as a test for ABS or caliper problems. I have had mushy brakes on my 91 (automatic, 138K) for, it seems like, forever. A couple of years ago, I put SS braided lines on all 4, replace the MC twice, once for bad seal and right after that one another for what I thought was a bad rebuild. Just rebuilt and added the J55 fronts, re-built the rears (I remembered to adjust the e-brake) new PFC pads all 4 corners.
Still mushy. They are fine for the street, but for AX, they suck. I did the CF search thing, found some helpful hints and a couple of tests to try before throwing more money at the problem.
I have bled these brakes ‘till my bill for Synpower Brake fluid almost equals the California State debt.
First, cracked the lines to the fronts at the ABS pump and bled. No changes. With a bit of agility, you can bleed the ABS unit with out an assistant.
Next, disconnected both brake lines from MC, plugged the MC and stood on the pedal. Both running and engine off with the air bled from the booster, pedal solid as a rock. Left the fronts plugged, re-connected the rear line, pushed the pedal and got the same results as test #1. Number 3 - Disconnect the rear line, re-connect the front line and MUSH.
I taped brown kraft paper under all connections, save the ABS, pushed hard on the pedal 6 or 7 times and all the paper is dry

Now the question – if I disconnect the braided line at the connection to the hard line or to the caliper on both sides and the pedal stays soft, the problem lies with in the ABS unit. If the pedal is solid, the problem lies between the ABS and the brake pads.. If either side has a solid pedal, the other side must be the problem, the line itself, the braided line, the calipers or any connection.

Since this an early version of the Bosch 2S ABS pump, there are no bleed valves and I have read the only way to purge air or correct an internal problem with the ABS unit is to use a scan tool at the stealership or a “qualified” Corvette shop. I know that there are times when the “book” doesn’t know there is a shortcut that we shadetree mechanics use. I don’t know of such a one for this application, but I’m hoping somebody does.

This has turn into a long dissertation, but hopefully, somebody out there has been there, done that and got a t-shirt that remembers enough to get me some brakes!

Thanks in advance
Subman