I am experiencing a perplexing brake problem. First a little history. I used to run a narrowed d60 rear with caddie e brake calipers, wilwood adjustable proportioning valve, 1976 Caddy hydroboost, agr hydro assist, 1983 Corvette M/C, narrowed 3/4 chevy front d44 with scout brakes. Steel braided lines in front, steel braided line running from body to axle in rear and rubber lines running from the rear to the calipers. This entire system worked fine, without issue.

Now the changes-- I narrowed a d60 for the front, converted to 5 lug, and am now running GM 1/2 ton calipers. I pulled the caddy calipers off the rear and put on a set of the slightly larger piston gm 1/2 tons. Same hardlines, softlines and proportioning valve, m/c, hydroboost and hydro assist.

Now the problem. I have completely bled the system, but cannot get good pressure from the rear calipers. When I pinch off either of the rear soft lines, the pressure for the other caliper is perfect. The front brakes are fine.

I am thinking that I am not getting enough flow out of the corvette m/c, but that doesn't make any sense as the m/c was originally used on a 4 piston, 4 wheel disk 'vette, so there should be plenty of flow.

I checked the m/c, proportioning valve, and all lines and everything is in proper working order. The problem is not the hydroboost or hydro assist as the problem I described above is evident while bleeding the brakes while the engine is not running.

Anyone have any suggestions?
Eric

Are the bleeders for the rear on top?

Yup--Bleeding is not the problem--there is definitely no air in the lines.

Sounds like you aren't moving enough volume of fluid to the rear.

I've had this discussion in my brain 1000 times. Once you got 1/2 ton + the corvette just says bite me I don't want to do it. If your 100% sure you have all the air out there's two things you can do.

1. Is the line closest to the hydroboost to the rear? If not, make it so, if it is go to 2.
2. Get the 1 ton hydro and an 1 5/16 master cylinder off a 1 ton chevy truck.

Sounds like you aren't moving enough volume of fluid to the rear.

That is what I was thinking as well, I just can't figure out why. The 1.125 bore of the mc should have no problem pushing enough volume. Any ideas on how to fix the problem? I know I could swap in a 1 5/16 bore mc, but then I'll need a new hydroboost. As an alternative, I was thinking about using a wilwood mc, http://www.hotrodsusa.com/store/product276.html, but need to make sure this will fix the problem before I spend the $200.

Also-- is that you Eddie (from Vanco), we talked last night regarding this problem. Not that I was doubting you--I am just trying to work with what I've got before I send you a pile of cash. Looks like I'll be sending you a pile of cash.
E-

I also say that you're not pushing enough volume. Listen to Vanco. Although I have never personally done business with them (I am about to install one of their kits) I've heard nothing but great things about these guys and their knowledge.
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Hey Jeff-
I am listening to the Vanco guys and pulling the HB and sending it to them for a rebuild, high flow porting for the hydroassist and set-up for a bigger mc. Eddie assues me that this will solve my braking woes, as well as prevent future problems with running both hydroboost brakes and hydroassist steering.

BTW- Your driveshaft is scheduled for delivery to Jesse today.

Eric

Thanks for the update. I still need to talk to Jesse about it as he didn't return my call earlier in the week. You should be seeing the check I sent you anytime now.
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