no brakes at all

[scotty]

I replaced the front calipers and master with new parts. I drove it for 6 months after the work. I needed to bleed it a couple of times to get them to work well. I checked the back brake cylinders for leaks and bleed them too. The rear brake arm to work ok when I just use the handbrake to stop the van. The rear shoes still had a lot of material, so I just bleed the lines and didn’t change anything on the back. I could replace the rear cylinders just to see if it makes any difference, I have a set on the shelf. But, I can’t really get past the fact that I’m only getting 1/4 of the vacuum that should be created from the manifold. Unless 5 Hgv is normal? Someone told me the car would barely run with that low a measurement, but it runs fine. I have tried a couple of different vacuum gauges with no change. I have also been told that the current amount of vacuum is enough to get
the brakes to work correctly.

I have only been able to find a new brake booster for the 84’ van. anyone know a source for one or if the 84’ will work on an 87’?

[timsrv]

Is it possible you got grease or brake fluid on the friction surfaces? Brakes rely on friction and grease/brake fluid contamination will destroy their ability to do their job. Rotors and drums can also become "glazed" and that can also have similar effects. If there is contamination, you will need to replace the shoes/pads and it's highly recommended the rotors/drums be turned or replaced. Tim

[scotty]

I don’t think so. I was pretty deliberate and clean when I did the work. I used a pneumatic brake bleeder and sprayed everything down afterward. They were working fine for about 5000 miles.

I built a little smoke machine and found a few leaks. There was a big one on the valve cover gasket, but fixing them made no change in the vacuum measurement or the performance of the brakes. I’m leaning towards replacing the booster now. It looks like a real pain in the ass, but an easier job than replacing the intake gasket with the engine in the van.

[Burntboot]

Even if the rear wheel cylinders were seized it wouldn't create your current issue.
I haven't used a vacuum gauge in years so can't advise there but there are ways to assess the integrity of the motor.

If the engine isn't producing sufficient vacuum to supply the booster, replacing the booster isnt going to solve that.

Either theres a blockage in the line between the engine and the booster or the engine has a problem.
You're going to have to work your way thru things.
Part of proper diagnostic procedures is as much ruling things out, as it is about finding whats at fault

Disconnecting the hose to the booster should cause the engine to stall at idle(massive vacuum leak)
If it doesn't, work your way back towards the engine till it does.
Knowing compression and leak-down numbers may also shed some light as would any stored codes.
Verifying timing is accurate and the balancer is intact would also be on my list.

It's still worth revisiting the front callipers, just to make sure the pads and sliders are free
Up here, servicing every 6 months is standard fare.

The more variables you can eliminate from the equation, the better

[timsrv]

To my knowledge, about the only thing that can go wrong with a vacuum booster is a busted diaphragm. You can test the diaphragm by putting vacuum to it, then seeing if it holds. If you don't have a mityvac or similar, you could put a hose on it, suck with your mouth, put your tongue over the hose (to trap vacuum). If you can't achieve a vacuum, then the diaphragm is broke. If you can achieve vacuum, and it stays there for a few seconds, then the diaphragm is good. Tim

[scotty]

I couldn’t find any more vac leaks with the smoker, so I went and rented a vac pump from autozone. I hooked it up to the booster and drove the van with an extension cord hanging out the window and only had to move the van about 10 feet to discover that the booster was working fine. My problem is low vacuum. I did the test with the vacuum gauge to check for a clogged exhaust. I revved it up and looked for a dropping vac level, but it came back to the starting point and didn’t move when it was revived up to 3k rpm. I pulled the o2 sensor out and tested with it out, and that didn’t change anything. I can’t really wrap my head around what could cause it to lose so much vacuum and yet be so hard to detect.

[VanCo]

Low vacuum, check for - Vacuum leaks (I see you've checked this), blocked exhaust (I see you've checked this too), low compression, excessive cylinder leak down, ignition timing off (verify TDC on balancer), timing chain stretch, timing chain skipped tooth.

When you're having trouble diagnosing something it's important to not assume anything. Test it all even if you feel it's unlikely.

[scotty]

I did a compression check cold and I got between 160
-170lbs on all cylinders. I’ll check the timing just to see,
but It runs fine, which I’ve been told is nearly impossible with the low vacuum pressure I’m getting. I’m starting to think I should just get an auxiliary vacuum pump and hook it directly to the booster and call it a day.

[timsrv]

I'm thinking it's gotta be a clog in a vacuum port or maybe a vacuum hose that's collapsing inside. There's also a check valve that helps the booster retain vacuum during times when engine vacuum is low. If the engine vacuum was that low it would run like total crap. Tim

[scotty]

I checked the valve at the booster, and it seems to be holding fine when I manually checked it. Is there another valve in the system? I’ll check the ports and lines. Thanks

[VanCo]

Have you checked vacuum at multiple different ports? PCV etc.

[timsrv]

I checked the valve at the booster, and it seems to be holding fine when I manually checked it. Is there another valve in the system? I’ll check the ports and lines. Thanks

Just the valve at the inlet of the booster. Vacuum is required for NA engines to idle, so if yours runs reasonably well, I would suspect a clog or maybe a leak somewhere in the booster supply. If you haven't already done it, follow that line all the way back from the booster to the manifold to insure there's no physical damage to it. You can also plug it on one end, then use a Mitivac or even your mouth to create a vacuum in it. If it leaks, you will be able to tell. Sometimes rubber hoses get soft and will collapse when a vacuum is applied. I've also seen them separate inside and collapse an inner layer while still looking good on the outside. Tim

[scotty]

I found the leak. Way up in the front near the bumper where the booster vacuum line exits the interior through the body it joins another long vacuum line that also comes from the engine area. They meet at a small plastic T connector that had broken.

[timsrv]

I found the leak. Way up in the front near the bumper where the booster vacuum line exits the interior through the body it joins another long vacuum line that also comes from the engine area. They meet at a small plastic T connector that had broken.