Aluminum Master cylinder - 2800 lbs?

[400Magnum]

Hey Everyone,

I have a few questions regarding the aluminum master cylinders available from Mopar. From what I understand, there are two versions available, and the difference between the two is the size of the bore. The description in the Mopar Parts book then goes on to say 2800 lbs. Is that the weight limit of the vehicle these can be installed in?

I'm sure I saw similar master cylinders in late 70's Cordobas and New Yorkers, and there's no doubt those cars were well over 2800 lbs, so what gives? And what about all the trucks running around with these aluminum master cylinders that can carry more than 2800 lbs, not counting the truck itself? Are these production master cylinders different than the ones available from Mopar Performance somehow?

I'd like to swap the iron master cylinder in my Magnum for an aluminum one, but I don't know which one to get. Should I just run down to NAPA and ask for a rebuilt unit for a Cordoba? I realize that I'll also need the adapter plate, but I want to understand which master cylinder I need to get and why I need that. For whatever it's worth, my car has power front discs and the big rear drums.

Thanks for any help you can give.

[Hammer 74]

I am running the small bore on my Dart without a problem. The master's are just updated parts like the lightweight starter. I have not looked at the latest edition of the chassis book to see a weight limit, but I have seen the master on heavier cars than mine and also on some fast strip cars so I feel confident.

[LarsD]

Hey Hammer, what brake rod did you use to adapt the new master cylinder to your Dart? I bought the MP adjustable rod, and the sucker was too long. I ordered one from Master Power, but I don't have it yet. TIA

L.C.D.

[Hammer 74]

I butchered up the MP one. It was very much too long. Cut the master threaded shaft down and rethreaded it and cut the pedal shaft down and drilled it deeper and threaded it as deep as possible. Took a while but it works. I compared the pedal height in relation to the gas pedal with a friends factory manual brake car. Not sure what the MP pushrod is meant to be used for, def. not an A-Body. I made the adapter for the master to the firewall from http://www.bigblockdart.com/. Look at the bottom of the page for tech info.

[George G. Leverette]

I usually change to a light weight starter and alumnium master immediately on getting started on a new project. If you have manual brakes the push rod will fit because the adapter plate will compensate for the difference in length. The after market now have new Sanyo master cyclinders that have increased fluid capicity, I have one installed on the cuda but not tested yet. A Cardoba rebuilt unit will also work. The master cylinders listed in the performance catalog are recommended for the disc brake conversion kit from Mopar, I have one and will sell it at the next swaps.

[LarsD]

OK, thanks. Yeah, when I compared the MP rod to my old rod, the old rod was about two inches shorter Heh... so I sent it back, I have the MP adapter plate too. If that Master Power rod I ordered doesn't work guess I'll pull out the trusty hacksaw

Thanks,
L.C.D.

[400Magnum]

Thanks for the input Hammer. Taking your information I started wondering just what would fit on what. So I just spent a little time at the Napa web site looking at various years and models of cars and trucks that used the aluminum master cylinder, and it would seem that there are all different sizes of the cylinder bores available.

I was wondering what would be the best one to pick? The mc for a 79 'Doba has a bore of just a hair over an inch. There is one for a 1/2-ton truck that has a 1.125" bore. Would getting the bigger bore be better for any reason? Or should I stick to the one that is most closely matched to my car size and weight? Will getting a smaller bore have more pedal travel and let me regulate the brake application better?

[Hammer 74]

Most people that I have talked to about their master cylinder desision is that the small bore is for manual brakes like I have and the large bore for power brakes. There would be less pedal effort with the smaller bore but more pedal travel to move the same amount of fluid. The large bore needs high effort and less pedal travel that works good for power brakes. The MP pushrod worked out good after some modification. It is not hardened and machines well. I think that there are many different lengths for different body styles so they tried to make a universal/modify to fit pushrod kit. It sort of worked. The master adapter cost me about $4 in material to make. Not sure what the MP costs.
Good luck

[Hammer 74]

I forgot to add that the 2 MP MC's have a built in proportioning valve. I guess they did this to make it easier to use with ABS on new vehicles. Mine works great with the original pro valve removed and a Wildwood/MP pro valve hooked to only the rear brakes.

[400Magnum]

Okay, thanks for the information. Sounds like I should be able to do what I want to do without too much trouble. Sounds like the worst part of the whole thing is getting the pushrod adjusted to the correct length.

Thanks for the input everyone!