So, I've bled the brakes on perhaps 20 vehicles and each of them perhaps 3 times on average. So, I'm no stranger to this. But something's not going as expected on my 90. I always use my wife or one of the kiddos pumping on the brake. Open the bleeder, yell "down", shut the bleeder, yell "up". basically. Always works.

On the fronts, it worked fine. On the rears it goes like this:

First pump - lots of fluid.
Second pump - very little fluid.
Third pump - almost no fluid and have to hurriedly shut the bleeder so no bubble in the clear hose comes back up to the bleeder.

I tried it a week ago and ran into this so thought I'd try today again. Same thing.

Now there is one crucial difference between other cars I've had and these rear calipers. These are the type of piston you have to screw back in when you put new pads in - the pistons do not simply stroke in and out. Is that the issue? Something to do with the fact that these pistons are not the normal retracting type?

Puzzled - thanks.

 

Might be time to invest in a Motive pressure bleeder. Underneath the MC is prop valve for the rear brakes it's fixed and not adjustable but it does have bleeder on it. The bleed sequence is prop valve RR LR RF LF Could also be the bleeder nipple is clogged with rust.

 

Anecdotally, I was looking for the proportioning valve mechanism on the rear suspension and could not figure it out. Normally there would be a lever that is moved up and down as the suspension does to change the valve position - but nothing there. Hmm. Is the proportioning valve simply a static type that is fixed, and does not respond to vehicle load? Must be.

Anyhow, I had already bled the master cylinder after I sucked it out and refilled with fresh fluid. The bleeder nipple on the bottom of the MC fed fluid fine. And the bleeders on the rear brakes are clear of debris (even had correct rubber bleeder covers on them), and there is no evidence of brake system neglect. Seems like its been serviced regularly.

I have a vacuum pump and used it on the rear bleeders before I had my son help me with the pedal instead. I can get fluid to flow that way, but it seems so reluctant after the initial flow - just like with the pedal technique. The vacuum was then pulling air bubbles from the threads around the bleeder, then into the bleeder's center hole and mixing with the fluid as it came out in a steady stream of bubbles. So, kinda frustrating to do that as I worried about stopping and having a bubble behind the bleeder. The pedal technique at least pushed bubble-free fluid out on the first stroke, ensuring that I got rid of any air.

So, the very oddest deal. I really think it has something to do with the piston design, which I've never dealt with. Weird.