Okay heres a short question for you guys/gals.

I need to replace the brake master cylinder on my 1968 Valiant. It has the factory 4 wheel, 9 " manual drum brakes with the factory cast iron 2 circuit M/C.

Rather than replacing the ailing M/C with a "new"4 bolt cast iron M/C, could I use a newer 2 bolt aluminum M/C with an ARengineering adaptor and it function the same as the old 4 bolt M/C?

Are the two M/C's interchangeable as far as function on my application?

The reason I ask is that I have a disc brake conversion lined up but won't be able to put them on for a few months. I would like to change to the newer aluminum style M/C with the disc brake conversion and don't want to have to purchase two different M/C's if I only need the one.

This is my daily driver right now so I need to be able switch this stuff out without a lot of trouble.

I've searched/snooped in a lot of previous posts to see if anyone has done this but didn't find exactly what I am talking about yet.

Any advice would be great.

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'68signet

"Living analog in the digital age."

I still have my 9"drums. I have a disc brake larger MC on there. It works great.

Either that I put one hell of a brake job on the front! Factory everything on the rear. Never even looked at them.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

Funny you brought this up. I logged on specifically tonight to ask that very same question. I hope to give it a try this week, if I can get all the parts lined up.

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I have used the two bolt aluminum MC in this car with three different brake combos, and it works fine. But, I did put a willwood proportioning valve in the rear line to adjust the bias of the rears.

If you have more time than money, you can make the adapter yourself. Take a hack saw, and cut the rear inch off of your old MC. Smooth out the front half with a grinder, and files. The drill and tap the piece for studs to match your new aluminum MC. This only took about half an hour. I did this simply because I did not want to wait for an adapter to arrive in the mail. I had ordered an entire new brake set from MP Brakes, and then decided to go with the aluminum MC after everything had arrived.

If you are interested, I have an adjustable push rod, new in the bubble pack I will sell it for half the new price now plus S&H. I can;t remember what I paid for it, but it turned out the old one was long enough, and I did not need it.

Sam

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Thanks for the replys. I dunno if I need the longer adjustable pushrod yet or not. I will get back to you if I do (thanks for the offer). I am still milling around this job in my head as of late. Ya know, doing the job wrong multiple times in my head so I can work all the problems out before I turn a wrench.

Great tip on the homemade adaptor for the MP aluminum M/C! I may have to give that one a try.

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'68signet

"Living analog in the digital age."

It would work fine and you should not need an adjustable pushrod. The piston in the cylinder ends up in the same spot relative to the firewall with the adapter plate.

You should use residual pressure valves with drum brakes. There is talk about how they are not needed if the wheel cylinders have expanders. Save yourself the trouble and be safe. Just use them. They do shorten up pedal travel a fair amount too, and that alone is a big reason to use them.

Having the pedal get mushy while the fluid level in the master rises is just a hassle no one needs, and thats what happens when the wheel cylinders start gulping air.

I have seen new wheel cylinders lately that DO NOT have the expanders, they were Centric brand. With all the imported junk in the market things like this are not getting better.

AnotherSix, Just clarifying here. The old cast iron 4 bolt M/C's had the residual pressure valves built in, and the newer aluminum 2 bolt M/C's do not?

Also, the M/C I've been told is the one to use, has an 1 1/32" bore, and was standard on production MoPars after '78. Using rockauto.com for my research, I can only find that M/C in cast iron. Once I find something in aluminum, it has an 1 1/8" bore. Is the MoPar Performance piece the only one available? Does anyone have a part#, or know what car to look up to find the right piece?

68Signet, if you decide not to make your own adapter, MoPar Performance sells one cheaper than AREngineering. I paid $32 at my local dealer, part# P5249315 I've been told the center hole must be enlarged slightly, we'll see when I get it.

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I have seen the later aluminum factory master cylinders with a residual pressure valve on the rear outlet. It is a steel piece about an inch long screwed into the port. You will see them on rebuilds and new iron versions, but it seems hit and miss.

