Aluminum master cylinder upgrade

Hi guys, I seen a lot of guys running these type of master cylinders on their early mopars I was told there was some type of part number or you order it through your local parts store and can buy them a lot cheaper than the aftermarket has them. Does anybody have any part numbers on them or what vehicle I should tell them I have
thank you guys, Mopar, or no car and I do have the adapter plate

I have a 69 dart with 73 disc brakes upfront and 11 inch drums in the rear

Any M body 1979 to 1989. Fifth avenue, Diplomat etc. Trucks had them too and some FWD cars but they're different part number and I don't know if bore sizes or anything else would make a difference in how they work.

Rockauto. 1-1/32" bore

I saved this chart when it was posted earlier.

That's a nice chart !!

The thing that needs defining is "caliper piston size" - What's large and what's small ?

The 1 1/8" master listed above will work very well with this but will give a very firm pedal and short throw. I love it!

The 1-1/8 master needs a booster IMO. I'm pretty sure that's the master that was in my 82 Cordoba. I removed the booster for valve cover clearance and made a spacer to take up the space that the booster once filled. The pedal was rock hard and the car was a handful to stop. I didn't know any better at the time but a master with a smaller bore was needed. Does the OP have a booster or do you have manual brakes?

Replacement boosters on Rockauto are inexpensive. Might have to experiment with a couple different sizes.

My experience as well. 65 Cuda, manual brakes, 11.75" discs, 11" drums, M cop car combination vavle.. the 1 1/8" MC is the wrong choice there.

go to Dr Diffs page, he has a fair price and you can get the adapter there as well.

The adapters piss me off. Would it have broke the bank to have added another 1/8" of material to adequately cover the hole in the stock M/C firewall plate ?!? And the recess around the bore is smaller than the m/c dust boot.

A body boosters seem to be unavailable. Needed on for my 74 Dart last year, no go. I could have sent the booster to Cardone ( from Canada), pay $160.00US for them to rebuild. Would have had to pay shipping etc. both ways. Went manual.

No hard to make your own, did that in the 90's.

I wouldn't recommend anything over 15/16' for anything without power brakes. I put either a 1 1/32" or a 1 1/8" on my Dart with manual disk front and back and it scared me in the driveway. Both hands on the wheel and both feet on the brake pedal to make it stop. The 15/16" I got from Dr Diff is much better, but when the time comes to replace it, I'll use a 7/8" bore.

The smaller the bore the less leg pressure is needed to stop the car with no power assisted brakes
I found that out the hard way when a master cylinder went south at Pomona one year and I didn't know the correct size of the master cylinder bore and replaced it with one that had a 5/16 bigger bore when I had to replace it because it wouldn't stop that car worth a hoot

DOCTORDIFF.COM Email him your question and he'll get ya figured out.

I have an all original brake booster set up out of a 72 Dart. A friend had said he should have more parts as well...

Most drag race calipers use 1.75" bores. Use number of bores in the system to determine piston area. Basic rule is 1-1/32" MC for 2 piston front/4 piston rear system. 1-1/8" MC for 4 piston front and rear.

Using anything else, you have to do the math. Total area = πr2 x number of pistons

Pedal ratios make a difference too.

Some of these kits use calipers with small (1-3/8") bores. I got caught (once) trying to figure out why the brakes wouldn't work on a car that had Wilwoods with these goofy bore sizes.

Plumb the brakes into the correct port on the MC, according to your configuration.

Spend some money, ditch the torn up rubber ring, and put one of these on the car. If I had a dollar for every car I've seen torn up...

I pulled one of these aluminum bodied mast cyl off the car . Car needed an anchor out the window to stop ( dont know size as I didnt measure it before it went in the trash can )
Put a 15/16 master for a 1975 Duster on it ( manual front disc and rear drums on a 1966 B body )

car actually stops now without much efffort

There are stock looking four bolt aluminum masters out there, too.

https://www.force10brakes.com/home/...um-and-disc-disc-applications-p235514315

Looking up the 15/16" from a Dakota on RockAuto, the reservoir is "angled", where the front is low - back high. I don't know if this reduces the amount of fluid the front holds vs. the 1 1/32" diplomat unit, which has a level reservoir. Also, there is an option to get the Dakota m/c without the reservoir. Does this mean you could a separate reservoir from the Diplomat (level) so you can use on the Dakota m/c? This would give you a level reservoir on the smaller 15/16" m/c.

The reason I ask is because I bought a 1 1/8" that is way too big for a car and I would like either the 15/16" or 1 1/32". This would be for an e body manual brake 11.75 disc / 10" drum set up. Can get local for less w/o reservoir.

**For manual brakes: bore that back of the piston on the 15/16",** Can someone explain exactly how to do this?

It means that the M/C piston does not have the retaining groove machined in it to use a manual brake pushrod.

I just used a 4 bolt 15/16th M/C.

Dorman M80266

in order to modify the piston for the groove the rubber retaining ring needs, the master needs to be disassembled, and the rear piston chucked up in a late.
you then need to know what push rod you are going to use, so you can determine the distance from the rear edge of the piston the groove needs to be machined.
then using the proper width grooving tool that fits inside the rear piston bore, you can easily make the groove necessary for the rubber retaining ring to fit into.
lacking a late and the necessary tooling to machine a groove, [and most do not have access to this stuff as i do] you can obtain a piston with the necessary groove already there that fits your master, find a master that is the size you need with the necessary retaining groove already in the rear piston, or make a substantial stop that will prevent the brake pedal rod from pulling out of the master cylinder, allowing the rod to fall toward the floor, causing complete brake system failure and possible severe damage to you and your car if this happens at the wrong time.

Bob, I don’t have those tools. Do you think the piston from a 1 1/8” m/c will fit in a 15/16? If not, I will just have to get a unit from dr. Diff. I don’t want the pushrod to fall out.

the 1 1/8 piston is 0.187 [3/16"] too big to fit into a 15/16" [0.937] bore master cylinder.
that said, even if one were to machine the 1 1/8" piston to fit the 15/16" master, i'm "ass"uming there would not be any structural integrity left in the piston because the basic piece would have very thin sections left in spots, due to being machined for the bigger bore to begin with.
i'm just guessing about that, because i do not have an inch and an eighth piston to compare to the fifteen sixteenth piston.
just do the right thing and get the 15/16 unit from the good doctor like you mentioned. brakes are not where you want to compromise safety.