Bought a big project year and a half ago 1989 Iroc t-top 5 speed. New everything, only thing original is the hood and hatch cover and interior plastics. Car came with 308 posi drum brake. Recently bought a 373 no posi but with disk rear end. I have already switched over the posi carrier and my 308 gears over into the disc rear end. I know I have to change the proportioning valve and the no brainer " fluid" and add posi additive. Just wondering if there is anything else I should keep in mind Thanks Jer

Trial fit your discs over the axels. There was a difference between disc and drum axels on the end where the rotor or drum indexes. Worst case scenario you will have to run the disc rear axelshafts. The master cylinder is different too. Just the combo valve won't be enough. The master must haev the right volume (discs use a lot more fluid that drums) and pressure valve. The combo valve just distributes fluid and sets the front/rear bias.

Check the following link on master cylinders:

http://www.thirdgen.org/techboard/su...fferences.html (Master Cylinder Differences)

JamesC

Interesting, but I'd still use a disc/disc master. I've converted several cars to rear discs over the years and had problems when trying to use the stock master. I've spoken to reps from several of the big name brake manufacturers too, and most of them said the same thing: you can use the stock master with an aftermarket proportioning valve. Well, I'm here to tell you from firsthand experience that it never worked right in any of the applications for which I tried it. I always had one of two problems, either the calipers needed too much fluid and lowered the master cylinder too far; allowing air into the system and creating a situation where the rear brakes worked worse than the stock drums, or the master cylinder just couldn't produce enough pressure to apply the rear calipers hard enough to get effective rear braking. The solution I found was to use a disc/disc master cylinder and the right combo valve. On my '87 K5 for example I run a C3 Corvette master cylinder, which I adapted to the stock power booster. I used a disc/disc GM combo valve from Master Power Brakes (fit right in place of the stocker, no adapters needed either). The front discs are stock 1/2 ton rotors and calipers. The rear discs are modified '89-up 1/2 ton rotors with '79 Cadillac calipers (custom brackets obviously). I think I used Monte Carlo front hoses to mate the calipers to the stock lines. It's a total mutt of a system but it works very well. I do have an adjustable proportioning valve inline to the rear brakes so I can set the bias too.

I'm not saying don't try it. Not all cars are the same, and my experience is not with 3rd gens specifically(other GMs though and Fords). I'm am saying don't be suprised if it doesn't work right the first time.

You would think that the 1LE set-up would require a disc master, but no, it's a J50.

JamesC

I think those masters may be able to crutch the fluid volume problem because there is a slot between the wall for the front and rear reservoirs. If the rear brakes need more fluid they can "steal" it from the front reservoir. GM with their interchangable parts may have built the masters without pressure valves and simply allowed the combo valve to do all the work, which in theory is possible. If you have experience with this setup and say it will work that's good enough for me. I just always caution people about "bolt on" swaps that may not be as simple as they think, and when it comes to something as important as brakes you can't be too safe.

BTW, I like the quote in your sig. Another good one is "Nothing in the world is more dangerous than sincere ignornance and conscientious stupidity." - Dr. Martin Luther King Jr.

I couldn't agree more.

Off topic, but if you're unfamiliar with Dr. King's "I Have a Dream" speech, I urge you to find it and give it a listen. It's quite beautiful in design and message. I used to tell my students that it was the finest speech of the century.

JamesC

Yes, off topic, but I think we thoroughly answered the question.

Thanks for urging me to read that in entirety. I would have to agree that it is indeed the finest speach of the twentieth century, and probably one of the five best in our nations history. Lincoln's Gettysburg Address and William Jennings Bryan's Cross of Gold speach are two of my other favorites.

Got it in!!! It was a nightmare, took it for a test drive erverything seems to be working properly so far. KNOCK ON WOOD . Thanks for the input