All the new two bolt cylinders from normal parts sources that I have seen are cast iron.

You can get a a smaller bore in aluminum. MagnumHP has them. He is a good one to deal with. You can get the plate from him too. Wilwood has a part number that is the same thing too. I think both of these are 1 & 1/16

The one I am using was supposed to have an internal valve in the rear circuit, it does not. I would have to check my notes (after finding them), but I think it is a 1 & 1/32".

You can go with a new two bolt in iron and still get the modern style reservoir out of the deal. It may come with the rear valve too so that might solve itself. I had a premium one from Napa and it did not have the valve.

Ok, I think I'm a bit confused.

The purpose of this swap is for better braking performance, right? And that is accomplished by a larger bore, or is there a design difference?

The factory piece for my '76 Dart has a 1 1/32" bore, but is 4 bolt.
The factory piece for a '79 Aspen has a 1 1/32" bore, but is 2 bolt.
The MagnumHP aluminum piece has a 1 1/16" bore, and is 2 bolt.
The factory aluminum piece for a '79 B100 has a 1 1/8" bore, and is 2 bolt.

So the '79 Aspen piece wouldn't improve things much, and the van one would be better than the Magnum HP one? I haven't been able to find much info on the principles and theory of it, just how to bolt it all up... My sources have been the October '96 issue of Mopar Action, and Tom Condran's Performance Handling book.

AnotherSix, You said you had the 1 1/32" bore, did it improve braking? I guess I'm just trying to make sure I get more than a silly plastic reservoir for my $. Thanks again. I think I'm going to call NAPA and cancel my order on that cast iron M/C until I get it all straightened out in my head.

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I swapped mine as part of a disk conversion.

The performance will be the same if the bore is the same. A larger bore will increase pedal effort and shorten the stroke. I would not go smaller, having more stroke would not be good, the pedal will be too close to the floor. Going up to 1 & 1/16 will not make the pedal too hard, it will just be a little more. When you get disks on there it will take less effort than it ever did with the original master with drums.

You could just get a 74 master for disk brakes and leave it at that.

The plastic reserviors usually seal better over time and keep the fluid cleaner and drier.

When I put the aluminum 2 bolt on my drag car, I got it from the parts store as a 85 or 86 Dodge truck piece.My 62 Valiant has 4 wheel disks now....and all is well. But I know the MC will need a plastic resivour if you dont have one already.Hit a wrecking yard and look around....mine came from carquest BTW.
Andrew.Kidd

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Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

I'm currently running a '76 disk M/C, and I'd like something more.

Kidd, the '85 D150 M/C is the aluminum 1 1/8" bore I wanted to go with, thanks for confirming it will work.

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Well, to catch y'all up on my progress here goes.

I'm gonna go ahead and trash the front 9" drums and install 11" discs in their place as of next week instead of limping it along until the ubiquitous "someday I'll have front disc brakes" arrives.

I decided to keep it simple and go with new replacement parts for a 1974 manual disc/drum Valiant (sans the 1981 Chrysler Lebaron spindles and floating calipers).

This car will probably never see the track but only public roadways so a trick aluminum 2 bolt M/C will only complicate my wrenchings and expenses at the moment.

I'll post the outcome for any interested people in a few weeks when everything is installed and working properly.

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'68signet

"Living analog in the digital age."

how did your brake upgrade go? what MC did you finally use, I used a 4 bolt 72 disc/drum MC with a 1 inbore for my swap..I was thinking of going with a 1 1/32 bore MC but i didnt want the peadal to hard..

It will not be too hard. THat's standard for manual disc/drum setups with the 2.6-inch front calipers (stock Valiant lbp disc).

I ran a 1 1/8" MC (the Van one) with my disc/drums on my '64 Dart and it was not too stiff either.

Any of them will be fine with a little difference in travel/pedal hardness. Try one and if you don't like it get another. They're only about $10 at the junkyard plus a $20 rebuild kit.

The best thing about the aluminum MCs is that they don't corrode (plus the better reservoir mentioned above). They are internally anodized and almost never wear out.