I swapped the drum brake rear on my 1988 ta for a 9 bolt borg warner disc brake rear. I also picked up a disc brake proportion valve.all lines fit except the ones from the master cylinder to the proportion valve.I also bought the master cylinder (It is the same as my disc/drum master cylinder)the proportion valve i replaced had much deeper threads then the disc brake valve i installed.If any one can help me out with the thread size or where i can purchase the correct lines Please post it

 

What kind (year/model) prop valve did you pick up? If you grabbed the valve and MC from the same car, they should work. I just replaced my stock MC and valve with an LS1 MC and adjustable valve. When I removed the stock components, the lines at the MC and prop valve were exactly the same. The fronts were M11x1.5 (3/16" line) and the rears were a 1/4" line, don't remember what thread exactly.

 

The master cylinder and prop were from a 1986 disc disc transam,

 

Sorry, I didn't get a notification of a post. I assume you bought them from someone who sent just the PV and the MC, if you can get your hands on the lines that ran between the two from them, or at least the fittings, that would be ideal. If not, M12x1.0 is the 1/4" line that I couldn't remember.
So M11x1.5 (3/16" rear most line) and M12x1.0 (1/4" front line). You may have to go to a dealership to get those, most parts places I've tried don't carry them. HTH

 

Any updates?
I just found my old front line (1/4" M12x1.0) with the fittings still in great shape if you wanted it. Just pay shipping and it's yours.

 

I switched the master cylinder/prop valve on my 1988 pontiac transam .I switched from a drum rear to a disc rear.The original master cylinder had 1 line with course threads and 1 fine thread to the prop valve.I bought a master cylinder and prop valve from this website for a disc/disc brake vehicle(i dont remember year)The master looks like the same as the 1 i had original FIne/course thread.The prop valve i bought(disc/disc)has what looks like the same size(course thread)front and back.How can i get this working? what can i change?master cylinder,propvalve,can i get lines to fit ? the lines from my master to prop valve are totally diffrent.Is the master the same on disc drum and disc/disc after 1988? is the thread the the same on the 1990 ile valve as the 1988 drum brake prop valve

 

Well, I checked NAPA's website, and there are indeed two different part numbers for disc/drum and disc/disc on '88 Firebirds. They both have the same thread size listed, so I'm not sure where the difference comes into play. As for the 1LE prop valve thread sizes being different, I don't know. Hopefully someone else can chime in with that info. I still have my old MC, prop valve, and the front line from my disc/disc '87. If you want a part or parts, let me know.

 

The disc/drum MC will have a residual pressure valve at the drum brake port. This holds around 5psi +/- to keep the cup seals flaired in the wheel cyl. So the fluid stays in and air/water vapor out. There is sometimes a differance in resivior volume, more for disc, less for drums. The disc/disc doesn't.

AIIR in burkes tech article on 1LE brake he talks about a change made to the brake fitting threads. It's worth a look.

 

From the aforementioned article:

1LE Combo Valve (proportioning valve)
14089496 1989 1st design: M1.0 tube nut threads (For 1982 - early 1989 applications)
10136840 1989 2nd design: M1.5 tube nut threads (Late 1989)
10136840 1990-'92: M1.5 tube nut threads.
Measure your existing brake line tube nut threads before ordering. The Master cylinder tubes have one that is M1.5 and one that is M1.0 so don't worry about them. Worry about your existing brake lines to the calipers and rear axle.
I used the 14089496 1st design because my car was built in 1984.

Mine required some relocating of the rear disk brake line: My old combo valve had the line coming in the front, whereas the 1LE piece had it coming in from the bottom of the valve. My existing line bent with no problems. Be prepared to replace that line if it's at all corroded. It might crack.

Ed Miller sells various proportioning valves:

http://www.flynbye.com/catalog/c1_p1.html

JamesC