19Chevrolet84

Is it possible to swap out an old third gen rear for a newer 4th gen rear? If so what work/parts would all be needed to do so?

Thanks, Brad.

3rdgenmaro

iTrader: (9)

yes, check out this

https://www.thirdgen.org/4thgenrear

I just finished swapping a 94 z28 rear into my 88

19Chevrolet84

Alright, thanks alot. I'm convinced that it'll be well worth the hassle... Now its up to my dad to let me do it. Still have to find a rear.

Stephen

iTrader: (12)

Search before asking & you can get your answers pretty quickly....After about 10 years of posts, there isn't much you can think of to ask, that doesn't already have an answer here.

Just the new stuff, like LSx engines & new products.

19Chevrolet84

True true, just learning the site.

TheMonster

Well good luck and Welcome! Im looking to do a 4th gen swap too.

3rdgenmaro

iTrader: (9)

If you swap to disks, be sure to change out the proportioning valve. The old disk brake valve will not work the brakes. Not enough pressure, just the fronts will work.

Stephen

iTrader: (12)

PLENTY of people here on TGO, have done even drum to disc swaps & never touched the master cylinder, and be perfectly happy.

There is a small difference in line pressure, but really not so much that some said there was so little difference in brake effectiveness. That it almost wasn't work the hassle of having to do a full brake line bleed.

So it isn't a HAVE to, its a WANT to/preference thing.

JamesC

iTrader: (5)

Changing the master isn't necessary:

https://www.thirdgen.org/forums/susp...fferences.html

Change the proportioning valve for best brake performance.

JamesC

3rdgenmaro

iTrader: (9)

With all do respect, read what I said. I never mentioned the master cylinder. But you DO need to change the proportioning valve. How do I know? I just installed a disk rear using a drum brake valve. With the car on the jackstands, if you put the car in drive, the brakes didnt work enough to stop the tires completely. I had to shift to neutral for the brakes to stop the wheels from spinning. Our driveway is dirt and from 20mph I slammed the brakes. Just the fronts locked up. Very dangerous to drive with only one set of brakes stopping your car.

The proportioning valve needs to be changed.

Stephen

iTrader: (12)

And that was YOUR experience. Call it a miswording on my part, but even still....Lot of swaps without any other parts being swapped.

Maybe it is best to swap the prop valve too, maybe YOURS was just really weak? While swapping it may be BEST, I wouldn't call it a definately neded part.

Like......Some people say the Delco Moraine iron rear calipers are so useless, they can't even stop a wheel at idle, with the car in the air. Yet I locked mine up at 60, dodging a deer. So much for useless iron calipers.

skiroulertx447

I have the 4th gen rear in my 86 Z28 the brakes seem to work very good and i didn't switch any prop valve. If i hit the brakes and get out and feel the rotors the back seem warmer then the fronts, and i have also hit them on a dirt road and the fronts do lockup before the backs, but you want that so you don't loose control in a panic stop.

TKOPerformance

There was another thread on here where this was discussed and a member provided an actual GM TSB regarding the master cylinder in a disc/drum and disc/disc cars. It was stated in the TSB that the disc/disc master was designed for improved road feel, and caused what some customers considered to be an overly hard pedal. The solution specified by GM was to sawp the disc/disc unit for a standard disc/drum unit. I cannot believe that GM would have authorized this if it would have compromised braking, as the resultant class action lawsuite could have ruined the company. Consequently I do not believe that a master cylinder swap is necessary.

That being said you really should change the combo valve. GM does not use a proportioning valve per se, rather they use a combo valve that sets front/rear bias, sets system pressure, and also distributes fluid. The system pressure for discs is higher than it is for drums. The front/rear bias is different too, since discs can clamp much harder before lockup.

c10crewchief

What kind of back spacing would be required for the wheels to not stick out 2"? I have found a deal on a rear but would hate to spend for wheels. But I cannot have my car looking like a hillbilly hot rod. LOL

tony_cogliandro

iTrader: (3)

lots of people dont change the back spacing and only have some scraping when hitting speed bumps.

Stephen

iTrader: (12)

Stock 16" 3rd gen rear wheels on a 4th gen rear end, will set the wheels out, but not out past the edge of the lip.

I've posted pics of a local car, with that exact setup.