Replacing a Iron master cylinder for a modern one?

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Mopar King

Mopar King

Beginner / Need of Help
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I been curious and wanted to get some imput on the modern plastic body master cylinders in mopars. I know that you need an adapter plate and the bore size is the same as the stock M.C. which is 1.031


  1. do they perform the same as a cast iron one?
  2. any safety issues? don't want to fall off a cliff :D
  3. can these hold more fuild than the cast iron ones?
  4. are all modern M.C. the same? looking at dorman's M99294 and C.P. M-83028
  5. I know that most of these are for disc brakes only but do they have one for drums? or can it be used with drums as well?
  6. any problems with the caps? keeping pressure and staying close tight
  7. any leaks or weak points?
  8. any change of size in brake lines?











Im thinking of getting one to test out. I have a 1972 manual disc brake with proportion valve just under MC - dodge dart that i want to clean up. thanks

I liked how daniel_depetro has it set up from slantsix.org - that where I got the idea

http://www.slantsix.org/forum/viewtopic.php?t=47497&sid=e187428ada6c8bd250aae7713ee74c40
 

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As long as you have a push rod from a manual master cylinder it should work.
 
If you get a 15/16" master cylinder you'll get a lighter pedal, more brake with less effort... The only downside is slightly more pedal travel.
 
I have one in one of my cars. Honestly,I dont feel it was worth the time or money. The only advantage I can see, is it is a little lighter. If you have a car where every ounce counts, than i could see it.Other than that I see no difference in braking between the 2 cars.
 
The part you are talking about only holds the reserve fluid; it won't make a lick of difference in the braking behavior, all other things being equal. The one advantage of a plastic reservoir is that it will not rust and contaminate the fluid over a long period of time; this can happen with cars that don't get regular fluid changeouts as the non-Dot 5 fluids absorb water. And you don't get rust along the edges like on the lips of a metal MC reservior. But, you cannot clean the plastic ones out as easily either.

The plastic reservoirs appeared in cars in the late-60's or early 70's so have a realible track record, and have been used for both disc and drum apps; there is no difference there. I've never had a cap loosen, even in racing.

Personally, I would spend the $$ and time on DOT 5 fluid that does not absorb water, does not eat your nice paint job, and which is good for cars that sit a lot. You need to reeeealy flush out/clean out the old stuff however. I would be tempted to remove the wheel cylinders and calipers and rebuild them all, but it may be just as well to just flush a lot of DOT 5 through the system over an over.
 
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