ChrisUlrich

On a 88Z... do you need to swap out master cylinders when converting to 4 wheel disc?

Irocvette355

nope...my swap works fine

Z28SORR

Most 4 wheel disc systems have both a larger master and different proportioning valve.
So, how do you know it's working fine? In many of these cases the rears do no braking at all.

Drkhrse89

I have heard that you do not need a new master cylinder but the proportioning valve is a must. I am going to be finding the same thing out very soon when I pick up my LS1 rear.

anthony714

heres the problem..a master may work to a degree,cause all it really does is push fluid,but if you ever lokes a t a drum/disk master,usually the front is real large for feeding the disk ..so that means your old drum resoviour is now feeding your new big drums and you may not be getting the volume you could use back there.it still may be activating the brakes,but how much force you getting?look at most disk/disk masters,youll find the usually have equal size resoviours unless its a newer plastic single style.also an old drum master has a residual valve in it to keep some line presure on the rear drums to keep the shoes closer to the drums so when you hit the brakes theres not as much pedal travel needed.disk dont need residual pressure...so you might also be driving around with rear disk that are slightly dragging....a new rebuilt master dont cost much..peace of mind is priceless

Drkhrse89

Thank you very much for the explaination that clears a lot of things up. Now thinking about it logically, like you explained makes perfect sense.

respectirocz

like previously stated you definatly would need to change the proportioning valve or the discs in the rear wont get enough brake pressure to be fully effective

i work at autozone and i looked up the master cylinders for the drum brakes and the disc brakes, they are two different master cylinders so to do the swap correctly you should change the master cylinder,

but

all a master cylinder does is push fluid,
really it pressurizes the fluid, and the biggest difference is the size of the bore, because that directly relates to the brake effort needed to apply adaquate brake pressure to the wheel cylinder or caliper

drums dont need as much brake pressure because they are usually self energizing and the wheel cylinders bore is considerably smaller than a calipers bore which directly effects braking pressure, so when u just slide in a disc rear end the rear calipers rarely get worked and as a result it takes u longer to come to a stop

to finish my babble
u can re-use the original master cylinder, but for peace of mind go with the disc/disc master cylinder
and you should change the proportioning valve, or your new discs are not effective

Chomp

I did this swap and didn't have a new prop valve for a few months. There was literally no difference with the new disc brakes UNTIL I installed a prop valve. Now the braking difference is huge.

However, I don't think you need a new MC. My front brakes have full pressure (they don't go through any type of prop valve) and the rears are adjustable. I calibrated them so that the rears lock up just after the front lock up under hard,hard braking. If you can get the rears to lock up, you don't need any more pressue (or a new MC).....

SS Joe

On a third gen, its not necessary...GM used 2 different MCs with rear disc brakes, and one was the same as used with rear drums. You should change the prop valve (the 1LE piece works very well, and is still available for about $60), but either MC will work, though the characteristics are a little different. GM did it, so can you.