Review on Jegs adjustable proportioning valve with LS1 rears - Third Generation F-Body Message Boards

vortec350s10 · 09-25-2009, 07:06 PM

I searched a lot and didn't find a lot of info on installing one of these besides the one in the tech section about the Wilwood unit. I bought the main "other one" that you can find all over, including Jegs and Summit. There are various "versions" of these proportioning valves with no difference besides the name printed on it, as far as I can tell. This is the black anodized aluminum one that is basically a rectangular block with the round knurled adjustment knob sticking out.
So anyway, my car is an '88 Iroc, which originally came with a 9 bolt with rear discs. I now have a 10 bolt with LS1 rear discs, and an LS1 master cylinder, which was a direct swap from my original M/C. With the stock P/V, there was little, to no pressure getting to my rear brakes. I couldn't stop the rears from spinning even at idle with rear tires off the ground. I had a buddy with LS1 rear brakes and an adjustable prop, and it solved his problem, so I couldn't wait to get mine in.
I started by removing the original combination valve, then the master cylinder. The master cylinder will drain out once the lines are disconnected, so you gotta have a lot of rags under all the brake lines if you care at all about your underhood paint.
I couldn't find a good list of line sizes and fittings so here's what I know about my car at least:

Factory line sizes on my '88 Iroc:

Front lines on the car: 3/16" which terminate at the combo valve with bubble flares.

Rear line on the car: 1/4" which terminates at the combo valve with a bubble flare.
Now I don't remember for certain if these 3 lines are metric or not but that is what size flare nuts fit the lines once they are re-flared.

Master cylinder to combo valve:
Front line - closest to the firewall: 3/16" flare nut fits it
Rear line - closest to the front of the car: 1/4" flare nut fits it. The actual O.D. of the line was more like .230 inches, so I had a lot of trouble flaring this line, because of the smaller diameter. It would not fit tightly in my flaring tool.

I will say this: these two stock lines are very hard, and after fighting them forever, I just went and bought two new lines at the auto parts store. The auto store lines are softer so they are a lot easier to flare and bend. You will need: 1/4" line with a bubble flare on one end, double flare on the other, and 3/16" line with bubble flare on one end, double flare on the other. I checked Orielly and Napa, and both had 3/16" lines with double flares on the both ends or bubble flares on both ends, but neither place had 3/16" lines with bubble flares. I ended up buying a 3/16" bubble line and flared a double flare on the other end, and bought a 1/4" line with a double flare and made a bubble flare on the other end. You can make a bubble flare with a double flaring tool. The problem I had making the bubble flare (first stage of a double flare) is getting the flare not lopsided. I had to be extremely careful that I had the die perfectly squared with the line to make a successful flare of either kind. The double flares on the lines on the car went ok, these lines seem to be softer than the lines going between the M/C and the combo valve. I bought a brass T fitting for 3/16" lines to T all 3 front lines together (which are all double flares), and then bought fittings that go from 1/4" flare to 1/8" NPT male which is what the new adjustable prop valve takes. As far as I know, they don't make different fittings for single or double 45 degree flares. I think the reason they recommend double flares is just because they are stronger than single flares, but fittings will work with either.
So after bench bleeding the M/C, which you must do, I connected everything up and bled the complete system.

How does it work?

Well, I turned it up all the way, clockwise, and pulled out for the first test drive. The brakes felt the same initially. I could slam on the brakes really quick and it was the same as before- I couldn't lock up the brakes if my life depended on it. I did some hard braking from higher speeds and suddenly the brakes became very grabby, once they were hot. If I slam on the brakes really fast, the brakes are weaker than if I apply the brakes a little slower. I could get the rears to start squealing under hard braking. I have ceramic pads all around, I'm not sure if this a normal characteristic of ceramics or not, but my brakes only become aggressive when hot, or at least pretty warm. I backed off the adjuster to the other extreme, and I could definitely tell the rears were not doing anything, even under light braking. I currently have the adjuster turned up almost all the way (giving the rears almost max pressure) to somewhat balance out my brakes. So overall, it works great, and I now have functional LS1 rear brakes for the first time.
Hope this helps somebody!

Stephen · 09-25-2009, 07:32 PM

Sounds like....Your saying they don't do much good?

vortec350s10 · 09-25-2009, 07:35 PM

No, I'm saying it works great, If I have it turned up all the way, the backs lock up too early. The ideal adjustment for my car is within the range of adjustement.