which do i need

ok ive narrowed my braking problem down to the master cylinder after i put a 87 iroc rear in w/ posi and four wheel discs, what i need to know is which one of these parts do i need for the master cylinder, both are for that model but the two are substantially different in cost and weight and i dont have a clue why, im thinkin though one is just the plastic resovoir and one is the whole assembly w/ the metal bar under it....which do i need. i know i need to have the bigger bores to allow more fluid to my back brakes but i dont know which one or if both will allow this??? here are the parts oh yeah and i have a wobbling noise in my back brake and when i got the rear put on i was told it was from not retaining the ebrake braket for it....well i would just go to a junk yard and get the part put i bought some after market calipers for it not baer or anything just after market ones, they didnt need any fabrication to fit so will that ebrake assembly still bolt up to it since i dont even know how it works for disc brakes , please if u can help me w/ one or both problems ive been battling this problem for a long time now heres the master cylinders

http://www.partsamerica.com/PartDetails.asp?SourceArea=&SourcePage=SEARCHRESULTS&MfrCode=A1C&MfrPartNumber=101997&PartType=230&PTSet=A

http://www.partsamerica.com/PartDetails.asp?SourceArea=&SourcePage=SEARCHRESULTS&MfrCode=RAY&MfrPartNumber=MC39576&PartType=230&PTSet=A

links dont show parts, but i would say get the whole assembly.

as far as the aftermarket calipers, if all the mounting holes are there, it should work. check them against the original units and see if they are externally the same, if so, you shouldnt have any problems.

which do i need. i know i need to have the bigger bores to allow more fluid to my back brakes but i dont know which one or if both will allow this???

So, just to catch up, you swapped from a drum rear to disc correct??
What you needed was either an adjustable proportioning valve, or at the least, the valve off of the car you got the rear end from.. Thats what controls the amount of fluid that gets distributed to the front/back..

yeah i swapped from a drum brake rear to a full disc w/ posi and i have already changed the proportioning valve for the car i got it from but i know i also need the master cylinder because the ones for the disc brakes all around have bigger bores to allow more fluid to the brakes, ill try and find the links again for those parts but my brakes feel really spungy and i have to press the pedal all the way to the floor almost to slow down the car but the brakes from the master cylinder back

and those links work for me just if it brings u to a page for a zip code use 40515 as the zip and it should bring them right up the ones im talking about

I'll assume you've bled the master cylinder and break lines properly??

yeah i bled the brakes my self and just to make sure i had a shop do it from the master cylinder and all four wheels and im pretty sure all i need is the master cylinder....like i said when i press the brakes they work and pretty well if im goin quick but if i am goin slow and press them it seems like it takes more pressure to actually bring the car to a full stop like it would if i was not getting enough fluid to my brakes, i dont have any leaks and my brake booster should be fine since it was right b4 the swap i just dont know which of the two parts i listed i need im assuming its the more expensive one but i dont know if both are the same and quality is just supposed to be that much better or what and i really would like to figure this one out cause my brakes where better w/ drums at this point and i would have to have wasted 120 somethin per caliper and have worse performance

Oh, in that case.. the reason one is so much more money than the other is because the cheaper one is a reman.. (remanufactured) someone brought their old one in for a core, and it was rebuilt, and then sold as a reman..

The other one costs a lot more because it is Raybestos and it is brand new..

Im not sure of the weight descrepancy.. But a remanufactured Master cylinder will be just fine

ooohhh ok i see and that does have the big metal peice that the master cylinder sits on top of cause i need that too i think thats what has the bigger bores to accomidate back discs

You mean the part that the plastic resovouir sits on top of?? yeah thats part of the master cylinder

ok just checking cause another product i didnt post was something about a master cylinder kit but was even more expensive and i assumed although it didnt say that it probably came w/ the cylinder, plumbing, and proportioning valve