-'70 drum brake master cylinders had a screw-down lid.

Didn't disc brake MC's have a larger reservoir for the front brakes whereas drum MC had pretty close to equal size reservoirs? Am basing my assumption as this MC defintely has a much larger front reservoir than the back one

Most of the disc brake master cylinders have unequally-sized reservoirs. The rearmost reservoir (closer to the firewall) serves the front brakes and on a disc brake master is usually larger.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I picked up an aluminum M/C with two screw-on caps today at my local
salvage yard. It came out of a New Yorker and has these numbers on
the bottom: 09104 4485297

Anyone know if it is one that will work, assuming I get one of the
2-bolt to 4-bolt adapters? It seems as though the two chambers are
approximately the same size. Which one is for the front brakes?

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

From the outside the plastic part looks equal but if you unscrew the caps you can see internally the reservoir is bigger.

The rearmost chamber is for the front brakes on those units as well.

Yes it should work with the adapter. I'm not sure about what the internal diameter is but from an adapter standpoint you should be ok.

With the aluminum M/C and adapter, will I still use the old push rod? Also, what about the old distribution block?

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Well, my MOPAR parts guy says 4485297 is not a number found in their system. Strange, since that is what is on the bottom of the M/C I got. I guess what I now need to know is whether this one will work, since it came off (I found out today) a 1989 New Yorker, and it is front wheel drive? Will the chambers be proportioned correctly for Aaron's front-disk/rear-drum combination?

Finally, will his current push rod work, seeing as how the required adapter will be about 3/8" thick? Will the rod be too short by the same 3/8"?

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Yes the rod will work. Due to the shape of the flange on the newer units and how the adapter positions it, the pistons will sit in the same positions.

If you are going from all drums to disc you have to replace the stock distribution block with a stock distribution/proportioning block combo (also available aftermarket), or add an adjustable valve on the rear line, or use different rear wheel cylinders.

Make sure your mc has the piston machined for the rubber retainer.

We already swapped front disks from a '76 Duster to Aaron's '74 Dart Sport.
Of course, we also swapped the distribution block. The brakes work fine, we just want to see about changing out the M/C to the aluminum style.

What's the purpose of that retaining groove?

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

The rubber piece fits over the rod, and is a tight fit in the piston, sitting in the groove. It prevents the pedal from lifting high enough and pulling the rod out of the piston. Otherwise, the only safety from preventing the pedal from coming too high up is the brake light switch/bracket. Just a safety item.

I think the mc's that originally came with power applications didn't have the groove in them because that mechanism was different.