OK, makes sense to me. Just sounded unlikely.

 

And this is off the critical path now; I'm borrowing my sister's car tomorrow. The most important accessory for Land rover owners: a spare car.

 

So now, my job is to try to determine whether my failure is the master cylinder, the modulator, or the SLABS... without benefit of a testbook.

I *assume* it's not the master, cause I can get fluid pressure on pump on both input pipes to the modulator. I found a page on working on your Hummer WABCO system that suggests that there's some external tests I can do to the modulator to see if it's obviously broken, and I found a Landy shop in Arizona (I think) that has a rebuid kit for the modulator for slightly over 100 bucks, that they're very proud includes some things the factory kit does not -- replacement seals, I think.

I've been a systems analyst for 20 years, I will eventually figure this out, but any datapoints from people who've done it already are always welcome.

 

You most likely don't have a brake issue but a lack of experience in bleeding brakes.
You are probabily going to need to do a gravity bleed, to get fluid back in the system then bleed the system again.
If you want some help, send me your number and I'll help you.

 

Could you clarify for me, Mike, how that would interact with "I can't get fluid pumped through the ABS modulator"?

There's only about a foot of pipe between that and the master cylinder, and I *can* get drips on the supply side of the WABCO when I pump... just not on the downstream side...

 

First, you never try to bleed the module, you bleed all 4 wheels and if needed activate the ABS pump to bleed the module.
What were your brakes doing prior to trying to bleed the system?

 

As noted earlier in this thread, I could not get any fluid at all out of any wheel cylinder on bleed-pumping, after the first burst.

The level in the reservoir, which started up in the neck of the tank, never went down more than about a millimeter or so.

Checking what was happening at the modulator body was a diagnostic test, to determine whether the body lines or hoses were clogged, though I thought it unlikely that *all four* would be.

The brakes were very weak before I started, having been going down hill since I bought it. I expected to have to do some intake work, and this is the second major item after the front propshaft.

I continue to assume, though, since no one's explicitly told me not to, that *I should be able to pump through the ABS modulator*, with the truck off, to bleed all the way to the wheels, and that if I can't (which I can't), that this suggests that *something's* wrong with the modulator, whether it's stuck, clogged, or merely not being told to fire.

Is that *not* a valid assumption?

 

Yes you should be able to pup through the modulator with the power off, if you have air in your modulator then you would not be able to.

I would try to gravity bleed them first. I've a couple friends with really soft brakes who have tried to bleed their brakes and not been able to. They took it to a mechanic and they just let them gravity bleed for a while and that got the air worked out of the modulator. If you have a good shop nearby take it over and let them have a shot, should not cost you much.

Also I assumed you were joking when you said you tried to bleed all 4 corners at once?

 

You assume correctly. :-)

We did them one at a time.

But lookie here what I found on the website of Robison Service:

(That page is at http://www.robisonservice.com/articl...R_aug2006.asp; they look fairly sensible.)

I saw this mentioned one other place, and it seems rather sensible, depending on the way the modulator works... but *no one* here has said it at all. Any comments on this, folks? And is Castrol fluid actually a requirement? I didn't see any local store still stocking it; the Valvo synth was the only DOT4 they had in quarts.

 

I use the valvoline synthetic dot 3/4 fluid. It is the only dot 4 fluid available around here, works great. Any synthetic dot 4 will do.

Also not sure if you have access to a Hawkeye scanner but it can open and close your modulator valves. I own one but your are nowhere near western NY.